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CS 509Design of Software Systems

Lecture #7Monday, March 8, 2004

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Brief discussion of CS562Term Project AdministrationQuestionsQuiz #4Review of Chapters 9 & 13

(Budgen)In-class Exercise:

Review Analysis of HIS

Class Format for Today

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CS562 – The Next Course

Tuesday afternoons, 3 – 7pmTo begin on April 13, end on June

15Topics TBD – suggestions?

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Term Project Administration

Return Phase 3 – CIS Design (and journals)

Phase 4 – HIS Analysis (and journals) due Hold on to your documents for now We will discuss later today Turn in at the end of class

Phase 5 assignment posted to the web Similar to Phase 3 assignment, based on UML Feel free to incorporate topics from Budgen

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Questions?

About what was covered last timeFrom the readingAbout the Term ProjectAnything else?

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Quiz #4

Chapters 10, 9*, 13*You have 15 minutes

*from Budgen

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Chapter 9

Design Processes andDesign Strategies

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Terminology

DVMDFDERDSTD

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Structure of Design

A software design method can be described in terms of the following components: Representation Process Set of heuristics

Examples of these components? See diagrams on pages 194, 195

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Form of Process

Process steps can be categorized into 2 forms Transformation Step Elaboration Step

What do they mean / how do they differ?What does viewpoint have to do with

them? See diagram on page 197

How are they related in the design process?

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Potts Process Model

Entity (box) types: Artifact, Issue, Argument, Step, Position

Relationship (arc) types: Modify, Raise, Review, Respond,

Support, Object to, Cite, ContributeWhat does the model describe? What

does it mean? See figures on page 198

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Design Strategies

Decompositional methodsCompositional methodsOrganizational methodsTemplate-based methods

What are these? How do they differ? See bullet list on page 199

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The D-Matrix

Description and purpose: Viewpoint-centered notation models the

procedural steps of a method Abstract description of the state of the

design model at any point in its evolutionWhat are the design elements in the D-

Matrix?What are the sub-scripts and super-

scripts? b, f, d, c 1, 2, 3, … n

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Describing Transformations

How the D-Matrix notation is deployed:

What does the null symbol () mean?Review diagram on top of page 203

What process does it describe? What are the elements? What does it mean?

Review diagrams on page 204 Describe D-matrices, what are E3 and T4?

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Top-down Decomposition

Also known as ‘stepwise refinement’, or ‘divide & conquer’

Describe this approach Where does it come from?

What are its strengths and weaknesses? What does it focus on? What does it ignore?

How are solutions (fig. 9.7, p. 205) derived?

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Design by Composition

Describe this approach How does it differ from decomposition?

What are its strengths and weaknesses? What does it focus on? What does it ignore?

Review bullet list on page 209

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Organizational Influences

Example of the British Civil Service What is the career of a civil servant like? How do job transitions impact SW

design?Use ‘standard’ methods for analysis

& design How does this help? (See bullets on p.

210) Are there any drawbacks?

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Chapter 13

Structured Systems Analysis and Structured

Design

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Background

Original development by Constantine and Yourdon, furthered by De Marco What distinguishes the terms SSA/SD

from ‘structured analysis and design’? What distinguishes SSA from SD? Are these approaches compositional or

decompositional? How does ‘call-and-return’ differ from

more object-oriented architectural forms?

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Background, Continued

If not very OO, what use is it?Assumed problem domain: Data

Processing Single sequential process Is this a restriction imposed by the

method?How widely applicable is the method?

What are some other common problem domains?

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Interlude from Chapter 7

Representation Forms: Data Flow Diagram

• Review figure 7.2, page 132• Repeated (without description) on page

260 Entity-Relationship Notation

• Review figure 7.7, page 137 Structure Chart

• Review figure 7.27, page 159• Another example on page 262

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Data Flow DiagramsProblem-oriented, functional

viewpoint, doesn’t involve ‘hierarchy’ What does this mean?

Often accompanied by P-Specs What does it describe? What data is

included? See example on page 260

Also accompanied by a Data Dictionary What is this? Example on page 261

Complementary with ERD’s – How so?

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Structure Charts

Program-oriented descriptionCall-and-return styleProvides run-time invocation

hierarchy See example on page 262

May also be accompanied by: Pseudocode, decision trees or tables,

ERDs STDs, CFDs, DFDs, etc.

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SSA/SD Process

Start with top-level description of problem In terms of operations performed by system

Then apply a series of transformations: A plan for a program Description of subprograms Details of interactions among subprograms

Review list of 5 steps on page 263 and transformation diagram on page 264

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Context Diagrams & Beyond

Highest level diagram describing system Single bubble, only data flows are external See fig. 13.6, page 265

2 common strategies for remaining levels Top-down functional decomposition Event partitioning

What’s the difference?

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Types of DFDsPhysicalLogical

What is the purpose of each? How do they differ?

What are DFDs good/bad at capturing?Recommendations for producing DFDs:

Review bullet list, pages 266 – 267 Benefits of paper-and-pencil over CASE

tools?

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Transaction Analysis

Concerned with architectural design choices

Separate components into network of cooperating subsystems

Identify Transactions in the system: How? What is a transaction? Review bullet list on page 267

Results of this step feed into next See fig. 13.7, page 268

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Transformation Analysis

What is the purpose of this step?How is it done?

Balloon analogy See fig. 13.9, page 270

The flow of arrows on the arcs change direction when this transformation is made What is meant by this statement?

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From DFD to Structure Chart

How do diagrams differ? DFD is non-sequential, describes

structure of problem SC describes solution, hierarchy of

program unitsBoth describe system in terms of

operations and flow of informationWhat is extra ‘central

transformation’ described in book?

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Completing the Design

The last step: Bring together SCs produced for different

transactions Resolve overlaps or mismatches

May be simple: Add top-level module to select among

transactionsReduce duplication – reuse operations

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Summary of Design Process

Review D-Matrix diagrams for steps 1 – 5 Pages 271 – 273

What is involved at each step? Design elements Transformations

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Heuristics in SSA/SD

Related to the design process, or form of solution? Why?

Some heuristics include Central transform Leveling Factoring Coupling and cohesion

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Additions to SSA/SD

More material on SSA/SD can be found in addition to what is described in the chapter: Variations Extensions Developments

What are these about? See bullet list on page 275

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In-class Exercise

Review analysis of HIS Class discussion: how did phase 4 go? How far did you get in the analysis? Teams give mini presentations Discuss any significant differences

Don’t forget to turn in Analysis at the end

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For Next Time

Read Chapters 14 & 15 in Budgen