Lecture 3 Software Requirements Analysis I PDF

Lecture 3 Software Requirements Analysis I Software Requirements Engineering “How to find out what the customer wants?” These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman....

Lecture 3 Software Requirements Analysis I Software Requirements Engineering “How to find out what the customer wants?” These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 1 What Are Software Requirements? What the customers want? How end users will interact with the software? What the software should be processing? What is the technical environment of the software system? How the software fits into the business processes? 2 What We Are Doing ABC Software! 3 Requirements Engineering is The First Task Problem Analysis Design Models Development Solution Testing 4  Requirements Engineering 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 Elaboration—create an analysis model that identifies data, function and behavioral requirements Negotiation—agree on a deliverable system that is realistic for developers and customers These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 5 Requirements Engineering 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 These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 6 Inception Identify stakeholders “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? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 7 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 These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 8 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. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 9 Quality Function Deployment Function deployment determines the “value” (as perceived by the customer) of each function required of the system Information deployment identifies data objects and events Task deployment examines the behavior of the system Value analysis determines the relative priority of requirements These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 10 Non-Functional Requirements Non-Functional Requirment (NFR) – quality attribute, performance attribute, security attribute, or general system constraint. A two phase process is used to determine which NFR’s are compatible: The first phase is to create a matrix using each NFR as a column heading and the system SE guidelines a row labels The second phase is for the team to prioritize each NFR using a set of decision rules to decide which to implement by classifying each NFR and guideline pair as complementary, overlapping, conflicting, or independent These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 11 Use-Cases A collection of user 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? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 12 Use-Case Diagram Arms/ disarms syst em Accesses syst em sensors via Internet homeowner Responds t o alarm event Encount ers an error condition syst em Reconf igures sensors administ rat or and relat ed syst em f eat ures These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 13 Building the Analysis Model 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 Implied by scenarios Behavioral elements State diagram Flow-oriented elements Data flow diagram These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 14 Eliciting Requirements Conduct FAST meetings Make lists of functions, classes Make lists of constraints, etc. formal prioritization? Elicit requirement s yes no Use QFD to informally define actors prioritize prioritize requirements requirements draw use-case write scenario diagram Create Use-cases complete template These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 15 Class Diagram From the SafeHome system … Sensor name/id type location area characteristics identify() enable() disable() reconfigure() These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 16 State Diagram Reading Commands State name System status = “ready” Display msg = “enter cmd” Display status = steady State variables Entry/subsystems ready Do: poll user input panel Do: read user input Do: interpret user input State activities These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 17 Analysis Patterns Pattern name: A descriptor that captures the essence of the pattern. Intent: Describes what the pattern accomplishes or represents Motivation: A scenario that illustrates how the pattern can be used to address the problem. Forces and context: A description of external issues (forces) that can affect how the pattern is used and also the external issues that will be resolved when the pattern is applied. Solution: A description of how the pattern is applied to solve the problem with an emphasis on structural and behavioral issues. Consequences: Addresses what happens when the pattern is applied and what trade-offs exist during its application. Design: Discusses how the analysis pattern can be achieved through the use of known design patterns. Known uses: Examples of uses within actual systems. Related patterns: On e or more analysis patterns that are related to the named pattern because (1) it is commonly used with the named pattern; (2) it is structurally similar to the named pattern; (3) it is a variation of the named pattern. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 18 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” These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 19 Requirements Monitoring Especially needes in incremental development Distributed debugging – uncovers errors and determines their cause. Run-time verification – determines whether software matches its specification. Run-time validation – assesses whether evolving software meets user goals. Business activity monitoring – evaluates whether a system satisfies business goals. Evolution and codesign – provides information to stakeholders as the system evolves. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 20 Validating Requirements - I Is each requirement consistent with the overall objective for the system/product? Have all requirements been specified at the proper level of abstraction? That is, do some requirements provide a level of technical detail that is inappropriate at this stage? 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? 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? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 21  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. Has the requirements model been “partitioned” in a way that exposes progressively more detailed information about the system. Have requirements patterns been used to simplify the requirements model. Have all patterns been properly validated? Are all patterns consistent with customer requirements? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 22 Requirements Analysis Requirements analysis specifies software’s operational characteristics indicates software's interface with other system elements establishes constraints that software must meet Requirements analysis allows the software engineer (called an analyst or modeler in this role) to: elaborate on basic requirements established during earlier requirement engineering tasks build models that depict user scenarios, functional activities, problem classes and their relationships, system and class behavior, and the flow of data as it is transformed. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 23 Elements of Requirements Analysis These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 24 Requirements Modeling Scenario-based system from the user’s point of view Data shows how data are transformed inside the system Class-oriented defines objects, attributes, and relationships Flow-oriented shows how data are transformed inside the system Behavioral show the impact of events on the system states These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 25  A Bridge system description analysis model design model These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 26 Rules of Thumb The model should focus on requirements that are visible within the problem or business domain. The level of abstraction should be relatively high. Each element of the analysis model should add to an overall understanding of software requirements and provide insight into the information domain, function and behavior of the system. Delay consideration of infrastructure and other non- functional models until design. Minimize coupling throughout the system. Be certain that the analysis model provides value to all stakeholders. Keep the model as simple as it can be. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 27 Domain Analysis Software domain analysis is the identification, analysis, and specification of common requirements from a specific application domain, typically for reuse on multiple projects within that application domain... [Object-oriented domain analysis is] the identification, analysis, and specification of common, reusable capabilities within a specific application domain, in terms of common objects, classes, subassemblies, and frameworks... Donald Firesmith These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 28 Domain Analysis Define the domain to be investigated. Collect a representative sample of applications in the domain. Analyze each application in the sample. Develop an analysis model for the objects. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 29 Scenario-Based Modeling “[Use-cases] are simply an aid to defining what exists outside the system (actors) and what should be performed by the system (use-cases).” Ivar Jacobson (1) What should we write about? (2) How much should we write about it? (3) How detailed should we make our description? (4) How should we organize the description? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 30 What to Write About? Inception and elicitation—provide you with the information you’ll need to begin writing use cases. Requirements gathering meetings, QFD, and other requirements engineering mechanisms are used to identify stakeholders define the scope of the problem specify overall operational goals establish priorities outline all known functional requirements, and describe the things (objects) that will be manipulated by the system. To begin developing a set of use cases, list the functions or activities performed by a specific actor. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 31 How Much to Write About? As further conversations with the stakeholders progress, the requirements gathering team develops use cases for each of the functions noted. In general, use cases are written first in an informal narrative fashion. If more formality is required, the same use case is rewritten using a structured format similar to the one proposed. These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 32 Use-Cases a scenario that describes a “thread of usage” for a system actors represent roles people or devices play as the system functions users can play a number of different roles for a given scenario These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 33 Developing a Use-Case What are the main tasks or functions that are performed by the actor? What system information will the 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? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 34 Reviewing a Use-Case Use-cases are written first in narrative form and mapped to a template if formality is needed Each primary scenario should be reviewed and refined to see if alternative interactions are possible Can the actor take some other action at this point? Is it possible that the actor will encounter an error condition at some point? If so, what? Is it possible that the actor will encounter some other behavior at some point? If so, what? These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 35 Use-Case Diagram SafeHome Access camera surveillance via the cameras Internet Configure SafeHome system parameters homeowner Set alarm These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 36 Exceptions Describe situations (failures or user choices) that cause the system to exhibit unusual behavior Brainstorming should be used to derive a reasonably complete set of exceptions for each use case Are there cases where a validation function occurs for the use case? Are there cases where a supporting function (actor) fails to respond appropriately? Can poor system performance result in unexpected or improper use actions? Handling exceptions may require the creation of additional use cases These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 37 Activity Diagram Supplements the enter password and user ID use case by providing a valid passwords/ ID invalid passwor ds/ ID graphical select major function prompt for reentry representation of ot her f unct ions may also be select ed input t ries r emain the flow of select surveillance no input t r ies r emain interaction within a t humbnail views select a specif ic camer a specific scenario select specific select camera icon camera - thumbnails view camera output in labelled window prompt for another view exit t his f unct ion see anot her camer a These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 38 Swimlane Diagrams home owne r c a m e ra i n t e rf a c e Allows the modeler to represent the flow of enter password activities described by and user ID the use-case and at the same time indicate valid p asswo rd s/ ID which actor (if there are in valid p asswor d s/ ID select major function multiple actors involved o t h er f u n ct io n s prompt for reentry in a specific use-case) may also b e select ed or analysis class has in p u t t r ies select surveillance r emain responsibility for the n o in p u t t r ies r emain action described by an activity rectangle t hu mb n ail views select a sp ecif ic camer a select specific select camera icon camera - thumbnails generate video output view camera output prompt for in labelled window another view exit t h is f un ct ion see ano t h er camer a These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 8/e (McGraw-Hill, 2014). Slides copyright 2014 by Roger Pressman. 39