What is database?
A database is a logically coherent collection of data with
some inherent meaning, representing some aspect of real world which is
designed, built and populated with data for a specific purpose.
What is DBMS?
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.
What is a Database system?
The database and DBMS software together is called as
Database system.
Advantages of DBMS?
·
Redundancy is controlled.
·
Unauthorised access is restricted.
·
Providing multiple user interfaces.
·
Enforcing integrity constraints.
·
Providing backup and recovery.
Disadvantage in File Processing System?
·
Data redundancy & inconsistency.
·
Difficult in accessing data.
·
Data isolation.
·
Data integrity.
·
Concurrent access is not possible.
·
Security Problems.
Describe the three levels of data abstraction?
There 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.
Define the "integrity rules"
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.
What is extension and intension?
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.
What is System R?
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.
How is the data structure of System R different from the
relational structure?
·
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
What is Data Independence?
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.
NOTE: Logical Data Independence is more difficult to
achieve
What is a view? How it is related to data independence?
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
directly 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.
What is Data Model?
A collection of conceptual tools for describing data, data
relationships data semantics and constraints.
What is E-R model?
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.
What is Object Oriented model?
This model is based on collection of objects. An object
contains values stored in instance variables within 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.
What is an Entity?
It is a 'thing' in the real world with an independent
existence.
What is an Entity type?
It is a collection (set) of entities that have same
attributes.
What is an Entity set?
It is a collection of all entities of particular entity
type in the database.
What is an Extension of entity type?
The collections of entities of a particular entity type are
grouped together into an entity set.
What is Weak Entity set?
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.
What is an attribute?
It is a particular property, which describes the entity.
What is Relation Schema and Relation?
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).
What is degree of a Relation?
It is the number of attribute of its relation schema.
What is Relationship?
It is an association among two or more entities.
What is Relationship set?
The collection (or set) of similar relationships.
What is Relationship type?
Relationship type defines a set of associations or a
relationship set among a given set of entity types.
What is degree of Relationship type?
It is the number of entity type participating.
What is DDL (Data Definition Language)?
A data base schema is specifies by a set of definitions
expressed by a special language called DDL.
What is VDL (View Definition Language)?
It specifies user views and their mappings to the conceptual
schema.
What is SDL (Storage Definition Language)?
This language is to specify the internal schema. This
language may specify the mapping between two schemas.
What is Data Storage - Definition Language?
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.
What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data
as organised by appropriate data model.
Procedural DML or Low level: DML requires a user to specify what data are needed and
how to get those data.
Non-Procedural DML or High level: DML requires a user to specify what data are
needed without specifying how to get those data.
What is DML Compiler?
It translates DML statements in a query language into
low-level instruction that the query evaluation engine can understand.
What is Query evaluation engine?
It executes low-level instruction generated by compiler.
What is DDL Interpreter?
It interprets DDL statements and records them in tables
containing metadata.
What is Record-at-a-time?
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.
What is Set-at-a-time or Set-oriented?
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.
What is Relational Algebra?
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.
What is Relational Calculus?
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.
How does Tuple-oriented relational calculus differ from
domain-oriented relational calculus?
The tuple-oriented calculus uses a tuple variables i.e.,
variable whose only permitted values are tuples of that relation. E.g. QUEL
The domain-oriented calculus has domain variables i.e.,
variables that range over the underlying domains instead of over relation. E.g.
ILL, DEDUCE.
What is normalization?
It is a process of analysing the given relation schemas
based on their Functional Dependencies (FDs) and primary key to achieve the
properties
·
Minimizing redundancy
·
Minimizing insertion, deletion and update
anomalies.
What is Functional Dependency?
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 t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This
means the value of X component of a tuple uniquely determines the value of
component Y.
When is a functional dependency F said to be minimal?
·
Every dependency in F has a single attribute for
its right hand side.
·
We cannot replace any dependency X A in F with a
dependency Y A where Y is a proper subset of X and still have a set of
dependency that is equivalent to F.
·
We cannot remove any dependency from F and still
have set of dependency that is equivalent to F.
What is Multivalued dependency?
Multivalued dependency denoted by X Y specified on relation
schema R, where X and Y are both subsets of R, specifies the following
constraint on any relation r of R: if two tuples t1 and t2 exist in r such that
t1[X] = t2[X] then t3 and t4 should also exist in r with the following
properties
·
t3[x] = t4[X] = t1[X] = t2[X]
·
t3[Y] = t1[Y] and t4[Y] = t2[Y]
·
t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
What is Lossless join property?
It guarantees that the spurious tuple generation does not
occur with respect to relation schemas after decomposition.
What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple,
indivisible) values.
45. What is Fully Functional dependency?
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.
What is 2NF?
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.
What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every
FD X A either of the following is true
·
X is a Super-key of R.
·
A is a prime attribute of R.
In other words, if every non prime attribute is
non-transitively dependent on primary key.
What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and
satisfies an additional constraint that for every FD X A, X must be a candidate
key.
What is 4NF?
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
·
X is subset or equal to (or) XY = R.
·
X is a super key.
What is 5NF?
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
·
Ri = R for some i.
·
The join dependency is implied by the set of FD,
over R in which the left side is key of R.
What is Domain-Key Normal Form?
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.
What are partial, alternate,, artificial, compound and
natural key?
Partial Key:
It is a set of attributes that can uniquely identify weak
entities and that are related to same owner entity. It is sometime called as
Discriminator.
Alternate Key:
All Candidate Keys excluding the Primary Key are known as
Alternate Keys.
Artificial Key:
If no obvious key, either stand alone or compound is
available, then the last resort is to simply create a key, by assigning a
unique number to each record or occurrence. Then this is known as developing an
artificial key.
Compound Key:
If no single data element uniquely identifies occurrences
within a construct, then combining multiple elements to create a unique
identifier for the construct is known as creating a compound key.
Natural Key:
When one of the data elements stored within a construct is
utilized as the primary key, then it is called the natural key.
What is indexing and what are the different kinds of
indexing?
Indexing is a technique for determining how quickly
specific data can be found.
Types:
·
Binary search style indexing
·
B-Tree indexing
·
Inverted list indexing
·
Memory resident table
·
Table indexing
What is system catalog or catalog relation? How is better
known as?
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.
What is meant by query
optimization?
The phase that identifies an efficient execution plan for
evaluating a query that has the
least estimated cost is referred to as
query optimization.
What is join dependency and inclusion dependency?
Join Dependency:
A Join dependency is generalization of Multivalued
dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2,
R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound
and complete inference rules for JD.
Inclusion Dependency:
An Inclusion Dependency is a statement of the form that
some columns of a relation are contained in other columns. A foreign key
constraint is an example of inclusion dependency.
What is durability in DBMS?
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.
What do you mean by atomicity and aggregation?
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.
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.
What is a Phantom Deadlock?
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.
What is a checkpoint and When does it occur?
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.
What are the different phases of transaction?
Different phases are
- Analysis phase
- Redo Phase
- Undo phase
What do you mean by flat file database?
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.
What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from
user.
Brief theory of Network, Hierarchical schemas and their
properties
Network schema uses a graph data structure to organize
records example for such a database management system is CTCG while a
hierarchical schema uses a tree data structure example for such a system is
IMS.
What is a query?
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.
What do you mean by Correlated subquery?
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.
E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE
From ORDER Where CUST.CNUM = ORDER.CNUM)
What are the primitive operations common to all record
management systems?
Addition, deletion and modification.
Name the buffer in which all the commands that are typed
in are stored
'Edit’ Buffer
What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
Are the resulting relations of PRODUCT and JOIN operation
the same?
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.
What is RDBMS KERNEL?
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
.
Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control,
Storage Management, Logging and Recovery, Distribution Control, Transaction
Control, Memory Management, Lock Management
Which part of the RDBMS takes care of the data dictionary?
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.
What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence
of the objects, provides access to them, and maps the actual physical storage
location.
Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the
data
How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query
Language (SQL)
Define SQL and state the differences between SQL and other
conventional programming
Languages
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.
Name the three major set of files on disk that compose a
database in Oracle
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.
What is an Oracle Instance?
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
What are the four Oracle system processes that must always be
up and running for the database
to be useable?
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).
What are database files, control files and log files. How
many of these files should a database
have at least? Why?
Database Files
The database files hold the actual data and are typically
the largest in size. Depending on their sizes, the tables (and other objects)
for all the user accounts can go in one database file—but that's not an ideal
situation because it does not make the database structure very flexible for
controlling access to storage for different users, putting the database on
different disk drives, or backing up and restoring just part of the database.
You must have at least one database file but usually, more
than one files are used. In terms of accessing and using the data in the tables
and other objects, the number (or location) of the files is immaterial.
The database files are fixed in size and never grow bigger
than the size at which they were created
Control Files
The control files and redo logs support the rest of the
architecture. Any database must have at least one control file, although you
typically have more than one to guard against loss. The control file records
the name of the database, the date and time it was created, the location of the
database and redo logs, and the synchronization information to ensure that all
three sets of files are always in step. Every time you add a new database or
redo log file to the database, the information is recorded in the control
files.
Redo Logs
Any database must have at least two redo logs. These are
the journals for the database; the redo logs record all changes to the user
objects or system objects. If any type of failure occurs, the changes recorded
in the redo logs can be used to bring the database to a consistent state
without losing any committed transactions. In the case of non-data loss
failure, Oracle can apply the information in the redo logs automatically
without intervention from the DBA.
The redo log files are fixed in size and never grow
dynamically from the size at which they were created.
What is ROWID?
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
What is Oracle Block? Can two Oracle Blocks have the same
address?
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.
What is database Trigger?
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.
Name two utilities that Oracle provides, which are use for
backup and recovery.
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.
What are stored-procedures? And what are the advantages of
using them?
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.
How are exceptions handled in PL/SQL? Give some of the
internal exceptions' name
PL/SQL exception handling is a mechanism for dealing with
run-time errors encountered during procedure execution. Use of this mechanism
enables execution to continue if the error is not severe enough to cause
procedure termination.
The exception handler must be defined within a subprogram
specification. Errors cause the program to raise an exception with a transfer
of control to the exception-handler block. After the exception handler
executes, control returns to the block in which the handler was defined. If
there are no more executable statements in the block, control returns to the
caller.
User-Defined Exceptions
PL/SQL enables the user to define exception handlers in the
declarations area of subprogram specifications. User accomplishes this by
naming an exception as in the following example:
ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code
associated with this handler is written in the EXCEPTION specification area as
follows:
EXCEPTION
when OT_FAILURE then
out_status_code := g_out_status_code;
out_msg := g_out_msg;
The following is an example of a subprogram exception:
EXCEPTION
when NO_DATA_FOUND then
g_out_status_code := 'FAIL';
RAISE ot_failure;
Within this exception is the RAISE statement that transfers
control back to the ot_failure exception handler. This technique of raising the
exception is used to invoke all user-defined exceptions.
System-Defined Exceptions
Exceptions internal to PL/SQL are raised automatically upon
error. NO_DATA_FOUND is a system-defined exception. Table below gives a
complete list of internal exceptions.
PL/SQL internal exceptions.
Exception Name
Oracle Error
CURSOR_ALREADY_OPEN ORA-06511
DUP_VAL_ON_INDEX ORA-00001
INVALID_CURSOR ORA-01001
INVALID_NUMBER ORA-01722
LOGIN_DENIED ORA-01017
NO_DATA_FOUND ORA-01403
NOT_LOGGED_ON ORA-01012
PROGRAM_ERROR ORA-06501
STORAGE_ERROR ORA-06500
TIMEOUT_ON_RESOURCE ORA-00051
TOO_MANY_ROWS ORA-01422
TRANSACTION_BACKED_OUT ORA-00061
VALUE_ERROR ORA-06502
ZERO_DIVIDE ORA-01476
In addition to this list of exceptions, there is a
catch-all exception named OTHERS that traps all errors for which specific error
handling has not been established.
Does PL/SQL support "overloading"? Explain
The concept of overloading in PL/SQL relates to the idea
that you can define procedures and functions with the same name. PL/SQL does
not look only at the referenced name, however, to resolve a procedure or
function call. The count and data types of formal parameters are also
considered.
PL/SQL also attempts to resolve any procedure or function
calls in locally defined packages before looking at globally defined packages
or internal functions. To further ensure calling the proper procedure, you can
use the dot notation. Prefacing a procedure or function name with the package
name fully qualifies any procedure or function reference.
Tables derived from the ERD
a) Are totally unnormalised
b) Are always in 1NF
c) Can be further denormalised
d) May have multi-valued attributes
(b) Are always in 1NF
Spurious tuples may occur due to
i. Bad normalization
ii. Theta joins
iii. Updating tables from join
a) i & ii b) ii & iii
c) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys
that are not primary keys.
A B C is a set of attributes. The functional dependency is as
follows
AB -> B
AC -> C
C -> B
a) is in 1NF
b) is in 2NF
c) is in 3NF
d) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the
primary key. Since C B is a FD given, where neither C is a Key nor B is a prime
attribute, this it is not in 3NF. Further B is not functionally dependent on
key AC thus it is not in 2NF. Thus the given FDs is in 1NF.
In mapping of ERD to DFD
a) entities in ERD should correspond to an existing
entity/store in DFD
b) entity in DFD is converted to attributes of an entity in
ERD
c) relations in ERD has 1 to 1 correspondence to processes in
DFD
d) relationships in ERD has 1 to 1 correspondence to flows in
DFD
(a) entities in ERD should correspond to an existing
entity/store in DFD
A dominant entity is the entity
a) on the N side in a 1 : N relationship
b) on the 1 side in a 1 : N relationship
c) on either side in a 1 : 1 relationship
d) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship
Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N'
Order By
CUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where
REGION = 'E'
Order By CUSTOMER
The above is
a) Not an error
b) Error - the string in single quotes 'NORTH' and 'SOUTH'
c) Error - the string should be in double quotes
d) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause
cannot be used in UNIONS
What is Storage Manager?
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.
What is Buffer Manager?
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.
What is Transaction Manager?
It is a program module, which ensures that database,
remains in a consistent state despite system failures and concurrent
transaction execution proceeds without conflicting.
What is File Manager?
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.
What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction
of integrity constraint and checks the authority of user to access data.
What are stand-alone procedures?
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.
What are cursors give different types of cursors.
PL/SQL uses cursors for all database information accesses
statements. The language supports the use two types of cursors
·
Implicit
·
Explicit
What is cold backup and hot backup (in case of Oracle)?
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 files from the latest backup.
All work performed on the database since the last backup is lost.
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.
So different means of backing up database must be used —
the hot backup. Issue a SQL command to indicate to Oracle, on a
tablespace-by-tablespace basis, that the files of the tablespace are to backed
up. The users can continue to make full use of the files, including making
changes to the data. Once the user has indicated that he/she wants to back up
the tablespace files, he/she can use the operating system to copy those files
to the desired backup destination.
The database must be running in ARCHIVELOG mode for the hot
backup option.
If a data loss failure does occur, the lost database files
can be restored using the hot backup and the online and offline redo logs
created since the backup was done. The database is restored to the most
consistent state without any loss of committed transactions.
What are Armstrong rules? How do we say that they are
complete and/or sound?
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.
How can you find the minimal key of relational schema?
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 make K a set of all attributes in R
2. For each attribute A in K
a. Compute (K – A)+ with respect to F
b. If (K – A)+ = R then set K = (K – A)+
What do you understand by dependency preservation?
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.,
((?R1(F)) U … U (?Rn(F)))+ = F+
if decomposition is not dependency preserving, then some
dependency is lost in the decomposition.
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 .
Simulatneous Update:
The updates that are applied to database at the same time
when it becomes effective in real world .
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