mc0067 fall drive assignment 2011

8/3/2019 MC0067 Fall Drive Assignment 2011

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1. Write about:Linear Search :

Linear search, also known as sequential search, means starting at the beginning of the data and checking eachitem in turn until either the desired item is found or the end of the data is reached. Linear search is a search algorithm, also

known as sequential search that is suitable for searching a list of data for a particular value. It operates bychecking every element of a list one at a time in sequence until a match is found. The Linear Search, or sequentialsearch, is simply examining each element in a list one by one until the desired element is found. The Linear Search is notvery efficient. If the item of data to be found is at the end of the list, then all previous items must be read and checkedbefore the item that matches the search criteria is found. This is a very straightforward loop comparing every element inthe array with the key. As soon as an equal value is found, it returns. If the loop finishes without finding a match, thesearch failed and -1 is returned. For small arrays, linear search is a good solution because it's so straightforward. In anarray of a million elements linear search on average will take500, 000comparisons to find the key. For a muchfaster search, take a look at binary search.

AlgorithmFor each item in the database

if the item matches the wanted infoexit with this item

Continue loopwanted item is not in database

Complexity of Linear search algorithm

Linear search provide complexity for finding an element in an array because linear search is

a step-by-step process, in which specific element is compared with each element of array.

In linear search complexity is due to two cases.

It is possible that required element occurs at the end of the array. So linear search consumes

more time.

It is also possible that required element is not present in the given array, this is the worst case.

In this case the algorithm requires f(n)=n+1 comparisons.

If the element is at first position in array then only one comparison will be needed

Collision Chain:In computer science, a hash table orhash map is a data structure that uses a hash function to map identifying values,known as keys (e.g., a person's name), to their associated values (e.g., their telephone number). Thus, a hash tableimplements an associate array. The hash function is used to transform the key into the index (the hash) of an arrayelement (the slot orbucket) where the corresponding value is to be sought.

Ideally, the hash function should map each possible key to a unique slot index, but this ideal is rarely achievable inpractice (unless the hash keys are fixed; i.e. new entries are never added to the table after it is created). Instead, mosthash table designs assume that hast collisionsdifferent keys that map to the same hash value - will occur and must beaccommodated in some way.


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2. Write about:

Integrity Rules

Relational Operators with examples for each

Linear Search

Collision Chain

Ans:22.1 Integrity Rules:

These are the rules which a relational database follows in order to stay accurate and accessible.These rules govern which operations can be performed on the data and on the structure of thedatabase. There are three integrity rules defined for a relational databse,which are:-

Distinct Rows in a Table - this rule says that all the rows of a table should be distinct to avoid

in ambiguity while accessing the rows of that table. Most of the modern database managementsystems can be configured to avoid duplicate rows.

Entity Integrity (A Primary Key or part of it cannot be null) - this rule says that 'null' isspecial value in a relational database and it doesn't mean blank or zero. It means theunavailability of data and hence a 'null' primary key would not be a complete identifier. Thisintegrity rule is also termed as entity integirty.

Referential Integrity - this rule says that if a foreign key is defined on a table then a valuematching that foreign key value must exist as th e primary key of a row in some other table.

The following are the integrity rules to be satisfied by any relation.

No Component of the Primary Key can be null.

The Database must not contain any unmatched Foreign Key values. This is called thereferential integrity rule.

Unlike the case of Primary Keys, there is no integrity rule saying that no component of theforeign key can be null. This can be logically explained with the help of the following example:

Consider the relations Employee and Account as given below. Employee

Emp# EmpName EmpCity EmpAcc#

X101 Shekhar Bombay 120001

X102 Raj Pune 120002

X103 Sharma Nagpur Null

X104 Vani Bhopal 120003

Account

ACC# OpenDate BalAmt120001 30-Aug-1998 5000

120002 29-Oct-1998 1200

120003 01-Jan-1999 3000

120004 04-Mar-1999 500

EmpAcc# in Employee relation is a foreign key creating reference from Employee to Account.

Here, a Null value in EmpAcc# attribute is logically possible if an Employee does not have abank account. If the business rules allow an employee to exist in the system without opening an

account, a Null value can be allowed for EmpAcc# in Employee relation.

In the case example given, Cust# in Ord_Aug cannot accept Null if the business rule insists that

the Customer No. needs to be stored for every order placed.


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2.2 Relational Operators:

In the relational model, the database objects seen so far have specific names:

Name Meaning

Relation Table

Tuple Record(Row)

Attribute Field(Column)

Cardinality Number of Records(Rows)

Degree(or Arity) Number of Fields(Columns)

View Query/Answer table

On these objects, a set of operators (relational operators) is provided to manipulate them:

1. Restrict

2. Project

3. Union

4. Difference

5. Product

6. Intersection

7. Join

8. Divide

Restrict:

Restrict simply extract records from a table.

it is also known as Select, but not the same SELECT as defined in SQL.

Project:

Project selects zero or more fields from a table and generates a new table


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that contains all of the records and only the selected fields (with no duplications).

Union:

Union creates a new table by adding the records of one table to another

tables, must be compatible: have the same number of fields and each of the field pairs has to have

values in the same domain.

Difference:

The difference of two tables is a third table which contains the records which appear in the first BUT

NOT in the second.

Product:

The product of two tables is a third which contains all of the records in the first one added to each of

the records in the second.

Intersection:

The intersection of two tables is a third tables which contains the records which are common to both.

Join:

The join of two tables is a third which contains all of the records in the first and the second which are

related.

Divide:

Dividing a table by another table gives all the records in the first which have values in their fieldsmatching ALL the records in the second.

The eight relational algebra operators are

1. SELECT To retrieve specific tuples/rows from a relation.


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Ord# OrdDat

e

Cust#

101 02-08-

94

002

104 18-09-

94

002

2. PROJECT To retrieve specific attributes/columns from a relation.

Description Price

Power Supply 4000

101-Keyboard 2000 2000

Mouse 800 800

MS-DOS 6.0 5000 5000

MS-Word 6.0 8000 8000

3. PRODUCT To obtain all possible combination of tuples from two relations.
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Ord# OrdDateO.Cust#C.Cust

#

CustNam

eCity

101 02-08-94 002 001 Shah Bombay

101 02-08-94 002 002 Srinivasan Madras

101 02-08-94 002 003 Gupta Delhi

101 02-08-94 002 004 Banerjee Calcutta

101 02-08-94 002 005 Apte Bombay

102 11-08-94 003 001 Shah Bombay

102 11-08-94 003 002 Srinivasan Madras

4. UNION To retrieve tuples appearing in either or both the relations participating in the

UNION.

Eg: Consider the relation Ord_Jul as

follows

(Table: Ord_Jul)

Ord# OrdDate Cust#

101 03-07-94 001

102 27-07-94 003

101 02-08-94 002

102 11-08-94 003

103 21-08-94 003

104 28-08-94 002

105 30-08-94 005

Note: The union operation shown above logically implies retrieval of records of Orders

placed in July or in August

5. INTERSECT To retrieve tuples appearing in both the relations participating in theINTERSECT.
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Eg:

To retrieve Cust# of Customers whove placed

orders in July and in August

Cust#

003

6. DIFFERENCE To retrieve tuples appearing in the first relation participating in the

DIFFERENCE but not the second.

Eg: To retrieve Cust# of Customers whove placed orders in

July but not in August

Cust#

001

7. JOIN To retrieve combinations of tuples in two relations based on a common field in

both the relations.

Eg:

ORD_AUG join CUSTOMERS (here, the common

column is Cust#)

Ord# OrdDate Cust# CustNames City

101 02-08-94 002 Srinivasan Madras

102 11-08-94 003 Gupta Delhi

103 21-08-94 003 Gupta Delhi

104 28-08-94 002 Srinivasan Madras

105 30-08-94 005 Apte Bombay
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Note: The above join operation logically implies retrieval of details of all orders and the

details of the corresponding customers who placed the orders. Such a join operation

where only those rows having corresponding rows in the both the relations are retrieved is

called the natural join or inner join. This is the most common join operation.

Consider the example of EMPLOYEE and ACCOUNT relations.

EMPLOYEE

EMP # EmpName EmpCity Acc#

X101 Shekhar Bombay 120001

X102 Raj Pune 120002

X103 Sharma Nagpur Null

X104 Vani Bhopal 120003

ACCOUNT

Acc# OpenDate BalAmt

120001 30. Aug. 1998 5000

120002 29. Oct. 1998 1200

120003 1. Jan. 1999 3000

120004 4. Mar. 1999 500

A join can be formed between the two relations based on the common column Acc#. The

result of the (inner) join is :

Emp# EmpName EmpCity Acc# OpenDate BalAmtX101 Shekhar Bombay 120001 30. Aug. 1998 5000

X102 Raj Pune 120002 29. Oct. 1998 1200

X104 Vani Bhopal 120003 1. Jan 1999 3000

Note that, from each table, only those records which have corresponding records in the

other table appear in the result set. This means that result of the inner join shows the

details of those employees who hold an account along with the account details.

The other type of join is the outer join which has three variations the left outer join, the

right outer join and the full outer join. These three joins are explained as follows:

The left outer join retrieves all rows from the left-side (of the join operator) table. If there

are corresponding or related rows in the right-side table, the correspondence will be

shown. Otherwise, columns of the right-side table will take null values.

EMPLOYEE left outer join ACCOUNT gives:
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Emp# EmpNameEmpCity Acc# OpenDate BalAmt

X101 Shekhar Bombay 120001 30. Aug. 1998 5000

X102 Raj Pune 120002 29. Oct. 1998 1200

X103 Sharma Nagpur NULL NULL NULL

X104 Vani Bhopal 120003 1. Jan 1999 3000

The right outer join retrieves all rows from the right-side (of the join operator) table. If

there are corresponding or related rows in the left-side table, the correspondence will be

shown. Otherwise, columns of the left-side table will take null values.

EMPLOYEE right outer join ACCOUNT gives:



X102 Raj Pune 120002 29. Oct. 1998 1200

X104 Vani Bhopal 120003 1. Jan 1999 3000

NULL NULL NULL 120004 4. Mar. 1999 500

(Assume that Acc# 120004 belongs to someone who is not an employee and hence the

details of the Account holder are not available here)

The full outer join retrieves all rows from both the tables. If there is a correspondence orrelation between rows from the tables of either side, the correspondence will be shown.

Otherwise, related columns will take null values.

EMPLOYEE full outer join ACCOUNT gives:



X102 Raj Pune 120002 29. Oct. 1998 1200

X103 Sharma Nagpur NULL NULL NULL

X104 Vani Bhopal 120003 1. Jan 1999 3000

NULL NULL NULL 120004 4. Mar. 1999 500

8. DIVIDE

Consider the following three relations:
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R1 divide by R2 per R3 gives:

a

Thus the result contains those values from R1 whose corresponding R2 values in R3

include all R2 values.

2.3 Linear Search

Linear search, also known as sequential search, means starting at the beginning of the data and

checking each item in turn until either the desired item is found or the end of the data is reached.

Linear search is a search algorithm, also known as sequential search that is suitable for searching a

list of data for a particular value. It operates by checking every element of a list one at a time in

sequence until a match is found. The Linear Search, or sequential search, is simply examining each

element in a list one by one until the desired element is found. The Linear Search is not very efficient.

If the item of data to be found is at the end of the list, then all previous items must be read and

checked before the item that matches the search criteria is found. This is a very straightforward loop

comparing every element in the array with the key. As soon as an equal value is found, it returns. If the

loop finishes without finding a match, the search failed and -1 is returned. For small arrays, linear

search is a good solution because it's so straightforward. In an array of a million elements linear search

on average will take500, 000 comparisons to find the key. For a much faster search, take a look at

binary search.

Algorithm

For each item in the database

if the item matches the wanted info

exit with this item

Continue loop

wanted item is not in database
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2.4 Collision Chain:

In computer science, a hash table orhash map is a data structure that uses a hash function to mapidentifying values, known as keys (e.g., a person's name), to their associated values (e.g., theirtelephone number). Thus, a hash table implements an associate array. The hash function is used totransform the key into the index (the hash) of an array element (the slotorbucket) where thecorresponding value is to be sought.

Ideally, the hash function should map each possible key to a unique slot index, but this ideal is rarelyachievable in practice (unless the hash keys are fixed; i.e. new entries are never added to the tableafter it is created). Instead, most hash table designs assume that hast collisionsdifferent keys thatmap to the same hash valuewill occur and must be accommodated in some way.

4. Discuss the correspondences between the ER model constructs and the

relational model constructs. Show how each ER model construct can be mapped

to the relational model, and discuss any alternative mappings.

Ans: 3Relational Data Model:The model uses the concept of a mathematical relation-which looks somewhat like a table of values-asits basic building block, and has its theoretical basis in set theory and first order predicate logic.The relational model represents the database a collection of relations. Each relation resembles a tableof values or, to some extent, a flat file of records. When a relation is thought of as a table of values,each row in the table represents a collection of related data values. In the relation model, each row inthe table represents a fact that typically corresponds to a real-world entity or relationship. The table

name and column names are used to help in interpreting the meaning of the values in each row. In theformal relational model terminology, a row is called a tuple, a column header is called an attribute, andthe table is called a relation. The data type describing the types of values that can appear in eachcolumn is represented by domain of possible values.ER Model:An entity-relationship model (ERM) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema orsemantic data model of a system, often a relational database, and its requirements in a top-downfashion. Diagrams created by this process are called entity-relationship diagrams, ER diagrams, orERDs.

The first stage of information system design uses these models during the requirements analysis to

describe information needs or the type of information that is to be stored in a database.In the case ofthe design of an information system that is based on a database, the conceptual data model is, at alater stage (usually called logical design), mapped to a logical data model, such as the relationalmodel; this in turn is mapped to a physical model during physical design. We create a relationalschema from an entity-relationship(ER) schema.In the case of the design of an information system that is based on a database, the conceptual datamodel is, at a later stage (usually called logical design), mapped to a logical data model, such as therelational model; this in turn is mapped to a physical model during physical design. Sometimes, both ofthese phases are referred to as "physical design". Key elements of this model are entities, attributes,identifiers and relationships.

Correspondence between ER and Relational Models:

ER Model Relational Model


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Entity type Entity relation

1:1 or 1:N relationship type Foregin key

M:N relationship type Relationship relation and two foreign keys

n ary relationship type Relationship relation and n foreign keys

Simple attributes Attributes

Composite attributes Set of simple component attributes

Multivalued attributes Relation and foreign key

Value set Domain

Key attribute Primary key or secondary key

Lets take COMPANY database example:

The COMPANY ER schema is below:

Numb

erWORKS_FOR


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1

1 N

N

N

EMPLOYEE

addre

ss

salar

ysex

Lnam

e

Initial

nam

Nam

e

END

DOB

DEPARTMENT

LocationNam

e

NoOfEmpl

oyee

MANAGES

DEPENDENTS_O

F

CONTROL

S

WORKSO

N

SUPERVISION

StartDat

e

HOUR

S

PROJECT

Nam

e

Numb

er

Locatio

n

Relationship

DOB

SexNam

e

DEPENDENT


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Result of mapping the company ER schema into a relational database schema:

EMPLOYEE

FNAM

E

INITIA

L

LNAM

E

ENO DOB ADDRE

SS

SEX SALAR

Y

SUPERE

NO

DNO

DEPARTMENT

DNAME DNUMBER MGRENO MGRSTARTDA

TE

DEPT_LOCATIONS

DNUMBER DLOCATION

PROJECT

PNAME PNUMBER PLOCATION DNUM

WORKS_ON

EENO PNO HOURS


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DEPENDENT

EENO DEPENDENT_N

AME

SEX DOB RELATIONS

HIP

Mapping of regular entity types:

For each regular entity type E in the ER schema, create a relation R that includes all the simpleattributes of E. Include only the simple component attributes of a composite attribute. Choose one ofthe key attributes of E as primary key for R. If the chosen key of E is composite, the set of simpleattributes that form it will together the primary key of R.If multiple keys were identified for E during the conceptual design, the information describing theattributes that form each additional key is kept in order to specify secondary (unique) keys of relation

R. Knowledge about keys is also kept for indexing purpose and other types of analyses.We create the relations EMPLOYEE, DEPARTMENT, and PROJECT in to correspond to the regularentity types EMPLOYEE, DEPARTMENT, and PROJECT. The foreign key and relationship attributes,if any, are not include yet; they will be added during subsequent steps. These, include the attributesSUPERENO and DNO of EMPLOYEE, MGRNO and MGRSTARTDATE of DEPARTMENT, andDNUM of PROJECT. We choose ENO, DNUMBER, and PNUMBER as primary keys for the relationsEMPLOYEE, DEPARTMENT, and PROJECT, respectively. Knowledge that DNAME of DEPARTMENTand PNAME of PROJCET are secondary keys is kept for possible use later in the design.The relation that is created from the mapping of entity types are sometimes called entity relationsbecause each tuyple represents an entity instance.

4. Define the following terms: disk, disk pack, track, block, cylinder, sector, interblock gap,

read/write head.

Ans: 5

Disk:

Disk s are used for storing large amounts of data. The most basic unit of data on the disk is a single bit

of information. By magnetizing a area on disk in certain ways, one can make it represent a bit value ofeither 0 or 1. To code information, bits are grouped into bytes. Byte sizes are typically 4 to 8 bits,

depending on the computer and the device. We assume that one character is stored in a single byte, andwe use the terms byte and character interchangeably. The capacity of a disk is the number of bytes itcan store, which is usually very large. Small floppy disks used with microcomputers typically hold from

400 kbytes to 1.5 Mbytes; hard disks for micros typically hold from several hundred Mbytes up to a few

Gbytes. Whatever their capacity, disks are all made of magnetic material shaped as a thin circular disk

and protected by a plastic or acrylic cover. A disk is single-sided if it stores information on only one ofits surface and double-sided if both surfaces are used.

Disk Packs:

To increase storage capacity, disks are assembled into a disk pack, which may include many disks and

hence many surfaces. A Disk packis a layered grouping of hard disk platters (circular, rigid discscoated with a magnetic data storage surface). Disk pack is the core component of a hard disk drive. In


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modern hard disks, the disk pack is permanently sealed inside the drive. In many early hard disks, the

disk pack was a removable unit, and would be supplied with a protective canister featuring a lifting

handle.

Track and cylinder:The (circular) area on a disk platter which can be accessed without moving the access arm of

the drive is called track. Information is stored on a disk surface in concentric circles of

small width, for each having a distinct diameter. Each circle is called a track. For

disk packs, the tracks with the same diameter on the various surfaces are called

cylinder because of the shape they would form if connected in space. The set of

tracks of a disk drive which can be accessed without changing the position of the access arm

are called cylinder.

The number of tracks on a disk range from a few hundred to a few thousand, and the capacity of eachtrack typically range from tens of Kbytes to 150 Kbytes.

Sector:A fixed size physical data block on a disk drive.A track usually contains a large amount of information; it is divided into smaller blocks or sectors. The

division of a track into sectors is hard-coded on the disk surface and cannot be changed. One type of

sector organization calls a portion of a track that subtends a fixed angle at the center as a sector. Severalother sector organizations are possible, one of which is to have the sectors subtend smaller angles at the

center as one moves away, thus maintaining a uniform density of recording.

Block and Interblock Gaps:A physical data record, separated on the medium from other blocks by inter-block gaps is called block.

The division of a track into equal sized disk blocks is set by the operating system during disk

formatting. Block size is fixed during initialization and cannot be changed dynamically. Typical diskblock sizes range from 512 to 4096 bytes. A disk with hard coded sectors often has the sectors

subdivided into blocks during initialization.

An area between data blocks which contains no data and which separates the blocks is calledinterblock gap.

Blocks are separated by fixed size interblock gaps, which include specially coded control information

written during disk initialization. This information is used to determine which block on the track

follows each interblock gap.

Read/write Head:

A tape drive is required to read the data from or to write the data to a tape reel. Usually, each group ofbits that forms a byte is stored across the tape, and the bytes themselves are stored consecutively on the

tape. A read/write head is used to read or write data on tape. Data records on tape are also stored in

blocks-although the blocks may be substantially larger than those for disks, and interblock gaps are alsoquite large. With typical tape densities of 1600 to 6250 bytes per inch, a typical interblock gap of 0.6

inches corresponds to 960 to 3750 bytes of wasted storage space.


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1. Explain the purpose of Data Modeling. What are the basic constructs of E-R Diagrams?


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Ans: 1

Data modeling in is the process of creating a data model by applying formal data model descriptions

using data modeling techniques.

Data modeling is the act of exploring data-oriented structures. Like other modeling artifacts data models can beused for a variety of purposes, from high-level conceptual models to physical data models.

Data modeling is the formalization and documentation of existing processes and events that occur

during application software design and development. Data modeling techniques and tools capture andtranslate complex system designs into easily understood representations of the data flows and processes,

creating a blueprint for construction and/or re-engineering.

Basic Constructs of E-R Modeling:

The ER model views the real world as a construct of entities and association between entities. The basicconstructs of ER modeling are entities, attributes, and relationships.

Entity:

An entity may be defined as a thing which is recognized as being capable of an independent existence

and which can be uniquely identified. An entity is an abstraction from the complexities of some domain.When we speak of an entity we normally speak of some aspect of the real world which can be

distinguished from other aspects of the real world.

An entity may be a physical object such as a house or a car, an event such as a house sale or a car

service, or a concept such as a customer transaction or order. Although the term entity is the one mostcommonly used, following Chen we should really distinguish between an entity and an entity-type. An

entity-type is a category. An entity, strictly speaking, is an instance of a given entity-type. There are

usually many instances of an entity-type. Because the term entity-type is somewhat cumbersome, mostpeople tend to use the term entity as a synonym for this term.

Entities can be thought of as nouns. Examples: a computer, an employee, a song, a mathematical

theorem.

Relationship:

A relationship captures how two or more entities are related to one another. Relationships can bethought of as verbs, linking two or more nouns. Examples: an owns relationship between a company

and a computer, asupervises relationship between an employee and a department, aperforms

relationship between an artist and a song, aprovedrelationship between a mathematician and a

theorem.

Attributes:

Entities and relationships can both have attributes. Examples: an employee entity might have a Social

Security Number(SSN) attribute; theprovedrelationship may have a date attribute.

2. Write about:

Types of Discretionary Privileges


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Propagation of Privileges using Grant Option

Physical Storage Structure of DBMS

Indexing

Ans:2

Types of Discretionary Privileges:

The concept of an authorization identifier is used to refer, to a user account. The DBMS must provide

selective access to each relation in the database based on specific accounts. There are two levels for

assigning privileges to use use the database system:

The account level: At this level, the DBA specifies the particular privileges that each account

holds independently of the relations in the database.

The relation (or table level):At this level, the DBA can control the privilege to access eachindividual relation or view in the database.

The privileges at the account level apply to the capabilities provided to the account itself and can

include the CREATE SCHEMA or CREATE TABLE privilege, to create a schema or base relation; theCREATE VIEW privilege; the ALTER privilege, to apply schema changes such adding or removing

attributes from relations; the DROP privilege, to delete relations or views; the MODIFY privilege, to

insert, delete, or update tuples; and the SELECT privilege, to retrieve information from the database by

using a SELECT query.The second level of privileges applies to the relation level,whetherthey are base relations or virtual

(view) relations.

The granting and revoking of privileges generally follow an authorization model for discretionaryprivileges known as the access matrix model, where the rows of a matrix M representssubjects (users,

accounts, programs) and the columns represent objects (relations, records, columns, views, operations).

Each position M(i,j) in the matrix represents the types of privileges (read, write, update) that subject i

holds on objectj.

To control the granting and revoking of relation privileges, each relation R in a database is assigned and

owner account, which is typically the account that was used when the relation was created in the first

place. The owner of a relation is given allprivileges on that relation. The owner account holder can passprivileges on R to other users by granting privileges to their accounts.

In SQL the following types of privileges can be granted on each individual relation R:

SELECT (retrieval or read) privilege on R: Gives the account retrieval privilege. In SQL thisgives the account the privilege to use the SELECT statement to retrieve tuples from R.

MODIFY privileges on R: This gives the account the capability to modify tuples of R. In SQL

this privilege is further divided into UPDATE, DELETE, and INSERT privileges to apply thecorresponding SQL command to R. In addition, both the INSERT and UPDATE privileges can

specify that only certain attributes can be updated or inserted by the account.

REFERENCES privilege on R: This gives the account the capability to reference relation R whenspecifying integrity constraints. The privilege can also be restricted to specific attributes of R.

Propagation of Privileges using the GRANT OPTION:

Whenever the owner A of a relation R grants a privilege on R to another account B, privilege can be

given to B with orwithoutthe GRANT OPTION. If the GRANT OPTION is given, this means that

B can also grant that privilege on R to other accounts. Suppose that B is given the GRANT

OPTION by A and that B then grants the privilege on R to a third account C, also with GRANTOPTION. In this way, privileges on R can propagate to other accounts without the knowledge of

the owner of R. If the owner account A now revokes the privilege granted to B, all the privileges

that B propagated based on that privilege should automatically be revoked by the system.

Physical Storage Structure of DBMS:


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The physical design of the database specifies the physical configuration of the

database on the storage media. This includes detailed specification of data

elements, data types, indexing options and other parameters residing in the DBMS

data dictionary. It is the detailed design of a system that includes modules & the

database's hardware & software specifications of the system. Physical structures

are those that can be seen and operated on from the operating system, such as the

physical files that store data on a disk.

Basic Storage Concepts (Hard Disk)

disk access time = seek time + rotational delay

disk access times are much slower than access to main memory.

overriding DBMS performance objective is to minimise the number of disk accesses

(disk I/Os)

Indexing:

Data structure allowing a DBMS to locate particular records more quickly and hence

speed up queries.Book index has index term (stored in alphabetic order) with a

page number.Database index (on a particular attribute) has attribute value (stored

in order) with a memory address.An index gives direct access to a record and

prevents having to scan every record sequentially to find the one required.

Using SUPPLIER(Supp# , SName, SCity)

Consider the query Get all the suppliers in a certain city ( e.g. London)

2 possible strategies:

a. Search the entire supplier file for records with city 'London'

b. Create an index on cities, access it for 'London entries and follow the pointer to

the corresponding records

SCity Index Supp# SName SCity

Dublin S1 Smith London

London S2 Jones Paris

London S3 Brown Paris

Paris S4 Clark London


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Paris S5 Ellis Dublin

3. What is a relationship type? Explain the differences among a relationship instance, a

relationship type, and a relationship set

Ans:3

There are three type of relationships

1) One to one

2) One to many

3) Many to many

Say we have table1 and table2

For one to one relationship, a record(row) in table1 will have at most one matching record or row in

table2

I.e. it mustnt have two matching records or no matching records in table2.

For one to many, a record in table1 can have more than one record in table2 but not vice versa

Lets take an example,

Say we have a database which saves information about Guys and whom they are dating.

We have two tables in our database Guys and Girls

Guy id Guy name

1 Andrew

2 Bob

3 Craig

Girl id Girl name

1 Girl12 Girl2

3 Girl3

Here in above example Guy ID and Girl ID are primary keys of their respective table.

Say Andrew is dating Girl1, Bob Girl2 and Craig is dating Girl3.

So we are having a one to one relationship over there.

So in this case we need to modify the Girls table to have a Guy id foreign key in it.

Girl id Girl name Guy id


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1 Girl1 1

2 Girl2 2

3 Girl3 3

Now let say one guy has started dating more than one girl.

i.e. Andrew has started dating Girl1 and say a new Girl4

That takes us to one to many relationships from Guys to Girls table.

Now to accommodate this change we can modify our Girls table like this

Girl Id Girl Name Guy Id

1 Girl1 1

2 Girl2 2

3 Girl3 3

4 Girl4 1

Now say after few days, comes a time where girls have also started dating more than one boy i.e.

many to many relationships

So the thing to do over here is to add another table which is called Junction Table, Associate Table or

linking Table which will contain primary key columns of both girls and guys table.

Let see it with an example

Guy id Guy name

1 Andrew

2 Bob

3 Craig

Girl id Girl name

1 Girl1

2 Girl2

3 Girl3

Andrew is now dating Girl1 and Girl2 and

Now Girl3 has started dating Bob and Craig

so ourjunction table will look like this

Guy ID Girl ID

1 1

1 2

2 22 3


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3 3

It will contain primary key of both the Girls and Boys table.

A relationship type R among n entity types E1, E2, , En is a set of associations among entities fromthese types. Actually, R is a set of relationship instances ri where each ri is an n-tuple of entities (e1,

e2, , en), and each entity ej in ri is a member of entity type Ej, 1jn. Hence, a relationship type is a

mathematical relation on E1, E2, , En, or alternatively it can be defined as a subset of the Cartesian

product E1x E2x xEn . Here, entity types E1, E2, , En defines a set of relationship, called

relationship sets.

Relationship instance: Each relationship instance ri in R is an association of entities, where the

association includes exactly one entity from each participating entity type. Each such relationship

instance ri represent the fact that the entities participating in ri are related in some way in the

corresponding miniworld situation. For example, in relationship type WORKS_FOR associates one

EMPLOYEE and DEPARTMENT, which associates each employee with the department for which the

employee works. Each relationship instance in the relationship set WORKS_FOR associates one

EMPLOYEE and one DEPARTMENT.

4. Write about:

Categories of Data Models

Schemas, Instances and Database States With an example for each

Ans. 4.1 Categories of Data ModelsA model is a representation of reality, real world objects and events, and their associations. It is an

abstraction that concentrates on the essential, inherent aspects of an organization and ignores the accidental

properties. A data model represents the organization itself. Let should provide the basic concepts and

notations that will allow database designers and end users unambiguously and accurately to communicate

their understanding of the organizational data.

Data Model can be defined as an integrated collection of concepts for describing and manipulating data,

relationships between data, and constraints on the data in an organization.

A data model comprises of three components:

A structural part, consisting of a set of rules according to which databases can be constructed.

A manipulative part. Defining the types of operation that are allowed on the data (this includes the

operations that are used or updating or retrieving data from the database and for changing the structure of

the database).

Possibly a set of integrity rules, which ensures that the data is accurate.

The purpose of a data model is to represent data and to make the data understandable.

There have been many data models proposed in the literature. They fall into three broad categories:

Object Based Data Models

Physical Data Models

Record Based Data Models


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The object based and record based data models are used to describe data at the conceptual and external

levels, the physical data model is used to describe data at the internal level.

A) Object Based logical Models:

These models are used to describe data at the logical and view levels. The following are the well known models in this group.

Entity Relationship Model.

The Object-Oriented Model.

The Semantic data model

The functional data model.

Entity Relationship Model:

Entity: An Entity is an object or a thing such as person, place about which an organization keeps information. Any two objects

or things are distinguishable.

E.g.: Each student is an entity.

Attribute: The describing properties of an entity are called Attributes.

E.g.: For a student entity, name, sex, date of birth are attributes.

Relationship: An association among entities is called a relationship.

The data model that consists of a set of entities and a set of relationships among those entities is called ER Model.

The set of all entities of the same type is called an entity set and the set of all relationship of the same type are called a

relationship set.

The Object-Oriented Model:

The object oriented model is a data model based on a collection of objects.

Each object has a unique identity. The group of objects containing the same type of values and the same methods are

called classes.

The Semantic data model:

These models were based on semantic networks. Inter dependencies among the entities can be expressed in this data

model.

Functional Data Model:

In this model objects, properties of objects, their relationships are viewed uniformly and are defined as functions.

C) Physical Data Models:

These models are used to represent data at the lowest level. Two important physical Data Models are:

Unifying Model

Frame Memory Model.


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B) Record Based Logical models:

This model is used to describe data at the logical and view levels. The database is structured in fixed format records of

different types. Each record type has a fixed number of fields. And each field is of fixed length. The following are the three

important record based logical models.

Relational Model

Network Model

Hierarchical Model.

Relational Model:

A data model in which both data and their relationships are represented by means of tables is called Relational Model.

The relation is the only data structure used in this model to represent both entities and their interrelationships. A relation is a

two dimensional table with a unique name.

Each row of a table is called a tuple and each column of a table is called an attribute. The set of all possible values in an

attribute is called the domain of the attribute.

Network Model:

The network model uses two different structures. The data are represented by a collection of records and the relationships

among data are represented by links.

Hierarchical Model:

In Hierarchical Model, data are represented by records and relationships among data are represented by links. But unlike in

Network model, data are organized in an ordered tree structure, which is called Hierarchical structure.

Ans. 4.1.1 Schemas

A database schema is described in a formal language supported by the database management system(DBMS). In a relational database, the schema defines the tables, the fields in each table, and therelationships between fields and tables.

Schemas are generally stored in a data dictionary. Although a schema is defined in text database language,the term is often used to refer to a graphical depiction of the database structure

Levels of database schema

1. Conceptual schema, a map of concepts and their relationships

2. Logical schema, a map of entities and their attributes and relations


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3. Physical schema, a particular implementation of a logical schema

4. Schema object, Oracle database object

5. Schema is the overall structure of the database

The following examples illustrate common schema designs based on the design considerations that are essentialto usability and performance.

This example illustrates a multi star schema, in which the primary and foreign keys are not composed of thesame set of columns. This design also contains a family of fact tables: a Bookings table, an Actual table, anda Promo_Schedule table.

This database tracks reservations (bookings) and actual accommodations rented for a chain of hotels, as well asvarious promotions. It also maintains information about customers, promotions, and each hotel in the chain.

In cases where payment is received in advance (for example, reservation deposits, cable TV subscriptions,automobile insurance), in accordance with proper accounting procedures, transactions must be made to reflectincome as it is earned, not when it is received, and the database must be designed to accommodate suchtransactions.

Ans. 4.1.2 Instances


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Every running Oracle database is associated with an Oracle instance. When a database is

started on a database server (regardless of the type of computer), Oracle allocates a memory

area called the System Global Area (SGA) and starts one or more Oracle processes. This

combination of the SGA and the Oracle processes is called an Oracle instance. The

memory and processes of an instance manage the associated database's data efficiently and

serve the one or multiple users of the database.

Below figure shows an Oracle instance.

Example: An organization with an employees database might have three different instances: production

(used to contain live data), pre-production (used to test new functionality prior to release into production) and

development (used by database developers to create new functionality).

Ans. 4.2.3 Database States

When a configuration is enabled, its databases can be in one of several states thatdirect the behavior of Data Guard, for example transmitting redo data or applyingredo data. The broker does not manage the state of the database (that is,mounted or opened). Below table describes the various database states.

Database States and Descriptions

Databas

e Role

State

Name Description

Primary TRANSPORT-ON

Redo transport services are set up to transmit redo data to the standby databases

when the primary database is open for read/write access.

If this is an Oracle RAC database, all instances open in read/write mode will

have redo transport services running.

This is the default state for a primary database when it is enabled for the first

time.


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Databas

e Role

State

Name Description

Primary TRANSPORT-OFF

Redo transport services are stopped on the primary database.

If this is an Oracle RAC database, redo transport services are not running on

any instances.

Physicalstandby

APPLY-ON Redo Apply is started on a physical standby database.

If the standby database is an Oracle RAC database, the broker starts Redo

Apply on exactly one standby instance, called the apply instance. If this

instance fails, the broker automatically chooses another instance that is eithermounted or open read-only. This new instance then becomes the apply

instance.

This is the default state for a physical standby database when it is enabled for

the first time.

If a license for the Oracle Active Data Guard option has been purchased, aphysical standby database can be open while Redo Apply is active. This

capability is known as real-time query.

Physical

standby

APPLY-OFF Redo Apply is stopped.

If this is an Oracle RAC database, there is no instance running Apply Services

until you change the database state to APPLY-ON.

Snapshot

standby

APPLY-OFF Redo data is received from the primary database but is not applied. The

database is opened for read/write access.

Logical

standby

APPLY-ON SQL Apply is started on the logical standby database when it is opened and the

logical standby database guard is on.

If this is an Oracle RAC database, SQL Apply is running on one instance, theapply instance. If this instance fails, the broker automatically chooses another

open instance. This new instance becomes the apply instance.

This is the default state for a logical standby database when it is enabled for the

first time.

Logicalstandby

APPLY-OFF SQL Apply is not running on the logical standby database. The logical standbydatabase guard is on.

If this is an Oracle RAC database, there is no instance running SQL Apply until

you change the state to APPLY-ON.

We can use the DGMGRL EDIT DATABASE command to explicitly change the state of adatabase. For example, the EDIT DATABASE command in the following examplechanges the state of the North_Sales database to TRANSPORT-OFF.

DGMGRL> EDIT DATABASE 'North_Sales' SET STATE='TRANSPORT-OFF';

Succeeded.


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