SE 555 Software Requirements & Specification Requirements Analysis

SE 555 Software Requirements & Specification

Requirements Analysis


Goals of Requirements Analysis

Create requirements containing sufficient detail and of high enough quality to allow realistic project planning as well as successful design and implementation.

Scrutinize requirements for errors, conflicts, omissions and boundaries.


Requirements Analysis Practices

Analyze feasibility Allocate requirements to subsystems Create prototypes where necessary Model the requirements Prioritize the requirements Define system boundaries and interfaces Create consistent data definitions


Requirements Analysis Checklist

Premature Design – Does the requirement include premature design or implementation information?

Combined Requirements – Does the description of a requirement describe a single requirement or could it be broken down into several different requirements?

Unnecessary Requirements – Is the requirement “gold plating”? That is, is the requirement a cosmetic addition to the system which is not really necessary.

Use of Non-standard Components – Does the requirement mean that non-standard hardware or software must be used?


Requirements Analysis Checklist – cont’d

Conformance with Business Goals – Is the requirement consistent with the business goals defined in the introduction to the requirements document/

Requirements Ambiguity – Is the requirement ambiguous i.e. could it be read in different ways by different people?

Requirements Realism – Is the requirement realistic given the technology which will be used to implement the system?

Requirements Testability – Is the requirement testable? Is it stated in such a way that a test can be derived to show if the system meets the requirement?


Requirements Analysis Artifacts

System Boundaries – Context Diagram Requirements Modeling – Class Diagrams, Activity State

Diagrams, Interaction Diagrams, Sequence Diagrams, Data Flow Diagrams, Entity-Relationship Diagrams

Data Definition – Data Dictionary Requirements Priority – Prioritization Matrix Requirements Definition, Risk Mitigation, Feasibility –

Prototypes


Context Diagram - Purpose

Highlights the boundary between the system and the outside world.

Highlights the people, organizations, and outside systems that interact with the system under development.

Special case of the data flow diagram.


Context Diagram - Notation

Process - Represents the proposed system

Terminator - Represents the external entities

Flow - Represents the in and out data flows


Context Diagram - Example

Credit Card Processing

Customer

CollectionCompany

CorporateAccounting

SystemStore

Customer ServiceApplication

Bills

Payment

Transaction

Payment

OverdueAccounts

Credit

AccountSummary


Use-Case Analysis Use-case analysis is where the requirements meet object-orientation

Recall: in the Unified Process, the use-case model is the primary artifact in the requirements model

In use-case analysis, identify the classes which perform a use-case flow of events

Distribute the use-case behavior to those classes Identifying the responsibility of the classes

Develop use case realizations that model the collaborations between instances of the identified classes

How the class instances work together to deliver the requirements

The result is a first-draft, rough-cut of the system object model An abstraction of the design model; refined during design


Use-Case Analysis - Steps

Supplement the Use-Case Description For each use-case realization

Find classes from use-case behavior Distribute use-case behavior to classes

For each resulting analysis class Describe responsibilities Describe attributes and associations Qualify architectural analysis mechanisms

Unify analysis classes Checkpoints


Analysis Classes: A First Step Towards Executables

Use-Cases AnalysisClasses

DesignElements

SourceCode

Executables

Use-Case Analysis


Data Flow Diagram - Purpose

Provides a means for functional decomposition. Primary tool in analysis to model data transformation in

the system.


Data Flow Diagram - Notation

Represents the external entities that the System communicates with

Represents data flows

Represents functions in the system(transforms Inputs into Outputs)

Represents data stores(a collection of data at “rest”)


DFD Example from Text


Data Dictionary

A repository that defines the data elements or attributes used in the system

It is not the project glossary Makes it easy to find info about the data Avoids redundancy and maintenance issues, over being in

various func. req. Have it as an appendix in your SRS (project)


DD Notation Primary data element

Where an element does not need or require further decomposition Defined with a comment * text * Data type, size, range of values etc. are presented.

Composition: + Used to show multiple data items Optional items are enclosed in ()

Iteration: min:max {item} Used to show that mult instances of an item can appear

Selection: [item | item] When a data element can be of a set of discrete values


DD Examples Customer Name Phone Number


DD Notation

Entry comprised of: (and listed in alphabetical order) Name: its name Aliases: if it goes by another name as well Used in: the use cases it is present in, by id and name Description: the notation goes here Notes: any special notes about it


Entity Relationship Diagram (ERD) - Purpose

A graphical representation of the data layout of a system at a high level of abstraction.

Defines data elements and their inter-relationships in the system.


Entity Relationship Diagram - Text Example

Documents

SE 555 Software Requirements & Specification Requirements Analysis