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Software Engineering: A Practitioner’s Approach, 7/e Chapter 5 Requirements Engineering Modified to include some Agile Concepts copyright © 1996, 2001,

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Presentation on theme: "Software Engineering: A Practitioner’s Approach, 7/e Chapter 5 Requirements Engineering Modified to include some Agile Concepts copyright © 1996, 2001,"— Presentation transcript:

1 Software Engineering: A Practitioner’s Approach, 7/e Chapter 5 Requirements Engineering Modified to include some Agile Concepts copyright © 1996, 2001, 2005 R.S. Pressman & Associates, Inc. NOTE: Some slides referenced from: Ian Sommerville Slides for Software Engineering. Coming up: What is a requirement?

2 What is a requirement? Requirements are used to describe all aspects of a system They may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification They serve many roles May be the basis for a bid for a contract - therefore must be open to interpretation May be the basis for the contract itself - therefore must be defined in detail Are always used to communicate what you intend to build Coming up: Requirements come in many forms

3 Requirements come in many forms
Requirements Statements – ex: “The system shall ….” UML Use-case diagrams eXtreme Programming “User Stories” Scrum Product Backlog Any other documents that communicate what you intend to build Prototypes can be used as requirements Existing systems can serve as requirements “Build this system, but use Java instead of Fortran” UML Sequence diagrams, State charts, activity diagrams… Coming up: All Requirements

4 All Requirements Should specify external behavior of the system
Includes functional and non-functional requirements Functional requirements are statements of the services that the system must provide What must the system do? (Start all with the phrase “The system shall…”) Non-functional requirements are constraints on the services and functions offered by the system How must it do it? or a constraint on the system Coming up: Typical Requirements Statements

5 Typical Requirements Statements
Functional: The system shall display the heart rate, blood pressure and temperature of a patient connected to the patient monitor. Non-Functional: "Display of the patient's vital signs must respond to a change in the patient's status within 2 seconds.” ‘ilities’ - Performance, Scalability, Capacity, Availability Reliability, Recoverability, Maintainability, Serviceability, Security,
Regulatory,Manageability What are some functional requirements on an iPod? Non-functional? Coming up: Why do we care?

6 I’ll destroy you and your little software project
Why do we care? Most large software systems address wicked problems Problems which are so complex that they can never be fully understood and where understanding develops during the system development Therefore, requirements are normally both incomplete and inconsistent Requirements help by giving you the best understanding you can have at the beginning I’ll destroy you and your little software project to! problem Coming up: Prescriptive versus Agile approach

7 Prescriptive versus Agile approach
Prescriptive – approach is to minimize/prevent change by understanding system thoroughly at the beginning Typically heard: “A change during implementation costs 10 times more than a change during requirements phase” Agile – approach is to manage change by being flexible (i.e. Agile) Typically heard: Requirements planned for 6 months from now are most likely completely inaccurate. Don’t waste resources planning far ahead. Plan short iterations and adjust the plan as you go. Coming up: Typical Prescriptive Requirements Engineering Process

8 Typical Prescriptive Requirements Engineering Process
Inception—ask a set of questions that establish … basic understanding of the problem the people who want a solution the nature of the solution that is desired, and the effectiveness of preliminary communication and collaboration between the customer and the developer Elicitation—elicit requirements from all stakeholders to identify the problem propose elements of the solution negotiate different approaches, and specify a preliminary set of solution requirements Elaboration—create an analysis model that identifies data, functional and behavioral requirements Negotiation—agree on a set of requirements among all stakeholders (realistic, non-conflicting, inline with budget) Inception - Basic Understanding. Just talking Elicitation - Try to get rqmt from users Elaboration - refined technical models software functions/features/constraints Negotiation - schedule/cost, feature A vs B Coming up: Requirements Engineering-II

9 Requirements Engineering-II
Specification—can be any one (or more) of the following: A written document A set of models A formal mathematical A collection of user scenarios (use-cases) A prototype Validation—a review mechanism that looks for errors in content or interpretation areas where clarification may be required missing information inconsistencies (a major problem when large products or systems are engineered) conflicting or unrealistic (unachievable) requirements. Requirements management Specification - final document Validation - checklists, not violating each other, etc… Management - similar to source code mgmt Coming up: Typical Prescriptive Requirements Document Structure

10 Typical Prescriptive Requirements Document Structure
Purpose Overall Description System Features (Functional Requirements/Use Cases) External Interface Requirements User interface requirements or standards Hardware interfaces to other systems Software interfaces to other systems Communication Interfaces Non-functional Requirements Appendices - analysis model diagrams See SRS Template on CS421 Project Page (provided by … but essentially from IEEE). Coming up: Analysis Model

11 Analysis Model Included to provide more clarification about textual requirements (where needed) Elements of the analysis model Scenario-based elements Functional—processing narratives for software functions Use-case—descriptions of the interaction between an “actor” and the system Class-based elements – e.g. class diagram Behavioral elements – e.g. state diagram, sequence diagram, activity diagram, etc.. Flow-oriented elements – e.g. data flow diagram Coming up: Use-Cases

12 Use-Cases A collection of usage scenarios that describe the thread of usage of a system Each scenario is described from the point-of-view of an “actor”—a person or device that interacts with the software in some way Each scenario answers the following questions: Who is the primary actor, the secondary actor (s)? What are the actor’s goals? What preconditions should exist before the story begins? What main tasks or functions are performed by the actor? What extensions might be considered as the story is described? What variations in the actor’s interaction are possible? What system information will the actor acquire, produce, or change? Will the actor have to inform the system about changes in the external environment? What information does the actor desire from the system? Does the actor wish to be informed about unexpected changes? Coming up: Use-Case Diagram

13 Use-Case Diagram Each stick figure is an actor in your system
The block is an external system that interacts with your system. Any system you aren’t developing is external Each oval is a separate use case that has a description Coming up: Use Case Description

14 Use Case Description ID - A unique to reference this use case U01, U02, etc…) Objective - What is the ultimate objective of the use-case. What is it trying to achieve? Priority – The overall priority of this use-case (Low, Medium, High) Source – Who is the main source of this use case. Who cares most about this functionality? This should be the one person you would ask if there is a question about this use-case. (Make up a name and cite their: John Smith (End-user) here.) Actors – Which actors/stakeholders are involved in the use-case? Flow of Events Basic Flow - flow of events normally executed in the use-case Alternative Flow(s) - a secondary flow of events due to infrequent conditions Exception Flow(s) - Exceptions that may happen during the execution of the use case Includes - other use case IDs that are referenced in steps in the flow of events. Preconditions - Any condition that must be satisfied before the use case begins. If the condition is “User is logged in”, then the first step of the use case is NOT “User logs in”. They are already logged in if that is a pre-condition! Post conditions - The conditions that will be satisfied after the use case successfully completes (typically same as objective) Notes/Issues - Any relevant notes or issues that need to be resolved Coming up: Alternate and Exception Flows

15 Alternate and Exception Flows
Basic Flow User enters user name User enters password User submits the form Password is validated as correct Main menu is displayed Alternate Flow 1: No password is present at step 1.4 System displays error message. System continues at step 1.2 Alternate Flow 2: Password is incorrect as step 1.4 Exception Flow 1: Database is unreachable System displays an unrecoverable error and exits. Show when in the basic flow this happens and where you end up after the alt flow You may not know when this happens. That’s okay Coming up: Includes and Preconditions

16 Includes and Preconditions
Basic Flow User selects option 4 from main menu screen Preconditions: User is logged in Includes: None Basic Flow User executes U2: Login User selects option 4 from main menu screen Preconditions: None Includes: U2: Login Don’t forget to show this on the use case diagram as “includes” Coming up: eXtreme Programming (XP): User Stories

17 eXtreme Programming (XP): User Stories
Serve as requirements within the XP/Scrum process Written by customers Time Estimated by developers Replaces large requirements documents Represents anything that is “progress” to the customer Examples: Students can purchase monthly parking passes online. Parking passes can be paid via credit cards. Parking passes can be paid via PayPal Professors can input student marks. Students can obtain their current seminar schedule.・Students can order official transcripts. Coming up: eXtreme Programming (XP): User Stories

18 eXtreme Programming (XP): User Stories
Short – 1 or 2 sentences. Usually supposed to fit on a 3x5 notecard Easy to estimate (project velocity) Allows requirements to change frequently with less impact Without accompanying validation tests may lead to misinterpretation Difficult to scale to very large projects Requires close customer contact to ensure correct implementation Got here 2/4/2009 Coming up: Format for User Stories (CS421 only… not standard!)

19 Format for User Stories (CS421 only… not standard!)
Unique Identifier Source – who should developer contact with questions about this? Story – short (1-3 sentence) high-level description of story. When the developer plans to implement they should discuss with the customer the details. As a [user role], I want to [goal], so I can [reason]. Time estimate – how long in “ideal development time” – time without meetings or any interruptions Client’s Priority – how important is the story to the client? (Low, Medium, High) Coming up: The web has MANY references about User Stories and Use Cases.

20 The web has MANY references about User Stories and Use Cases.
Which is better? Many arguments – here is one: Coming up: Agile and Traditional Requirements share more than they differ

21 Agile and Traditional Requirements share more than they differ
Coming up: Negotiating Requirements

22 Negotiating Requirements
Identify the key stakeholders These are the people who will be involved in the negotiation Determine each of the stakeholders’ “win conditions” Win conditions are not always obvious Negotiate Work toward a set of requirements that lead to “win-win” Coming up: Reasons we need to negotiate

23 Reasons we need to negotiate
Discuss Large software systems must improve the current situation. It is hard to anticipate the effects that the new system will have on the organization Discuss Prototyping is often required to clarify requirements Negotiate Different users have different requirements and priorities. There is a constantly shifting compromise in the requirements Negotiate System end-users and organizations who pay for the system have different requirements Coming up: Requirements Rationale

24 Requirements Rationale
It is important to provide rationale with requirements This helps the developer understand the application domain and why the requirement is stated in its current form Particularly important when requirements have to be changed. The availability of rationale reduces the chances that change will have unexpected effects In this class we’ll provide the requirement’s source and assume they can contact the source to get a rationale if needed instead of an explicit “rationale”. This is more “agile” Got here 9/11/2008 Coming up: Non-Functional Requirement Types

25 Non-Functional Requirement Types
Remember: Non Functional = How the system should do something Product requirements Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc. Organizational requirements Requirements which are a consequence of organizational policies and procedures e.g. process standards used, implementation requirements, etc. External requirements Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc. Coming up: Non-Functional Requirement Examples

26 Non-Functional Requirement Examples
Product requirement 4.C.8 It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set. Organizational requirement The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP-STAN-95. External requirement The system shall provide facilities that allow any user to check if personal data is maintained on the system. A procedure must be defined and supported in the software that will allow users to inspect personal data and to correct any errors in that data. constraint: interoperability constraint: quality For Agile either a non-functional user story or a set of “global” test cases to run for all stories. Got here 9/15/2009 security, maintainability Agile stories? How? Coming up: Requirements must be testable

27 Requirements must be testable
Traditional requirements must be written so that they can be objectively verified. XP requirements have explicit acceptance test cases written by the customers to solve this problem. The problem with this requirement is its use of vague terms such as ‘errors shall be minimized” The system should be easy to use by experienced controllers and should be organized in such a way that user errors are minimized. The error rate should be been quantified Experienced controllers should be able to use all the system functions after a total of two hours training. After this training, the average number of errors made by experienced users should not exceed two per day. Coming up: Requirements: testable metrics

28 Requirements: testable metrics
Coming up: System Level Requirements

29 System Level Requirements
Some requirements place constraints on the system as a whole rather than specific system functions Example The time required for training a system operator to be proficient in the use of the system must not exceed 2 working days. These may be emergent requirements which cannot be derived from any single sub-set of the system requirements Coming up: Requirements Validation

30 Requirements Validation
Concerned with demonstrating that the requirements define the system that the customer really wants Requirements error costs are high so validation is very important Fixing a requirements error after delivery may cost up to 100 times the cost of fixing an implementation error Coming up: Validating Requirements-I

31 Validating Requirements-I
Is each requirement consistent with the overall objective for the system/product? Work with all parties on this question! Is the requirement really necessary or does it represent an add-on feature that may not be essential to the objective of the system? Is each requirement bounded and unambiguous? (e.g. testable) Does each requirement have attribution? That is, is a source (generally, a specific individual) noted for each requirement? Do any requirements conflict with other requirements? Unneccessary example with our ATM system? Buy Stamps! :-) Coming up: Validating Requirements-II

32 Validating Requirements-II
Is each requirement achievable in the technical environment that will house the system or product? Is each requirement testable, once implemented? Does the requirements model properly reflect the information, function and behavior of the system to be built. Coming up: Requirements Reviews

33 Requirements Reviews Regular reviews should be held while the requirements definition is being formulated Both client and contractor staff should be involved in reviews Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage Coming up: Requirements final thoughts…

34 Requirements final thoughts…
Requirements should specify one and only one thing Requirements and User Stories can only pass or fail, they can’t partially pass. If you want to partially pass a requirement split into two Requirements must be testable Requirements must specify what YOUR system must do, not what other (external) systems do To make this easier, in this class all functional requirements must begin with “The system shall…” Must have a source (make it up for CS421) Coming up: Requirements final thoughts…

35 Requirements final thoughts…
Should not be a design choice (this is hard to get right). The system shall store user information including name, DOB, address and SSN. <-- Good! The system shall store user information in an Oracle database including name, DOB, address, SSN. <-- bad Is Oracle really REQUIRED? Hard to say… maybe, but probably not. This is a decision you would make at implementation design time. Question: Does the customer care that you use Oracle? MySQL? Etc.. Maybe someone found some other MUCH BETTER approach storing the data on moon rocks. Again: This is hard to avoid… and I’m not to concerned with it on the SRS, but I want you to be very aware of when you are making design choices instead of required features. Coming up: Requirements must have a unique ID

36 Requirements must have a unique ID
When testing you need to reference REQ-1 or REQ-287. Multiple things cannot be labeled REQ-1. Later our test cases will say: This test case validates requirements REQ-1, REQ-27, and REQ-56. Coming up: Bad Example Requirements Statements

37 Bad Example Requirements Statements
Bad requirements examples: The system shall validate and accept credit cards and cashier’s checks. High priority. The system shall process all mouse clicks very fast to ensure user’s do not have to wait. The user must have Adobe Acrobat installed. These don’t have a source or unique ID, but what else is wrong? Coming up: Bad Examples

38 Bad Examples The system shall validate and accept credit cards and cashier’s checks. High priority. Problem: two requirements instead of one. If the credit card processing works, but the cashier’s check validation does not… is this requirement pass or fail? Has to be fail, but that is misleading. Maybe only credit cards are high priority and cashier’s checks are low priority. The system shall process all mouse clicks very fast to ensure user’s do not have to wait. Problem: This is not testable. Quantify how fast is acceptable? The user must have Adobe Acrobat installed. Problem: This is not something our system must do. It could be in the constraints/assumptions or maybe operating environment sections, but is not a functional requirement of our system Coming up: The Result of Good Requirements

39 The Result of Good Requirements
Your wicked problems melt into small manageable problems …. I’m melting! Coming up: Inception

40 Inception Identify stakeholders Recognize multiple points of view
“who else do you think I should talk to?” Recognize multiple points of view Work toward collaboration The first questions Who is behind the request for this work? Who will use the solution? What will be the economic benefit of a successful solution Is there another source for the solution that you need? Stakeholders - anyone with a valid interest Viewpoints - marketing, management, developers, end-users, etc… Collaboration - assign voting rights, etc… who am I trying to satisfy? (Impossible to answer). Coming up: Eliciting Requirements

41 Eliciting Requirements
meetings are conducted and attended by both software engineers and customers rules for preparation and participation are established an agenda is suggested a "facilitator" (can be a customer, a developer, or an outsider) controls the meeting a "definition mechanism" (can be work sheets, flip charts, or wall stickers or an electronic bulletin board, chat room or virtual forum) is used the goal is to identify the problem propose elements of the solution negotiate different approaches, and specify a preliminary set of solution requirements XP - does only user scenarios, Documenting requirements - in DB or Excel or wherever Coming up: Eliciting Requirements

42 Eliciting Requirements
QFD - look at everything through the “voice of the customer” Coming up: Elicitation Work Products

43 Elicitation Work Products
a statement of need and feasibility. a bounded statement of scope for the system or product. a list of customers, users, and other stakeholders who participated in requirements elicitation a description of the system’s technical environment. a list of requirements (preferably organized by function) and the domain constraints that apply to each. a set of usage scenarios that provide insight into the use of the system or product under different operating conditions. any prototypes developed to better define requirements. End of presentation

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