2Waterfall model 1 [aka Royce1970] Systems EngineeringSoftware Req. AnalysisOperation/MaintenanceProject PlanningDesignImplementationTesting/VerificationRelease
3System Engineering Elements of a computer-based system Software HardwarePeopleDatabaseDocumentationProceduresSystemsA hierarchy of macro-elements
4Business Process (Re-)Engineering to identify how information systems can best meet the strategic goals of an enterprise, using an integrated set of procedures, methods, and tools, given a set of business rules and constraints.focuses first on the enterprise and then on the business areacreates enterprise models, data models and process models(processes/services and interrelationships of processes and data)creates a framework for better information management, distribution, and control
5System ArchitecturesThree different architectures must be analyzed and designed within the context of business objectives and goals:data architecture provides a framework for the information needs of a business or business function (e.g., incident location, patient status, ambulance location, drivers’ lunch hours and break, hospital locations, etc.)application architecture encompasses those elements of a system that transform objects within the data architecture for some business purpose(e.g., determine ambulance availability, determine hospital availability, etc.)technology infrastructure provides the foundation for the data and application architectures (e.g., communication lines, computer platforms, etc.)
6System Modeling with UML Deployment diagramsEach 3-D box depicts a hardware element that is part of the physical architecture of the systemActivity diagramsRepresent procedural aspects of a system elementClass diagramsRepresent system level elements in terms of the data that describe the element and the operations that manipulate the data
8Conveyor Line Sorting System (CLSS) CLSS must be developed such that boxes moving along a conveyor line will be identified and sorted into one of six bins at the end of the line. The boxes will pass by a sorting station where they will be identified. Based on an identification number printed on the side of the box and a bar code, the boxes will be shunted into the appropriate bins. Boxes pass in random order and are evenly spaced. The line is moving slowly.A desk-top computer located at the sorting station executes all CLSS software, interacts with the bar-code reader to read part numbers on each box, interacts with the conveyor line monitoring equipment to acquire conveyor line speed, stores all part numbers sorted, interacts with a sorting station operator to produce a variety of reports and diagnostics, sends control signals to the shunting hardware to sort the boxes, and communicates with a central factory automation system.
13Requirements Engineering Process: A Basic Framework [Loucopolos] Many variations and extensions3 fundamental activities:understand, (formally) describe, attain an agreement on, the problemUserUser reqsUser feedbackknowledgeReq. modelsElicitationSpecificationValidationVal. resultFor more knowledgeDomain knowledgeDomain knowledgeProblemDomain(domain experts, laws, standards, policies, documents, etc.)Elicitation: determine what’s really needed, why needed, whom to talk toSpecification: produce a (formal) RS model: translate "vague" into "concrete", etc. make various decisions on what & howValidation: assure that the RS model satisfies the users’ needs
14Requirements Engineering Elicitation - Inception—ask a set of questions that establish …(basic) understanding of the problemthe people who want a solutionthe nature of the solution that is desired, andthe effectiveness of preliminary communication and collaboration between the customer and the developerSpecification — can be any one (or more) of the following:A written documentA set of models - A formal mathematical?A collection of user scenarios (use-cases)A prototypeValidation — a review mechanism that looks forerrors in content or interpretationareas where clarification may be requiredmissing informationinconsistencies (a major problem when large products or systems are engineered)conflicting or unrealistic (unachievable) requirements.
15Eliciting Requirements - Inception Identify (key) stakeholdersThese are the people who will be involved in the negotiation“who else do you think I should talk to?”Recognize multiple points of viewWork toward collaborationThe first questionsWho is behind the request for this work?Who will use the solution?What will be the (economic) benefit of a successful solutionIs there another source for the solution that you need?
16Eliciting Requirements meetings are conducted and attended by both software engineers and customersrules for preparation and participation are establishedan agenda is suggesteda "facilitator" (can be a customer, a developer, or an outsider) controls the meetinga "definition mechanism" (can be work sheets, flip charts, or wall stickers or an electronic bulletin board, chat room or virtual forum) is usedthe goal isto identify the problempropose elements of the solutionnegotiate different approaches, andspecify a preliminary set of solution requirements
17Elicitation Work Products a statement of need, scope, and feasibility.a list of customers, users, and other stakeholders who participated in requirements elicitationa description of the system’s technical environment (cf. enterprise model in system engineering).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.
18Building the Analysis Model Elements of the analysis modelScenario-based elementsFunctional—processing narratives for software functionsUse-case—descriptions of the interaction between an “actor” and the systemClass-based elementsImplied by scenariosBehavioral elementsState diagramFlow-oriented elementsData flow diagram
20Use-CasesA collection of user scenarios that describe the thread of usage of a systemEach scenario is described from the point-of-view of an “actor”—a person or device that interacts with the software in some wayEach 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?
24Validating Requirements 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?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.