CS 2255 DATABASE
MANAGEMENT SYSTEMS
(Common to CSE & IT)
2 Mark Question Answer
UNIT I
PART A
1.What is
Database Management System? Why do we need a DBMS ?
DBMS
is a collection of interrelated data and a set of programs to access those
data. It is to provide a way to store and retrieve information that is both
convenient and efficient.
2.List any two
advantages of database systems.
Security,
Integrity, Atomicity, Concurrent access anomalies
3.Define Data
Model and its types.
Data
model is a collection of tools for describing Data, Data relationships, Data
semantics, Data constraints. Types: Relational model, Entity-Relationship data
model Object-based data models, Semi structured data model (XML), Network
model, Hierarchical model.
4.Explain the
role and functions of the database administrator(DB Manager).
Coordinates all the activities of the database
system, Storage structure and access method definition, Schema and physical
organization modification, Granting users authority to access the database,
Backing up data, Monitoring performance and responding to changes.
5.Give the
limitations of E-R model? How do you overcome this?
·
Limited constraint
representation
·
Limited relationship
representation
·
No data manipulation
language
·
Loss of information
content
6.What are the
limitations of file system.
Data
redundancy and inconsistency, Difficulty in access data, data isolation,
integrity, atomicity, concurrent access anomalies.
7.What is
logical data Independency ?.
Application
programs are said to exhibit physical data independence if they do not depend
on the physical schema and thus need not be rewritten if the physical schema
changes.
8.Define DML?.
DML
is a language that enables users to access or manipulate data as organized by
the appropriate data model. Data Manipulation Language Insert, Select, Delete
9.Define
Data Dictionary?.
A
data dictionary is a data structure which stores meta data about the structure
of the database ie. the schema of the database.
10.Define Data
independence.
Application
programs are said to exhibit physical data independence if they do not depend
on the physical schema and thus need not be rewritten if the physical schema
changes.
11.With an
relevant example explain Ternary Relationship.
A
relationship is an association among several entities. Ternary relationship has
three relationship. Eg. Parent related to child.
12.List any
eight applications of DBMS.
a)
Banking
b) Airlines
c) Universities
d) Credit card
transactions
e) Tele
communication
f) Finance
g) Sales
h) Manufacturing
i) Human resources
13.What are the
advantages of DBMS?.
Controlling
redundancy
b) Restricting
unauthorized access
c) Providing
multiple user interfaces
d) Enforcing
integrity constraints.
e) Providing back
up and recovery
14.Give the
levels of data abstraction?
a)
Physical level
b) logical level
c) view level
15.Define
instance and schema?
Instance:
Collection
of data stored in the data base at a particular moment is called an
Instance of the database.
Schema: The overall
design of the data base is called the data base schema.
16. Define the
terms 1) physical schema 2) logical schema.
Physical
schema: The physical schema describes the database design at
the physical level, which is the lowest level of abstraction describing
how the data are actually stored.
Logical
schema: The logical schema describes the database design at
the logical level, which describes what data are stored in the database
and what relationship exists among the data.
17.What is
conceptual schema?
The
schemas at the view level are called subschemas that describe different views
of the database.
18. What is
storage manager?
A
storage manager is a program module that provides the interface between the
low level data stored in a database and the
application programs and queries submitted to the system.
19.What are the
components of storage manager?
The
storage manager components include
a) Authorization
and integrity manager
b) Transaction
manager
c) File manager
d) Buffer manager
20.What is the
purpose of storage manager?
The
storage manager is responsible for the following
a) Interaction with
he file manager
b) Translation of
DML commands in to low level file system commands
c) Storing,
retrieving and updating data in the database
21.List
the data structures implemented by the storage manager.
The storage manager implements the following data structure
a) Data files
b) Data dictionary
c) indices
UNIT II
PART A
1.Define query
language. Give the classification of query language.
Query language is used to query a database. It can
define the structure of the data, modify and specify security constraints.
Procedural and non procedural query language
2.What are three
characteristics of a Relational Database System?
Three
characteristics of a Relational Database System are BCNF, Lossless join and
Dependency preservation.
3.State the
differences between Security and Integrity?
Integrity
ensures that changes made to the database by authorized users do not result in
loss of data consistency. Eg. Check constraints. Security refers to protection
from malicious access. It is done in database systems, OS, Network physical,
Human.
4.What are the
pitfalls in relational database design?.
Repetition
of Information.
Inability to
represent certain information.
5.Distinguish
between primary key and candidate key.
Primary
key denotes a candidate key for identify entities with in entity set. Super
keys for which no proper subset is a super key is called candidate key.
6.Give the
reasons why Null values might be introduces into the database.
Null
values are introduced into the database to indicate the absence of information
about the value. Eg. Select loan number form loan where amount is null.
7.What is static
SQL? How does it differ from dynamic SQL?
In
static SQL, SQL queries must be present in compile time. Dynamic SQL allows
programs to construct and submit SQL queries at run time.
8.What
are the different types of integrity constraints used in designing a relational
database?
Domain
constraints, Referential Integrity, Check constraints, Assertion, Triggers.
9.With an
example explain a weak entity in an ER diagram.
An
entity without primary key is weak entity. Eg. Payment number in payment
relation having payment number payment date and payment amount as fields.
10.What is referential integrity.
The
condition that value which is appearing in one relation for a given set of
attributes also appears for a certain set of attributes in another relation is
called as referential integrity.
11.What is
domain integrity? Give example.
There
are many domain types, such as integer, character and date/time. Create domain
can be used to define new domains. Value of one type can be cast to other.
Eg.
Create domain Dollars numeric (12,2) Create domain Pounds numeric (12,2) Cast
r.A as pounds
12.Consider the
following relations.
Empno(Eno,Name,Date_of_Birth,
Sex,Date_Of_Joining,Basic_Pay,Dept)
Develop an SQL query that will find and
display the Dept and Average Basic_Pay in eac Dept.
Select
dept, Average(Basic_Pay) from empno Group by dept.
13.Define a
distributed database management system.
A
distributed database system consists of loosely coupled sites that share no
physical component. Database systems that run on each site are independent of
each other. Transactions may access data at one or more sites
14.List
the SQL statements used for Transaction control.
Commit, roll back.
15.What is a
nested relation ?
Attributes
in relations have multiple values. Example: library information system. Each
book has title, a set of authors, Publisher, and a set of keywords.
16.State the
advantages of distributed systems.
·
A distributed database system consists
of loosely coupled sites that share no physical component
·
Database
systems that run on each site are independent of each other
·
Transactions may access data at one or
more sites
17.Name the
different types of joins supported in SQL.
Inner
join, Natural inner join, natural left join, natural right join and full outer
join.
18.Define the
terms fragmentation and replication, in terms of where data is stored.
System
maintains several identical replica of relation and stores each replica and a
different site. Fragmentation is that the system partitions the relation into
several fragments and stores each fragment at a different site.
19.What
are the types of transparencies that a distributed database must support? Why?
Fragmentation,
Replication and location. The user of a distributed database system should not
be required to know either where the data are physically located ore how the
data can be accessed at the specific local site.
20.What is an
entity relationship model?
The
entity relationship model is a collection of basic objects called entities and
relationship among those objects. An entity is a thing or object in the real
world that is distinguishable from other objects.
21.Define the
terms
i) Entity set
ii)
Relationship set
Entity set: The
set of all entities of the same type is termed as an entity set.
Relationship set: The set of all relationships of the same type is termed
as a relationship set.
22. Define single
valued and multivalued attributes.
Single
valued attributes: attributes with a single value for a
particular entity are called single valued attributes.
Multivalued
attributes: Attributes with a set of value for a particular
entity are called multivalued attributes.
23.What are
stored and derived attributes?
Stored
attributes: The attributes stored in a data base are called
stored attributes. Derived attributes: The attributes that are derived
from the stored attributes are called derived attributes.
24.What are
composite attributes?
Composite
attributes can be divided in to sub parts.
25.Define null
values.
In
some cases a particular entity may not have an applicable value for an
attribute
or
if we do not know the value of an attribute for a particular entity. In these
cases null value is used.
26.Define the
terms
i) Entity type
ii)
Entity set
Entity
type: An entity type defines a collection of entities that
have the same attributes.
Entity set: The set of all
entities of the same type is termed as an entity set.
27.What is a
candidate key?
Minimal
super keys are called candidate keys.
28.What is a
primary key?
Primary
key is chosen by the database designer as the principal
means of identifying an entity in the entity set.
29.What is a
super key?
A
super key is a set of one or more attributes that collectively
allows us to identify uniquely an entity in the entity set.
30.Define-
relational algebra.
The
relational algebra is a procedural query language. It consists of a set of
operations that take one or two relation as input and produce a new relation as
output.
31.Write short
notes on domain relational calculus
The
domain relational calculus uses domain variables that take on values from an
attribute domain rather than values for entire tuple.
32.What is
foreign key?
A
relation schema r1 derived from an ER schema may include among its
attributes the primary key of another relation
schema r2.this attribute is called a foreign key from
r1 referencing r2.
33.What is
horizontal fragmentation?
Horizontal
fragmentation splits the relation by assuming each tuple of r to one or more
fragments.
34.What is
vertical fragmentation?
Vertical
fragmentation splits the relation by decomposing the scheme R of relation r.
35. Give the
forms of triggers?
_
The triggering event can be insert or delete. _ For updated the trigger can
specify columns. _ The referencing old row as clause
_
The referencing new row as clause
_ The triggers
can be initiated before the event or after the event.
UNIT III
PART A
1.
With an example explain a Functional Dependency.
Let
R be a relation schema, α subset of R.β is also subset of R.
The functional dependency α->βholds on R if and only if for any legal
relations r(R), whenever any two tuples t1 and t2 of r
agree on the attributes α, they also agree on the attributes β . That
is, t1[α] = t2 [α] =>t1[ β ]
= t2 [ β ] eg.
Here A->C.
2.Define
Normalization?
Normalization
is to generate a set of relation schemas that allows to store information with
out redundancy and to retrieve information easily
3.Justify the
need for normalization.
A bad relational database have the following pit
falls: inability to represent some data and redundancy. To overcome this pit
falls, normalization is to be done. Good database design should be Lossless
join and Dependency preservation. Decomposition of databases are done to make
the database consistent and efficient.
4.Why it is
necessary to decompose a relation?
A
relation is to be decomposed in order to avoid repetition of information and
inability to represent certain information.
5.What is
decomposition and how does it address redundancy?
Decomposition is reducing a large
database to set of smaller database. When splitting database, some of the
fields will be repeated in databases to maintain association with records.
6.Give the
comparison between BCNF and 3NF.
3NF
can be achieved without sacrificing losslessness or dependency preservation.
Disadvantage: Use null values to represent some of the meaningful relation and
repetition of information. If it is difficult to get a dependency-preserving
BCNF algorithm, it is preferable to opt for BCNF and use techniques such as
materialized views.
7.Explain
trivial dependency?
Functional
dependency of the form α->β is trivial if β is subset of α. Trivial
functional dependencies are satisfied by all the relations.
8.Define
canonical cover?
A
canonical cover Fc for F is a set of dependencies such that F logically implies
all dependencies in FC and Fc logically implies all dependencies in F. Fc must
have the following properties.
9.List the
properties of canonical cover.
Fc
must have the following properties.
_
No functional dependency in Fc contains an extraneous attribute. _ Each left
side of a functional dependency in Fc is unique.
10. Explain the
desirable properties of decomposition.
_
Lossless-join decomposition _ Dependency preservation
_ Repetition of
information
11.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.
12.Define Boyce
codd normal form
A
relation schema R is in BCNF with respect to a set F of functional dependencies
if, for all functional dependencies in F+ of the form α->β.
13.What is first
normal form?
The
domain of attribute must include only atomic (simple, indivisible) values.
14.What is meant
by computing the closure of a set of functional dependency?
The
closure of F denoted by F+ is the set of functional dependencies logically
implied by F.
15.What are
axioms?
Axioms
or rules of inference provide a simpler technique for reasoning about
functional dependencies.
16.What are the
uses of functional dependencies?
_
To test relations to see whether they are legal under a given set of functional
dependencies.
_ To specify
constraints on the set of legal relations.
17.What is meant
by normalization of data?
It
is a process of analyzing the given relation schemas based on their Functional
Dependencies (FDs) and primary key to achieve the properties
_ Minimizing
redundancy
_ Minimizing
insertion, deletion and updating anomalies.
18.Why certain
Functional dependencies are called trivial dependency?.
The
functional dependency α->βis trivial if βC α
19.What is multi
valued dependency?
If
A->B then, two tuples with same A value have different B value. Eg. Customer
name -> customer street, customer city.
20. What is
fourth normal form?.
A
relation schema R is in 4NF with respect to a set D of functional
and multivalued dependencies if for all multivalued dependencies in D+
of the form
a ®® b, where a Í R and b Í
R, at least one of the following hold: 1.a ®® b
is trivial (i.e., b Í a
or a È b = R)
2.a
is a superkey for schema R If a relation is in 4NF it is in BCNF
21.What are the
closure set of functional dependency?.
-Given
a set F of functional dependencies, there are certain other functional
dependencies that are logically implied by F.
- For example: If A ®
B and B ®
C,
then we can infer that A ®
C -The
set of all functional dependencies logically implied by F is the closure
of F. -We denote the closure of F by F+.
-F+ is a superset of F.
22.What are the
goals of normalization?.
Let
R be a relation scheme with a set F of functional dependencies.
Decide whether a relation scheme R is in “good” form.
In
the case that a relation scheme R is not in “good” form, decompose it
into a set of relation scheme {R1, R2, ..., Rn} such that
-
each
relation scheme is in good form
-
the decomposition is a lossless-join
decomposition
-
Preferably, the decomposition should be
dependency preserving.
23.How would you
find the extraneous attribute?.
Consider a set F
of functional dependencies and the functional dependency a ® b in
F.
- Attribute A is
extraneous in a if A Î a
and F logically implies (F – {a ® b}) È
{(a – A) ® b}. - Attribute A is
extraneous in b if A Î b
and the set of
functional dependencies
(F – {a ® b}) È {a ®(b – A)}
logically implies F.
24. What do you
mean by lossless join decomposition?.
A
decomposition of R into R1 and R2 is lossless join if and
only if at least one of the following dependencies is in F+:
o R1 Ç
R2 ®
R1 o R1 Ç
R2 ®
R2
25.Give the uses
of Multivalued dependency?.
We
use multivalued dependencies in two ways:
- To
test relations to determine whether they are legal under a given set of
functional and multivalued dependencies
- To
specify constraints on the set of legal relations. We shall thus concern
ourselves only with relations that satisfy a given set of functional and
multivalued dependencies.
UNIT IV
PART A
1.State
the atomicity property of a transaction.
Atomicity:
Either
all operations of the transaction are properly reflected in the database or
none.
Correctness: Execution
of a transaction in isolation preserves the consistency Isolation.: Each
transaction must be unaware of other concurrently executing transactions. Durability:
After a transaction completes successfully, the changes it has made to the
database persist, even if there are system failures.
2.Define
deadlock.
A
transaction waits for another transaction to release lock on data item. Mean
while, transaction also waits for some other data item to be released by first
transaction.
3.When are two
schedules conflict equivalent?
If
a schedule S can be transformed into a schedule S´
by a series of swaps of nonconflicting instructions, we say that S and S´
are conflict equivalent.
4.State the
benefits of strict two-phase locking.
Cascading
rollbacks can be avoided by a modification of two-phase locking. Any data
written by an uncommitted transaction are locked in exclusive mode until the
transaction commits, preventing any other transactions from reading the data.
5.What
benefit is provided by strict-two-phase locking? What are the disadvantages
results?
The
transactions can be serialized in the order of their lock points. In
strict two-phase locking, transaction must hold all its exclusive locks till it
commits/aborts.
6.What is
concurrency control ?
Concurrency
control is maintaining consistency
7.What is
transaction?
Collections
of operations that form a single logical unit of work are called transactions.
8.What are the
two statements regarding transaction?
The
two statements regarding transaction of the form: _ Begin transaction
_ End
transaction
9.When is a
transaction rolled back?
Any changes that the aborted transaction
made to the database must be undone. Once the changes caused by an aborted
transaction have been undone, then the transaction has been rolled back.
10.What are the
states of transaction?
The
states of transaction are
-
Active
-
Partially committed
-
Failed
-
Aborted
-
Commited
-
Terminated
11.What is a
shadow copy scheme?
It
is simple, but efficient, scheme called the shadow copy schemes. It is based on
making copies of the database called shadow copies that one transaction is
active at a time. The scheme also assumes that the database is simply a file on
disk.
12.Give the
reasons for allowing concurrency?
The reasons for allowing concurrency is if the
transactions run serially, a short transaction may have to wait for a preceding
long transaction to complete, which can lead to unpredictable delays in running
a transaction.
So concurrent
execution reduces the unpredictable delays in running transactions.
13.What is
average response time?
The
average response time is that the average time for a transaction to be
completed after it has been submitted.
14.What are the
two types of serializability?
The
two types of serializability is _ Conflict serializability
_ View
serializability
15.Define lock?
Lock
is the most common used to implement the requirement is to allow a transaction
to access a data item only if it is currently holding a lock on that item.
16.What are the
different modes of lock?
The
modes of lock are: _ Shared
_ Exclusive
17.Differentiate
strict two phase locking protocol and rigorous two phase locking protocol.
In
strict two phase locking protocol all exclusive mode locks taken by a
transaction is held until that transaction commits.
Rigorous
two phase locking protocol requires that all locks be held
until the transaction commits.
18.How the time
stamps are implemented
-Use
the value of the system clock as the time stamp. That is a transaction’s time
stamp is equal to the value of the clock when the transaction enters the
system.
-Use
a logical counter that is incremented after a new timestamp has been assigned;
that is the time stamp is equal to the value of the counter.
19. What are the
time stamps associated with each data item?
-W-timestamp
(Q) denotes the largest time stamp if any transaction that executed WRITE (Q)
successfully.
-
R-timestamp (Q) denotes the largest time stamp if any transaction that executed
READ (Q) successfully.
20.What is
recovery management component?
Ensuring
durability is the responsibility of a software component of the base system
called the recovery management component.
21.Define the
phases of two phase locking protocol
_
Growing phase: a transaction may obtain locks but not release any lock.
_
Shrinking phase: a transaction may release locks but may not obtain any new
locks.
22.What is meant
by log-based recovery?
The
most widely used structures for recording database modifications is the log.
The
log is a sequence of log records, recording all the update activities in the
database. There are several types of log records.
23.What are the
two methods for dealing deadlock problem?
The
two methods for dealing deadlock problem is deadlock detection and deadlock
recovery.
24.What are the
two types of errors?
The
two types of errors are: _ Logical error
_ System error
25. What are the
storage types?
The
storage types are: _ Volatile storage
_ Nonvolatile
storage
UNIT V
PART A
1)What are
ordered Indices?
In an ordered index, index entries are stored
sorted on the search key value. E.g., author catalog in library.
Two types:
Sparse Index and Dense index.
2)Distinguish
between sparse index and dense index.
An
index record appears for every search key value in the file is dense index. An
index record appears for only some of the search key values is sparse index.
Each index record contains a search key value and a pointer to the first data
record with that search value.
3.What is a heap
file? How are pages organized in a heap file?
Heap
file:- Any record can be placed anywhere in the file where there is space for
the record. There is no ordering of records.
4.How
does a B-tree differ from B+ - tree? Why is a B+ - tree usually preferred as an
access structure to a data file?
B-tree
allows search-key values to appear only once; eliminates redundant
storage
of search keys. Search keys in nonleaf nodes appear nowhere else in the B-tree;
All paths from root to leaf are of the same length. Each node that is not a
root or a
leaf has between
n/2 and
n children. A leaf node has between (n-1)/2 and n-1
values.
5.Define
Static hashing. Static Hashing:
Hash function h is a function from the set of
all search-key values K to the set of all bucket addresses B.
Hash function is used to locate records for access, insertion as well as
deletion. In static hashing, function h maps search-key values to a
fixed set of B of bucket addresses.
6.Define Dynamic
hashing.
Dynamic
Hashing: Good for database that grows and shrinks in size,
allows the hash function to be modified dynamically. The number of
buckets also changes dynamically due to coalescing and splitting of buckets.
7.How does a
DBMS represent a relational query plan?
Parsing
and translation: Translate the query into its internal
form. This is then translated into relational algebra. Parser checks
syntax, verifies relations Evaluation: The query-execution engine takes
a query-evaluation plan, executes that plan, and returns the answers to
the query.
8.Define RAID:
Redundant
Arrays of Independent Disks.
9.Compare
sequential access devices versus random access devices with an example.
Records are stored in sequential order
according to the value of a search key. If n th record has to be accessed then
all n-1 records has to be passed eg. Tape. In random access device, n th record
can be pointed directly eg. Disk.
10.What
can be done to reduce the occurrences of bucket overflows in a hash file
organization?
The
bucket overflows can be reduced by using overflow buckets. Overflow handling
can be done using linked list. This is called overflow chaining.
11.Give the measures
of quality of a disk.
_
Capacity
_
Access time _ Seek time
_
Data transfer rate _ Reliability
_ Rotational
latency time.
12.
Compare sequential access devices
versus random access devices with an example sequential access devices random
access devices
Must be accessed from the beginning It
is possible to read data from any location Eg:- tape storage Eg:-disk storage
Access
to data is much slower Access to data is faster Cheaper than disk Expensive
when compared with disk
13. What are the
types of storage devices?
_
Primary storage
_
Secondary storage _ Tertiary storage
14.Define access
time.
Access
time is the time from when a read or write request is issued to when data
transfer begins.
15.Define seek
time.
The
time for repositioning the arm is called the seek time and it increases with
the distance that the arm is called the seek time.
16.Define
average seek time.
The
average seek time is the average of the seek times, measured over a sequence of
random requests.
17.Define
rotational latency time.
The
time spent waiting for the sector to be accessed to appear under the head is
called the rotational latency time.
18.Define
average latency time.
The
average latency time of the disk is one-half the time for a full rotation of
the disk.
19.What is meant
by data-transfer rate?
The
data-transfer rate is the rate at which data can be retrieved from or stored to
the disk.
20.What is meant
by mean time to failure?
The
mean time to failure is the amount of time that the system could run
continuously without failure.
21.What are a
block and a block number?
A
block is a contiguous sequence of sectors from a single track of one platter.
Each
request specifies the address on the disk to be referenced. That address is in
the form of a block number.
22.What is the
use of RAID?
A
variety of disk-organization techniques, collectively called redundant arrays
of independent disks are used to improve the performance and reliability.
23.Explain how
reliability can be improved through redundancy?
The simplest approach to introducing redundancy is
to duplicate every disk. This technique is called mirroring or shadowing. A
logical disk then consists of two physical disks, and write is carried out on
both the disk. If one of the disks fails the data can be read from the other.
Data will be lost if the second disk fails before the first fail ed disk is
repaired.
24.What is
called bit-level striping?
Data
striping consists of splitting the bits of each byte across multiple disks.
This is called bit-level striping.
25.What is
called block-level striping?
Block
level striping stripes blocks across multiple disks. It treats the array of
disks as a large disk, and gives blocks logical numbers.
26.Distinguish
between fixed length records and variable length records? Fixed length records
Every
record has the same fields and field lengths are fixed.
Variable length
records
File
records are of same type but one or more of the fields are of varying size.
27.What
are the ways in which the variable-length records arise in database systems?
_
Storage of multiple record types in a file.
_
Record types that allow variable lengths for one or more fields. _ Record types
that allow repeating fields.
28.Explain the
use of variable length records.
_
They are used for Storing of multiple record types in a file.
_
Used for storing records that has varying lengths for one or more fields. _
Used for storing records that allow repeating fields
29.What is known
as heap file organization?
In
the heap file organization, any record can be placed anywhere in the file where
there is space for the record. There is no ordering of records. There is a
single file for each relation.
30.What is known
as sequential file organization?
In
the sequential file organization, the records are stored in sequential order,
according to the value of a “search key” of each record.
31.What is
hashing file organization?
In
the hashing file organization, a hash function is computed on some attribute of
each record. The result of the hash function
specifies in which block of the file the record should be placed.
32.What is known
as clustering file organization?
In
the clustering file organization, records of several different relations are
stored in the same file.
33.What is an
index?
An
index is a structure that helps to locate desired records of a relation
quickly, without examining all records.
34. What are the two
types of ordered indices?
_
Primary index
_ Secondary
index
35. What are the
types of indices?
_
Ordered indices _ Hash indices
36.What are the
techniques to be evaluated for both ordered indexing and hashing?
_
Access types _ Access time _ Insertion time _ Deletion time
_ Space overhead
37.What is
linear probing?
Linear
probing is a type of open hashing. If a bucket is full the system inserts
records in to the next bucket that has space. This is known as linear probing.
38.What is
called query processing?
Query
processing refers to the range of activities involved in extracting data from a
database.
39.What are the
steps involved in query processing?
The
basic steps are:
_
parsing and translation _ optimization
_ evaluation
40.What is
called an evaluation primitive?
A
relational algebra operation annotated with instructions on how to evaluate is
called an evaluation primitive.
41.What is
called a query evaluation plan?
A
sequence of primitive operations that can be used to evaluate ba query is a
query evaluation plan or a query execution plan.
42.What is
called a query –execution engine?
The
query execution engine takes a query evaluation plan, executes that plan, and
returns the answers to the query.
43.How do you
measure the cost of query evaluation?
The
cost of a query evaluation is measured in terms of a number of different
resources including disk accesses, CPU time to execute a query, and in a
distributed database system the cost of communication
44.List out the
operations involved in query processing
Selection
operation Join operations. Sorting.
Projection
Set operations Aggregation
45.Define query
optimization.
Query
optimization refers to the process of finding the lowest –cost method of
evaluating a given query.
46.Which level
of RAID is best? Why?
RAID
level 1 is the RAID level of choice for many applications with moderate
storage requirements and high I/O requirements. RAID
1 follows mirroring and provides best write performance.
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