Subject Name Code Credit HoursDatabase System COMP 219 3

Chapter VI

Subject Name Code Credit HoursDatabase System COMP 219 3

E-R Diagram

• Symbol Description

Entity Type

Attribute

Key Attribute

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E-R DiagramSymbol Description

Composite Attribute

Multivalued attribute Attribute

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E-R Diagram

Symbol DescriptionDerived Attribute

Relationship

Subject Name Code Credit HoursDatabase System COMP 219 3

E-R Diagram

• Symbol Description

Identifying Relationship

Weak Entity Type

Subject Name Code Credit HoursDatabase System COMP 219 3

E-R Diagram• Symbol Description

E1 E2RTotal participation of E2 in R & Partial Participation of E1 in R

E1 E2R1 1

Cardinality Ratio

E2RMin,max

Structural constraints (min,max) on participation of Environmental in R

Subject Name Code Credit HoursDatabase System COMP 219 3

Recursive Relationship

• If the same entity type partcipates in a relationship more than once in different roles.

• E.g.. Employee

Supervising

SupervisorSupervise

Subject Name Code Credit HoursDatabase System COMP 219 3

Design of an E-R Database Schema

The steps involved in designing an E-R database schema are,• Identify entity types and their entity sets.• List out the attributes of each entity type.• Relate several entities by specifyiing some relationship that

exists among them.• Specify some attributes of relation if any.• Specify Generalization and specialization any exists.• Specify Aggregation (global) if any used.

Subject Name Code Credit HoursDatabase System COMP 219 3

Design Process:• The main phases involved in designing a ER db schema is shown below,

Mini world

Requirements collection & Analysis

Data Requirements

Conceptual Design

Conceptual schema

Logical Design

Physical designLogical schema

Internal SchemaTransaction implementation

Functional Requirements

Functional Analysis

High level Transaction specification

Application program Design

App.pgms

DBMS Independent

DBMS Specific

Subject Name Code Credit HoursDatabase System COMP 219 3

Requirements collection & Analysis

• The db designers interview db users to understand & document their requirements.

• They find out data requirements (what data are stored in the db).

Conceptual Design:• Once the requirements are documented , the next step is to create

conceptual schema which carried out in conceptual design Phase.• It describes the structure of a db in the form of entity type, relationship

among them & constraints.

Subject Name Code Credit HoursDatabase System COMP 219 3

Logical Design

• The actual implementation of the db is carried out using DBMS.

Physical Design The last phase is the internal storage structures, indexes,

access paths, and file organizations for the db files are specified.

In parallel with these activities, Application programs are designed and implemented as db transactions.

Subject Name Code Credit HoursDatabase System COMP 219 3

EER Model- Enhanced or Extended E-R model

• Using E-R model only the basic features of a db.• Some enhanced features such as Specialization, Generalization, Union &

aggregation can be shown using EER model.

A. SPECIALIZATION:

The process of designating sub grouping within an entity set..

Subject Name Code Credit HoursDatabase System COMP 219 3

E.g…..

Employee

IS A

Secretary Technician Manager

eid ename eaddr Job

Typing speed

Mgrid

Subject Name Code Credit HoursDatabase System COMP 219 3It is also represented as

Employee

eid ename eaddr Job

d

Secretary Technician Manager

d

Job TypeSalary Type

Hourly Regular

Defining attribute

Sub classes

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Generalization

• The process of defining a generalized entity type from the given entity types.

Subject Name Code Credit HoursDatabase System COMP 219 3E.g…

CAR TRUCK

PriceMax speed

Vehicle ID No. of seats Vehicle ID

PriceNo. Of Axles

Tonnage

Subject Name Code Credit HoursDatabase System COMP 219 3

Vehicle

Vehicle ID Price

d

CARTRUCK

Max speedNo. of seats Tonnage

No. Of Axles

Subject Name Code Credit HoursDatabase System COMP 219 3

History of Database Systems• 1950s and early 1960s:

– Data processing using magnetic tapes for storage• Tapes provide only sequential access

– Punched cards for input• Late 1960s and 1970s:

– Hard disks allow direct access to data– Network and hierarchical data models in widespread use– Ted Codd defines the relational data model

• Would win the ACM Turing Award for this work• IBM Research begins System R prototype• UC Berkeley begins Ingres prototype

– High-performance (for the era) transaction processing

Subject Name Code Credit HoursDatabase System COMP 219 3

History (cont.)

• 1980s:– Research relational prototypes evolve into commercial systems

• SQL becomes industrial standard– Parallel and distributed database systems– Object-oriented database systems

• 1990s:– Large decision support and data-mining applications– Large multi-terabyte data warehouses– Emergence of Web commerce

• 2000s:– XML and XQuery standards– Automated database administration