DATABASE APPLICATION DEVELOPMENTSAK 3408

Database Design I(week 2)

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REMEMBER

Des

ign

SQ

L

Pro

gram

Best:

Spend your time

on design and SQL.Des

ign

SQ

L

Pro

gram

Worst:Compensate for poor designand limited SQL with programming.

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Database System Design

User viewsof data.

Conceptualdata model.

Customer(CustomerID, Name, Address, …)

SalesPerson(EmployeeID, Name, Commission, … )

Order(OrderID, OrderDate, CustomerID, EmployeeID, … )

OrderItem(OrderID, ItemID, Quantity, Price, … )

Item(ItemID, Description, ListPrice, …)

Implementation(relational)data model.

Physicaldatastorage.

Class diagram that shows business entities, relationships, and rules.

List of nicely-behaved tables. Use data normalization to derive the list.

Indexes and storage methods to improve performance.

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The Need for Design Goal: To produce an information system

that adds value for the user Reduce costs Increase sales/revenue Provide competitive advantage

Objective: To understand the system To improve it To communicate with users and IT staff

Methodology: Build models of the system

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Designing Systems

Designs are a model of existing & proposed systems They provide a picture or

representation of reality They are a simplification Someone should be able to read your

design (model) and describe the features of the actual system.

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How to builds your model?

You build models by talking with the users Identify processes Identify objects Determine current problems and future

needs Collect user documents (views)

Break complex systems into pieces and levels

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Initial Steps of Design

1. Identify the exact goals of the system.

2. Talk with the users to identify the basic forms and reports.

3. Identify the data items to be stored.

4. Design the classes (tables) and relationships.

5. Identify any business constraints.

6. Verify the design matches the business rules.

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Design Stages

Initiation Scope Feasibility Cost & Time estimates

Requirements Analysis User Views & Needs

Forms Reports

Processes & Events Objects & Attributes

Conceptual Design Models

Data flow diagram Entity Relationships Objects

User feedback

Physical Design Table definitions Application development

Queries Forms Reports Application integration

Data storage Security Procedures

Implementation Training Purchases Data conversion Installation

Evaluation & Review

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Overview of Database Design Process

REQUIREMENTS COLLECTION & ANALYSIS

Data requirement

CONCEPTUAL DESIGN

Conceptual Schema

LOGICAL DESIGN(DATA MODEL MAPPING)

Logical SchemaIn the data model of specific DBMS

PHYSICAL DESIGN

Internal Schema

Functional Requirements

FUNCTIONAL ANALYSIS

APPLICATION PROGRAM DESIGN

TRANSACTION IMPLEMENTATION

High-Level Transaction Specification

Application Program

DBMS-independentDBMS-specific

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Unified Modeling Language (UML)

A relatively new method to design systems.Contains several types of diagrams:

Contains several types of diagrams:

The class diagram is the most important for database design.

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Definitions

Entity: Something in the real world that we wish to describe or track.

Class: Description of an entity, that includes its attributes (properties) and behavior (methods).

Object: One instance of a class with specific data.Property: A characteristic or descriptor of a class or entity.Method: A function that is performed by the class.Association: A relationship between two or more classes.

Entity: Customer, Merchandise, SalesClass: Customer, Merchandise, SaleObject: Joe Jones, Premium Cat Food, Sale #32Property: LastName, Description, SaleDateMethod: AddCustomer, UpdateInventory, ComputeTotalAssociation: Each Sale can have only one Customer.

Pet Store Examples

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Business Rule

BR are important in data modelling because they govern how data are – handled and stored.

Basic BR : Data names Data definition

Names and definition must provide for : Entity types Attribute Relationship

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Guideline Data Names

Relate to business – customer \ File10

Be meaningful – avoid is, it, has Be unique – homeadd, campusadd Repeatable–studbirthdate,

stafbirthdate

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Data Definition

“ A course is a module of instruction in a particular area.”

“A customer may request a model car from a rental branch in a particular date.”

Guideline : A definition will state such characteristics of

the data objects. Whether the data is singular or plural Who determine the value for the data Whether data is static or changes over time Whether the data is optional or an empty Where, when and how data is created.

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The E-R Model

E-R model – a logical representation of the data for an organization or for a business area

E-R diagram – a graphical representation of an entity-relationship model

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E-R Model Constructs

EntityAttributeRelationship

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Basic E-R Notation

Entity symbols

Relationship symbols

Attribute symbols

A special entity that is also a relationship

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Figure 2.3 Sample E-R Diagram

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Entity

An entity is a person, place, object, event or concept in the user environment about which the organization wishes to maintain data.

Ex: Person – EMPLOYEE, STUDENT, PATIENT Place – STORE, WAREHOUSE, STATE Object – MACHINE, BUILDING, AUTOMOBILE Event – SALE, REGISTRATION, RENEWAL Concept – ACCOUNT, COURSE

Entity type, entity instances, strong entity, weak entity

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Entity Type vs. Entity Instance

Entity Type Share common characteristic Given a name (CAPITAL LETTER) Rectangle Collection of entities (often corresponds to a

table). Ex: EMPLOYEE

Entity Instances a single occurrence of an entity type (often

corresponds to a row in a table) Ex: may be 100 of instances of entity

EMPLOYEE stored in database.

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Entity Type vs. Entity Instance (cont.)

Entity Type : EMPLOYEE

Attribut : EMP_NUM CHAR(10)NAME CHAR(25)STATE CHAR(35)

2 instances of EMPLOYEE :00123 02345Ali AmirPerak Kedah

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Strong vs. Weak Entity Types

Strong Entity Type entity that exists independently of other entity

types Unique characteristic Called an identifier Ex: STUDENT, EMPLOYEE

Weak Entity Type entity type whose existence depends on

some other entity type No meaning in ERD without strong entity.

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Figure 2.10 Strong and weak entities

Strong entity Weak entityIdentifying relationship

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Attribute property or characteristic of an entity

type (often corresponds to a field in a table)

Ex: entity type – STUDENT Attributes – name, add, id, program

Simple att vs composite att. Single-valued att vs multivalued att Stored att vs derived att Identifier att.

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Example

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Simple vs. Composite Attribute

Simple attribute – cannot broken into smaller components

Composite attribute – can broken into component parts

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Simple key attribute

The key is underlined

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a) Composite attribute

An attribute broken into component parts

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b) Composite key attribute

The key is composed of two subparts

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Single-Valued vs. Multivalued Attribute

Single-Valued – each of the attributes has one value

Multivalued – attribute more than one value

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Entity with a multivalued attribute (Skill)

Multivalued: an employee can have more than one skill

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Stored vs. Derived Attributes

Stored attribute – data input or set

Derived Attribute – attribute whose values can be calculated from related attribute values.

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Entity with a derived attribute (Years_Employed)

Derived from date employed and current date

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Identifiers (Keys)

Identifier (Primary Key) - An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type

Composite Identifier – an identifier that consists of a composite attribute.

Candidate Key – an attribute that could be a key…satisfies the requirements for being a key

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Characteristics of Identifiers

Will not change in value Will not be null No intelligent identifiers (e.g.

containing locations or people that might change)

Substitute new, simple keys for long, composite keys

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Ex: identifier

The key is composed of two subparts

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Relationship

Relationship link between entities (corresponds to

primary key-foreign key equivalencies in related tables)

Relationship Types vs. Relationship Instances The relationship type is modeled as the

diamond and lines between entity types…the instance is between specific entity instances

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Relationships (cont.)

Relationship Types vs. Relationship Instances

The relationship type is modeled as the diamond and lines between entity types…the instance is between specific entity instances

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Figure 2.6 (a) Relationship type

Figure 2.6 (b) Entity and Relationship instances

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Relationships (cont.)

Relationships can have attributes These describe features pertaining to the

association between the entities in the relationship

Two entities can have more than one type of relationship between them (multiple relationships)

Associative Entity = combination of relationship and entity

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Degree of Relationships Degree of a Relationship is the

number of entity types that participate in it Unary Relationship Binary Relationship Ternary Relationship

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Figure 2.7 Degree of relationships

One entity related to another of the same entity type

Entities of two different types related to each other

Entities of three different types related to each other

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Cardinality of Relationships

One – to – One Each entity in the relationship will have

exactly one related entity One – to – Many

An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity

Many – to – Many Entities on both sides of the relationship can

have many related entities on the other side

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Figure 2.8 Degree of relationships and Cardinality(a) Unary relationships

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(b) Binary relationships

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(c) Ternary relationships

Note: a relationship can have attributes of its own

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Cardinality Constraints

Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.

Minimum Cardinality If zero, then optional If one or more, then mandatory

Maximum Cardinality The maximum number

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Figure 2.8 Cardinality Mandatory and Optional

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(a) Basic relationship with only maximum cardinalities showing

(b) Mandatory minimum cardinalities

Figure 2.9 Cardinality Constraints

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Employees and departments – entities can be related to one another in more than one way

Figure 2.10 Examples of multiple relationships

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Strong vs. Weak Entities, andIdentifying Relationships

Strong entities exist independently of other types of entities has its own unique identifier represented with single-line rectangle

Weak entity dependent on a strong entity…cannot exist on its

own Does not have a unique identifier represented with double-line rectangle

Identifying relationship links strong entities to weak entities represented with double line diamond

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Associative Entities

It’s an entity – it has attributes

AND it’s a relationship – it links entities together When should a relationship with attributes instead be an

associative entity? All relationships for the associative entity should be many The associative entity could have meaning independent of

the other entities The associative entity preferably has a unique identifier,

and should also have other attributes The associative may be participating in other relationships

other than the entities of the associated relationship Ternary relationships should be converted to associative

entities

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Figure 2.11 An associative entity

Associative entity involves a rectangle with a diamond inside.Note that the many-to-many cardinality symbols face toward the associative entity and not toward the other entities

(a) An associative entity (CERTIFICATE)

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(b)Ternary relationship as an associative entity

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Components of E-R Model

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Recalled : Teaching Plan W2

Database design stages Conceptual data model Unified Modeling Language Entity Relationship Diagram (ERD)