csdp preparation course module ii: software requirements

CSDP Preparation CourseModule II: Software Requirements

Module II. Software Requirements 2

Specifications

The exam specific topics covered in this module are listed below, and are the basis for the outline of its’ content.A. Requirements Engineering Process B. Requirements Elicitation C. Requirements Analysis D. Software Requirements Specification E. Requirements Validation F. Requirements Management


Objectives

After completing this module, you should be able to…• To present an overview of software requirements

engineering


Organization

The organization of information for each specification topic is as follows:

• Topic Content Slides - detail the important issues concerning each topic and support the module objectives

• Topic Reference Slides - detail the sources for the topical content and provides additional references for review

• Topic Quiz Slides - allow students to prepare for the exam


Introduction

What is Software?• software -- Computer programs, procedures, and possibly

associated documentation and data pertaining to the operation of a computer system. Contrast with hardware. [IE610]

What is a Requirement?• requirement -- (1) A condition or capability needed by a user

to solve a problem or achieve an objective. (2) A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed documents. (3) A documented representation of a condition or capability as in (1) or (2). [IE610]


Introduction – 2

A Perspective

• These definitions imply concern for the user of the software as well as the developer.

• Wiegers emphasizes that the term users in such a definition should be generalized to stakeholders, because not all stakeholders are users.

• CAUTION: Don’t assume that all your project stakeholders share a common notion of what requirements are. Establish definitions up front so that you’re all talking about the same things. [KW03, p. 8]


Introduction – 3

Major Issues in Software Requirements • The incorrect and incomplete software requirements

specification • The truncation of requirements activities over programming

and testing• The lack of cooperation by customers:

• To verify that the software requirements are correct• To understood the structure and purpose of the software

requirements specifications • The problems associated with identifying which tool and/or

methodology to use in developing and representing a software requirements specification [RT04, p. 4-9]


Introduction – 4

Fundamentals of Requirements• In order to properly identify a requirement, we may apply the

general property distinctions that the SWEEBOK Guide has identified [SW04, p. D-3]: • Product and process requirements • Functional and non-functional requirements • Emergent properties• Quantifiable requirements • System requirements and software requirements


Introduction – 5

Product and Process Requirements - I• Product parameter – a requirement on software to be

developed

• Product requirement – Requirements which apply to the product of services to be developed• Qualitative parameters – not directly measurable

• Functional – What it does• External Interfaces – Data or command inputs or

outputs • Quantitative parameters – directly measurable

• Performance metrics – How fast, how much memory• Quality metrics – Reliability, maintainability, security

[RT04, p. 4-13]


Introduction – 6

Product and Process Requirements - II• Process parameter – essentially a constraint on the

development of the software (AKA process requirements)

• Process (Program) requirements – Applies to the activities associated with enabling the creation of a product or service• Task – Perform and analyze, develop a product, operate

a system• Compliance evaluation – Measure compliance with a

product parameter • Regulatory/Standards – Compliance with laws,

standards, regulations, and rules


Introduction - 7

Functional and Non-functional Requirements• Functional requirements – describes functions software is to

execute• Example: formatting text

• Non-functional requirements – ones that act to constrain the software solution• Further classes – performance, maintainability, safety,

reliability, and others.


Introduction - 8

Emergent Properties• Emergent properties – those which cannot be addressed by

a single component, but system component interoperability• Highly sensitive to the system architecture

• Sommerville provides three examples [IS01, p. 22]: • Overall weight of the system • Reliability of the system• Usability of the system


Introduction – 9

Quantifiable Requirements• Avoid vague and unverifiable requirements which depend for

their interpretation on subjective judgment

• This is critical for non-functional requirements


Introduction – 10

System Requirements and Software Requirements• System requirements - are for the system as a whole;

sometimes referred to as user requirements • Includes hardware, software, firmware, people,

information, techniques, facilities, services, and other support elements

• Software requirements – derived from system requirements


Introduction – 11

Recognizing the Importance of Software Requirements Engineering [RT04, p. 4-7]

• Better quality in the software development process and the software product can be obtained if our methods and tools for gathering, modeling and analyzing user requirements are more effective, robust and codified in practice, i.e. an engineering approach

• Therefore, software requirements engineering (SRE) has emerged as an “engineering” approach to what used to be called requirements analysis and specifications


Introduction – 12

Role of Software Requirements in the Lifecycle [RT04, p. 4-17]

• Describes what the user wants or needs done• Describes the final product, not methods and techniques

for building the software • Provides the basis for cost, schedule, and other resource

estimates

• Primarily developed during the requirements phase of the lifecycle

• Can be developed in other phases of the lifecycle


Introduction Quiz

1. Which of the following requirement properties would be considered an emergent property of a software program?

A. The fault detection system of the software

B. The programming language of the system

C. The reliability of the software

D. The number of lines of code


Introduction Quiz – 2

2. Which of the following would most likely be considered a product requirement?

A. The software shall be written in Ada.

B. The student name shall be entered before the student grade.

C. The system requirements for the software shall be formatted according to IEEE Std 1233.

D. The software is built with company standards.


Introduction Quiz – 3

3. Which of the following is most true about a non-functional requirement?

A. Describes functions software is to execute.

B. Is highly sensitive to the system architecture.

C. Is derived from hardware requirements.

D. Acts to constrain the software solution.


Introduction References

• [IE610] IEEE Std 610.12-1990, Standard Glossary of Software Engineering Terminology

• [IE1233] IEEE Std 1233-1998, Guide for Developing System Requirements

• [IS01] Sommerville, Ian, Software Engineering, 6th Edition, Addison-Wesley, NY, 2001

• [KW03] Weigers, Karl E., Software Requirements, 2nd Edition, Microsoft Press, Redmond, WA, 2003

• [RT04] Thayer, Richard, 2004 Certified Software Development Professional (CSDP) Preparation Course, Chapter 4: Software Requirements Engineering Concepts

• [SW04] SWEBOK – Guide to the Software Engineering Body of Knowledge: 2004 Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements


A. Requirements Engineering Process

A Process Defined

• process -- (1) A sequence of steps performed for a given purpose; for example, the software development process. (2) An executable unit managed by an operating system scheduler. (3) To perform operations on data. [IE610]

• Software requirements engineering (SRE) is a process, not a discrete activity


A. Requirements Engineering Process - 2

Software Requirements Engineering Process - I

1. Collect and categorize the various requirements (requirements elicitation) a. Identify relevant sources of requirements (usually the

customers)b. Determine what information is needed (this will change

as the requirements are developed) c. Collect the requirements from all parties



Software Requirements Engineering Process - II

2. Analyze the gathered information, looking for implications, inconsistencies, or unresolved issues (analysis)

3. Synthesize appropriate statements of the requirements (specifications)

4. Confirm your understanding of the requirements with the users (verification)

5. Plan and control the effort from beginning to end (management) [RT04, p. 4-20]



SRE Process Activities - I

• Software requirements elicitation – The process through which the customers (buyers and/or users) and developers (contractors) of a software system discover, review, articulate, and understand their requirements

• Software requirements analysis – Reasoning and analyzing the customers’ and users’ needs to arrive at a definition of software requirements



SRE Process Activities - II

• Software requirements specification – A document that clearly and precisely records each of the requirements of the software system

• Software requirements verification – The assurance that software requirements specifications are in compliance with the system requirements, conforms to document standards of the requirements phase, and is an adequate basis for the architectural (preliminary) design phase

• Software requirements management - Planning and controlling the requirements elicitation, analysis, and verification activities [RT04, p. 4-19]



Process Models

• Provide a basic outline of the requirements process• Obtaining software requirements is not a discrete front-end

activity• Initiated at the beginning of the project, and is refined

throughout the life cycle• Software requirements are configuration items for

management • The process is adapted to the organization and the project • Four major activities: elicitation, analysis, specification, and

validation



Process Actors - I

• Those who participate in the process

• The requirements specialist mediates between domain of the stakeholder and software engineer

• Always include users (or operators) and customers (they may not be the same)



Process Actors - II

• Typical software stakeholders• Users – Will operate software • Customers – Commissioned the software• Market analyst – Act as proxy customers • Regulators – Authorities from application domains (EX:

banking,) • Software engineers – Have a stake in reusing

components in successful products; must weigh their personal against the stake of the customer

• Must negotiate trade-offs with stakeholders to their satisfaction, within project constraints

• Stakeholders must be identified before this negotiation to occur [SW04, p. 2-3]



The Importance of Software Requirements

These People Depend on SW Req. to:

Acquisition management Establish their needs

Project management Determine tasks and schedule

System engineers Req. allocated to SW

Testers Establish what is to be tested

SW engineers Establish top-level design

Configuration control Establish req. baseline

Everyone Guide their effort

- [RT04, p. 4-22]



Process Support and Management

• Linked to the four major process activities: elicitation, analysis, specification, and validation

• Concerned with issue of cost, human resources, training, and tools



Process Quality and Improvement

• Concerned with assessment of the process

• Measured by cost, schedule, and customer satisfaction

• Uses:• Process improvement standards and models • Requirements process measures and benchmarking • Improvement planning and implementation



Other Issues in Software Requirements Engineering – I

• Requirements specifications often do not reflect the need and desires of the users and the customer

• Software requirements specifications are often incomplete and incorrect

• Users’ knowledge, experience, and cooperation greatly influence the quality of the specifications

• Developer’s knowledge of the customer domain greatly influence the quality of the specifications


A. Requirements Engineering Process – 13

Other Issues in Software Requirements Engineering – II

• Software requirements are constantly undergoing change

• Requirements sometimes specify the software design (a design constraint)

• Design is changed without a corresponding change in requirements [RT04, p. 4-22]


A. References





A. Quiz

1. According to the SWEBOK Guide, what are the four major activities of the requirements engineering process?

A. Identification, specification, construction, and testing

B. Elicitation, analysis, specification, and validation

C. Analysis, planning, construction, and verification

D. Elicitation, planning, construction, and testing


A. Quiz – 2

2. Which of the following property is least critical to the interaction between process actors and the requirements process?

A. Process actor identification

B. The nature of their ‘stake’ in the process

C. The education of the actor

D. The requirements they elicit


A. Quiz – 3

3. The requirements engineering process is:

A. A discrete front-end activity of the software life cycle.

B. Initiated at the beginning of a project and continues to be refined throughout the lifecycle.

C. A continuous process that ends when requirements are specified and documented.

D. The same for each organization and process.


A. Quiz – 4

4. Process quality and improvement relies most on which of the following?

A. Product operator performance

B. Human factors

C. Requirements process measures

D. Customer preferences


A. Quiz – 5

5. Product requirement validation occurs primarily after:

A. Elicitation

B. Analysis

C. Specification

D. Testing


B. Requirements Elicitation

What is Requirements Elicitation?

• Concerned with where software requirements come from and how the software engineers can collect them.

• Stakeholders are identified and relationships established between the development team and the customer

• Also known as ‘requirements capture’, ‘requirements discovery’, and ‘requirements acquisition’ [SW04, p. 2-4]


B. Requirements Elicitation - 2

Major Issues Involving Requirements Elicitation - I

• It is not always clear who your customers or users are.

• Your customers/users cannot always state their requirements clearly or completely.

• Users don’t know what they want; they only know what they do.

• What they say they want may not be what they need or you may begin to define what you think they need, instead of what they want.



Major Issues Involving Requirements Elicitation - II

• Their concept of the solution may not solve their problem.

• The customers or users will have expectations that may be unreasonable – or unknown to you.

• Not all of your customers or users talk to or agree with one another, so you must talk to all of them.

• Your customers or users may change. [RT04, p. 4-25]



Requirements Sources - I• From the SWEBOK Guide [SW04, p. 2-4]

• Goals – • Sometimes called ‘business concern’ or ‘critical success

factor’• Provides motivation for the software, but are often

vaguely formulated • Focus is to assess the value (relative priority) and cost of

goals • A feasibility study can do this at low cost

• Domain knowledge - • The software engineer needs to be knowledgeable of the

application domain • Allows for assessment of that which is not articulated



Requirements Sources - II• Stakeholders –

• Also known as Process Actors • The software engineer needs to identify, represent, and

manage the ‘viewpoints’ of many different types of stakeholders

• The operational environment – • The environment that software will be executed in will

reveal system constraints and system element interoperability

• The organizational environment – • May impose previously unidentified user processes



Elicitation Techniques - I• From SWEBOK Guide [SW04, p. 2-4]• Once requirements sources have been identified, the

software engineer can start eliciting requirements from them.

• Even if sources are cooperative and articulate, the relevant information must be captured.

Some of these techniques are:

• Interviews – • A traditional means of eliciting requirements



Elicitation Techniques - II

• Scenarios – • Provides a context for elicitation of user requirements • Asks ‘what if’ and ‘how is this done’ questions • The most common type of scenario is the use case• Link to Conceptual Modeling because of scenario

notations such as use cases and diagrams are common in modeling software

• Prototypes – • Form paper mock-ups of screen designs to beta-test

versions of software products • Valuable tool for clarifying unclear requirements • Overlap for use in requirements elicitation and

requirements validation


B. Requirements Elicitation – 8

Elicitation Techniques - III

• Facilitated meetings – • A group of people may bring more insight to achieve a

summative effect to the requirements • Conflicting requirements may surface earlier in this

setting • Beware of stakeholder politics

• Observation – • Software engineers are immersed in the environment to

observe the user interact between the software and other users

• Expensive to implement • Helps reveal process subtleties and complexities



ConOps - An Elicitation Tool - I

• Definition – concept of operations (ConOps) document – A user oriented document that describes a system’s operational characteristics from the end user’s viewpoint. [IE1362, Definition 3.4]

• It describes the user organization(s), mission(s), and organizational objectives from an integrated systems point of view.

• Applied to all types of software intensive systems: software-only or software/hardware/people systems



ConOps - An Elicitation Tool - II

• Describes the user’s general system goals, missions, function, and components

• Helps bring the users’ views and expectations to the surface

• Provides an outlet for the users’ wishes and wants

• Helps the user feel in control

• May or may not be the responsibility of the acquisition manager [RT04, p. 4-29]



The ConOps Document Style

• A ConOps document must be written in the user’s language using the user’s format

• A ConOps document should be written in narrative prose (in contrast to a technical requirements specification)

• ConOps should make use of visual forms (diagrams, illustrations, graphs, etc.) and storyboards wherever possible

• ConOps provides a bridge between the user needs and the developer’s technical requirements documents [RT04, p. 4-28]



Elements of IEEE 1362 (ConOps) - I

• Clauses describe essential elements • Provides information the writer wants the reader to know

prior to reading the document

• Title and revision notice: • Project name • Version number of the document, • Date of release, • Approval signatures, • A list of sub clauses that have been changed in the

current version of the document



Elements of IEEE 1362 (ConOps) - II

• Scope (Clause 1) • Identification • Document overview• System overview

• Referenced documents (Clause 2)

• Current system or situation (Clause 3) • Background, objectives, and scope• Operational policies and constraints• Description of the current system or situation • Modes of operation for the current system or situation • User classes and other involved personnel (Note)



Elements of IEEE 1362 (ConOps) - III

• Justification for and nature of changes (Clause 4) • Justification for changes • Description of desired changes • Priorities among changes • Changes considered but not included • Assumptions and constraints

• Concepts for the proposed system (Clause 5) • Background, objectives and scope • Operational policies and constraints • Description of the proposed system • Modes of operation • User classes and other involved personnel (Note)



Elements of IEEE 1362 (ConOps) - IV

• Operational scenarios (Clause 6)

• Summary of impacts (Clause 7) • Operation impacts • Organizational impacts • Impacts during development

• Analysis of the proposed system (Clause 8) • Summary of improvements • Disadvantages and limitations • Alternatives and trade-offs considered

• Notes (Clause 9) • Appendices of the ConOps • Glossary of the ConOps


B. References

• [IE1362] IEEE Std 1362-1998, Guide for Information Technology – System Design – Concept of Operations Document

• [JC04] Cleland-Huang, Jane, “Software Requirements,” in R.H. Thayer and M. Carstensen, Software Engineering, Vol. 1: The Development Process. IEEE Computer Society Press, Los Alamitos, CA 2004




B. Quiz

1. As requirements are elicited, what source is most likely to impose previously unidentified user processes?

A. The organizational environment

B. The operational environment

C. Stakeholders

D. Application domain specialists


B. Quiz – 2

2. What is considered the traditional means or requirements elicitation?

A. Observations

B. Scenarios

C. Interviews

D. Prototypes


B. Quiz – 3

3. What is the most common type of scenario elicitation technique?

A. The prototype

B. The use case

C. The facilitator meeting

D. Observation


B. Quiz – 4

4. Which technique overlaps for use in requirements elicitation and requirements validation?

A. Prototypes

B. Facilitator meetings

C. Interviews

D. Observations


B. Quiz – 5

5. A concept of operations document (ConOps) should not be written

A. In the user’s language using the user’s format

B. Mostly in narrative prose

C. With visual forms

D. Primarily in the developers technical language


B. Quiz – 6

6. In the IEEE Std 1362 Concept of Operations (ConOps) Document, which of the following is fundamentally not included under the Concepts for the Proposed System (Clause 5)?

A. Proposed design method of system

B. Operational policies and constraints

C. Description of the proposed system

D. Modes of operation


B. Quiz – 7

7. In the IEEE Std 1362 Concept of Operations (ConOps) Document, which of the following is fundamentally not included in the document?

A. Current system or situation

B. Proposed design method of system

C. Justification for the nature of the change

D. Operational scenarios


C. Requirements Analysis

Definitions

• software requirements analysis -- • (1) The process of studying user needs to arrive at a

definition of system, hardware, or software requirements. • (2) The process of studying and refining system, hardware,

or software requirements. [IE610] • (3) Reasoning and analyzing the customers and users

needs to arrive at a definition of software requirements. [RT02, p. 93]


C. Requirements Analysis – 2

First, Find Requirements Sources

• Systems requirements specifications • Statements of work (SOW) and procurement specifications • Customer prepared needs documents • Concept of operations (ConOps) documents • Observations and measurements of the current system • Interviews with the customers and users • Current system documentation • Feasibility studies • Models and prototypes [RT04, p. 4-33]



Software Requirements Analysis - I

• Software requirements analysis: The process of:• Studying and refining system, hardware, or software

requirements [IE610] • Determining the feasibility of the requirements • Detecting and resolving conflicts between requirements • Discovering the system boundaries and its external

interfaces • Conducting trade-offs between requirement features • Producing of the software requirements specification



Software Requirements Analysis - II

• Other activities during the requirement analysis phase: • Determine the project management plan • Determine the test plan and test specifications • Determine draft user’s manual • Determine the system interfaces [RT04, 4-32]



Distinct Processes of Requirements Analysis• The SWEBOK has identified several distinct processes that

occur during a successful requirements analysis

• Requirements classification (RC)– Helps to inform trade-offs

• Conceptual modeling (CM)– To understand the problem

• Architectural design and requirements allocation (AD & RA) – What parts will meet requirements

• Requirements negotiation (RN)– Establishes trade-offs



Requirements Classification - I

Several dimensions:

• Whether it is functional or non-functional

• Whether it is derived from high-level requirement or is emergent • Imposed by stakeholder or other source

• Whether it is on the product or the process



Requirements Classification - II

• The requirement priority: The higher, the more essential

• The requirement scope: A global requirement may affect architecture

• Volatility/stability: Identification for tolerant design

• Others are possible, and some may overlap



RC / Attributes - I• Each Software Requirement Shall Have:

• Identifier: Every requirement must be assigned a unique identifier that allows it to be unambiguously referenced.

• Source: The source of the requirement may be (e.g.) a stakeholder from whom it was elicited or a higher-level requirement from which it was derived

• Date: When the requirement was formulated



RC / Attributes - II• Each Software Requirement Shall Have:• Rationale: The rationale explains the purpose of the

requirement. This helps subsequent analysis, particularly if the requirement is challenged or needs to be reworked at a later stage.

• Type: This attribute records, for example, whether the requirement is functional or non-functional; whether it is a user interface requirement, a safety requirement, etc., or it is an original requirement or a derived requirement

• Priority: Each requirement need to be prioritized in relationship to other requirements, e.g., essential, conditional, optional (IEEE Std 830)



RC / Attributes - III• Each Software Requirement Shall Have:

• Stability: Uncertainty surrounds a requirement should be recorded so that its likely volatility is made explicit and appropriate risk containment measures can be taken.

• Verification procedure: This attribute defines how to verify that the requirement has been satisfied once the software has been implemented.

• Status: The requirements status records its current position in the life-cycle of the requirement. [RT04, p. 4-43,44]



RC / Types of Software Requirements – I • Functional requirements – A requirement that specifies a

function that a system or system component must be capable of performing

• Performance requirements – A requirement that specifies a performance characteristic that a system or system component must posses • For example, speed, accuracy, or frequency

• External interface requirements – A requirement that specifies a hardware, software, or database element with which a system component must interface, or that sets forth constraints on formats, timing or other factors caused by such an interface



RC / Types of Software Requirements – II• Design constraints – A requirement that impacts or

constrains the design of a software system or system component (sometimes called a negative requirement);• For example, functional requirements, physical

requirements, performance requirements, software development standards, software quality assurance standards

• Quality Attributes – A requirement that specifies the degree of an attribute that affects the quality the software must possess; • For example: correctness, reliability, maintainability, or

portability [RT04, 4-35]



RC / Examples of Design Constraints• Execution speed – Use maximum of 50% of available cycle

time (also called performance requirement) • Language – Use Ada • Maintenance – Meet available requirements of 0.98 (also

called quality attribute) • Human computer interface – Menus are require for system

interface • Memory utilization – Use maximum of 75% of available

memory (also called performance requirements)• Reliability – Meet reliability requirements of 0.99 (also called

quality attributes) • Security – Meet security requirements of 4 hours to break

into the system (also called quality attributes)



RC / Examples of Quality Requirements• Reliability – Probability that the software will perform its

logical operation in the specified environment without failure • Survivability – Probability that the software will continue to

perform or support critical functions when a portion of the system is inoperable

• Maintainability - Average effort required to locate and fix a software failure

• User friendliness – The degree of ease of use or learning of a software system

• Securability – The probability that the software system can be made secure for a predetermined amount of time



Conceptual Modeling – I• Their purpose is to aid in understanding the problem, not

begin a design solution

• Types of models include data and control flows, state models, event traces, and others

• Factors that influence choice of model:• The nature of the problem • The expertise of the software engineer • The process requirements of the customer • The availability of methods and tools



Conceptual Modeling – II

• Useful to start with building model of the software context • explains operational environment and identifies

interfaces

• UML (Unified Modeling Language) is a widely used set of notations



CM / Structured Analysis (Yourdon)

[RT04, p. 4-38]



CM / Real Time Structured Analysis (Ward & Miller)

[RT04, p. 4-39]



CM / Object-Oriented Analysis (Object Diagram)

[RT04, p. 4-40]



CM / Use Cases


C. Requirements Analysis - 21

Architectural Design and Requirements Allocation

• Point the requirements process overlaps with software or system design.

• Allocation is the assigning of responsibility to components for satisfying requirements.

• Permits detailed analysis of requirements

• Allows requirements to be broken down further

• IEEE Std 1471-2000 is a Recommended Practice for Architectural Description of Software Intensive Systems


C. Requirements Analysis - 22

Requirements Negotiation• Also known as ‘conflict resolution’

• Conflicts between stakeholders arise from differences:• Between incompatible features • Between requirements and resources • Between functional and non-functional requirements

• Unwise for software engineer to make unilateral decision • Consultation leads to consensus trade-off• Decision traceable back to the customer for contractual

reasons


C. References


• [RT02] Thayer, Richard H., Software Engineering, Volume 1: The Development Process, 2nd Edition, IEEE Computer Society, Los Alamitos, CA, 2002

• [RT04] Thayer, Richard H., 2004 Certified Software Development Professional (CSDP) Preparation Course, Chapter 4: Software Requirements Engineering Concepts



C. Quiz

1. Which dimension of requirement classification is critical for consideration of tolerant design?

A. Whether the requirement is functional or non-functional.

B. Whether the requirement is on the product or process.

C. Whether the requirement is volatile or stable.

D. Whether the requirement is a high or low priority.


C. Quiz – 2

2. What is the most important attribute of a requirement?

A. Identifier

B. Source

C. Verification procedure

D. Priority


C. Quiz – 3

3. Which of the following is not a type of software requirement?

A. Functionality

B. Performance

C. External Interface

D. Complexity


C. Quiz – 4

4. What does allocation try to satisfy in the assigning of responsibility to components?

A. Requirements

B. Validation

C. External interfaces

D. Testing


C. Quiz – 5

5. What is a software engineer most likely to resolve by making a unilateral decision?

A. Differences between incompatible features

B. Differences between developer perception and developer reality

C. Differences between requirements and resources

D. Differences between functional and non-functional requirements


D. Software Requirements Specification

Two Descriptions

• software requirements specification (software requirements) – 1. A document that specifies the requirements for a system or component. Typically included are functional requirements, performance requirements, interface requirements, design requirements, and development standards. [IE610] 2. A document that clearly and precisely records each of the requirements of the software system. [RT02, p. 143]

• In software engineering jargon, ‘software requirements specification’ typically refers to the production of a document, or its electronic equivalent, which can be systematically reviewed, evaluated, and approved. [SW04, p. 2-7]


D. Software Requirements Specification - 2

Role in Software Development

• Foundation for the software project

• Describes the system to be delivered

• Separates essential, desirable, and optional requirements

• Identifies which items are stable and which might be volatile

• States problems, not solutions

• States “what” not “how” [RT04, p. 4-47]



In Context with Other Requirement Documents

• The System Definition Document – defines high-level system requirements

• System Requirements Specification – for system components

• Software Requirements Specification – for software components of the system


D. Software Requirements Specification – 4

The System Definition Document • Sometimes known as the user requirements document or

concept of operations document • Records the system requirements• Defines high level system requirements in language/terms

understood by the system users or customers• It may include conceptual models, usage scenarios, data,

information, or workflows to illustrate the system concept [SW04, p. 2-7]

• The IEEE Std 1362 is a guide which describes the elements of a ConOps document



IEEE 1362 - The ConOps Document

• The IEEE Std 1362 is a guide which describes the elements of a ConOps document



System Requirements Specification (SyRS)• Software is always an element of a larger system

• EXAMPLES: Airplanes, the Space Shuttle, a cell phone• Is a systems engineering activity • System requirements are specified here, not software

requirements• Software requirements are derived from the system

requirements • The requirements for the software components of the system

are then specified [SW04, p. 2-7]

• The IEEE Std 1233 is a guide for developing system requirements specifications



IEEE Std 1233 (SyRS)

• Recommended practice for developing system requirements specifications



Software Requirements Specification (SRS) - I• Establishes understanding of the software product is to do,

as well as what it is not expected to do• Often accompanied by definition document for clarity

• Written in natural language• Supplemented by formal or semi-formal description

• This allows for a more precise and concise description of software architecture

• Permits rigorous assessment of requirements before design • Provides realistic basis for estimating product costs, risks,

and schedules



Software Requirements Specification (SRS) - II• Choice of notation constrained by the documents’ writers

• Training, skills, preferences

• Quality indicators for SRS statements• Imperatives, directives, weak phrases, opinions, and

continuances • Quality indicators for entire SRS

• Size, readability, specification, depth, and text structure

• The IEEE Std 830 is a guide for developing software requirements specifications



IEEE Std 830 (SRS) • Recommended practice for developing software

requirements specifications (You should read this standard!)

• Lists Considerations for producing a good SRS

• Identifies The Parts of an SRS



Considerations for Producing a Good SRS - I

• Nature of the SRS – The writer(s) shall address the following issues• Functionality • External interfaces • Performance • Attributes • Design constraints imposed on an implementation • The SRS writer(s) should avoid placing either design or

project requirements in the SRS Environment of the SRS



Considerations for Producing a Good SRS - II

• Environment of the SRS – The SRS writer(s) plays a specific role in the software development process • Should correctly define all of the software requirements. • Should not describe any design or implementation

details. • Should not impose additional constraints on the software.

• The SRS limits the range of valid designs, but does not

specify any particular design



Considerations for Producing a Good SRS - III

• Characteristics of a good SRS (I) – An SRS should be • Correct – Only if every stated SRS is one the software

shall meet • Unambiguous – The particular context of the SRS is

clear and there is only one interpretation • Natural language pitfalls • Requirements specification languages • Representation tools

• Complete – Only if it addresses: • All significant requirements • Definition of the software response • Identification of all references • TBD’s are marked for resolution



Considerations for Producing a Good SRS - IV

• Characteristics of a good SRS (continued - II) • Consistent – With higher level documents; types of conflicts

• Specified characteristics of real-world objects • Logical or temporal conflicts with two specified actions • Redundancy

• Ranked for importance and/or stability – All of the software requirements are not equally important

• Degree of stability (expected changes to occur) • Degree of necessity: Essential, Conditional, or Optional

• Verifiable – a requirement is verifiable if and only if there exists some finite cost-effective process with which a person or machine can check that the software product meets the requirement.

• Non-verifiable - Terms such as “good”, “well”, or “usually” are impossible to define



Considerations for Producing a Good SRS - V

• Characteristics of a good SRS (continued – III) • Modifiable – Requires that the SRS

• Has a coherent and easy-to-use organization • Not be redundant • Express each requirement separately (redundancy

can lead to errors) • Traceable – If the origin of each of its requirements is

clear and it facilitates the referencing of each requirement in future development or enhancement documentation

• Backward traceability ( i.e., to previous stages of development)

• Forward traceability (i.e., to all documents spawned by the SRS)



Considerations for Producing a Good SRS - VI

• Joint preparation of the SRS – Should begin with supplier and customer agreement on what completed software must do. • Customers usually don’t understand software

development well enough to write a usable SRS• Software developers usually don’t understand customers

well enough to specify requirements for a satisfactory system



Considerations for Producing a Good SRS - VII

• SRS evolution – The SRS may need to evolve, as some details are impossible to obtain during the project’s initial phases. To handle this situation • Specify as completely and thoroughly as possible; note

incompleteness if it is known. • Utilize a formal change process



Considerations for Producing a Good SRS - VIII

• Prototyping – Should be used as a way to elicit software requirements • More likely for customer to react to view than to reading • Displays unanticipated aspects of system behavior • SRS tends to undergo less change during development,

thus shortening development time



Considerations for Producing a Good SRS - IX

• Embedding design in the SRS – avoid it• A requirement specifies an externally visible function or

attribute • A design describes a method to achieve that requirement • Every requirement in the SRS limits design alternatives• The SRS should not specify

• Partitioning of software into modules • Allocating functions to the modules • Describe the flow of information or control between

modules • Choose data structures



Considerations for Producing a Good SRS - X

• Embedding project requirements in the SRS – The SRS should address the software product, not the process of producing the product. • These following project requirements are reserved for

other documents: • Cost, delivery schedule, reporting procedures,

software development methods, quality assurance, verification and validation, or acceptance procedures



IEEE 830 - The Parts of an SRS - ITable of Contents 1. Introduction

1. Purpose 2. Scope 3. Definitions, Acronyms, and Abbreviations 4. References 5. Overview

2. Overall Description 1. Product Perspective 2. Product Functions 3. User Characteristics 4. Constraints 5. Assumptions and Dependencies

3. Specific Requirements Appendices Index



IEEE 830 - The Parts of an SRS - IIFunctional Hierarchy [RT04, p. 4-51]3. Specific requirements

1. External Interfaces 2. Functional requirements

1. Function 11. Introduction 2. Input 3. Process 4. Output

2. Function 23. …4. Function n

3. Performance requirements 4. Design constraints 5. Quality attributes



Writing a Requirement• Suggested Method [RT04, p. 4-53]• Requirement should be written as a single sentence, with a

minimum number of conjunctions, and using modal verbs consistently i.e. shall, will, can, may. Example:• Arm011: On completion of the arming sequence, there

shall be a time delay equal to the escape period before the alarm enters the armed state

• This statement of requirements requires that the terms arming sequence, escape period, and armed state be defined in a glossary

• Use model verbs, e.g., use shall to indicate an essential requirement

• Arm011 is the requirement’s unique identifier


D. References


• [IE830] IEEE Std 830-1998, Recommended Practice for Software Requirements Specification

• [IE1233] IEEE Std 1233-1998, Guide for Developing System Requirements

• [IE1362] IEEE Std 1362-1998, Guide for Information Technology – System Design – Concept of Operations Document




D. References – 2



D. Quiz

1. Which document is used to derive the software requirements specification?

A. The System Definition Document

B. System Requirements Specification

C. IEEE 1362 Concept of Operations

D. IEEE 1016 Software Design Descriptions


D. Quiz – 2

2. What should the software requirements specification (SRS) writer avoid placing in the SRS environment of the SRS?

A. External interfaces

B. Performance or functionality

C. Attributes or classification

D. Either design or project requirements


D. Quiz – 3

3. Which of the following is not embedded design that would be written in the SRS?

A. Partitioning of software into modules

B. Specify logical requirements for the software

C. Describe the flow of information or control between modules

D. Choose data structures


D. Quiz – 4

4. Which of the following phrases most closely approaches verifiable language?

A. “A good operability”

B. “Well enough”

C. “According to Standard X”

D. “Usually acceptable”


D. Quiz – 5

5. Which of the following is not a good characteristic well written of a software requirements specification?

A. Consistent

B. Ranked

C. Redundant

D. Verifiable


E. Requirements Validation

Defined

• Validation – 1. The process of evaluating a system or component during or at the end of the development process to determine whether it satisfies specified requirements. Contrast with verification. [IE610] 2. The process is a process for determining whether the requirements and the final, as-built system or software product fulfills its specific intended use [IEEE/EIA Std 12207.2, Para 6.5]

• Validation (error = external customer requirements - product)

• Verification (error = internal specified requirements - product)


E. Requirements Validation – 2

Objectives of Verification and Validation • To find errors in the software process and product as early

as feasible • To assist in determining good requirements and design • To ensure that quality is built into the software and that the

software will satisfy the software requirements • To provide software management with insights into the state

of the software project and product • To satisfy users that the system is being developed

according to standards and specifications • To predict how well the interim products will result in a final

product that will satisfy the software requirements [RT04, p. 4-58]



Requirements Validation - I • Requirements documents may be subject to validation and

verification procedures

• Formal notation permits • Software requirements validated to ensure that software

engineer has understood the requirements • Verify that a requirements document conforms to

• company standards • that it is understandable, consistent, and complete



Requirements Validation - II• Different stakeholders should be able to review requirements

documents

• Requirements documents subject to software configuration management as are other deliverables of software lifecycle processes

• Multiple points of validation in requirements process schedule • Pick up problems before resources are committed • Helps ensure requirements document defines the right

software [SW04, p. 2-8]



Subjects of Requirements Validation

• The SWEBOK has identified several knowledge areas of importance for the study of software requirements validation:• Requirements reviews • Prototyping • Model validation • Acceptance Testing



RV / Requirements Reviews – I

• reviews -- A process or meeting during which a work product, or set of work products, is presented to project personnel, managers, users, customers, or other interested parties for comment or approval. Types include code reviews, design reviews, formal qualification reviews, and requirements reviews, test readiness reviews. [IE610]



RV / Requirements Reviews – II

• Validation often done by inspection or reviews of requirements documents

• Reviewers look for errors, mistaken assumptions, lack of clarity, and deviation from standard practice

• Composition of reviewer group should include important stakeholders (customer for customer-driven project)

• Checklists are helpful



RV / Requirements Reviews – III

• Can be done after completion of • systems definition document • systems specification document • software requirements specification document • the baseline specification for new release • any other steps in the process

• IEEE Std 1028 provides guidance for reviews



RV / Prototyping – I• A means of validating the software engineer’s interpretation

of the software requirements

• Also for eliciting new requirements

• Many different techniques

• Many different points in the process where prototype validation is appropriate



RV / Prototyping – II

• Makes it easier to interpret the software engineer’ assumptions • And give feedback when wrong

• Danger is distraction of resources from core functionality towards cosmetic issues • Some suggestion prototypes that avoid software, such as

flip-chart based mockups



RV / Model Validation

• Validating the quality of models developed during analysis • Example: In object models, perform static analysis to

verify the communication paths exist between objects which exchange data

• If formal specification notation used, use formal reasoning to prove specification properties

• Validation (error = external customer requirements - product) • Verification (error = internal specified requirements -

product)



RV / Acceptance Tests

• Essential property of software requirement is that it should be possible to verify that finished product satisfies it

• Requirements which cannot be validated are ‘wishes’

• Must plan how to verify each requirement

• Validation requires quantitative expression

• Non-functional requirements difficult to validate



Levels of Testing Versus Types of Errors Found

Levels of Test Types of Errors Found

Unit Coding

Integration Design

System Requirements (Developer’s Interpretation)

Acceptance Requirements (User’s Interpretation)

• “Errors made first are discovered last” [RT04, p. 4-56]


E. References


• [IE830] IEEE Std 830-1998, Recommended Practice for Software Requirements Specification

• [IE1028] IEEE Std 1028-1997, Standard for Software Reviews



• [IE12207.2] IEEE/EIA Std 12207.2 Standard for Information Technology, Software Life Cycle Processes – Implementation Considerations


E. Quiz

1. Software requirements validation should be viewed by whom and how often?

A. Requirements analysts, often

B. Stakeholders, often

C. Customers, never

D. Users, never


E. Quiz – 2

2. Requirements reviews:

Can not be done before completion of the

A. Systems definition document

B. Systems specification document

C. Software requirements specification document

D. Baseline specification for new release


F. Requirements Management

Defined

• software requirements management -- In system/software system engineering, the process of controlling the identification, allocation, and flowdown of requirements from the system level to the module or part level, including interfaces, verification, modifications, and status monitoring. [Thayer & Thayer Software Requirements 1997]


F. Requirements Management – 2

Observations • The requirements process suggests a linear sequence (from

elicitation through validation)• A strict linear logic breaks down for complex system

development • Not every organization has a culture of documenting and

managing requirements • As products evolve:

• Need for feature changes demands review of original requirements

• Need to asses the impact of proposed changes • Requirements documentation and change management key

to successful requirements process [SW04, p. 2-9]



Two Type of Management

Both of these Approaches Manage the Requirements • Project management

• Planning the project • Organizing the project • Staffing the project • Directing the project • Controlling the project

• Technical management • Problem definition• Solution analysis • Process planning • Process control • Product evaluation [RT04, p. 4-60]



Duties of the Software Project Manager - I

• The project manager is responsible for: • Estimating the cost of the system based on the

requirements • Re-estimating the cost and schedule of the project when

the requirements change



Duties of the Software Project Manager – II

• The technical manager is responsible for: • Determining the adequacy of the requirements

specifications • Managing the requirements configuration of the system • Controlling the volatility of the requirements and manage

change history • Perform requirements traceability • Negotiating requirements changes between the acquirer

(customer) and the developer

• The chief system engineer is frequently the technical manager [RT04, p. 4-61]



Key Requirements Tasks of the Project Manager

• Change control – Change control is the process of inhibiting unapproved changes to the software system

• Version control – Version control is the process of insuring the various versions of the software system is indeed that version

• Requirements tracing – Requirements tracing is the process of assuring that every requirement can be connected downward to the design module that implements it and upward to the system requirements that initiated it

• Status tracking – A system for maintaining information on the processing and implementation of the requirements [RT04, p. 4-62]



Subjects of Requirements Management

• The SWEBOK has identified several knowledge areas of importance for the study of software requirements management:• Iterative nature of the Requirements Process • Change Management • Requirements Attributes • Requirements Tracing



RM / Iterative Nature of Requirements Process - I

• Shorter development cycles, especially in competitive industries

• Often project is upgrade or revision of existing software

• Often requirements are never perfectly understood or perfectly verified • Understanding that requirements continue to evolve as

development proceeds


F. Requirements Ma1nagement – 9

RM / Iterative Nature of Requirements Process - II• Risk of rework spans the whole software life cycle• Change has to be managed through review and approval

process• Requirements tracing • Impact analysis • Software configuration management

• Configuration management (CM) -- In system/software engineering, a discipline applying technical and administrative direc tion and surveillance to: identify and document the functional and physical characteristics of a configuration item, control changes to those characteristics, record and report change processing and implementation status, and verify compliance with specified requirements. [IE610]



RM / Change Management

• Procedures need to be in place and applied to proposed changes



RM / Requirements Attributes • Requirements are not just composed of a specification, they

should also include: • Additional information to manage and interpret

requirements • The various classification dimensions of the requirement• Verification method or acceptance test plan

• May also include additional information • Summary rational of each requirement • Source of each requirement and change history

• Most important requirement attribute:• A unique and unambiguous identifier



RM / Requirements Tracing

• Concerned with: • Recovering the source of requirements

• From software requirement back to system requirement it supports

• Predicting the effects of requirements • From system requirement into software requirement

and code modules that satisfy it

• Requirements tracing for a typical project form a complex directed acyclic graph (DAG) of requirements



RM / Measuring Requirements

• Concept of ‘volume’ of requirements for particular software product

• Useful in evaluating ‘size’ of change in requirements

• Useful in estimating cost of development or maintenance task

• A denominator in other measurements

• Technique: Functional Size Measurement (FSM)



Graphic, next slide: The Relative Cost to Correct A Software Requirements Error [RT02, p. 155]


F. References





• [Thayer & Thayer Software Requirements 1997] Reference unknown


F. Quiz

1. Which of the following is the technical manager not responsible for?

A. Determining the adequacy of the requirements specifications.

B. Controlling the volatility of the requirements and manage change history.

C. Re-estimating the cost and schedule of the project when the requirements change.

D. Negotiating requirements changes between the acquirer (customer) and the developer.


F. Quiz – 2

2. Due to the iterative nature of the requirements process, change has to be managed through the review and approval process. Which of the following is likely to require the least amount of management?

A. Requirements tracing

B. Impact analysis

C. Software configuration management

D. System definition


F. Quiz – 3

3. Requirements tracing is most likely concerned with the following:

Recovering the source of requirements from:

A. Software requirement back to the system requirement it supports

B. Observation to elicitation technique

C. Analysis into requirements specification document

D. Software requirement to validation test

csdp preparation course module ii: software requirements

Documents

unverifiable requirements

fundamentals of requirements

requirements management

functions software

software solution

system slide

requirements analysis

requirements elicitation