1 cs 501 spring 2002 cs 501: software engineering lecture 9 techniques for requirements definition...

1 CS 501 Spring 2002

CS 501: Software Engineering

Lecture 9

Techniques for Requirements Definition and Specification I


Administration

Projects

• Comments are being sent to each group by email. Should complete today.

• Teaching Assistants assigned to each project. Will contact you.

Observations about Assignment 1

• Some projects too ambitious

• Do not design the project before requirements analysis.

Assignment 2 will be posted shortly


Assignment 2: What is in a Requirements Document?

Remember

• The requirements document specifies the functionality that you plan to deliver to the client

• It must be comprehensive and detailed. Everything must be written out -- no hand waving!

The requirements document is likely to be several times as long as Assignment 1.


Techniques for Requirements Analysis and Definition

• A variety of tools and techniques.

• Many are familiar from other courses.

• There is no correct technique that fits all situations.

The craft of requirements analysis and specification is to select the appropriate tool for the particular task.

(Other tools are described in Pfleeger, Chapter 4.)


Bad Example: Decision Table

University Admission Decision

Note that the rules are vague.

High SAT T F F F F F

High grades - T F F F F

Sports - - T T F F

Recommendations - - T F T F

Reject X X X

Accept X X X


Good Example: Decision Table

University Admission Decision

Note that the rules are now specific and testable.

SAT > S T F F F F F

GPA > G - T F F F F

Athletics code = - - T T F F

Recommendations > A- - - T F T F

Send rejection letter X X X

Send acceptance letter X X X


Data-Flow Models

External entities

Processing steps

Data stores or sources

Data flows


Data-Flow Example: University Admissions

Applicant

Applicationform Receive

application

Completedapplication

Evaluate

Rejection

Acceptance


Data-Flow Example: Assemble Application Stage

Applicant

Applicationform

Receive

Completedapplication

Supportinginformation

Pendingdatabase

Acknowledgment

Initiateevaluation

Applicantdatabase

Evaluationrequest

AND

AND

Acknowledgment

10 CS 501 Spring 2002

Data-Flow Example:Process Completed Application Stage

Rejection

Evaluation

Applicantdatabase

Evaluationrequest Acceptance Financial

aid

Offer

Specialrequest

11 CS 501 Spring 2002

Procedural Models: Flowchart

Operation

Decision

Manual operation

Report

12 CS 501 Spring 2002

Flowchart: University Admissions

Form received New?

Database record

T

Notify student

F Update database

Complete?

Notify student

T

FEvaluate

13 CS 501 Spring 2002

Procedural Models: Pseudo-code

Example: Check project plan

check_plan (report)

if report (date_time) > due_date_time then error (too_late) if report (client) = none then error (no_client) if report (team) < min_team or > max_team then error (bad_team) if error() = none then comments = read_report (report) return (comments (text), comments (grade)) else return error()

14 CS 501 Spring 2002

Entity-Relation Model

A Design Methodology for Relational Databases

• A database of entities and relations

• Tools for displaying and manipulating entity-relation diagrams

• Tools for manipulating the database (e.g., as input to database design)

Warning: There is much confusion about definitions and notation

15 CS 501 Spring 2002

Entity-Relation Diagram

An entity

A relation between entities

An entity or relation attribute

An inheritance relation

16 CS 501 Spring 2002

Example: CS 501 Project

Student

CS501 Student

Major

Project

5 to 7

1

Member of

Person

Client1

Tech contact

0:n0:n

0:n

17 CS 501 Spring 2002

Example: MARC Catalog Record

Caroline R. Arms, editor, Campus strategies for libraries and electronic information. Bedford, MA: Digital Press, 1990.

18 CS 501 Spring 2002

MARC Format for Books

001 89-16879 r93245 Campus strategies for libraries and electronic information260 {Bedford, Mass.} : Digital Press, c1990.650 Academic libraries--United States--Automation.650 Libraries and electronic publishing--United States.700 Arms, Caroline R. (Caroline Ruth)

19 CS 501 Spring 2002

Entity-Relation Diagram for MARC

Book

Short title

Catalog record

Describes

Control numb

Subject heading

Is about

CreatorEditor of

Author of

1:n

1

0:n

0:n

0:n

0:n

0:n

0:n

20 CS 501 Spring 2002

Data Dictionaries

A data dictionary is a list of names used by the system

• Brief definition (e.g., what is "date")

• What is it (e.g., number, relation)

• Where is it used (e.g., source, used by, etc.)

• May be combined with a glossary

As the system is implemented, the data dictionary in the requirements is input to the system data dictionary, which is a formal part of the system specification.

21 CS 501 Spring 2002

A Note on Object Models

This course teaches object models as a tool for design.

Some people recommend object models for requirements definition, but it is difficult to use them without constraining the system design.

22 CS 501 Spring 2002

Examples

For examples of requirements documentation, see the Pfleeger web site:

http://www.cs.umd.edu/~sharip/swebook/requirement.html

23 CS 501 Spring 2002

Discussion of Pfleeger, Chapter 4

Format:

State a question.

Ask a member of the class to answer.

(Sorry if I pronounce your name wrongly.)

Provide opportunity for others to comment.

When answering:

Stand up.Give your name or NetID. Make sure the TA hears it.

Speak clearly so that all the class can hear.

24 CS 501 Spring 2002

Question 1: Terminology

(a) What is the purpose of requirements definition?

(b) What is the purpose of requirements specification?

(c) What are functional requirements?

(d) What are non-functional requirements?

25 CS 501 Spring 2002

Question 2: Static descriptions of requirements

(a) What is a static requirements definition?

(b) Give two examples of application areas where a static requirements description might be used.

(c) How do static definitions of requirement relate to system testing?

(d) How do static definitions of requirement relate to system and program design?

26 CS 501 Spring 2002

Question 3: Transition Diagrams

(a) What does the book mean by a state? Give an example.

(b) What does the book mean by a transition? Give an example.

(c) Explain the notation in the expression:

f (Si, Cj) = Sk

Use the following diagram as an example:

S1 S2

S30

0

0

1

11

27 CS 501 Spring 2002

Question 4: Petri Nets

Explain the following diagrams:

A

S1

Sm

S

S

A

Event 1

Event n

Event

A

Event 1

Event n

..

28 CS 501 Spring 2002

Question 5: Prototyping Requirements

(a) How does rapid prototyping differ from other forms of prototyping?

(b) Under what circumstances would you use rapid prototyping?

1 cs 501 spring 2002 cs 501: software engineering lecture 9 techniques for requirements definition...

Documents