CSDP Preparation Course Module II: Software Requirements

CSDP Preparation Course Module II: Software Requirements
Time per slide (min.) / Section Milestone (min) Facilitator Notes: Module II. Software Requirements

Module II. Software Requirements
Specifications The exam specific topics covered in this module are listed below, and are the basis for the outline of its’ content. Requirements Engineering Process Requirements Elicitation Requirements Analysis Software Requirements Specification Requirements Validation Requirements Management Module II. Software Requirements Module II. Software Requirements

Objectives After completing this module, you should be able to… To present an overview of software requirements engineering 2 min. / 20 min. Facilitator Notes: Module II. Software Requirements Module II. Software Requirements

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 Module II. Software Requirements Module II. Software Requirements

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] Topic Estimate: 26 minutes Note: Start with the basics Module II. Software Requirements Module II. Software Requirements

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] Module II. Software Requirements

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] Note: These issues can be resolved with a professional application of SWE Module II. Software Requirements Module II. Software Requirements

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 Module II. 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] Module II. Software Requirements

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 Note: Program requirements are normally defined in a contract statement of work (SOW), NOT in the software requirements specifications [RT04, p. 4-14] Module II. Software Requirements Module II. Software Requirements

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. Module II. Software Requirements

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 Module II. Software Requirements

Introduction – 9 Quantifiable Requirements
Avoid vague and unverifiable requirements which depend for their interpretation on subjective judgment This is critical for non-functional requirements Module II. Software 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 Module II. Software 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 Module II. Software Requirements

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 Module II. Software Requirements

Introduction Quiz 1. Which of the following requirement properties would be considered an emergent property of a software program? The fault detection system of the software The programming language of the system The reliability of the software The number of lines of code 1) Answer: C. The reliability of the software Module II. Software Requirements Module II. Software Requirements

Introduction Quiz – 2 2. Which of the following would most likely be considered a product requirement? The software shall be written in Ada. The student name shall be entered before the student grade. The system requirements for the software shall be formatted according to IEEE Std 1233. The software is built with company standards. 2) Answer: B. The student name must be entered before the student grade. Module II. Software Requirements Module II. Software Requirements

Introduction Quiz – 3 3. Which of the following is most true about a non-functional requirement? Describes functions software is to execute. Is highly sensitive to the system architecture. Is derived from hardware requirements. Acts to constrain the software solution. 3) Answer: D. Acts to constrain the software solution. Module II. Software Requirements Module II. Software Requirements

Introduction References
[IE610] IEEE Std , Standard Glossary of Software Engineering Terminology [IE1233] IEEE Std , 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: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements Module II. 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 Topic Estimate: 28 minutes Module II. Software Requirements Module II. Software Requirements

A. Requirements Engineering Process - 2
Software Requirements Engineering Process - I Collect and categorize the various requirements (requirements elicitation) Identify relevant sources of requirements (usually the customers) Determine what information is needed (this will change as the requirements are developed) Collect the requirements from all parties Module II. Software Requirements

Software Requirements Engineering Process - II Analyze the gathered information, looking for implications, inconsistencies, or unresolved issues (analysis) Synthesize appropriate statements of the requirements (specifications) Confirm your understanding of the requirements with the users (verification) Plan and control the effort from beginning to end (management) [RT04, p. 4-20] Module II. Software Requirements

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 Module II. 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] Module II. Software Requirements

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 model (Software Engineering Process) – A development strategy, incorporated by a software engineer or team of engineers, that encompasses process, methods, and tools. [Pressman 1997] Module II. Software Requirements Module II. Software Requirements

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) Module II. Software Requirements

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] Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

A. References [IE610] IEEE Std , Standard Glossary of Software Engineering Terminology [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: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements Module II. Software Requirements

A. Quiz 1. According to the SWEBOK Guide, what are the four major activities of the requirements engineering process? Identification, specification, construction, and testing Elicitation, analysis, specification, and validation Analysis, planning, construction, and verification Elicitation, planning, construction, and testing 1) Answer: B. Elicitation, analysis, specification, and validation Module II. Software Requirements Module II. Software Requirements

A. Quiz – 2 2. Which of the following property is least critical to the interaction between process actors and the requirements process? Process actor identification The nature of their ‘stake’ in the process The education of the actor The requirements they elicit 2) Answer: C. The education of the actor Module II. Software Requirements Module II. Software Requirements

A. Quiz – 3 3. The requirements engineering process is: A discrete front-end activity of the software life cycle. Initiated at the beginning of a project and continues to be refined throughout the lifecycle. A continuous process that ends when requirements are specified and documented. The same for each organization and process. 3) Answer: B. Initiated at the beginning of a project and continues to be refined throughout the lifecycle. Module II. Software Requirements Module II. Software Requirements

A. Quiz – 4 4. Process quality and improvement relies most on which of the following? Product operator performance Human factors Requirements process measures Customer preferences 4) Answer: C. Requirements process measures Module II. Software Requirements Module II. Software Requirements

A. Quiz – 5 5. Product requirement validation occurs primarily after: Elicitation Analysis Specification Testing 5) Answer: C. Specification Module II. Software Requirements Module II. Software Requirements

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] Topic Estimate: 33 minutes requirements elicitation (software requirements) -- The process through which the customers (buyers and/or users) and developer (contractor) of a software system discover, review, articulate, and understand the requirements of the system. [Thayer 2001] Module II. Software Requirements Module II. Software Requirements

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. Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Negotiating with respect to a standard set – Beginning with an existing set of requirements or features, negotiate with users which of those features will be included, excluded, or modified [JC04] Module II. Software Requirements Module II. Software 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 Module II. Software Requirements

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 Module II. Software Requirements

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 May be used for hardware only systems, though not emphasized Module II. Software Requirements Module II. Software Requirements

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] Provides a place to document vague and immeasurable requirements, i.e., users can state their desire for “fast response” or “reliable operation.” (These desires are quantified during the process of developing the requirements specifications and during the flowdown of requirements to the system architecture) [RT04, 4-29] Module II. Software Requirements Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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) Note: User classes and other involved personnel ….details… Organizational structure Profile of user classes Interactions among user classes Other involved personnel Support environment Module II. Software Requirements Module II. Software Requirements

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) Note: User classes and other involved personnel ….details… Organizational structure Profile of user classes Interactions among user classes Other involved personnel Support environment Module II. Software Requirements Module II. Software Requirements

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 Module II. Software Requirements

B. References [IE1362] IEEE Std , 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 [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: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements Module II. Software Requirements

B. Quiz As requirements are elicited, what source is most likely to impose previously unidentified user processes? The organizational environment The operational environment Stakeholders Application domain specialists 1) Answer: A. The organizational environment Module II. Software Requirements Module II. Software Requirements

B. Quiz – 2 2. What is considered the traditional means or requirements elicitation? Observations Scenarios Interviews Prototypes 2) Answer: C. Interviews Module II. Software Requirements Module II. Software Requirements

B. Quiz – 3 3. What is the most common type of scenario elicitation technique? The prototype The use case The facilitator meeting Observation 3) Answer: B. The use case Module II. Software Requirements Module II. Software Requirements

B. Quiz – 4 4. Which technique overlaps for use in requirements elicitation and requirements validation? Prototypes Facilitator meetings Interviews Observations 4) Answer: A. Prototypes Module II. Software Requirements Module II. Software Requirements

B. Quiz – 5 5. A concept of operations document (ConOps) should not be written In the user’s language using the user’s format Mostly in narrative prose With visual forms Primarily in the developers technical language 5) Answer: D. Primarily in the developers technical language Module II. Software Requirements Module II. Software Requirements

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)? Proposed design method of system Operational policies and constraints Description of the proposed system Modes of operation 6) Answer: A. Proposed design method of system Module II. Software Requirements Module II. Software Requirements

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? Current system or situation Proposed design method of system Justification for the nature of the change Operational scenarios 7) Answer: B. Proposed design method of system Module II. Software Requirements Module II. Software Requirements

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] Topic Estimate: 48 minutes Module II. Software Requirements Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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) Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

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) Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

CM / Structured Analysis (Yourdon) [RT04, p. 4-38] Module II. Software Requirements

CM / Real Time Structured Analysis (Ward & Miller) [RT04, p. 4-39] Module II. Software Requirements

CM / Object-Oriented Analysis (Object Diagram) [RT04, p. 4-40] Module II. Software Requirements

CM / Use Cases Module II. Software Requirements

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 is a Recommended Practice for Architectural Description of Software Intensive Systems Module II. Software Requirements

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 Module II. Software Requirements

C. References [IE610] IEEE Std , Standard Glossary of Software Engineering Terminology [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 [SW04] SWEBOK – Guide to the Software Engineering Body of Knowledge: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements Module II. Software Requirements

C. Quiz Which dimension of requirement classification is critical for consideration of tolerant design? Whether the requirement is functional or non-functional. Whether the requirement is on the product or process. Whether the requirement is volatile or stable. Whether the requirement is a high or low priority. 1) Answer: C. Whether the requirement is volatile or stable. Module II. Software Requirements Module II. Software Requirements

C. Quiz – 2 2. What is the most important attribute of a requirement? Identifier Source Verification procedure Priority 2) Answer: A. Identifier Module II. Software Requirements Module II. Software Requirements

C. Quiz – 3 3. Which of the following is not a type of software requirement? Functionality Performance External Interface Complexity 3) Answer: D. Complexity Module II. Software Requirements Module II. Software Requirements

C. Quiz – 4 4. What does allocation try to satisfy in the assigning of responsibility to components? Requirements Validation External interfaces Testing 4) Answer: A. Requirements Module II. Software Requirements Module II. Software Requirements

C. Quiz – 5 5. What is a software engineer most likely to resolve by making a unilateral decision? Differences between incompatible features Differences between developer perception and developer reality Differences between requirements and resources Differences between functional and non-functional requirements 5) Answer: B. Differences between developer perception and developer reality Module II. Software Requirements Module II. Software 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] Topic Estimate: 50 minutes Module II. Software Requirements Module II. Software Requirements

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] Serves as a basis of understanding between the customer and developer. Provides a basis for writing the preliminary version of the users’ manual. Supports development of the acceptance test plan. Is the first step in project planning. Module II. Software Requirements Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

IEEE The ConOps Document The IEEE Std 1362 is a guide which describes the elements of a ConOps document Module II. Software Requirements

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 Module II. Software Requirements

IEEE Std 1233 (SyRS) Recommended practice for developing system requirements specifications Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 A software requirement may exist because of the nature of the task or because of a special characteristic of the project These should be described in the design stage of the project. These are properly specified in other documents such as the software quality assurance plan. Module II. Software Requirements Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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) Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

IEEE The Parts of an SRS - I Table of Contents Introduction Purpose Scope Definitions, Acronyms, and Abbreviations References Overview Overall Description Product Perspective Product Functions User Characteristics Constraints Assumptions and Dependencies Specific Requirements Appendices Index Module II. Software Requirements

IEEE The Parts of an SRS - II Functional Hierarchy [RT04, p. 4-51] Specific requirements External Interfaces Functional requirements Function 1 Introduction Input Process Output Function 2 … Function n Performance requirements Design constraints Quality attributes Module II. Software Requirements

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 Module II. Software Requirements

D. References [IE610] IEEE Std , Standard Glossary of Software Engineering Terminology [IE830] IEEE Std , Recommended Practice for Software Requirements Specification [IE1233] IEEE Std , Guide for Developing System Requirements [IE1362] IEEE Std , Guide for Information Technology – System Design – Concept of Operations Document [RT02] Thayer, Richard H., Software Engineering, Volume 1: The Development Process, 2nd Edition, IEEE Computer Society, Los Alamitos, CA, 2002 [RT04] Thayer, Richard, 2004 Certified Software Development Professional (CSDP) Preparation Course, Chapter 4: Software Requirements Engineering Concepts Module II. Software Requirements

D. References – 2 [SW04] SWEBOK – Guide to the Software Engineering Body of Knowledge: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements Module II. Software Requirements

D. Quiz Which document is used to derive the software requirements specification? The System Definition Document System Requirements Specification IEEE 1362 Concept of Operations IEEE 1016 Software Design Descriptions 1) Answer: B. System Requirements Specification Module II. Software Requirements Module II. Software Requirements

D. Quiz – 2 2. What should the software requirements specification (SRS) writer avoid placing in the SRS environment of the SRS? External interfaces Performance or functionality Attributes or classification Either design or project requirements 2) Answer: D. Either design or project requirements Module II. Software Requirements Module II. Software Requirements

D. Quiz – 3 3. Which of the following is not embedded design that would be written in the SRS? Partitioning of software into modules Specify logical requirements for the software Describe the flow of information or control between modules Choose data structures 3) Answer: B. Specify logical requirements for the software Module II. Software Requirements Module II. Software Requirements

D. Quiz – 4 4. Which of the following phrases most closely approaches verifiable language? “A good operability” “Well enough” “According to Standard X” “Usually acceptable” 4) Answer: C. “According to Standard X” Module II. Software Requirements Module II. Software Requirements

D. Quiz – 5 5. Which of the following is not a good characteristic well written of a software requirements specification? Consistent Ranked Redundant Verifiable 5) Answer: C. Redundant Module II. Software Requirements Module II. Software Requirements

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 , Para 6.5] Validation (error = external customer requirements - product) Verification (error = internal specified requirements - product) Topic Estimate: 28 minutes Module II. Software Requirements Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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) Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

E. References [IE610] IEEE Std , Standard Glossary of Software Engineering Terminology [IE830] IEEE Std , Recommended Practice for Software Requirements Specification [IE1028] IEEE Std , Standard for Software Reviews [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: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements [IE ] IEEE/EIA Std Standard for Information Technology, Software Life Cycle Processes – Implementation Considerations Module II. Software Requirements

E. Quiz Software requirements validation should be viewed by whom and how often? Requirements analysts, often Stakeholders, often Customers, never Users, never 1) Answer: B. Stakeholders, often Module II. Software Requirements Module II. Software Requirements

E. Quiz – 2 2. Requirements reviews: Can not be done before completion of the Systems definition document Systems specification document Software requirements specification document Baseline specification for new release 2) Answer: A. Systems definition document Module II. Software Requirements Module II. Software Requirements

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] Topic Estimate: 33 minutes Module II. Software Requirements Module II. Software Requirements

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] Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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] Module II. Software Requirements

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] Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software Requirements

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 direction 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] Module II. Software Requirements

RM / Change Management Procedures need to be in place and applied to proposed changes Module II. Software Requirements

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 Module II. Software Requirements

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 Module II. Software 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) Module II. Software Requirements

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

Module II. Software Requirements

F. References [IE610] IEEE Std , Standard Glossary of Software Engineering Terminology [RT02] Thayer, Richard H., Software Engineering, Volume 1: The Development Process, 2nd Edition, IEEE Computer Society, Los Alamitos, CA, 2002 [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: Version, IEEE Computer Society, Los Alamitos, CA, Chapter 2 – Software Requirements [Thayer & Thayer Software Requirements 1997] Reference unknown Module II. Software Requirements

F. Quiz Which of the following is the technical manager not responsible for? Determining the adequacy of the requirements specifications. Controlling the volatility of the requirements and manage change history. Re-estimating the cost and schedule of the project when the requirements change. Negotiating requirements changes between the acquirer (customer) and the developer. 1) Answer: B. Re-estimating the cost and schedule of the project when the requirements change. Module II. Software Requirements Module II. Software Requirements

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? Requirements tracing Impact analysis Software configuration management System definition 2) Answer: D. System definition Module II. Software Requirements Module II. Software Requirements

F. Quiz – 3 3. Requirements tracing is most likely concerned with the following: Recovering the source of requirements from: Software requirement back to the system requirement it supports Observation to elicitation technique Analysis into requirements specification document Software requirement to validation test 3) Answer: A. Software requirement back to the system requirement it supports Module II. Software Requirements Module II. Software Requirements

CSDP Preparation Course Module II: Software Requirements

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CSDP Preparation Course Module II: Software Requirements

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