Requirements Analysis&Requirements Specification

Requirements Analysis&

Requirements Specification

Originally developed by Michael MadiganStorageTekManager, PAL Engineering

Software Engineering of Standalone ProgramsUniversity of Colorado, Boulder

Requirements Engineering

Requirements Elicitation Requirements Analysis

Requirements Specification Requirements Verification

Requirements Management

Requirements Engineering

Requirements Analysis & Specification Definitions

Requirements Analysis–The process of studying and analyzing the customer and the

user/stakeholder needs to arrive at a definition of software requirements.1

Requirements Specification–A document that clearly and precisely* describes, each of the

essential requirements of the software and the external interfaces. (functions, performance, design constraint, and quality attributes)

–Each requirement is defined in such a way that its achievement is capable of being objectively verified by a prescribed method; for example inspection, demonstration, analysis, or test.2

Types of Requirements

Functional requirementsPerformance requirements

–Speed, accuracy, frequency, throughputExternal interface requirementsDesign constraints

–Requirements are usually about “what”, this is a “how”.

Quality attributes– i.e. reliability, portability, maintainability,

supportability

What vs. How Dilemma3

User NeedsUser Needs

System Requirements

System Requirements

System DesignSystem Design

SoftwareRequirements

SoftwareRequirements

SoftwareDesign

SoftwareDesign

WhatHow

WhatHow

WhatHow

WhatHow

Requirements vs. Design

Requirements Design

Describe what will be delivered3 Describe how it will be done3

Primary goal of analysis:UNDERSTANDING3

Primary goal of design:OPTIMIZATION3

There is more than one solution There is only one (final) solution

Customer interested Customer not interested (Most of the time) except for external

Software Quality Attributes4

Correctness Reliability

– Rating = 1 – (Num Errors/ Num LOC)– Can be allocated to subsystems

Efficiency Integrity Usability Survivability Maintainability Verifiability Flexibility Portability Reusability Interoperability Expandability

Analysis of Elicitation results helps to create a VisionSettle on which problem

- Explain in the problem statement (2.2)Marketing group establishes positioning of the product (2.3)Stakeholder and User Summaries

- User is a special case of stakeholder- Identify all stakeholders w.r.t. development: Name Represents Role- Identify all users w.r.t. system: Name Description Stakeholder

Stakeholder Profiles (3.5)Representative - who (name) is representing this stakeholder

type.Description - brief description of the stakeholder typeType - Qualify s-h’s expertise, technical background, degree

of sophisticationResponsibilities - List s-h’s key responsibilities with regard to

the system being developed - why a stakeholder?Success Criteria - How does the stakeholder define success?

How rewarded?Involvement - involved in the project in what way?

Requirements reviewer, system tester, ...Deliverables* - required by the stakeholderComments/Issues - Problems that interfere w/ success, etc.

User Profiles (3.6)Representative - Who represents this user? (might be a

stakeholder)Description - of the user typeType - qualify expertise, technical background, degree of

sophisticationResponsibilities - user’s key resp.’s w.r.t. system being

developed Success Criteria - how this user defines success? rewarded?Involvement - How user involved in this project? what role?Deliverables - Are there any deliverables the user produces?

For whom?Comments/Issues - Problems that interfere w/ success, etc. This includes trends that make the user’s job easier or

harder

User Environment (3.4)-- working environment of target user

Number of people involved in doing this now? Changing?How long is a task cycle now? Changing?Any unique environmental constraints: mobile, outdoors, in-

flight, etc.Which system platforms are in use today? future?What other applications are in use? Need to integrate?

Key Stakeholder or User Needs (3.7)

List key problems with existing solutions as perceived by the stakeholder or user.

What are the reasons for this problem?How is it solved now?What solutions does the stakeholder want?

What is relative importance of solving each problem?

Alternatives and Competition (3.8)

Product Overview (4.)(at last!)

4.1 Product perspective (context)Put the product in perspective to other related products

and the user’s environment.Independent? Component of a larger system? How do the subsystems interact with this? Known interfaces between them and this component? Block diagram

Product Overview (4.)(at last!)

4.2 Summary of CapabilitiesCustomer Benefit Supporting Features1. 2. 3. 4.

Product Overview (4.)(at last!)

4.3 Assumptions and dependenciesWhat factors affect the features above?List assumptions that, if changed, ALTER this document

4.4 Cost and pricing -- not done by engineering4.5 Licensing and installation -- different types of license

enforcement will create more requirements for the development effort

What’s a feature?- high level capability necessary to deliver benefit to the user- externally desired service that typically requires inputs to

achieveLevel of detail must be general -- this is not the requirements

spec for the developers.Provide the basis for product definition, scope management,

and project management.Each will be expanded in the use-cases or other

requirementsExternally perceivable by users or external systems

Product Features (5.)

What is not in theProduct Features Section?

DesignConstraints -- These go in section 6.

–Design constraints–External constraints

Quality Ranges -- These go in section 7– ranges for performance, robustness, fault tolerance, etc. that

are not really features (specific capabilities, functions)

Precedence and Priority (8.)

Which features essential?–We will delay shipment in order to have these–We will postpone the feature in order to meet first-release goal

Other Product Requirements

These are requirements that are not features (functions) of the product–hardware platform requirements -- –system requirements -- supported host o.s.’s, peripherals,

companion software–environmental requirements -- temperature, shock, humidity,

radiation, usage conditions, resource availability, maintenance issues, type of error recovery

–applicable standards -- legal, regulatory, communications

Documentation Requirements

What must be developed to support successful deployment?–User Manual?–Online Help?– Installation guide? Read Me file?–Labeling, packaging?

Vision Doc adds basis for SRS

Use Case Internals -- Compare to example in Larman text (p. 68 ff.). Terms: 73-78

Use Case Name Scope Level Primary Actor Stakeholders & interests Preconditions Success Guarantee (post-

conditions)

Basic Flow Alternate Flows (extensions) Error Flows Subflows Special requirements Technology & data variations

list Frequency of occurrence Open Issues

Fully Dressed Example: Process Sale, Larman text, p. 68 ff.

Primary Actor: CashierStakeholders and Interests:- Cashier: Wants accurate, fast entry, and no payment errors, as cash

drawer shortages are deducted from his/her salary.- Salesperson: Wants sales commissions updated.- Customer: Wants purchase and fast service with minimal effort. Wants

proof of purchase to support returns.- Company: Wants to accurately record transactions and satisfy customer

interests. Wants to ensure that Payment Authorization Service payment receivables are recorded. Wants some fault tolerance to allow sales capture even if server components are unavailable. Wants automatic and fast update of accounting and inventory.

Fully Dressed Example: Process Sale, Larman text, p. 68 ff. - continued

- Government Tax Agencies: Want to collect tax from every sale. May be multiple agnecies such as national, state, and county.

- Payment Authorization Service: Wants to receive digital authorization requests in the correct format and protocol. Wants to accurately account for their payables to the store.

Preconditions: Cashier is identified and authenticated.Success Guarantee (Postconditions): Sale is saved. Tax is

correctly calculated. Accounting and Inventory are updated. Commissions recorded. Receipt generated. Payment authorization approvals are recorded.

Fully Dressed Example: Process Sale, Larman text, p. 68 ff. - continued

Main Success Scenario (of Basic Flow):

1. - 10.Extensions (Alternative Flows):*a.*b.1a2-4a

3a.3b.3c.3-6a-c4a5a-c6a7a-f9a-c

Special Requirements:- Touch Screen UI on a large flat panel monitor. Text visible from 1

meter.- Credit auth. response within 30 seconds 90% of the time....Technology and Data Variations List:...Frequency of Occurrence: Could be nearly continuous.Open Issues:- What are the tax law variations?- Explore the remote service recovery issue.- What customization is needed for different businesses?

Fully Dressed Example: Process Sale, Larman text, p. 68 ff. – cont.

Now what -- after development of use case(s)

Look for consistency, correctness, completeness–Most important for core requirements likely to be implemented

soonBy translation to other formats

–See Vision Document–State diagrams and tables–Event tables–Condition tables–Domain diagram (UML)

References

1 “Requirements Analysis,” Richard Thayer, SMC 10/97 Version 2, 1997

2 “IEEE Guide for Software Requirements Specification,” IEEE 830-1998

3 “Software Requirements:Objects, Functions, and States”, Prentice Hall, 1993

4 Software Quality Measurement for Distributed Systems, RADC-TR-83-175