Data Modeling.1

8/13/2019 Data Modeling.1

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Conceptual Data Modeling

Using E-R Diagrams

PM [email protected]


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5-Sep-11 Data Modeling Using E-R Diagrams 2

What is data model ?

You have seen some data models.

Company Schema (in relational model)

Some example of ER diagram

Depicts structure of database.


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What is data model

Depicts structure of database.

Database Structure, we mean types, relationships,

and constraints

Data Model (modeling technique) provides a set of

concepts that can be used to describe database

structure.


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Term gotcha

Company (relational) Schema is a data model

Using relational implementation data model


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Types of Data Model Conceptual or Higher Data Model

Easily understood by End-Users and Managers

Capturing of Correct and Complete data is goal here

Implementation model

This modeling technique is what on which DBMS are based

Relational, Object Relational, OO are the examples.

Physical Model (normally hidden by DBMS) Depicts how files are stored on disk deals with file

organization, indexes, clustering etc


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We have seen-

Relational as Implementation model

Have a basic unit of database called a relation.

Relations are stored on disk transparent to the user

Relational Model provides

Means by which you can define database structures as

relations and constraints on relations

Also defines various operations that can be used tomanipulate relations and hence database operations are

defined in logical manner


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Conceptual Model Correct and Formal representation of data items are the

objectives here

Intuitive and Simple to understand end users andmanagers can easily understand

Centers on what data items and business rules itcontains not on how they are stored or organized inapplication (or structured in a DBMS logically orphysically)

ER Diagrams and UML class diagrams are popularConceptual models

Implementation neutral (relational or whatever it is)


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E-R Diagram (or Model ? )

As said, it is a popular high level Conceptual Data

Model

ER Diagram are simple, consists of just three concepts-

Entities contains their name and attributes Relationshipbetween entities

Cardinality/Participation Constraints on entities for

their participation into relationships

Let us understand what these terms mean here?


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How we see data around us-

Address

....

..11-07-88Arpit060103

..10-02-89Anurag060102

..12-10-88Aditi060101

..Fasthers

Name

DOBNameStudID

List of Students IIyr BTech(CS)

..

.....

40BTech(Information Technology)BIT

40BTech(Computer Science)BCS

IntakeProgNameProgID

List of Programs Offered by CSE Department


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How do we describe this data Careful watch reveals that we have two types of entity

sets here-

Students and Programs (note: later we may discover thatit has one more entity department)

Let us call all students together an entity set, andProgram together another entity set

Each Student entity has certain properties (or attributes)like Name, DOB, Fathers Name etc., and their valuesdrawn from a predefined value set,

and similarly each program has certain attributes, andtheir values


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How do we describe this data If we attempt to describe student entity, typically it can

be like this-

Name of Entity: Student

Attributes: StudID, Name, DOB, FathersName, ..

Each Attribute derives value from a value set (domain)

StudID uniquely identifies a student entity in the set

This is description of Student entity, and we call it

Entity Type

Similarly we describe ProgramEntity Type


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ERD notation for the Entity types

Notations used here are,

originally suggested by

Dr Peter Chen in 76,

known as Chens notation


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Entities and Attributes Entity is the basic object in ER model. It is thing

which exists

Each entity has attributes- properties that describe the

entity, for example as we have seen-

Entity: Student

Attributes: StudID, Name, DOB, Fathers Name,

Address,

Entity: Program

Attributes: ProgID, ProgName, Intake


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Entities and Attributes Attributes could be

Atomic can not be meaningfully decomposed:

Example DOB can not be decomposed in

Day/Month/Year DOB is atomic data

Student-Name may or may not be atomic

If FirstName, LasteName have individual meaning

Key Attributes

Composite: Example Address (Street, City, PIN)

Single valued and multi-valued

Stored and Derived attributes


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Entities and Attributes in ERDCompositeAttribute

Multi-value

Attribute

Key

Attribute

Key attribute Uniquely Identifies an Entity in Entity Set


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Entities and Attributes

Derived

Attribute


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Entity Type Casually, very often term entity is used for Entity Type.

AnEntity Type describes schema or intention for a set of

entities sharing the same structure. In OO terminology, an entity type is similar to a class, and an

entity is similar to an instance

Definition (Elmasri/Navathe):

Entity Type defines a collection (or set)

of entities that have the same attributes.Each Entity Type in the database

is described by its name and attributes


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Entity Set The collection of entities of a particular entity type are

grouped into an entity set, is also called extension of entity

type. The entity set usually referred with the same name as of

Entity Type

Address

....

..11-07-88Arpit060103

..10-02-89Anurag060102

..12-10-88Aditi060101

..FasthersName

DOBNameStudID

Definition (Elmasri/Navathe):The collection of all entities of a particular type

in the database at any point of time is called an entity set.


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Key Attributes It is Attribute or set of Attributes, called Key Attribute

which are used to uniquely identify the entity in the set

An important constraint on entities of an entity type isthe key constraint or uniqueness constraint.

Key

Attribute

Address

..

11-07-88Arpit060103

10-02-89Anurag060102

12-10-88Aditi060101

DOBNameStudID


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Value Sets (Domains) of Attributes

Each simple attribute of an entity type is associated

with a value set (or a domain of values), whichspecifies the set of values that may be assigned to that

attribute for each individual entity

Also known as domain constraint on an attribute


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What we have talked about is

Entity: for example a student rahul

Entity Type: student

Entity Set: set of all entitities belonging to a

type, for example all students


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Relationship Type, Instance, and Set Let us look at following facts

Aditi studies in BIT

Amit studies in BCS

Arpit studies in BIT

Varun studies in BEE

Radhika studies in BIT

Shyam studies in BCS

This showsRelationshipbetween Student and Programentities (entity types to be precise) let us give aname to it Studies obvious choice

Relationship also has type and set, here studies isRelationship Type,

Each of above statement is instance of the type, andAll together form relationship set


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Relationship Instance Diagram

Relationship

Set


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Simple ER Diagram: Student-Program

Relationship


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Relationships can also have attributes In our previous example, suppose we also want to have

study duration of a student in a program, then

Let us say, we have attributes year_from, and year_to

Can you create relationship instance diagram for this?


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How do we identify entities in a scenario ?

Some thumb Rules:

When recite the scenario description, nouns and

objects are candidate for entity, and

Verbs are candidate for relationship between

entities

For example read next slide.


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ERD for XIT database


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XIT Scenario - modified X Institute of Technology (XIT) has a number of

departments.

Each department offer a number of programs

Each program has a definite category wise approvednumber of sheets; that is state quota, and national

quota, and in each quota you have Gen, SC, ST, etc.

Students are registered in various programs as peravailable seats in each category.


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How do we identify entities

Let us give a try to another relatively new scenario and

figure out entities, their attributes, and relationships init.


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IBM TGMC A number of Teams from various institutes Participate in the

competition.

Each Team has a mentor, a faculty from same institute

Every team has to register online at their site www.tgmc.in,

while registering they are required to furnish following

details- Team Name, Login ID, Password, team members

(email id and contact number), mentor and institute names

IBM awards to Winner, Runner and top 20 teams.

Also they award best 10 participating institutes

Objective of Database: IBM want to keep record of all

teams registered for the event and for there after math


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Thanks

Data Modeling.1

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