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PowerPoint Course Material for SCELE Graduate Program Information TechnologyFaculty of Computer Science – UNIVERSITY OF INDONESIA

PERANCANGAN SISTEM INFORMASI

Session 5 Data Modeling

Based on System Analysis & Design 2nd EditionAuthors : Alan Dennis & Barbara Haley Wixom

Publisher : John Wiley & Sons

Session 5 Data ModelingSession 5 Data Modeling

Based on System Analysis & Design 2nd EditionAuthors : Alan Dennis & Barbara Haley Wixom

Publisher : John Wiley & Sons

2PowerPoint Course Material for SCELE Graduate Program Information TechnologyFaculty of Computer Science – University of Indonesia

ObjectivesObjectives

Understand the rules and style guidelines for creating entity relationship diagrams.Be able to create an entity relationship diagram.Become familiar with the data dictionary and metadata.Become familiar with the process of normalization.Understand how to balance between entity relationship diagrams.


Key DefinitionsKey Definitions

Data modelA formal way of representing the data that are used and created by a business systemShows the people, places and things about which data is captured and the relationships among them.

Logical data modelshows the organization of data without indicating how it is stored, created, or manipulated


Key DefinitionKey Definition

Physical data modelshows how the data will actually be stored in databases or files.

Normalization is the process analysts use to validate data models.Data models should balance with process models


THE ENTITY-RELATIONSHIP DIAGRAM (ERD)


What Is an ERD?What Is an ERD?

A picture showing the information created, stored, and used by a business system. Entities generally represent similar kinds of informationLines drawn between entities show relationships among the dataHigh level business rules are also shown


Using the ERD to Show Business RulesUsing the ERD to Show Business Rules

Business rules are constraints that are followed when the system is in operation.ERD symbols can show when one instance of an entity must exist for an instance of another to exist

A doctor must exist before appointments the doctor can be made


An ERD ExampleAn ERD Example


ERD ElementsERD Elements


EntityEntity

A person, place, event, or thing about which data is collectedMust be multiple occurrences to be an entity

Example: If a firm has only one warehouse, the warehouse is not an entity. However, if the firm has several warehouses, the warehouse could be an entity if the firm wants to store data about each warehouse instance.


Entities and InstancesEntities and Instances


Case Repository Entry for Patient EntityCase Repository Entry for Patient Entity


AttributesAttributes

Information captured about an entityOnly those used by the organization should be included in the modelAttribute names are nounsSometimes entity name is added at the beginning of the attribute name for clarity


IdentifiersIdentifiers

One or more attributes can serve as the entity identifier, uniquely identifying each entity instanceConcatenated identifier consists of several attributesAn identifier may be ‘artificial,’ such as creating an ID numberIdentifiers may not be developed until the Design Phase


Identifier TypesIdentifier Types


Case Repository Entry for Patient_SSNAttributeCase Repository Entry for Patient_SSNAttribute


RelationshipsRelationships

Associations between entitiesThe first entity in the relationship is the parententity; the second entity in the relationship is the child entityRelationships should have active verb namesRelationships go in both directions


CardinalityCardinality

Cardinalityrefers to the number of times instances in one entity can be related to instances in another entity• One instance in an entity refers to one and only

one instance in the related entity (1:1)• One instance in an entity refers to one or more

instances in the related entity (1:N)• One or more instances in an entity refer to one or

more instances in the related entity (M:N)


ModalityModality

ModalityRefers to whether or not an instance of a child entity can exist without a related instance in the parent entity• Not Null means that an instance in the related

entity must exist for an instance in another entity to be valid

• Null means that no instance in the related entity is necessary for an instance in another entity to be valid


Case Repository Entry for a RelationshipCase Repository Entry for a Relationship


The Data Dictionary and MetadataThe Data Dictionary and Metadata

Metadata is information stored about components of the data modelMetadata is stored in the data dictionary so it can be shared by developers and users throughout the SDLCA complete, shareable data dictionary helps improve the quality of the system under development


CREATING AN ENTITY-RELATIONSHIP DIAGRAM


ERD BasicsERD Basics

Drawing the ERD is an iterative process of trial and revisionERDs can become quite complex


Steps in Building ERDsSteps in Building ERDs

Identify the entitiesAdd appropriate attributes for each entityDraw the relationships that connect associated entities


Identify the EntitiesIdentify the Entities

Identify major categories of informationIf available, check the process models for data stores, external entities, and data flowsCheck the major inputs and outputs from the use cases

Verify that there is more than one instance of the entity that occurs in the system


Add Appropriate AttributesAdd Appropriate Attributes

Identify attributes of the entity that are relevant to the system under development

Check the process model repository entries for details on data flows and data storesCheck the data requirements of the requirements definitionInterview knowledgeable usersPerform document analysis on existing forms and reports

Select the entity’s identifier


Draw the RelationshipsDraw the Relationships

Start with an entity and identify all entities with which it shares relationshipsDescribe the relationship with the appropriate verb phraseDetermine the cardinality and modality by discussing the business rules with knowledgeable users


ERD Building TipsERD Building Tips

Data stores of the DFD should correspond to entitiesOnly include entities with more than one instance of informationDon’t include entities associated with implementation of the system (they will be added later)


Advanced SyntaxAdvanced Syntax

Independent EntitiesCan exist without the help of another entityIdentifiers created from the entity’s own attributesAttributes from other entities are not needed to uniquely identify instances of these entities

Non-identifying relationshipsRelationships with an independent child entity



Dependent EntitiesA child entity uses attributes from the parent entity as part or all of its identifiersAlso called associative entity

Identifying relationshipRelationships having a dependent child entity



Intersection EntitiesA new entity created to store information about two entities sharing an M:N relationship• Remove the M:N relationship between two entities

and insert new entity between them• Create two 1:N relationships: original entities are

parents to the new child intersection entity• Name the intersection entity


VALIDATING AN ERD


Design GuidelinesDesign Guidelines

Best practices rather than rulesEntities should have many occurrencesAvoid unnecessary attributesClearly label all components Apply correct cardinality and modalityBreak attributes into lowest level neededLabels should reflect common business termsAssumptions should be clearly stated


NormalizationNormalization

Technique used to validate data modelsSeries of rules applied to logical data model to improve its organizationThree normalization rules are common


Normalization StepsNormalization Steps


Unnormalized EntityUnnormalized Entity

Begin with an entity fromthe logical data model


First Normal Form (1NF)First Normal Form (1NF)

Look for repeating groups of attributes and remove them into separate entities


Second Normal Form (2NF)Second Normal Form (2NF)If an entity has a concatenated identifier, look for attributes that depend only on part of the identifier. If found, remove to new entity.


Third Normal Form (3NF)Third Normal Form (3NF)Look for attributes that depend only on another nonidentifying attribute. If found, remove to new entity. Also remove any calculated attributes.


Balancing ERDs with DFDsBalancing ERDs with DFDs

All analysis activities are interrelatedProcess models contain two data components

Data flows and data stores

The DFD data components need to balance the ERD’sdata stores (entities) and data elements (attributes)Many CASE tools provide features to check for imbalanceCheck that all data stores and elements correspond between models

Data that is not used is unnecessaryData that has been omitted results in an incomplete system

Do not follow thoughtlessly -- check that the models make sense!


SummarySummary

The ERD is the most common technique for drawing data models. The building blocks of the ERD are:

Entities describe people, places, or thingsAttributes capture information about the entityRelationships associate data across entities

Intersection, dependent, and independent entities must be recognized.The ERD must be balanced with the DFD.

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