DATA BASE DESIGN PROCESS CHAPTER NO 3 COMPUTER SCIENCE

COMPUTER
SCIENC
E 12
(MS Access and C)
CHAPTER 3:
DATABASE DESIGN PROCESS
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• Analysis and Steps of Analysis Stage
• Data Modeling
• Entity Class & Instance
• Types of Relationships
• Cardinality & Modality
• ER Diagram
• Database Design Process
• Components of Logical Model
• Physical Database Design
• Components of Database Design
• Data Distribution Strategies
• File Organization
Topics

• Process of Studying the existing system
• Basic purpose is to know which activities are performed in the current system
• Determines what should take place in the new system
Important Steps in Analysis Stage
• Feasibility Study
• Requirement Analysis
• Project Planning
• Data Analysis
Analysis and Steps of Analysis Stage
Feasibility
Study
Requirement
Analysis
Project Planning
Data Analysis

Feasibility Study
• Conducted to investigate the required system
• Determines whether the proposed system is affordable, possible and acceptable
Requirement Analysis
• Collect the requirements for the project(proposed system) include:
• Possible inputs for database
• Required functionality of project
• The user describe their requirements and expectations from the proposed system
Steps of Analysis Stage

Project Planning
• Comprehensive planning and time schedule must be developed to complete project
successfully
• Cost factors ( Hardware, Software, Salaries of Team ) are taken into consideration
Data Analysis
• Activities of data analysis
• Data Flow Diagrams
• Decision Tables
• Decision Trees
Steps of Analysis Stage

Model - Representation of real world objects, events and their associations
Data Modeling - Process of identifying data objects and relationship between them
• E-R model is a popular conceptual data model
Data Modeling and its Ingredients
Ingredients of
Data
Modeling
Entity Attribute Relationship

Entity
• Anything that is participating in the system is known as entity or object
• Can be person, place, thing or event
Examples
• Person: TEACHER,PLAYER
• Place: COUNTRY
• Object: VEHICAL
• Event: REGISTRAION,SALE, PURCHASE
• Represented by rectangle in data model
• Name of entity is written inside the rectangle
Ingredients of Data Modeling

Attribute
• Characteristics of an entity
• Entity may have many attributes
Example
• Entity - TEACHER
• Attributes - Name, Gender, Last Degree, Appointment Date, Pay Scale , Telephone etc.
• Represented by an oval in the data model
• Name of entity is written inside the oval

• A BOOK STORE orders BOOK(s)
• A BOOK STORE displays BOOK(s)
• A BOOK STORE stocks
• A BOOK STORE sells
• A BOOK STORE returns
BOOK(s)
BOOK(s)
BOOK(s)
• All relationships define relevant connections between two entities
• All relationships are bi-directional
• Consider only relevant relationship
Relationship
• A logical connection between different entities
• Relationship indicates how the entities are related to each other
• Example
• Relationship between two entities BOOK and BOOK STORE
• Entities are connected with different ways

ER Model and ER Diagram
• The Entity Relationship (ER) Model is one of the most widely used method for
conceptual design
•The ER Model can be neatly mapped / Convert to a Relational Model
Entity-Relationship model is a logical representation of
data in an organization
• ER Model is represented by ER Diagram
• A visual Representation of ER Model
• Three types of symbols are used:
• Rectangle used to represent entities
• Diamond used to represent relationships
• Oval is used to represent attributes

Entity Class
• A group of entities of the same type is called entity class
• It is also known as entity type
Example
• STUDENT entity class is a set of all students
Entity Instance
• A member if an entity class is called entity instance
• It is also known as entity occurrence
Example
• StudentAbdullah of STUDENT entity type is an entity instance.
Entity Class & Instance

• Binary relationships exists between the instance of two entities.
Types of relationships
• One-to-One Relationship
• One-to-Many Relationship
• Many-to-Many Relationship
Types of Relationships

One-to-One Relationship
• This type of relationship is used when:
• For each instance in first entity class, there is only one instance in the second entity class
and
• For each instance in second entity class, there is only one instance in the first entity class
Examples

One-to-Many Relationship
• For each instance in first entity class, there can be many instances in the second entity class
and
• For each instance in second entity class, there is only one instance in the first entity class.
Examples

Many-to-Many Relationship
•For each instance in first entity class, there can be many instances in the second entity class
and
• For each instance in second entity class, there can be many instances in the first entity class
Examples

• Maximum number of instances of one entity that can be associated with each
instance of another related entity
• The cardinality can be one (1) or many
• Cardinality One
• Indicates single instance of an entity
• Denoted by vertical line () next to first entity or before second entity
• Cardinality Many
• Indicates multiple instances of an entity
• Denoted by crow’s foot
Cardinality

Minimum number of instances of one entity associated with each instance of the
related entity
• The modality can be ‘0’ or ‘1’.
• Modality ‘0’(zero)  Optional Relationship
• The relationship is called optional when the minimum number is zero
• Denoted by small circle O, after cardinality symbol of first entity
or before cardinality symbol of second entity
• Modality ‘1’(one)  Mandatory Relationship
• The relationship is called mandatory when the minimum number is one
• Denoted by small vertical line (), after cardinality symbol of first entity or before cardinality symbol of
second entity
Modality

• One-to-One
• One-to-Many
• Many-to-Many
Cardinality of Relationship

ER Diagram - Car Manufacturing Car
Shipper
Entities Manufacturer
Dealership
Relationships
1. MANUFACTURER Builds CAR
2. MANUFACTURER Lincenses DEALERSHIP
3. MANUFACTURER Contracts SHIPPER
4. SHIPPER Transports CAR
5. DEALERSHIP Stocks CAR

ER Diagram - College Admission System
Group
Entities Student
Fee
Relationships
1. STUDENT Applies for GROUP
2. STUDENT deposit FEE

• Map the conceptual data model (ERD) to an implementation model
• A particular DBMS must be able to process this model
• Performance of DBMS must be acceptable to all users throughout the
organization
• Users also need to access the information quickly and easily
Database Design Process

Phases of
Database
Development
Planning Analysis Database
Design
Physical
Design
Logical Design
Implementation
Phases of Database Development Process

1. Planning
• Begins when customer requests to develop a database system
• Consists of various activities
• Used to identify the resource needed to develop the system
• Also identifies the time limits for the completion of the system
2. Analysis
• Used to study the current system in detail
• Identifies how the current system works and where the improvements are
required
• It includes a detailed study of various operations performed in the system

3. Database Design
• Divided into two parts
• Logical Database Design
• Complete description of data to be stored in database
• Physical Database Design
• Translate the logical database design into physical storage structure
• Implement the database as a set of records, files, indexes etc.
Bad logical database design
results in bad physical
database design, and
generally results in poor
database performance

4. Implementation
• Database System is implemented after design and developed
• Database system installed and executed for the user
• It may require a particular type of computer like server
• May require network hardware if accessed at multiple locations
• Users are provided authorization by managers
• Example of NADRA & CRICKINFO

Components of Logical Database Design

1. Represent Entities
• Each Entity is represented as a relation in relational model
• The identifier of entity type becomes the primary key of relation
• The remaining attributes of the entity type become non-key attributes of the relation
• ER Model is one of the most widely used model for conceptual design
• ER Model is represented by ER Diagram
Example
• EMPLOYEE entity is converted into relation
• EmployeeID as an identifier and is underlined
• EmployeeID as primary key for the relation

2. Represent Relationships
• Each relationship in an ER diagram must be represented in relational model
• Depends upon nature of relationship
• Represent a relationship by making primary key of one relation a foreign key of another
relation
• Create a separate relation to represent a relationship

3. Merge the Relations
• There may be redundant relations
• Means two or more relations may describe the same entity type
• View integration is the process of merging relations to remove the redundancy
Example
• EMP1 (EmployeeID, Name, Address, Phone)
• EMP2 (EmployeeID, EmpName, Addr, Designation, DOB)
• The above relations EMP1 and EMP2 describe the same entity EMPLOYEE
• They can be merged into one relation
• EMP (EmployeeID, Name, Address, Phone, Designation, DOB)

4. Normalize the Relations
• The relations that are created in step (1) and (2) may have:
• Unnecessary redundancy
• Anomalies (errors) may arise while updating relations
• Normalize the relations to avoid these problems
• Normalization is the process of producing a simpler and more reliable database
structure

• Last stage of database design process
• A process of mapping logical database structure into actual database
structure:
• Set of records
• Files
• Indexes etc.
Physical Database Design

Major Inputs to Physical Database Design
1. Logical Database Structures
• Developed during logical database design such as normalized relations
2. User Processing Requirements
• Includes size & frequency of use of database, response time, security, backup, recovery etc.
3. Characteristics of the DBMS
• Includes characteristics of DBMS and other components of computer operating environment

1. Data Volume and Usage Analysis
• Estimates of database size are used to select physical storage devices and
storage cost estimation
• Estimates of usage paths or patterns are used to select file organization and
access methods, plans for the use of indexes and strategy for data distribution
Elements or Components of Physical Database Design

2. Data Distribution Strategy
• For organization which uses distributed computing networks, there is necessity
to decide which nodes (or sites ) in the network to locate the data physically
• Data allocation or distribution – A process of deciding where to locate the data
• Data Distribution Strategies are:
• Centralized - All data is located at a single site
• Partitioned - Database is divided into partitions (fragments)
• Replicated - Full copy of database is assigned to more than one site on network
• Hybrid - Database is partitioned into critical & non-critical fragments

3. File Organization
• Technique for arranging the records of file on secondary storage devices
• System designer must recognize several constraints for selecting a file organization
• Physical characteristics of secondary storage devices
• Available operating systems & file management software
• User requirements for storing & accessing data
4. Indexes
• A separate table that contains organization of records for quick retrieval
• May be created on primary key, secondary key, foreign key etc.

5. Integrity Constraints
• Data integrity means correctness and consistency of data
• Another form of database protection or security
• Integrity is related to the quality of data
• Maintained with help of integrity constraints
• Integrity constraints are rules designed to keep data consistent and correct
• These rules act like a check on the incoming data
• Example
• Fee of the student should not be greater than 10000
• The ID should not be assigned to two or more employees
Elements or Components Physical Database Design

1. Centralized
• All data is located at single site
• Advantage
• Simple and easy to conduct
• Disadvantages
• Data stored at remote sites is not accessible readily
• Data communication cost is high
• The database system fails totally when the central system fails
2. Partitioned
• Database is divided into partitions or fragments
• Each partition is assigned to a particular site
• Advantages
• Data is moved closer to local users
• Data becomes more easily accessible
Data Distribution Strategies

3. Replicated
• Full Copy of database is assigned to more than one site in the network
• This strategy maximizes local access but it creates update problems
4. Hybrid
• Database is divided into critical and non critical fragments
• Critical fragments are stored at multiple sites
• Non Critical fragments are stored at one site only
Data Distribution Strategies

DATA BASE DESIGN PROCESS CHAPTER NO 3 COMPUTER SCIENCE

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