CS 509 Design of Software Systems

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CS 509Design of Software Systems

• Lecture 3
• Thursday, Sept. 18, 2003

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Class Format for Today

• Term Project administration
• Return Quiz 1 well done!
• Questions
• Phase 2 Functional Specifications
• Specifications Exercises
• Review Chapter 5
• Analysis Exercises

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Meeting Coordinator Project

• Turn in Phase 1 (Requirements) document and group
  evaluation forms
• An email was sent out to the class mailing list
  to remind students about the evaluation forms.
  Did everyone receive the message?
• Hand out Phase 2 document

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Return Quiz 1

• Solutions are available on
• Course Web Site

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Questions?

• From last weeks class
• From the reading
• Anything else?

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Phase 2

• Functional Specifications

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Discussion

• What is a Functional Specification?
• What purpose does it serve?
• What goes into a FS document?

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Introduction

• One of the most common documents used in
  commercial software industry
• Developers might not have much input into
  requirements
• Often your only chance to negotiate features
• May need to be updated if requirements change

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Purpose

• Further define goals and scope of the system by
  detailing functionality
• Determine which features impact usability
• Distinguish between necessary features and wish
  list features
• Get client to sign-off
• Consider FS to be like a contract

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Contents

• Introduction
• State purpose, scope and objectives
• Detailed Functionality
• Explain how requirements will be covered
• Glossary
• Mock-up or Prototype
• Show what features will look like
• Pictures often worth more than words

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Specifications

• Exercises

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Exercise 1 Functionality

• Design and build a chair
• Definition what is a chair?
• What is its purpose?
• What are its salient characteristics?
• Functional decisions
• What choices are there?
• How do you choose?

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Exercise 2 Content Index

• Review functional requirements
• Configure which types of files to include in
  Index
• Provide editable text box for query input
• Remember previous queries for later recall
• Provide mechanism to initiate execution of a
  query
• Provide mechanism to cancel execution of a query
• Switch between case-sensitive and -insensitive
  queries
• Display query results as a list of files
• Choose a few to describe in more detail

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Analysis

• Chapter 5

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Purpose of Analysis

• Preliminary stage of Design activities
• Identifying various objects object types
• Identifying associations
• Modeling Interactions between objects
• Identifying Attributes
• Modeling Nontrivial Behavior
• Modeling Generalization Relationships

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Terminology

• Entity Object
• Boundary Object
• Control Object
• Association
• Nontrivial Behavior (typo in book)

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Identifying Object Types

• Entity Object
• Persistent information tracked by system
• E.g. Month, Day, Year
• Boundary Object
• Interactions between actors system
• E.g. Button, Display
• Control Object
• Tasks performed by User, supported by System
• E.g. ChangeDate

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Heuristics for Object Types

• Entity objects
• Box on page 141
• Boundary objects
• Box on page 143
• Control objects
• Box on page 145

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Associations Multiplicity

• Types of associations (Example on p. 136)
• one-to-one
• one-to-many
• many-to-many
• Symbols used to represent multiplicity
• 1 - may be assumed by default, 2 n
• - zero or more
• - one or more
• ? - zero or one

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Qualified Associations

• Technique for reducing multiplicity, thereby
  reducing complexity

Figure 5-9 (page 138). Example of how a qualified
association rule reduces multiplicity
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Modeling Interactions

• Interactions between objects can be modeled using
  UML Sequence Diagrams
• Heuristics for drawing sequence diagrams on page
  146
• Points 4 5 do these make sense?
• New objects may be identified during the Sequence
  Diagramming activity

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Identifying Attributes

• Properties of individual objects
• Each attribute should have
• name identifying it within an object
• description to remember what its for
• type defining legal values it can take on
• Heuristics for identifying attributes on page 152

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Modeling Nontrivial Behavior

• Statechart diagrams represent behavior of a
  single object
• Gives a different perspective when compared to
  Sequence diagrams
• How do we know what behavior is Nontrivial?
• Examples of trivial vs. nontrivial behavior?

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Generalization Relationships

• Generalization relationships between objects can
  be modeling using UML Class diagrams
• Organize concepts into hierarchies from most
  general to most specific
• Eliminate redundancy
• Not to be confused with Inheritance
• For organizational purposes only, not reuse
• Inheritance comes in during Object Design

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Analysis Model

• Is this a useful activity?
• Identifying object types terminology, concepts
• Constructing sequence state-chart diagrams
• Associations and generalizations
• At what point does analysis apply to a software
  development project?
• Is it required for this course?

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Analysis Exercise

• Identifying Objects
• Object Types

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Exercise 3 File System

• (From textbook, exercises 1-5, page 164)
• File system with GUI e.g., File Explorer
• Activity copy file from floppy to hard disk
• How is this accomplished?
• Tasks
• Identify objects object types
• Identify associations, attributes, generalizations

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For Next Time

• UML Chapter 2