Systems Analysis and Design in a Changing World, Thursday, Feb 22

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Today’s Schedule

Using Events for Requirements Using “Things” for Requirements For Tuesday, February 27

Finish Reading Chapter 5, ERDs and Class Diagrams

Try out ERDs in Visual Paradigm

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Recall … Where You Are Headed

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

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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 “Transactions” for One Specific Customer >> Many Events

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Defer Some Events Until Design

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Event Table: Catalog of Information about Each Use Case

How do the “events” in Activity Diagram fit?

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“Things” in 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

Analysts identify these types of things by considering each use case in the event table

– What things does the system need to know about and store information about?

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Types of Things

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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

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Questions for Refining List

Should you include it?– A unique thing system needs to know about?– Inside scope of this system?– Need to remember more than one of these?

Should you exclude it?– Synonym for another thing already in list?– Is it really an output?– Input that results in recording info already in list?

Should you research it?– Is it a characteristic of another “thing”?– What if assumptions change, is it still needed?

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“Things” have …

Relationship– Naturally occurring association among specific

things– Occur in two directions– Number of associations is cardinality or multiplicity

Binary, unary, ternary, n-ary

Attribute (characteristic)– One specific piece of information about a thing

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Cardinality/Multiplicity of Relationships

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Attributes and Values

Identifier or Key – Attribute that Uniquely identifies the “thing”

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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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Objects Objects do the work in a system and store information in the object-oriented approach

Objects have behaviors and attributes– Class – type of thing– Object – each specific thing– Methods – behaviors of objects of the class

Objects contain values for attributes and methods for operating on those attributes

An object is encapsulated – a self-contained unit

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Data Entities Compared with Objects (Figure 5-22)

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The Entity-Relationship Diagram (ERD)

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Cardinality Symbols of Relationships for ERD

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Expanded ERD with Attributes Shown

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Customers, Orders, and Order Items

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ERD with Many-to-Many Relationship

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

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RMO Customer Support System ERD(Figure 5-29)

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Now you try it …

Case Study: (Page 194-5) The Spring Breaks ‘R’ Us Travel Service Booking System

#1 Events and event Table #2 Data Entities and their relationships

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For Tuesday, February 27

For Tuesday, February 27Finish Reading Chapter 5, ERDs and Class Diagrams

Try out ERDs in Visual Paradigm