CS 5150Software

EngineeringLecture 9

Requirements 3

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Administrivia

• Quiz response• High level project goals:• Generic versus particular• User-relevant versus implementation

• Copyright versus license• Risk: finding users to test with

• Surveys• Feasibility Reports

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Modeling Techniques for Requirements Analysis and Specification

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

• A variety of tools and techniques. • Many familiar from other courses.• No correct technique that fits all situations.

• As you build understanding of the requirements through viewpoint analysis, scenarios and use cases, etc., use models to specify requirements. The models provide a bridge between the client's understanding and the developers.

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The “Ur-models” of Software Engineering

• Functions• Data (storage)• Processes

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Data-Flow Models

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Data-Flow Example 1: University Admissions

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Receive Application Stage

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Evaluate Stage

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Decision Table

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Flowcharts

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University Admissions as Flowchart

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Pseudo-code

• Example: Check project plan• check_plan (report)

if report (date_time) > due_date_timethen error (too_late)

if report (client) = none then error (no_client)

if report (team) < min_team or > max_teamthen error (bad_team)

if error() = nonethen comments = read_report (report)

return (comments (text), comments (grade))

else return error()

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Transition Diagrams• A system is a set of states and rules for

transitioning from one state to another• Transitions can be conditional• Outputs can be associated with states or

transitions• Transition rules often expressed as a

function:• next state = f(current state, inputs)

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State Machine Example: Therapy Control Console

• Example: Radiation Therapy Control Console• You are developing requirements for the

operator's control console. In an interview, the client describes the procedures that the operator must follow when operating the machine.

• You use a finite state machine to specify the procedures

• This shows the client that you understand the requirements and specifies the procedures for the developers

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Therapy Control Console Scenario• "The set up is carried out before the

patient is made ready. The operator selects the patient information from a database. This provides a list of radiation fields that are approved for this patient. The operator selects the first field. This completes the set up.

• "The patient is now made ready. The lock is taken off the machine and the doses with this field are applied. The operator then returns to the field selection and chooses another field."

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Console State Transition Diagram

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Console State Transition Table

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Transition Diagrams for User Interfaces (CS 5150 Website)

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Andrew Durdin’s iOS Home Button Guide

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Entity-Relation Models

• A requirements and 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)

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Entity-Relation Diagrams

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Entity-Relation Example: 5150 Project

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Database Schema for Web Data

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Sequence Diagrams for Interaction/Concurrency

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Modeling Trump Card: Prototyping

• Rapid prototyping is the most comprehensive (and potentially expensive) of all modeling methods • A method for specifying requirements

by building a system that demonstrates the functionality of key parts of the required system

• Particularly valuable for user interfaces

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Dictionaries to Support Other Requirements Documents

• A data dictionary is a list of names used by the system• Name (e.g., "start_date")• Brief definition (e.g., what is "date")• What is it? (e.g., integer, relation)• Where is it used (e.g., source, used by,

etc.)• May be combined with a glossary

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A Few Concluding Remarks

• In this course we discuss class and object models as a tool for design

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

• Flow charts and finite state machines are supported by UML as design models, but are equally useful for requirements