Question 1.
What Is A Dbms?
Answer
: DBMS stands for Database Management
System. A DBMS receives requests from applications and translates those
requests into actions on a specific database. A DBMS processes SQL statements
or uses other functionality to create process and administer databases.
Question 2.
What Is Relationship Set?
Answer
: The collection (or set) of similar
relationships.
Question 3.
What Is Relationship Type?
Answer
: Relationship type defines a set of
associations or a relationship set among a given set of entity types.
Question 4.
What Is Degree Of Relationship Type?
Answer
: It is the number of entity type
participating.
Question 5.
What Is Ddl (data Definition Language)?
Answer
: A data base schema is specifies by a
set of definitions expressed by a special language called DDL.
Question 6.
What Is Vdl (view Definition Language)?
Answer
:
It specifies user views and their
mappings to the conceptual schema.
Question 7.
What Is Sdl (storage Definition Language)?
Answer
: This language is to specify the
internal schema. This language may specify the mapping between two schemas.
Question 8.
What Is Data Storage - Definition Language?
Answer
: The storage structures and access
methods used by database system are specified by a set of definition in a
special type of DDL called data storage-definition language.
Question 9.
What Is Dml (data Manipulation Language)?
Answer : This language that enable user to
access or manipulate data as organised by appropriate data model.
1. Procedural DML or Low level: DML requires a user to specify what data are
needed and how to get those data.
2. Non-Procedural DML or High level: DML requires a user to specify what data
are needed without specifying how to get those data.
Question 10.
What Is Dml Compiler?
Answer
: It translates DML statements in a
query language into low-level instruction that the query evaluation engine can
understand.
Question 11.
What Is Query Evaluation Engine?
Answer
: It executes low-level instruction
generated by compiler.
Question 12. What
Is Ddl Interpreter?
Answer
: It interprets DDL statements and
record them in tables containing metadata.
Question 13.
What Is Record-at-a-time?
Answer
: The Low level or Procedural DML can
specify and retrieve each record from a set of records. This retrieve of a
record is said to be Record-at-a-time.
Question 14.
What Is Set-at-a-time Or Set-oriented?
Answer
: The High level or Non-procedural DML
can specify and retrieve many records in a single DML statement. This retrieve
of a record is said to be Set-at-a-time or Set-oriented.
Question 15.
What Is Relational Algebra?
Answer
: It is procedural query language. It
consists of a set of operations that take one or two relations as input and
produce a new relation.
Question 16.
What Is Relational Calculus?
Answer
: It is an applied predicate calculus
specifically tailored for relational databases proposed by E.F. Codd. E.g. of
languages based on it are DSL ALPHA, QUEL.
Question 17.
How Does Tuple-oriented Relational Calculus Differ From Domain-oriented Relational
Calculus?
Answer
:
1. The
tuple-oriented calculus uses a tuple variables i.e., variable whose only
permitted values are tuples of that relation. E.g. QUEL
2. The
domain-oriented calculus has domain variables i.e., variables that range over
the underlying domains instead of over relation. E.g. ILL, DEDUCE.
Question 18. What Is Normalization?
Answer
: It is a process of analysing the
given relation schemas based on their Functional Dependencies (FDs) and primary
key to achieve the properties
(1)Minimizing
redundancy,
(2)Minimizing
insertion, deletion and update anomalies.
Question 19.
What Is Functional Dependency?
Answer
: A Functional dependency is denoted
by X Y between two sets of attributes X and Y that are subsets of R specifies a
constraint on the possible tuple that can form a relation state r of R. The
constraint is for any two tuples ti and t2 in r if tl[XJ = t2[Xj then they have
tl[Y] = t2[Y]. This means the value of X component of a tuple uniquely
determines the value of component V.
Question 20.
What Is Lossless Join Property?
Answer
: It guarantees that the spurious
tuple generation does not occur with respect to relation schemas after
decomposition.
Question 21.
What Is 1 Nf (normal Form)?
Answer
: The domain of attribute must include
only atomic (simple, indivisible) values.
Question 22.
What Is Fully Functional Dependency?
Answer
: It is based on concept of full
functional dependency. A functional dependency X Y is full functional
dependency if removal of any attribute A from X means that the dependency does
not hold any more.
Question 23.
What Is 2nf?
Answer
: A relation schema R is in 2NF if it
is in 1NF and every non-prime attribute A in R is fully functionally dependent
on primary key.
Question 24.
What Is 3nf?
Answer : A relation schema R is in 3NF if it
is in 2NF and for every FD X A either of the following is true
1. X is a Super-key of R.
2. A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on
primary key.
Question 25.
What Is Bcnf (boyce-codd Normal Form)?
Answer
: A relation schema R is in BCNF if it
is in 3NF and satisfls an additional constraint that for every FD X A, X must
be a candidate key.
Question 26.
What Is 4nf?
Answer : A relation schema R is said to be in
4NF if for every Multivalued dependency X Y that holds over R, one of following
is true.
1.) X is subset or equal to (or) XY = R.
2.) X is a super key.
Question 27.
What Is 5nf?
Answer
: A Relation schema R is said to be
5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the
following is true 1.) Ri = R for some i.
Question 28.
What Is Domain-key Normal Form?
Answer
: A relation is said to be in DKNF if
all constraints and dependencies that should hold on the the constraint can be
enforced by simply enforcing the domain constraint and key constraint on the
relation.
Question 29.
What Is System Catalog Or Catalog Relation? How Is Better Known As?
Answer
: A RDBMS maintains a description of
all the data that it contains, information about every relation and index that
it contains. This information is stored in a collection of relations maintained
by the system called metadata. It is also called data dictionary.
Question 30.
What Is Meant By Query Optimization?
Answer
: The phase that identifies an efficient
execution plan for evaluating a query that has the least estimated cost is
referred to as query optimization.
Question 31.
What Is Durability In Dbms?
Answer
: Once the DBMS informs the user that
a transaction has successfully completed, its effects should persist even if
the system crashes before all its changes are reflected on disk. This property
is called durability.
Question 32.
What Do You Mean By Atomicity And Aggregation?
Answer
:
1. Atomicity:
Either all actions are carried out or none are. Users should not have to worry
about the effect of incomplete transactions. DBMS ensures this by undoing the
actions of incomplete transactions.
2. Aggregation: A concept which is used to model a relationship between a
collection of entities and relationships. It is used when we need to express a
relationship among relationships.
Question 33.
What Is A Phantom Deadlock?
Answer
: In distributed deadlock detection,
the delay in propagating local information might cause the deadlock detection
algorithms to identify deadlocks that do not really exist. Such situations are
called phantom deadlocks and they lead to unnecessary aborts.
DBMS+RDBMS
Interview Questions
Question 34.
What Is A Checkpoint And When Does It Occur?
Answer
: A Checkpoint is like a snapshot of
the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work
to be done during restart in the event of subsequent crashes.
Question 35.
What Are The Different Phases Of Transaction?
Answer : Different phases are
1.) Analysis phase,
2.) Redo Phase,
3.) Undo phase.
Question 36.
What Do You Mean By Flat File Database?
Answer
: It is a database in which there are
no programs or user access languages. It has no cross-file capabilities but is
user-friendly and provides user-interface management.
Question 37.
What Is "transparent Dbms"?
Answer
: It is one, which keeps its Physical
Structure hidden from user.
Question 38.
What Is A Query?
Answer
: A query with respect to DBMS relates
to user commands that are used to interact with a data base. The query language
can be classified into data definition language and data manipulation language.
Question 39.
What Do You Mean By Correlated Subquery?
Answer
: Subqueries, or nested queries, are used
to bring back a set of rows to be used by the parent query. Depending on how
the subquery is written, it can be executed once for the parent query or it can
be executed once for each row returned by the parent query. If the subquery is
executed for each row of the parent, this is called a correlated subquery.
A correlated subquery can be easily
identified if it contains any references to the parent subquery columns in its
WHERE clause. Columns from the subquery cannot be referenced anywhere else in
the parent query. The following example demonstrates a non-correlated subquery.
Example:
Select’ From CUST Where ‘10/03/1990’
IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)
Question 40.
What Are The Unary Operations In Relational Algebra?
Answer
: PROJECTION and SELECTION.
Question 41.
Are The Resulting Relations Of Product And Join Operation The Same?
Answer : No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
Question 42.
What Is Rdbms Kernel?
Answer
: Two important pieces of RDBMS
architecture are the kernel, which is the software, and the data dictionary,
which consists of the system-level data structures used by the kernel to manage
the database You might think of an RDBMS as an operating system (or set of
subsystems), designed specifically for controlling data access; its primary
functions are storing, retrieving, and securing data. An RDBMS maintains its
own list of authorized users and their associated privileges; manages memory
caches and paging; controls locking for concurrent resource usage; dispatches
and schedules user requests; and manages space usage within its table-space
structures.
Question 43.
Name The Sub-systems Of A Rdbms?
Answer
: I/O, Security, Language Processing,
Process Control, Storage Management, Logging and Recovery, Distribution
Control, Transaction Control, Memory Management, Lock Management.
Question 44.
Which Part Of The Rdbms Takes Care Of The Data Dictionary? How?
Answer
: Data dictionary is a set of tables
and database objects that is stored in a special area of the database and
maintained exclusively by the kernel.
Question 45.
What Is The Job Of The Information Stored In Data-dictionary?
Answer
: The information in the data
dictionary validates the existence of the objects, provides access to them, and
maps the actual physical storage location.
Question 46.
How Do You Communicate With An Rdbms?
Answer
: You communicate with an RDBMS using
Structured Query Language (SQL).
Question 47.
Define Sql And State The Differences Between Sql And Other Conventional
Programming Languages?
Answer
: SQL is a nonprocedural language that
is designed specifically for data access operations on normalized relational
database structures. The primary difference between SQL and other conventional
programming languages is that SQL statements specify what data operations
should be performed rather than how to perform them.
Question 48.
Name The Three Major Set Of Files On Disk That Compose A Database In Oracle?
Answer : There are three major sets of files
on disk that compose a database. All the files are binary. These are
1.) Database files
2.) Control files
3.) Redo logs
The most important of these are the database files where the actual data
resides. The control files and the redo logs support the functioning of the
architecture itself. All three sets of files must be present, open, and
available to Oracle for any data on the database to be useable. Without these
files, you cannot access the database, and the database administrator might
have to recover some or all of the database using a backup, if there is one.
Question 49.
What Is Database Trigger?
Answer
: A database trigger is a PL/SQL block
that can defined to automatically execute for insert, update, and delete
statements against a table. The trigger can e defined to execute once for the
entire statement or once for every row that is inserted, updated, or deleted.
For any one table, there are twelve events for which you can define database
triggers. A database trigger can call database procedures that are also written
in PL/SQL.
Question 50.
What Are Stored-procedures? And What Are The Advantages Of Using Them?
Answer
: Stored procedures are database
objects that perform a user defined operation. A stored procedure can have a
set of compound SQL statements. A stored procedure executes the SQL commands
and returns the result to the client. Stored procedures are used to reduce
network traffic.
Question 51.
What Is Storage Manager?
Answer
: It is a program module that provides
the interface between the low-level data stored in database, application
programs and queries submitted to the system.
Question 52.
What Is Buffer Manager?
Answer
: It is a program module, which is
responsible for fetching data from disk storage into main memory and deciding
what data to be cache in memory.
Question 53.
What Is Transaction Manager?
Answer
: It is a program module, which
ensures that database, remains in a consistent state despite system failures
and concurrent transaction execution proceeds without conflicting.
Question 54.
What Is File Manager?
Answer
: It is a program module, which
manages the allocation of space on disk storage and data structure used to
represent information stored on a disk.
Question 55.
What Is Authorization And Integrity Manager?
Answer
: It is the program module, which
tests for the satisfaction of integrity constraint and checks the authority of
user to access data.
Question 56.
What Are Stand-alone Procedures?
Answer
: Procedures that are not part of a
package are known as stand-alone because they independently defined. A good
example of a stand-alone procedure is one written in a SQL*Forms application.
These types of procedures are not available for reference from other Oracle
tools. Another limitation of stand-alone procedures is that they are compiled
at run time, which slows execution.
Question 57.
What Are Cursors Give Different Types Of Cursors?
Answer
: PL/SQL uses cursors for all database
information accesses statements. The language supports the use two types of
cursors
1.)
Implicit
2.)
Explicit
Question 58.
What Is Cold Backup And Hot Backup (in Case Of Oracle)?
Answer
:
1. Cold Backup:
It is copying the three sets of files (database files, redo logs, and control
file) when the instance is shut down. This is a straight file copy, usually
from the disk directly to tape. You must shut down the instance to guarantee a
consistent copy. If a cold backup is performed, the only option available in
the event of data file loss is restoring all the flies from the latest backup.
All work performed on the database since the last backup is lost.
2. Hot Backup:
Some sites (such as worldwide airline reservations systems) cannot shut down
the database while making a backup copy of the files. The cold backup is not an
available option. What is meant by Proactive, Retroactive and Simultaneous
Update. Proactive Update: The updates that are applied to database before it
becomes effective in real world. Retroactive Update: The updates that are
applied to database after it becomes effective in real world. Simultaneous
Update: The updates that are applied to database at the same time when it
becomes effective in real world.
Question 59.
What Are Data And Information, And How Are They Related In A Database?
Answer
: Data is recorded facts and figures,
and information is knowledge derived from data. A database stores data in such
a way that information can be created.
Question 60.
What Is Enterprise Resource Planning (erp), And What Kind Of A Database Is Used
In An Erp Application?
Answer
: Enterprise Resource Planning (ERP)
is an information system used in manufacturing companies and includes sales,
inventory, production planning, purchasing and other business functions. An ERP
system typically uses a multiuser database.
Question 61.
Why Is A Database Considered To Be "self-describing"?
Answer
: In addition to the users’ data, a
database contains a description of its own structure. This descriptive data is
called “metadata.”
Question 62.
Who Is E.f. Codd, And Why Is He Significant In The Development Of Modern
Database Systems?
Answer
: While working at IBM, E.F. Codd
created the relational database model. A paper he published in 1970 presented
his ideas to the world at large. His work is the foundation for most of the
DBMSs currently in use, and thus forms the basis for database systems as we
know and use them today.
Question 63.
What Is Sql, And Why Is It Important?
Answer
: SQL stands for Structured Query
Language, and is the most important data processing language in use today. It
is not a complete programming language like Java or C#, but a data sublanguage
used for creating and processing database data and metadata. All DBMS products
today use SQL.
Question 64.
Write An Sql Select Statement To Display All The Columns Of The Student Table
But Only Those Rows Where The Grade Column Is Greater Than Or Equal To 90?
Answer
: SELECT * FROM STUDENT WHERE Grade
>= 90;
Question 65.
Name And Briefly Describe The Five Sql Built-in Functions?
Answer
: COUNT: computes the number of rows
in a table. SUM: totals numeric columns. AVG: computes the average value. MAX:
obtains the maximum value of a column in a table. MIN: obtains the minimum
value of a column in a table.
Question 66.
Write An Sql Select Statement To Count The Number Of Rows In Student Table And
Display The Result With The Label Num Students?
Answer
: SELECT COUNT(*) AS NumStudents FROM
STUDENT;
Question 67.
What Is An Sql Subquery?
Answer
: An SQL subquery is a means of
querying two or more tables at the same time. The subquery itself is an SQL
SELECT statement contained within the WHERE clause of another SQL SELECT
statement, and separated by being enclosed in parenthesis. Some subqueries have
equivalent SQL join structures, but correlated subqueries cannot be duplicated
by a join..
Question 68.
Discuss The Alternative Terminology That Is Used In The Relational Model?
Answer
: Relations are also called tables,
and sometimes by the older data processing term files. A row is known as a
tuple in the relational model, but may also be referred to as a record.
Finally, relational model attributes are known as table columns and sometimes
as fields.
Question 69.
Why Are Functional Dependencies Not Equations?
Answer
: Equations deal with numerical
relationships. A functional dependency deals with the existence of a
determinant relationship between attributes, regardless of whether or not there
is a numerical relationship between them. Thus, if we know that there is no hot
water every Wednesday, No-Hot-Water is functionally dependent on Wednesday. So,
if we know it is Wednesday, then we know we will have No-Hot-Water. This is a
functional dependency, but not an equation.
Question 70.
What Is A Foreign Key, And What Is It Used For?
Answer
: A foreign key is used to establish
relationships among relations in the relational model. Technically, a foreign
key is a column (or columns) appearing in one relation that is (are) the
primary key of another table. Although there may be exceptions, the values in
the foreign key columns usually must correspond to values existing in the set
of primary key values. This correspondence requirement is created in a database
using a referential integrity constraint on the foreign key.
Question 71.
What Are Insertion And Deletion Anomalies?
Answer
: A deletion anomaly occurs when, by
deleting the facts about one entity, we in advertently delete facts about
another entity; with one deletion, we lose facts about two entities. For
example, if we delete the tuple for Student 001289 from a table, we may lose
not only the fact that Student 001289 is in Pierce Hall, but also the fact that
he has $200 left in his security deposit. An insertion anomaly happens when we
encounter the restriction that we cannot insert a fact about one entity until
we have an additional fact about another entity. For example, we want to store
the fact that the security deposit for Pierce Hall is $300, but we cannot enter
this data into the Student relation until a student registers for Pierce Hall.
Question 72.
You Have Been Given A Set Of Tables With Data And Asked To Create A New
Database To Store Them. When You Examine The Data Values In The Tables, What
Are You Looking For?
Answer
:
Multivalued
dependencies,
Functional
dependencies,
Candidate
keys,
Primary
keys and
Foreign
keys.
Question 73.
Why Do Normalized Tables Require More Complex Sql When Sql Statements Are Used
In Application Programs?
Answer
: Tables that are normalized contain
data that has been distributed among the tables, but which may need to be
recombined to answer queries from an application. To recombine the data, the
programmer will have to use subqueries and/or joins. These SQL structures are
more complex to write than a simple SELECT statement.
Question 74.
What Is The Inconsistent Values Problem? Include An Example Not Used In The
Text?
Answer
: The inconsistent values problem
occurs when different users or data sources use slightly different forms of the
same data value. One example is where automobiles are specified as “Ford,
2-door, Red” in one cell and “Red Ford 2-door’ in another.
Question 75.
Explain The Relationship Between Entity, Entity Class, And Entity Instance?
Answer
: An entity is something that can be
identified in the users’ work environment, something that the users want to
track. Entities of a given type are grouped into entity classes. An entity
instance is the representation of a particular entity.
Question 76.
Explain The Difference Between Attributes And Identifiers?
Answer
: Entities have attributes. Attributes
are properties that describe the entity’s characteristics. Entity instances
have identifiers. Identifiers are attributes that name, or identify, entity
instances.
Question 77.
Name And Describe Three Types Of Binary Relationships?
Answer
:
1:1 - a single
entity instance of one type is related to a single-entity instance of another
type.
1:N - a single entity instance of one type is related to many-entity instances
of another type.
M:N - many-entity instances of one type relate to many-entity instances of
another type.
Question 78.
What Are The Steps For Transforming An Entity Into A Table?
Answer
: The steps are:
1.
specify
the primary key,
2.
specify
candidate keys,
3.
specify
column properties including null status, data type, default value (if any), and
data constraints (if any), and
4.
verifying
normalization.
Question 79.
Define A Surrogate Key, Describe The Ideal Primary Key And Explain How
Surrogate Keys Meet This Ideal?
Answer
: The ideal primary key is short,
numeric and fixed. A surrogate key is a unique, DBMS-supplied identifier
intended to be used as the primary key of a table. Further, the DBMS will not
allow the value of a surrogate key to be changed. The values of a surrogate key
have no meaning to the users and are usually hidden on forms and reports. By
design, they are short, numeric and fixed and thus meet the definition of the
ideal primary key.
Question 80. Define
And Discuss Data Constraints?
Answer
: Data constraints on a column are the
limits put on the values the data can have.
There are four
types of data constraints:
1.
domain
constraints, which define a limited set of values for the column,
2.
range
constraints, which specify that the values must fall within a certain range,
3.
intrarelation
constraints, which define what values the column can have based on values of
other columns in the same table, and
4.
interrelation
constraints, which define values the column can have based on values of columns
in other tables.
Question 81. In
General, How Are Recursive Relationships Handled In A Database Design?
Answer
: A recursive relationship is a
relationship among entities of the same class, and is represented in the same way
as other relationships are. The rows of the tables can take two different
roles, however. Some are parent rows, and others are child rows. Further, the
table will contain both its own primary key and the foreign key that links back
to the table itself. If a row has no parent, then the value of the foreign key
column in that row will be null. If the row has a parent, then there must be a
foreign key value in that row that corresponds to the primary key value of
another row in the table.
Question 82.
What Is A Cascading Update?
Answer
: Referential integrity constraints
require that foreign key values in one table correspond to primary key values
in another. If the value of the primary key is changed -- that is, updated --
the value of the foreign key must immediately be changed to match it. Cascading
updates will set this change to be done automatically by the DBMS whenever
necessary.
Question 83.
What Is A Sql View? Briefly Explain The Use Of Views?
Answer
: A SQL view is a virtual table built
from other tables or views.
Views are used
to:
·
hide
columns or rows,
·
the
results of computed columns,
·
hide
complicated SQL syntax,
·
layer
built-in functions,
·
provide
a level of indirection between application programs and tables,
·
assign
different sets of processing permissions to tables, and
·
to
assign different sets of triggers to the same table.
Question 84.
Explain The "paradigm Mismatch" Between Sql And Application
Programming Languages?
Answer
: SQL statements return a set of rows,
while an application program works on one row at a time. To resolve this
mismatch the results of SQL statements are processed as pseudofiles, using a
cursor or pointer to specify which row is being processed.
Question 85.
Name Four Applications For Triggers?
Answer
:
providing
default values,
enforcing
data constraints,
updating
views and
enforcing
referential integrity.
Question 86.
What Are Stored Procedures, And How Do They Differ From Triggers?
Answer
: A stored procedure is a program that
is stored within the database and is compiled when used. They can receive input
parameters and they can return results. Unlike triggers, their scope is
database-wide; they can be used by any process that has permission to use the
database stored procedure.
Question 87.
What Are The Advantages Of Using Stored Procedures?
Answer
: The advantages
of stored procedures are:
greater
security,
decreased
network traffic,
the
fact that SQL can be optimized and
code
sharing which leads to less work, standardized processing, and specialization
among developers.
Question 88.
Why Is Database Redesign Necessary?
Answer
: Database redesign is necessary for
two reasons. First, redesign is necessary both to fix mistakes made during the
initial database design. Second, redesign is necessary to adapt the database to
changes in system requirements. Such changes are common because information
systems and organizations do not just influence each other they create each
other. Thus, new information systems cause changes in systems requirements.
Question 89.
What Is The Difference Between Sql Server 2000 Complete And Differential
Backups?
Answer
: A complete backup makes a copy of
the entire database. A differential backup makes a copy of the changes that
have been made to the database since the last complete backup. A complete backup
must be made before the first differential backup. Because differential backups
are faster, they can be taken more frequently and the chance of data loss is
reduced. Complete backups take longer but are slightly simpler to use for
recovery.
Question 90.
Explain The Meaning Of Each Of The Transaction Levels Supported By Sql Server?
Answer
: The strictest isolation level is
SERIALIZABLE. With it, SQL Server places a range lock on the rows that have
been read. This level is the most expensive to use and should only be used when
absolutely required. The next most restrictive level is REPEATABLE READ, which
means SQL Server places and holds locks on all rows that are read. It is
possible to make dirty reads by setting the isolation level to READ UNCOMMITTED,
which is the least restrictive level. READ COMMITTED is the default isolation
level.
Question 91.
Explain The Difference Between The Sql Server 2000 Simple, Full, And
Bulk-logged Recovery Models?
Answer
: With the simple recovery model, no
logging is done. The only way to recover a database is to restore the database
to the last backup. With full recovery, all database changes are logged. With
bulk-logged database recovery, all changes are logged except those that cause
large log entries.
Question 92.
What Is The Difference Between Sql Server 2000 Clustered And Nonclustered
Indexes?
Answer
: With a clustered index, the data are
stored in the bottom level of the index and in the same order as that index.
With a nonclustered index, the bottom level of an index does not contain data;
it contains pointers to the data. For data retrieval, clustered indexes are
faster than nonclustered indexes.
Question 93.
What Triggers Does Sql Server 2000 Support?
Answer
: SQL Server 2000 supports INSTEAD OF
and AFTER triggers only. There is no SQL Server support for BEFORE triggers. A
table may have one or more AFTER triggers for insert, update and delete
actions; AFTER triggers may not be assigned to views. A view or table may have
at most one INSTEAD OF trigger for each triggering action of insert, update or
delete.
Question 94.
What Is The Relationship Of Odbc, Ole Db, And Ado?
Answer
: Developed first, the ODBC standard
is for relational databases; while the OLE DB standard provides functionality
for both relational and other databases. Finally, ADO was developed to provide
easier access to OLE DB data for the non-object-oriented programmer.
Question 95.
What Are The Three Types Of Data Sources Used With Odbc?
Answer
: An ODBC file data source is a file
that can be shared among database users. A ODBC system data source is one that
is local to a single computer. A ODBC user data source is only available to the
user who created It.
Question 96.
What Disadvantage Of Odbc Does Ole Db Overcome?
Answer
: By breaking the features and the
functions of a DBMS into COM objects, OLE DB characteristic overcomes a major
disadvantage of ODBC. With ODBC, a vendor must create an ODBC driver for almost
all DBMS features and functions in order to participate in ODBC at all. This is
a large task that requires a substantial initial investment. With OLE DB,
however, a DBMS vendor can implement portions of their product.
Question 97.
What Are To Goals Of Ole Db?
Answer
:
The major goals
of OLE DB are to:
Create
object interfaces for DBMS functionality pieces;
Increase
flexibility for developers and users;
provide
an object interface over any type of data; and
do
not force data to be converted or moved from where it is.
Question 98. In
Ole Db, What Is The Difference Between An Interface And An Implementation?
Answer
: An OLE DB interface is specified by
a set of objects, and the properties and methods that they expose, and OLE DB
defines standardized interfaces. An object need not expose all of its
properties and methods in a given interface. An OLE DB implementation defines
how the object supports the interface. The implementation is completely hidden
from the user. Thus developers of an object are free to change the
implementation whenever they want, but they should not change the interface
without consulting their users.
Question 99.
Why Is Xml A Better Markup Language Than Html?
Answer
: XML is a better markup language than
HTML, primarily because XML provides a clear separation between document
structure, content, and materialization. Symbols cannot be used ambiguously
with XML.
Question 100.
What Are The Two Means To Describe The Content Of Xml Documents?
Answer
: DTD (Document Type Declarations) and
XML Schemas. An XML document that conforms to its DTD is called type-valid. A
document can be well-formed and not be type-valid, either because it violates
the structure of its DTD or because it has no DTD. However, DTD5 have
limitations and to overcome these limits XML Schemas were created. XML Schemas
are XML documents that are the preferred method for defining document
structure.
Question 101.
What Is The Difference Between Simple Elements And Complextype Elements?
Answer
: Simple elements have only one data
value. ComplexType elements can have multiple elements nested within them.
ComplexTypes may also have attributes. The elements contained in a complexType
may be simple or other complexTypes. ComplexTypes may also define element
sequences.
Question 102.
How Are Surrogate Keys And Metadata Handled In Mysql?
Answer
: MySQL uses integer data types combined
with the property AUTO_INCREMENT to create surrogate keys. This creates a
sequence that starts at one (1) and increases by one (2) for each new record.
MySql maintain its metadata in a database named mysql. For example, this
database maintains two tables named user and db.
Question 103.
What Is A Data Mart?
Answer
: A data mart Is a collection of data
smaller In scope and size than a data warehouse. It is dedicated to data from a
particular business component of business functional area. A data mart may
function as a subset of a larger data warehouse. Users of a data mart are
usually knowledgeable analysts in the business area using the data mart.
Question 104.
What Are The Functions Of A Reporting System?
Answer
: A reporting system has three
functions: 1. Report authoring -- connecting to data sources, creating the
report structure and formatting the report. 2. Report management -- defining
who receives which reports, when they receive them and how the reports are
delivered. 3. Report delivery -- based on report management metadata, either
pushing the reports to the recipients or allowing them to be pulled by the
recipients.
Question 105.
What Is Olap?
Answer
: OnLine Analytical Processing (OLAP)
is a Business Intelligence (BI) reporting system. OLAP provides the user with
the capability to sum, count, average and do other simple arithmetic operations
on groups of data. An OLAP report has measures and dimensions. Measures are the
data values to be displayed. Dimensions are characteristics of the measures.
OLAP reports are called OLAP cubes, although such reports are not limited to
three dimensions.
Question 106.
What Is Market Basket Analysis?
Answer
: Market basket analysis is a data
mining technique that determines which sets of products tend to be purchased
together. A common technique uses conditional probabilities. In addition to the
basic probability that an item will be purchased, three results are of
particular interest:
Support -- the probability of two items being purchased together. Confidence --
the probability of a second item being purchased GIVEN that another item has
been purchased. Lift -- calculated as confidence divided by a basic
probability, this shows the likelihood of a second item being purchased IF an
item is purchased.
Question 107.
Explain The Differences Between Structured Data And Unstructured Data?
Answer
: Structured data are facts concerning
objects and events. The most important structured data are numeric, character,
and dates. Structured data are stored in tabular form. Unstructured data are
multimedia data such as documents, photographs, maps, images, sound, and video
clips. Unstructured data are most commonly found on Web servers and Web-enabled
databases.
Question 108.
Explain Why It Is Still Necessary To Have At Least Some Familiarity With File
Processing Systems Even Though It Has Become Evident That Traditional File
Processing Systems Have A Number Of Shortcomings And Limitations?
Answer
: Many businesses still use file
processing systems today. This is especially true in the creation of backups
for a database system. In addition, if you understand some of the limitations
of a file processing system such as program-data dependence, duplication of
data, limited data sharing, lengthy development times, and excessive program
maintenance, you can try and avoid them as you design and develop a databases.
Question 109.
What Are Some Of The Disadvantages Associated With Conventional File Processing
Systems?
Answer
: There are five disadvantages.
Program-data dependence occurs when file descriptions need to be changed in all
programs whenever a file description changes. Duplication of data is storing
the data more than one time. Limited data sharing occurs when the files are
private so no one outside of one application can access the data. Lengthy
development times exist because file processing systems takes longer to
develop. Lastly, excessive program maintenance exists since the effort to
maintain a program is larger in this environment.
Question 110.
The Range Of Database Applications Can Be Divided Into Five Categories. Explain
The Five Different Categories?
Answer
: Databases can support from a single
user (personal database) up to supporting the requests of the world (internet
database). In between, a database can support a workgroup (a relatively small
group of people), department database (a functional unit in an organization
such as marketing), or an enterprise database (entire organization).
Question 111.
Explain The Differences Of The Two Principal Types Of Packaged Data Models?
Answer
: Universal data models are common to
many organizations. These models may be useful for similar functions that are
used across companies or organizations such as purchasing and accounting.
Industry-specific data models are used by specific industries.
Question 112.
Briefly Explain An Erd?
Answer
: An ERD is a detailed logical
representation of the data for an organization. The ERD includes entities,
attributes, relationships, and cardinalities. An ERD is the mechanism where an
entity-relationship model is displayed.
Question 113.
List Some Of The Chrematistics Of Good Data Definitions?
Answer
: Definitions are gathered from the
same sources and should be accompanied diagrams. A definition will include
special conditions, examples, how the data is created, whether the data can
change, who owns the data, whether the data is optional, and whether the data
can be broken into something more atomic.
Question 114.
Explain Minimum And Maximum Cardinality?
Answer
: Minimum cardinality is the minimum
number of instances of an entity that can be associated with each instance of
another entity. Maximum cardinality is the maximum number of instances of an
entity that can be associated with each instance of another entity.
Question 115.
Why Is Modeling Time-dependent Data With A Time Stamp Important?
Answer
: The values of data may change. A
time stamp helps to ensure that the previous value of the data stays in the
database after it has changed so that you can see the before and after values
through time. Without a time stamp, you will most likely lose some of the
history.
Question 116.
Explain The Difference Between Total Specialization And Partial Specialization?
Answer
: Total specialization exists when
every instance of a supertype must also be an instance of a subtype. Partial
specialization exists when every instance of a supertype does not have to be an
instance of a subtype.
Question 117.
Explain The Difference Between An Erd And Eer?
Answer
: An EER includes everything in an ERD
and an EER allows for more complex relationships than an ERD. An EER allows for
object-oriented data modeling and include supertypes and subtypes entities and
inheritance.
Question 118.
Explain The Difference Between The Disjoint And Overlap Rule?
Answer
: The disjoint rule states an entity
instance of a supertype can only be a member of one subtype. The overlap rule
states an entity instance of a supertype can be a member of multiple subtypes.
Question 119.
List The Three Types Of Business Rules And Define Each Of Them?
Answer
: A derivation is a statement that is
derived from other knowledge. A structured assertion is a statement that
expresses some aspect of the static structure of an organization. An action
assertion is a statement of a constraint on the actions of an organization.
Question 120.
Explain How A Scenario Is Used For Business Rules?
Answer
: A scenario is used to test business
rules. It is a short script that describes how a business reacts to certain
situations.
Question 121.
Explain Some Of The Main Goals Of Normalization?
Answer
: Normalization should minimize data
redundancy. It should also simplify referential integrity constraints.
Normalization will also make it easier to insert, update, and delete data. And
finally, it provides better design.
Question 122.
List Some Of The Properties Of A Relation?
Answer
: Relations in a database have a
unique name and no multivalued attributes exist. Each row is unique and each
attribute within a relation has a unique name. The sequence of both columns and
rows is irrelevant.
Question 123.
Explain What Needs To Happen To Convert A Relation To Third Normal Form?
Answer
: First you must verify that a
relation is in both first normal form and second normal form. If the relation
is not, you must convert into second normal form. After a relation is in second
normal form, you must remove all transitive dependencies.
Question 124.
Describe How A Supertype/ Subtype Relationship Is Mapped Into A Relation?
Answer
: A separate relation is created for
each supertype and subtype. The attributes common for all of the subtypes are
assigned to the supertype. Each subtype has the primary key from the supertype
assigned to it. A subtype discriminator is added to the supertype.
Question 125.
Describe Domain Constraints?
Answer
: Domain constraints include entity
integrity and referential integrity. The domain is a set of values that may be
assigned to an attribute. The entity integrity rule states that no part of a
primary key cannot be null. Referential integrity states that each foreign key
value must match a primary key value or be null.
Question 126.
What Are The Four Objectives Of The Selection Of A Data Type?
Answer
: A data type should be selected so
that all possible values are represented using minimal storage space. The data
type should help to ensure data integrity and support all possible data
manipulations (i.e., cannot place a letter in a field such as salary where a
number is required).
Question 127.
Describe The Differences Between Vertical And Horizontal Portioning?
Answer
: Horizontal portioning is where the
rows in a relation are separated by some criteria and placed into a new
relation or file with the same layout as the original relation (in this case
only the records in each file differ). Vertical portioning is where the columns
in a relation are separated by some criteria and placed into a new relation or
file with a different layout as the original relation.
Question 128.
Explain The Difference Between A Dynamic And Materialized View?
Answer
: A dynamic view may be created every
time that a specific view is requested by a user. A materialized view is
created and or updated infrequently and it must be synchronized with its
associated base table(s).
Question 129.
Discuss Some Of The Techniques That Can Be Used To Tune Operational Performance?
Answer
: Choosing primary and secondary keys
can increase the speed of row selection, joining, and row ordering. Selecting
the appropriate file organization for base tables and indexes can also improve
performance. Clustering related rows together and maintaining statistics about
tables and indexes can lead to increased efficiency.
Question 130.
Briefly Describe The Three Types Of Sql Commands?
Answer
: Data definition language commands
are used to create, alter, and drop tables. Data manipulation commands are used
to insert, modify, update, and query data in the database. Data control
language commands help the DBA to control the database.
Question 131.
What Are The Steps To Follow When Preparing To Create A Table?
Answer
:
· Identify the data type, length, and
precision for each attribute.
· Identify the columns that can accept
a null value.
· Identify the columns that need to be
unique.
· Identify primary and related foreign
keys with the parent table being created before the child.
· Determine default values.
· Determine where the domain values
are that need to be constrained.
· Create the indexes.
Question 132.
What Are Some Disadvantages Of A Standard Language Such As Sql?
Answer
: A standard language can hinder the
effort to create a new language. One standard is never enough to meet all of
the business needs. A standard can be a compromise among interested parties
which can cause the standard to not be ideal. If a standard is altered by some,
than portability between platforms could be hurt.
Question 133.
Describe And Contrast A Trigger And A Procedure?
Answer
: Triggers are stored and controlled
in the DBMS. A trigger is executed automatically when a condition is met
(INSERT, UPDATE, or DELETE). A procedure is also stored in a database. A
procedure is not executed automatically.
Question 134.
Briefly Describe An Outer Join?
Answer
: An outer join includes the records
that match and those that do not have a matching value in another table. Outer
joins can be a LEFT outer join (includes all records from the first table
listed) or a RIGHT outer join (includes all records from the second table
listed). Outer joins are not easily used with more than two tables.
Question 135.
Describe A Subquery?
Answer
: A subquery is a query that is
composed of two queries. The first query (inner query) is within the WHERE
clause of the other query (outer query). In some cases the inner query provides
results for the outer query to process. In other cases, the outer query results
provide results for the inner query (correlated subquery).
Question 136.
Describe The Difference Between Embedded And Dynamic Sql?
Answer
: Embedded SQL is the process of
including hard coded SQL statements. These statements do not change unless the
source code is modified. Dynamic SQL is the process of generating SQL on the
fly. The statements generated do not have to be the same each time.
Question 137.
Explain The Difference Between Two And Three-tier Architectures?
Answer
: A three-tier architecture includes a
client and two server layers. The application code is stored on the application
server and the database is stored on the database server. A two-tier
architecture includes a client and one server layer. The database is stored on
the database server.
Question 138.
Describe And Contrast Sql And Qbe?
Answer
: QBE is a direct-manipulation
database language that uses a graphical approach to query construction. Some
database systems translate QBE queries into SQL. QBE does not adhere to a
standard but SQL does. Both SQL and QBE are relational database languages.
Question 139.
Describe Odbc?
Answer
: ODBC is a standard that contains an
interface that provides a common language for application programs to access
and process SQL databases. In order to use ODBC, a driver, server name,
database name, user id, and password are required. ODBC is important for
Internet applications and has gained wide acceptance.
Question 140.
Compare A Thin And A Fat Client?
Answer
: A fat client is a PC that is
responsible where most processing occurs on the client rather than the server.
Some of the fat client activities include processing, presentation logic, and
business rules logic. A thin client is a PC where only limited processing
occurs. In these cases, more processing should occur on the application server.
Question 141.
Describe Some Reasons That Someone Familiar With Microsoft Access Will Want To
Learn Vba?
Answer
: You can perform more complex
functions and error handling can be accommodated by VBA. VBA code will execute
faster since code runs faster than macros and maintenance is easier because VBA
modules are stored with the forms and reports. Reading VBA is easier because
you can see the entire code. Finally, you can pass parameters and use OLE
automation better.
Question 142.
Describe Middleware Applications That Ease The Connection Of Databases To Web
Applications?
Answer
: Both ASP and ColdFusion are
middleware that ease the connection of databases to Web applications. Both
require the use of several files. Both use tags and are executed on the server.
Both Internet Explorer and Netscape can access these files. The programmer does
not need to be concerned with the client when they work with this middleware.
Question 143.
Describe Web Services?
Answer
: Web Services are improving the
ability of computers to communicate over the Internet. These services use XML
programs and usually run in the background. Easier integration of applications
may be possible because developers do not need to be familiar with the
technical details with applications that are being integrated. UDDI is a
technical specification for creating a distributed registry of Web services and
businesses that are open to communicating through Web services.
Question 144.
Provide An Overview Of Xml?
Answer
: XML Is used to structure and
manipulate data involved with a browser and is becoming the standard for ec
ommerce. XML uses tags that are similar to HTML in that they use the angle
brackets, but XML describes the content whereas HTML describes the appearance.
The XML schema standard was published in May 2001 by W3C.
Question 145.
Describe Website Security Issues?
Answer
: Website security issues include
unauthorized access to the several aspects of one’s Website. Security measures
should include all aspects of the system such as the network, operating level,
database, and Web server. Regular monitoring and security testing by a company
should help to avoid intrusion into one’s system.
Question 146.
Describe A Data Warehouse?
Answer
: A data warehouse is organized around
specific subjects. The data is defined using consistent naming, format, and
encoding structure standards. The data contains a time element, so that the
data can be studied for trends. No data in a data warehouse can be updated by
end users.
Question 147.
Explain Why An Information Gap Exists In Most Organizations?
Answer
: One reason that an information gap
exists is the fact that systems have been developed in separate, segmented
efforts. This has helped the data from being stored in an integrated database
and thus the data is in an inconsistent structure. The other reason for the gap
is that most systems are created to support the operational aspect of an
organization. The systems were not developed for decision making.
Question 148.
Describe The Differences Between A Data Warehouse And Data Mart?
Answer
: A data warehouse is for the
enterprise and contains multiple subjects. A data mart is for a specific
functional area and focuses on one subject. A data warehouse is flexible and
data-oriented and contains detailed historical data. A data mart is restrictive
and project-oriented and contains some historical data.
Question 149.
Describe The Difference Between Data And Database Administration?
Answer
: Data administration is responsible
for the overall management of data resources. Some of the core roles include
the creation of data polices, procedures and standards, resolve data ownership
issues, and manage the information repository. Database administration is
physical database oversight. Some of the core duties include the selection of
the DBMS and software tools, the installation and upgrade of the DBMS, and
database performance tuning.
Question 150.
What Are Some Of The Important Security Features Of A Dbms?
Answer
: One of the features includes the use
of views which allows the presentation of only data needed by someone and
limits the capability of database updates. The use of integrity controls
includes such things as domains, assertions, and checks. Also authorization
rules, user-defined procedures, encryption, authentication schemes, and backups
are important.
Question 151.
Describe Concurrency Control?
Answer
: Concurrency control is the process
managing simultaneous operations against a database so that database integrity
is not compromised. There are two approaches to concurrency control. The
pessimistic approach involves locking and the optimistic approach involves
versioning.
Question 152.
Explain Locking?
Answer
: Locking is denying others the
ability to update a record until someone completes the update or releases the
record. Locking can occur on many different levels in a database. It can occur
at the database, table, record, or field level. A lock can be shared (another
can read the record while an update is in progress) or exclusive (no one can
read the record while an update is in progress).
Question 153.
Explain Issues For Database Performance?
Answer
: The installation of the database is
an important issue since the better the installation, the better the
performance could be. Memory usage is learning how the DBMS uses main memory
and then using that knowledge to enable better performance. I/O is usually very
intense in a DB, so understanding how users will use the data will help to
prepare the database better. CPU usage and application tuning are also
important considerations.
Question 154.
Explain Snapshot Replication?
Answer
: Snapshot replication can be used
when an application does not require that the data always be current. These
applications can be updated by periodic table copying or snapshots. As part of
the snapshot effort, all of the data to be included in the snapshot is
collected at a primary point. Then a read-only snapshot is taken and the
snapshot is sent to each site so that the update can be made.
Question 155.
Explain Concurrency Transparency?
Answer
: Concurrency transparency is where
each transaction in a distributed database is treated as if it is the only one
in the system. Therefore If several transactions are running at one time, the
results will be the same as If each transaction was run in serial order. The
transaction manager helps to provide concurrency control. The three methods
that may be used are locking, versioning, and time stamping.
Question 156.
What Is The Difference Between Horizontal And Vertical Partitioning?
Answer
: Horizontal partitioning is where
some rows of a table are placed into the base relations at one site and other
rows are placed at another site. Vertical partitioning is where some columns of
a table are placed into the base relations at one site and other columns are
placed at another site but each all of these relations must share a common
domain.
Question 157.
What Is A Distributed Database?
Answer
: A distributed database is a single
logical database that is spread across more than one node or locations that are
all connected via some communication link. It requires multiple DBMSs, running
at each remote site. A distributed database can be either homogenous (same DBMS
at each node) or heterogeneous (different DBMS at some nodes).
Question 158.
Describe The Difference Between Homogeneous And Heterogeneous Distributed
Database?
Answer
: A homogenous database is one that
uses the same DBMS at each node. Either each node can work independently or a
central DBMS may coordinate database activities. A heterogeneous database is
one that may have a different DBMS at each node. It may support some or all of
the functionality of one logical database. It may support full Distributed DBMS
functionality or partial Distributed DBMS functionality.
Question 159.
What Is Database?
Answer
: A database is a logically coherent
collection of data with some inherent meaning, representing some aspect of real
world and which is designed, built and populated with data for a specific
purpose.
Question 160.
What Is Dbms?
Answer
: It is a collection of programs that
enables user to create and maintain a database. In other words it is
general-purpose software that provides the users with the processes of
defining, constructing and manipulating the database for various applications.
Question 161.
What Is A Database System?
Answer
: The database and DBMS software
together is called as Database system.
Question 162.
Advantages Of Dbms?
Answer
:
·
Redundancy
is controlled.
·
Unauthorised
access is restricted.
·
Providing
multiple user interfaces.
·
Enforcing
integrity constraints.
·
Providing
backup and recovery.
Question 163.
Disadvantage In File Processing System?
Answer
:
· Data redundancy & inconsistency.
· Difficult in accessing data.
· Data isolation.
· Data integrity.
· Concurrent access is not possible.
· Security Problems.
Question 164.
Describe The Three Levels Of Data Abstraction?
Answer
:The are three levels of abstraction:
•Physical
level: The lowest level of abstraction describes how data are stored.
• Logical level: The next higher level of abstraction, describes what data are
stored in database and what relationship among those data.
• View level:
The highest level of abstraction describes only part of entire database.
Question 165.
Define The "integrity Rules"?
Answer
: There are two Integrity rules.
• Entity
Integrity: States that “Primary key cannot have NULL value”
• Referential
Integrity: States that “Foreign Key can be either a NULL value or should be
Primary Key value of other relation.
Question 166.
What Is Extension And Intension?
Answer
: Extension –
It is the
number of tuples present in a table at any instance. This is time dependent.
Intension –
It is a
constant value that gives the name, structure of table and the constraints laid
on it.
Question 167.
What Is System R? What Are Its Two Major Subsystems?
Answer
: System R was designed and developed
over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and
its purpose was to demonstrate that it is possible to build a Relational System
that can be used in a real life environment to solve real life problems, with
performance at least comparable to that of existing system. Its two subsystems
are
• Research
Storage
• System
Relational Data System.
Question 168.
How Is The Data Structure Of System R Different From The Relational Structure?
Answer
:Unlike Relational systems in System
R
• Domains are
not supported
• Enforcement
of candidate key uniqueness is optional
• Enforcement
of entity integrity is optional
• Referential
integrity is not enforced
Question 169.
What Is Data Independence?
Answer
: Data independence means that “the
application is independent of the storage structure and access strategy of
data”. In other words, The ability to modify the schema definition in one level
should not affect the schema definition in the next higher level. Two types of
Data Independence:
• Physical Data
Independence: Modification in physical level should not affect the logical
level.
• Logical Data Independence: Modification in logical level should affect the
view level.
Question 170.
What Is A View? How It Is Related To Data Independence?
Answer
: A view may be thought of as a
virtual table, that is, a table that does not really exist in its own right but
is instead derived from one or more underlying base table. In other words,
there is no stored file that direct represents the view instead a definition of
view is stored in data dictionary. Growth and restructuring of base tables is
not reflected in views. Thus the view can insulate users from the effects of
restructuring and growth in the database. Hence accounts for logical data
independence.
Question 171.
What Is Data Model?
Answer
: A collection of conceptual tools for
describing data, data relationships data semantics and constraints.
Question 172.
What Is E-r Model?
Answer
: This data model is based on real
world that consists of basic objects called entities and of relationship among
these objects. Entities are described in a database by a set of attributes.
Question 173.
What Is Object Oriented Model?
Answer
:
This model is based on collection of
objects. An object contains values stored in instance variables with in the
object. An object also contains bodies of code that operate on the object.
These bodies of code are called methods. Objects that contain same types of
values and the same methods are grouped together into classes.
Question 174.
What Is An Entity?
Answer
: It is a 'thing' in the real world
with an independent existence.
Question 175.
What Is An Entity Type?
Answer
: It is a collection (set) of entities
that have same attributes.
Question 176.
What Is An Entity Set?
Answer
: It is a collection of all entities
of particular entity type in the database.
Question 177.
What Is An Extension Of Entity Type?
Answer
: The collections of entities of a
particular entity type are grouped together into an entity set.
Question 178.
What Is Weak Entity Set?
Answer
: An entity set may not have
sufficient attributes to form a primary key, and its primary key compromises of
its partial key and primary key of its parent entity, then it is said to be
Weak Entity set.
Question 179.
What Is An Attribute?
Answer
: It is a particular property, which
describes the entity.
Question 180.
What Is A Relation Schema And A Relation?
Answer
: A relation Schema denoted by R(A1,
A2, …, An) is made up of the relation name R and the list of attributes Ai that
it contains. A relation is defined as a set of tuples. Let r be the relation
which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list
of n-values t=(v1,v2, ..., vn).
Question 181.
What Is Degree Of A Relation?
Answer
: It is the number of attribute of its
relation schema.
Question 182.
What Is Relationship?
Answer
: It is an association among two or
more entities.
Question 183.
What Do You Understand By Dependency Preservation?
Answer
: Given a relation R and a set of FDs
F, dependency preservation states that the closure of the union of the
projection of F on each decomposed relation Ri is equal to the closure of F.
i.e.,
((PR1(F)) U … U (PRn(F)))+ = F+
if
decomposition is not dependency preserving, then some dependency is lost in the
decomposition.
Question 184.
How Can You Find The Minimal Key Of Relational Schema?
Answer
: Minimal key is one which can
identify each tuple of the given relation schema uniquely. For finding the
minimal key it is required to find the closure that is the set of all
attributes that are dependent on any given set of attributes under the given
set of functional dependency.
Algo. I
Determining X+, closure for X, given set of FDs F
1.
Set
X+ = X
2.
Set
Old X+ = X+
3.
For
each FD Y Z in F and if Y belongs to X+ then add Z to X+
4.
Repeat
steps 2 and 3 until Old X+ = X+
Algo.II
Determining minimal K for relation schema R, given set of FDs F
1.
Set
K to R that is making K a set of all attributes in R
2.
For
each attribute A in K
3.
a. Compute (K – A)+ with respect to F
b. If (K – A)+ = R then set K = (K – A)+
Question 185.
What Are Armstrong Rules? How Do We Say That They Are Complete And/or Sound?
Answer
:
The well-known inference rules for
FDs
• Reflexive rule :
If Y is subset or equal to X then X Y.
• Augmentation rule:
If X Y then XZ YZ.
• Transitive rule:
If {X Y, Y Z} then X Z.
• Decomposition rule :
If X YZ then X Y.
• Union or Additive rule:
If {X Y, X Z} then X YZ.
• Pseudo Transitive rule :
If {X Y, WY Z} then WX Z.
Of these the first three are known as Amstrong Rules. They are sound because it
is enough if a set of FDs satisfy these three. They are called complete because
using these three rules we can generate the rest all inference rules.
Question 186.
What Are Stored-procedures? And What Are The Advantages Of Using Them?
Answer
: Stored procedures are database
objects that perform a user defined operation. A stored procedure can have a
set of compound SQL statements. A stored procedure executes the SQL commands
and returns the result to the client. Stored procedures are used to reduce
network traffic.
Question 187.
Name Two Utilities That Oracle Provides, Which Are Use For Backup And Recovery?
Answer
: Along with the RDBMS software,
Oracle provides two utilities that you can use to back up and restore the
database. These utilities are Export and Import.
The Export utility dumps the
definitions and data for the specified part of the database to an operating
system binary file. The Import utility reads the file produced by an export,
recreates the definitions of objects, and inserts the data.
If Export and Import are used as a
means of backing up and recovering the database, all the changes made to the
database cannot be recovered since the export was performed. The best you can
do is recover the database to the time when the export was last performed.
Question 188.
What Is Oracle Block? Can Two Oracle Blocks Have The Same Address?
Answer
:
Oracle "formats" the
database files into a number of Oracle blocks when they are first
created—making it easier for the RDBMS software to manage the files and easier
to read data into the memory areas.
The block size should be a multiple
of the operating system block size. Regardless of the block size, the entire
block is not available for holding data; Oracle takes up some space to manage
the contents of the block. This block header has a minimum size, but it can
grow. These Oracle blocks are the smallest unit of storage. Increasing the
Oracle block size can improve performance, but it should be done only when the
database is first created. Each Oracle block is numbered sequentially for each
database file starting at 1. Two blocks can have the same block address if they
are in different database files.
Question 189.
What Is Rowid?
Answer
: The ROWID is a unique database-wide
physical address for every row on every table. Once assigned (when the row is
first inserted into the database), it never changes until the row is deleted or
the table is dropped.
The ROWID
consists of the following three components, the combination of which uniquely
identifies the physical storage location of the row.
• Oracle database file number, which
contains the block with the rows
• Oracle block address, which contains the row
• The row within the block (because each block can hold many rows)
The ROWID is used internally in indexes as a quick means of retrieving rows
with a particular key value. Application developers also use it in SQL
statements as a quick way to access a row once they know the ROWID.
Question 190.
What Are The Four Oracle System Processes That Must Always Be Up And Running
For The Database To Be Useable?
Answer
: The four Oracle system processes
that must always be up and running for the database to be useable include DBWR
(Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process
Monitor).
Question 191.
What Is An Oracle Instance?
Answer
: The Oracle system processes, also
known as Oracle background processes, provide functions for the user
processes—functions that would otherwise be done by the user processes
themselves Oracle database-wide system memory is known as the SGA, the system
global area or shared global area. The data and control structures in the SGA
are shareable, and all the Oracle background processes and user processes can
use them.
The combination of the SGA and the
Oracle background processes is known as an Oracle instance.
Question 192.
Name The Three Major Set Of Files On Disk That Compose A Database In Oracle?
Answer : There are three major sets of files
on disk that compose a database. All the files are binary. These are
• Database files
• Control files
• Redo logs
The most important of these are the
database files where the actual data resides. The control files and the redo
logs support the functioning of the architecture itself.
All three sets of files must be
present, open, and available to Oracle for any data on the database to be
useable. Without these files, you cannot access the database, and the database
administrator might have to recover some or all of the database using a backup,
if there is one.
Question 193.
Define Sql And State The Differences Between Sql And Other Conventional
Programming Languages?
Answer
: SQL is a nonprocedural language that
is designed specifically for data access operations on normalized relational
database structures. The primary difference between SQL and other conventional
programming languages is that SQL statements specify what data operations
should be performed rather than how to perform them.
Question 194.
Name The Sub-systems Of A Rdbms?
Answer
: I/O, Security, Language Processing,
Process Control, Storage Management, Logging and Recovery, Distribution
Control, Transaction Control, Memory Management, Lock Management.
Question 195.
Which Part Of The Rdbms Takes Care Of The Data Dictionary? How?
Answer
:
Data dictionary is a set of tables
and database objects that is stored in a special area of the database and
maintained exclusively by the kernel.
Question 196.
What Are The Primitive Operations Common To All Record Management Systems ?
Answer
: Addition, deletion and modification.
Question 197.
What Is A Candidate Key?
Answer
: candidate key is a column in a table
which has the ability to become a primary key.
Question 198.
What Is The Foreign Key?
Answer
: A foreign key is a field in a table
that refers to parent records in another table. The references are represented
by the primary key values of the corresponding parent records. A foreign key
field is the same data type as the primary key field of the referenced table.
Usually, a foreign key field is named the same as the primary key field of the
parent table. This very beneficial convention is called key migration in data
modeling terminology. Child table foreign key references to parent table
primary keys embody database relationships.
Question 199.
What Is Union,union All?
Answer
:
UNION retrieves
a single set of rows and columns removing the duplicated row.
UNION ALL
retrieves all the rows including duplication.
Question 200.
Explain The Difference Between A Database Administrator And A Data
Administrator?
Answer
:
Database Administrator :- A person
(or group of people) responsible for the maintenance and performance of a
database and responsible for the planning, implementation, configuration, and
administration of relational database management systems.
Data Administrator :- The individual
or organization responsible for the specification, acquisition, and maintenance
of data management software and the design, validation, and security of files
or databases. The DA is in charge of the data dictionary and data model.
Question 201.
Why Is It Important To Write To The Log Before Changing The Database Values?
Answer
: The most important objective to
write the log before the database is changed is if there is any need to
rollback or rollforward any transaction then if the log are not present then
the rollback rollforward cannot be done accurately.
Question 202.
Define Rollback And Roll Forward?
Answer
:
Rollback :- Undoing the changes made
by a transaction before it commits or to cancel any changes to a database made
during the current transaction.
RollForward :- Re-doing the changes
made by a transaction after it commits or to overwrite the chnaged calue again
to ensure consistency.
Question 203.
Explain How A Database Could Be Recovered Via Reprocessing. Why Is This
Generally Not Feasible?
Answer
: If we reprocess the transaction then
the database can be made to come to a state where the database is consistent
and so reprocessing the log can recover the database. Reprocessing is not very
feasible for a very simple reason that its very costly from time point of view
and requires lots of rework and many transaction are even rollback giving more
and more rework.
Question 204.
Explain The Necessity Of Defining Processing Rights And Responsibilities. How
Are Such Responsibilities Enforced?
Answer
: One of the reason to define rights
is the security in the database system. If any user is allowed to define the
data or alter the data then the database would just be of no use and so
processing rights and responsibilities are clearly defined in any database
system. The resposibilities are enforced using the table space provided by the
database system.
Question 205.
Explain The Meaning Of The Expression Acid Transaction?
Answer
: ACID means Atomic, Consistency,
Isolation, Durability, so when any transaction happen it should be Atomic that
is it should either be complete or fully incomplete. There should not be
anything like Semi complete. The Database State should remain consistent after
the completion of the transaction. If there are more than one Transaction then
the transaction should be scheduled in such a fashion that they remain in
Isolation of one another.Durability means that Once a transaction commits, its
effects will persist even if there are system failures.
Question 206.
In General, How Should The Boundaries Of A Transaction Be Defined?
Answer
: transaction ensures that one or more
operations execute as an atomic unit of work. If one of the operations within a
transaction fails, then all of them are rolled-back so that the application is
returned to its prior state. The boundaries that define a group of operations
done within a single transaction.
Question 207.
What Is Lock Granularity?
Answer
: There are many locks available for
the database system to have likeIntent Shared, Shared, Intent exclusive,
exclusive and Shared Intent exclusive.
Locking granularity refers to the size and hence the number of locks used to ensure the consistency of a database during multiple concurrent updates.