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Systems Analysis and Design in a Changing World, Fifth Edition

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Learning Objectives

• Explain why identifying use cases is the key to defining functional requirements
• Use three techniques for identifying use cases
• Write brief, intermediate, and fully developed use case descriptions

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Learning Objectives (continued)‏

• Explain how the concept of things in the problem domain also defines requirements
• Identify and analyze data entities and domain classes needed in the system
• Read, interpret, and create an entity-relationship diagram
• Read, interpret, and create a domain model class diagram

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Overview

• Document functional requirements by creating models
• Models created during analysis phase activity – Define system requirements
• Two concepts help identify functional requirements in the traditional approach and object-oriented approach
• Use cases and the events that trigger them
• Things in the users’ work domain

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User Goals, Events, and Use Cases

• Use Case -- An activity the system performs in response to a user request
• Techniques for identifying use cases
• User goal technique
• Each goal at the elementary business process (EBP) level is a use case
• EBP – a task performed by one user, in one place in response to a business event, that adds measurable business value, and leaves system and data in consistent state

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User Goals, Events, and Use Cases (continued)

• CRUD analysis technique (create, read, update, delete)‏
• Event decomposition technique

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Identifying Use Cases Based on User Goals

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Figure 5-1

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Use Case Based on CRUD Technique

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Figure 5-2

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Event Decomposition Technique

• Event – an occurrence at a specific time and place and which needs to be remembered
• Business events trigger elementary business processes (EBPs)‏
• EBPs are at correct level of analysis for use cases
• Identify business events to decompose system into activities/use cases

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Types of Events

• External
• Outside system
• Initiated by external agent or actor
• Temporal
• Occur as result of reaching a point in time
• Based on system deadlines
• State
• Something inside system triggers processing need

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Events Affecting a Charge Account Processing System that Lead to Use Cases

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Figure 5-3

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External Event Checklist

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Figure 5-4

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Temporal Event Checklist

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Figure 5-5

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Identifying Events

• Can be difficult to determine
• Often confused with conditions and responses
• May be useful to trace a transaction’s life cycle
• Certain events left to design phase
• System controls to protect system integrity
• Perfect technology assumption defers events

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Sequence of Actions that Lead Up to Only One Event Affecting the System

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Figure 5-6

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Sequence of “Transactions”
for One Specific Customer
Resulting in Many Events

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Figure 5-7

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Events Deferred Until the Design Phase

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Figure 5-8

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Events in the RMO case

• Important external events involve customers
• Customer checks item availability, customer places order, customer changes or cancels order
• Other external events involve departments
• Shipping fulfills order, marketing sends promotion to customer, merchandising updates catalog
• Temporal events include periodic reports
• Time to produce order summary reports, Time to produce fulfillment summary reports

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RMO External Events

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Figure 5-9

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RMO Temporal Events

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Figure 5-10

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Events and Use Cases

• Event Table – a catalog of use cases listed by event. Contains detailed information
• Trigger – a signal that indicates an event has occurred
• Source – an external agent that initiates event and supplies data for the event
• Response – an output produced by the system
• Destination – an external agent that receives the response

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Information about Each Event
in an Event Table

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Figure 5-11

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RMO Event Table‏

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Figure 5-12

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Use Case Descriptions

• Use case description – a description of the processing steps for a use case
• Actor – a person or thing that uses the system. Actors have contact with the system
• Scenario or Instance – a particular set of internal steps that represent a unique path of the use case
• Three types of descriptions
• Brief description
• Intermediate description
• Fully developed description

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Brief Description

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Figure 5-13

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Intermediate Description

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Figure 5-14

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Fully Developed Description

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Figure 5-16

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“Things” in the Problem Domain

• Define system requirements by understanding system information that needs to be stored
• Store information about things in the problem domain that people deal with when they do their work

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Types of Things

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Figure 5-18

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Procedure for Developing an
Initial List of Things

• Step 1: Using the event table and information about each use case, identify all nouns
• Step 2: Using other information from existing systems, current procedures, and current reports or forms, add items or categories of information needed
• Step 3: Refine list and record assumptions or issues to explore
• Questions to include it, exclude it, or research it

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RMO Example “Things”

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Figure 5-19

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Characteristics of Things

• Relationship
• Naturally occurring association among specific things
• Occur in two directions
• Number of associations is cardinality or multiplicity
• Binary, unary, ternary, n-ary
• Attribute
• One specific piece of information about a thing

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Relationships Naturally Occur Between Things

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Figure 5-20

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Cardinality/Multiplicity of Relationships

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Figure 5-21

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Attributes and Values‏

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Figure 5-22

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Data Entities

• Things system needs to store data about in traditional IS approach
• Modeled with entity-relationship diagram (ERD)‏
• Requirements model used to create the database design model for relational database

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The Entity-Relationship Diagram (ERD)‏

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Figure 5-23

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Cardinality Symbols of Relationships for ERD

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Figure 5-24

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Expanded ERD with Attributes Shown

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Figure 5-25

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Customers, Orders, and Order Items

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Figure 5-26

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ERD with Many-to-Many Relationship

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Figure 5-27

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Many-to-Many Relationship Converted to Associative Entity to Store Grade Attribute

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Figure 5-28

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RMO Customer Support System ERD

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Figure 5-29

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The Domain Model Class Diagram

• Unified Modeling Language (UML) diagram
• Domain model class diagram
• Models things in the users’ work domain
• Used to define requirements for OO (very similar to entities in ERD)‏

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UML Class Symbol

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Figure 5-30

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Simple Domain Model Class Diagram

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Figure 5-31

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Simple Domain Model Class Diagram (continued)

• No methods shown in domain model
• Domain classes are not software classes
• Very similar to ERD
• UML and domain model can be used in place of ERD in traditional approach

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Multiplicity of Associations

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Figure 5-32

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University Course Enrollment Domain Model Class Diagram

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Figure 5-33

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Refined Model with Association Class and Grade Attribute

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Figure 5-34

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More Complex Class Concepts

• Generalization/specialization hierarchies
• General superclasses to specialized subclasses
• Inheritance allows subclasses to share characteristics of their superclasses

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A Generalization/Specialization
Class Hierarchy for Motor Vehicles

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Figure 5-35

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A Generalization/Specialization
Class Hierarchy for RMO Orders

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Figure 5-36

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Whole-Part Hierarchies

• Whole-part hierarchies – hierarchies that structure classes by components
• Aggregation – whole-part relationships between and object and its removable parts
• Parts can exist separately
• Like car and its tires
• Composition – whole-part relationships between and object and its non-removable parts.
• Parts cannot exist separately
• Like Hand is composed of fingers and thumb

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Whole-Part Aggregation Relationships

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Figure 5-37

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RMO Domain Model Class Diagram‏

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Figure 5-38

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Where You Are Headed‏

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Figure 5-39

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Summary

• Analysis phase – defines system requirements
• Models created to further learning process, reduce complexity, communicate with team members, and document requirements
• Key early step in modeling is to identify and list
• Events that require a use case in the system
• Things users deal with in work environment

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Summary (continued)‏

• Use cases (activities) are identified from user goals and business events that trigger elementary business processes
• Business events are memorable, can be described, and occur at a specific time and place
• External events, temporal events, and state events
• Event table records event, trigger, source, use case, response, and destination
• A catalog of information about each use case

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Summary (continued)‏

• “Things” are what user deals with and system remembers, such as customer placing an order
• Traditional approach uses entity-relationship diagrams (ERD) for data entities, attributes of data entities, and relationships between entities
• Object-oriented approach uses UML class diagrams for classes, attributes, methods of class, and associations among classes
• Domain model class diagram

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