Modeling System Requirements:

1

• Chapter 5
• Modeling System Requirements
• Events and Things
• Part 2

2
Things and System Requirements

• Things define what information the system needs
  to store
• Things become models in the analysis phase
• In the traditional approach, they become data
  entities
• In the object-oriented approach they become
  Objects

3
Types of Things
4
Developing an Initial List of Things

• Step 1 Identify all nouns about the system
• Use the event table
• Step 2 Define all types/categories of
  information needed
• Augment event list with information from current
  systems, forms, other documents
• Step 3 Refine list and record assumptions or
  issues to explore
• Is this a thing that the system needs to know
  about (e.g., product inquiry)?
• In scope?
• System needs to remember more than one?
• Look for and eliminate synonyms
• Eliminate things that system outputs (e.g.,
  reports)
• Eliminate things that are inputs that you record
  information from (e.g., a form)

5
Characteristics of Things

• Once list of things finalized, need to define
  characteristics of each thing.
• Relationships
• Attributes

6
Relationships Naturally Occur Between Things

• Naturally occurring association among specific
  things
• Occur in two directions
• Cardinality/multiplicity
• Types
• Binary
• Unary (recursive),
• Ternary
• n-ary

7
Attributes and Values

• Attribute
• One specific piece of information about a thing
• Primary key special type of attribute that
  uniquely identifies a specific thing

8
Data Entities

• Things the system needs to store data about in
  traditional IS approach
• Modeled with entity-relationship diagram
• Generally used with relational database
  development
• Single occurrence of an entity instance

9
Simple ERD
Each data entity has a set of attributes,
including primary key (unique identifier)
10
Cardinality Symbols of Relationships
11
Objects

• Do the work in the system and store information
• Behaviors and attributes
• Class Type of thing
• Object Specific thing
• Methods Behaviors of objects

12
Class Diagram

• Classes objects rather than data entities

13
Bank Account System Class Diagram
14
Aggregation or Whole-Part Relationships
15
Data Entities Compared with Objects
16
Example Student Enrolls in Course
What data entities would be involved? What are
relationships?