System Engineering based on Chapter 6 Software Engineering

System Engineering based on Chapter 6 - Software Engineering: A Practitioner’s Approach, 6/e copyright © 1996, 2001, 2005 R. S. Pressman & Associates, Inc. For University Use Only May be reproduced ONLY for student use at the university level when used in conjunction with Software Engineering: A Practitioner's Approach. Any other reproduction or use is expressly prohibited. 1

Waterfall model 1 [aka Royce 1970] Systems Engineering Software Req. Analysis Operation/Maintenance Project Planning Design Implementation Testing/Verification Release 2

System Engineering n Elements of a computer-based system n Software n Hardware n People n n Database Documentation Procedures Systems n A hierarchy of macro-elements 3

Business 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 area creates 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 4

System Architectures n Three different architectures must be analyzed and designed within the context of business objectives and goals: n 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. ) n 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. ) n technology infrastructure provides the foundation for the data and application architectures (e. g. , communication lines, computer platforms, etc. ) 5

System Modeling with UML n Deployment diagrams n n Activity diagrams n n Each 3 -D box depicts a hardware element that is part of the physical architecture of the system Represent procedural aspects of a system element Class diagrams n Represent system level elements in terms of the data that describe the element and the operations that manipulate the data 6

Skip – Self Reading Possibly One Lecture on UML 7

Conveyor 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. 8

Deployment Diagram 9

Activity Diagram 10

Class Diagram 11

Requirements Engineering based on Chapter 7 - Software Engineering: A Practitioner’s Approach, 6/e copyright © 1996, 2001, 2005 R. S. Pressman & Associates, Inc. For University Use Only May be reproduced ONLY for student use at the university level when used in conjunction with Software Engineering: A Practitioner's Approach. Any other reproduction or use is expressly prohibited. 12

Requirements Engineering Process: A Basic Framework [Loucopolos] Many variations and extensions 3 fundamental activities: understand, (formally) describe, attain an agreement on, the problem v User reqs User knowledge Elicitation Specification For more knowledge User feedback Req. models Val. result Validation Domain knowledge Problem Domain (domain experts, laws, standards, policies, documents, etc. ) n n n Elicitation: determine what’s really needed, whom to talk to Specification: produce a (formal) RS model: translate "vague" into "concrete", etc. make various decisions on what & how Validation: assure that the RS model satisfies the users’ needs 13

Requirements Engineering n Elicitation - Inception—ask a set of questions that establish … n n n Specification — can be any one (or more) of the following: n n n (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 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 n n n 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. 14

Eliciting Requirements - Inception n Identify (key) stakeholders n n These are the people who will be involved in the negotiation “who else do you think I should talk to? ” n Recognize multiple points of view Work toward collaboration n The first questions n n n 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? 15

Eliciting Requirements n n n 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 n n to identify the problem propose elements of the solution negotiate different approaches, and specify a preliminary set of solution requirements 16

Elicitation Work Products n n n a statement of need, scope, and feasibility. a list of customers, users, and other stakeholders who participated in requirements elicitation a 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 17

Building the Analysis Model n Elements of the analysis model n Scenario-based elements n n n Class-based elements n n Implied by scenarios Behavioral elements n n Functional—processing narratives for software functions Use-case—descriptions of the interaction between an “actor” and the system State diagram Flow-oriented elements n Data flow diagram 18

Skip – Self Reading Possibly One Lecture on UML 19

Use-Cases n A collection of user scenarios that describe 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 n Each scenario answers the following questions: n n n 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? 20

Use-Case Diagram 21

Class Diagram From the Safe. Home system … 22

State Diagram 23

Validating Requirements n n n n n 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. 24