Unit1_DBMS

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: The data is sorted hierarchically, using a downward tree.This model uses pointers to navigate between stored data. It was the first DBMS model.

: like the hierarchical model, this model uses pointers towardstored data. However, it does not necessarily use a downward tree structure.

( , Relational database management system): The data

is stored in two-dimensional tables (rows and columns). The data is manipulated basedon the relational theory of mathematics. (This model will be studied in detail.)

: Data is represented as a table, but is manipulated using

predicate calculus. ( , object-oriented database management system): the data

is stored in the form of objects, which are structures called classesthat display the datawithin. The fields are instances of these classes


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In 3-Layered architecture there are three levels. The three levels of the architecture are threedifferent views of the data:

1. External- individual user view

2. Conceptualor logical- community user view3. Internal- physical or storage view

Three-Schemes Architecture

1. The external level is the view that the individual user of the database

has. This view is often a restricted view of the database and the same database may


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a. Storage allocation e.g. B-trees, hashing etc.

b. Access paths e.g. specification of primary and secondary keys, indexes and

pointers and sequencing.c. Miscellaneous e.g. data compression and encryption techniques, optimization ofthe internal structures.

With knowledge about the three-schemes architecture the term data independence can be

explained as followed: Each higher level of the data architecture is immune to changes of thenext lower level of the architecture.

Therefore, the logical scheme may stay unchanged even though the storage space ortype of some data is changed for reasons of optimization or reorganization.

Also the external scheme may stay unchanged for most changes of the logical scheme.This is especially desirable as in this case the application software does not need to bemodified or newly translated.

A relational model database is defined as a database that allows you to group its data items into

one or more independent tables that can be related to one another by using fields common toeach related table.

A relation is usually described as a table, which is organized intorows andcolumns.Thetable below summarizes some of the most important relational database terms and their SQLdatabase equivalents.
http://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Row_(database)http://en.wikipedia.org/wiki/Row_(database)http://en.wikipedia.org/wiki/Column_(database)http://en.wikipedia.org/wiki/Column_(database)http://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Row_(database)http://en.wikipedia.org/wiki/Column_(database)


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relation, base relvar tablederived relvar view, query result, result set

tuple row

attribute column

2. Tuples: Each row of data is a tuple.

3. Cardinality: It is defined as the number of tuples in a relation. For example if there is 4 rows ina table, cardinality of this table entity is 4.

4. Degree of a relation: Each column in the tuple is called as an attribute. The number ofattributes in a relation is defined as its degree. For example. If there is four columns(attributes)in a table, its degree will be four.

Entity is a person, place, object, event or concept in the user environment about whichthe organization wishes to maintain data. This is represented by a rectangle in E-R diagrams.

A collection of entities that share common properties or characteristics.

Regular Vs. Weak entity type

Regular Entity: Entity that has its own key attribute (s).e.g.: Employee, student ,customer, policy holder etc.

Weak entity: Entity that depends on other entity for its existence and doesnt have key attribute(s) of its own.

e.g. : spouse of employee.

Difference between Entity Type & Entity Instance:It might help to think of an entity as a thing. So you are asking about a type of thing, and anactual instance of that thing For example one type of thing is a Person Anil P is an instance of a
http://en.wikipedia.org/wiki/Relation_(database)http://en.wikipedia.org/wiki/Relvarhttp://en.wikipedia.org/wiki/Relation_(database)http://en.wikipedia.org/wiki/Relvar


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Composite attribute: can be split into components

E.g.: Date of joining of the employee can be split into day, month and year.

Composite Vs. Simple Attributes

Composite attributes can be divided intosmaller parts which represent simpleattributes with independent meaning

Simple Attribute: Aircraft -Type

Complex Attribute: Aircraft -Locationwhich is comprised of :

Aircraft -Latitude

Aircraft -Longitude

Aircraft -Altitude

Notation

There is no formal concept of compositeThere is no formal concept of composite

attribute in the relational modelattribute in the relational model

Single Vs Multi-valued AttributesSingle valued : can take on only a single value for each entity instance

e.g.: age of employee. There can be only one value for this.

Multi-valued: can take up many values.

e.g.: skill set of employee

SingleVs. Multivalued Attributes


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Derived attribute vs Stored Attributes

Stored Attribute: Attribute that need to be stored permanently.e.g.: name of an employee

Derived Attribute: Attribute that can be calculated based on other attributes.e.g. : years of service of employee can be calculated from date of joining and current date

Derived Vs. Stored Attributes

Some attribute values can be derived from

related attribute values:

Age Date - B-day

Y-Sal 12 * M -Sal

EMPLOYEE

M-sal

B-days Y-sal

Age

NotationNotation

5. Null Values Attributes

NullValuedAttributes


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widowed.

2. The domain of the attribute month is having twelve values ranging from January to December.

A relationship type between two entity types defines the set of all associations

between these entity types

Each instance of the relationship between members of these entitytypes is called a relationship instance.e.g if Works-for is the relationship between the Employee entity and the TTI_Department entity,then Rohan works-for CSE_department, Riya works for CS department ..etc are relationship

instances of the relationship, works-for.

Degree of a RelationshipThe number of entity types involved in a relationship is called degree of a relationship.

If One entity type is involved in a relationship, it is called Unary.If two entity type is involved in a relationship, it is called Binary.

If Three entity type is involved in a relationship, it is called Ternary.

e.g: employee manager-of employee is unary.

employee works-for department is binary.customer purchase item, shop keeper is a ternary relationship.

Relationship Degree

The degree of a relationship type isthe number of participating entitytypes 2 entities: Binary Relationship

3entities:TernaryRelationship

BinaryBinary


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E.g.:

Employee head-of department (1:1)Lecturer offers course (1:N) assuming a course is taught by a single lecturerStudent enrolls course (M:N)

Possible Cardinality Ratios

1to -1 (1 : 1)

Both entities can

participate in only one

relationship instance

1-to -Many, Many -to -1

(1 : N, N : 1)

One entity can

participate in many

relationship instances Many -to -Many (N: M)

Both entities can participate in

many relationship instance

.

.

.

.

.

.

.11-- toto -- ManyMany

.

.

.

.

.

.

.

ManyMany -- toto --

11

.

.

.

.

.

.

.

.

.

.

.

.

.ManyMany --toto --ManyMany

Representing Cardinality


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Employee: partial

Department: total

Representing Participation

Every employee must work for adepartment

Every department must have a managerEvery department must have employees

Not every employee is a manager

N 1

1 1

Each entity type must have an attribute or set of attributes that distinguishes one instancefrom other instances of the same type.

Example: name is Key for Beers

Beers

isa

name manf


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Relationship Constraints

What are Relationship Constraints ?

Constraints on the relationship type limit the

possible combination of entities that mayparticipate in the corresponding relationship

set

Kinds of ConstraintsWhat kind of constraints can be defined in the

ER Model?

Cardinality Constraints

Participation Constraints

Together called Structural Constraints

Constraints are represented byConstraints are represented byspecific notation in the ER diagramspecific notation in the ER diagram


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Specialization Is the process of defining a set of subclasses of a

superclass

The set of subclasses is based upon some distinguishingcharacteristics of the entities in the superclass

Example: {SECRETARY, ENGINEER, TECHNICIAN}is a specialization of EMPLOYEE based upon job type .

May have several specializations of the same superclass

Example: Another specialization of EMPLOYEE based inmethod of pay is {SALARIED_EMPLOYEE,HOURLY_EMPLOYEE}.

Superclass /subclass relationships and specialization canbe diagrammatically represented in EER diagrams

Attributes of a subclass are called specific attributes.For example, TypingSpeed of SECRETARY

The subclass can participate in specific relationshiptypes. For example, BELONGS_TO of

HOURLY_EMPLOYEE

Example of a Specialization


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Generalization

The reverse of the specialization process

Several classes with common features are generalized into

a superclass ; original classes become its subclasses

Example: CAR, TRUCK generalized into VEHICLE; both

CAR, TRUCK become subclasses of the superclass

VEHICLE.

We can view {CAR, TRUCK} as a specialization of VEHICLE

Alternatively, we can view VEHICLE as a generalization of CAR

and TRUCK

Generalization and Specialization

Arrow pointing to the generalized superclass represents ageneralization

Arrows pointing to the specialized subclasses represent aspecialization


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Subclasses and Superclasses (1)

An entity type may have additional meaningfulsubgroupings of its entities

Example: EMPLOYEE may be further grouped intoSECRETARY, ENGINEER, MANAGER, TECHNICIAN,

SALARIED_EMPLOYEE, HOURLY_EMPLOYEE, Each of these groupings is a subset of EMPLOYEE entities

Each is called a subclass of EMPLOYEE

EMPLOYEE is the superclass for each of these subclasses

These are called superclass /subclass relationships.

Example: EMPLOYEE/SECRETARY,EMPLOYEE/TECHNICIAN

Modeling Subclasses

Some objects ina class maybe special

define a newclass better: define a subclass

Products


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Product

name category

price

Is a Is a

Educational ProductSoftware Product

Age Groupplatforms

Subclasses

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Subclasses to Relations

Product

name category

price

Is a Is a

Educational ProductSoftware Product

Age Groupplatforms

gadget39Toy

photo49Camera

gadget99Gizmo

CategoryPriceName

unixGizmo

platformsName

retiredToy

todlerGizmo

Age GroupName

Product

Sw.Product

Ed.Product


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S U M M A R Y O F E R - D I A G R A M

N O T A T I O N F O R E R S C H E M A S

M e a n i n g

E N T IT Y T Y P E

W E A K E N T I T Y T Y P E

R E L A T I O N S H I P T Y P E

I D E N T I F Y I N G R E L A T I O N S H I P T Y P E

A T T R I B U T E

K E Y A T T R I B U T E

M U L T I V A L U E D A T T R I B U T E

C O M P O S IT E A T T R I B U T E

D E R I V E D A T T R I B U T E

T O T A L P A R T IC I P A T IO N O F E2 IN R

C A R D I N A L IT Y R A T IO 1 :N F O R E1:E2 IN R

S y m b o l

E1 R E2

E1 R E2N


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Designing an ER Diagram

Consider the following set of requirements for a University database. Design a n ER diagramfor this application:

The university keeps track of each student's name, student number, social securitynumber, current address and phone num ber, permanent address andphon e number,

bir thdate, sex , cla ss (fre shman, graduate) , major departm ent, minor department (if any),degree program (B.A., B.S., ... Ph.D.).Som e user applications need to r efer to the city,state, and zip code of the student's permanent address and to the student's lastname. Both social security number and student number are unique for each student.All students will have at least a major department.

Each department is described by a name, department code, officenumber, office phone,and college.Both the nam e and code have unique values for each department.

Each course has a course name, description, course number, number of credits, level and

offering department.The course number is unique for each course. Each section has an instructor, semester, year, course, and section number.T he section

number distinguishes sections of the same course that are taughtduring the samesemester/year; its value is an integer (1, 2, 3, ... up to the number of sections taughtduring each sem ester).

A grade report must be generated for each student that lists thesection, letter grade, andnumeric grade (0,1,2,3, or 4) for each student and calculates his or her average GPA.


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University ER Diagram

Student

Class

StudentID SSN

Sex

Zip

Degree

City

Birth date

State

Name

Address

Department

DName DCode OfficeNumber

OfficePhone

College

Course

CName

CourseDesc

CNumber

Credits

Section

Instructor Year

SemesterSectionNumber

GPA

Numeric Grade

Letter Grade

Grade_Report

Belong_To

Offer

Minor In

Major In

TTI INSTITUTE, SHALIMAR BAGH, ND-88 9582324716 18


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FIGURE 3.17An ER diagram

for an

AIRLINE

database

schema.


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Unit1_DBMS

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