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CS 5150 1 CS 5150 Software Engineering Lecture 2 Software Processes.

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Presentation on theme: "CS 5150 1 CS 5150 Software Engineering Lecture 2 Software Processes."— Presentation transcript:

1 CS 5150 1 CS 5150 Software Engineering Lecture 2 Software Processes

2 CS 5150 2 Administration Project teams Any announcement to class? People who would like to form teams?

3 CS 5150 3 Administration Project teams When you have formed your team and reached agreement with your client, please send a message to: and with the names of the team, the client's name, and the topic of the project.

4 CS 5150 4 A Classic Book Frederick P. Brooks, Jr. The Mythical Man Month. Addison-Wesley, 1972.

5 CS 5150 5 Software Process Fundamental Assumption: Good processes lead to good software Good processes reduce risk Good processes enhance visibility

6 CS 5150 6 Variety of Software Processes Software products are very varied... Therefore, there is no standard process for all software engineering projects BUT successful software development projects all need to address similar issues. This creates a number of process steps that must be part of all software projects

7 CS 5150 7 Basic Process Steps in all Software Development Feasibility and planning Requirements System and program design Implementation and testing Acceptance testing and release Operation and maintenance It is essential to distinguish among these process steps and to be clear which you are are doing at any given moment. Do not confuse requirements and design

8 CS 5150 8 Process Step: Feasibility and Planning A feasibility study precedes the decision to begin a project. What is the scope of the proposed project? Is the project technically feasible? What are the projected benefits? What are the costs, timetable? A feasibility study leads to a decision: go or no-go.

9 CS 5150 9 Process Step: Requirements Requirements define the function of the system from the client's viewpoint. The requirements establish the system's functionality, constraints and goals by consultation with the client and users. They are specified in a manner that is understandable by both the client and the development staff.

10 CS 5150 10 Process Step: System and Program Design Design describes the system from the software developers' viewpoint System design: Match the requirements to hardware or software systems. Establishes an overall system architecture Program design: Represent the software system functions in a form that can be transformed into one or more executable programs

11 CS 5150 11 Process Step: Implementation and Testing Implementation (coding) The software design is realized as a set of programs or program units. (The software components may be written specifically, acquired from elsewhere, or modified.) Testing Individual components are tested against specifications. The components are integrated and tested against the design by the development staff as a complete system.

12 CS 5150 12 Process Step: Acceptance Testing and Release Acceptance testing The system is tested against the requirements by the client. Delivery and release The system is delivered to the client and released into production.

13 CS 5150 13 Process Step: Operation and Maintenance Operation: The system is put into practical use. Maintenance: Errors and problems are identified and fixed. Evolution: The system evolves over time as requirements change, to add new functions or adapt the technical environment. Phase out: The system is withdrawn from service. This is sometimes called the Software Life Cycle

14 CS 5150 14 Sequence of Processes Every software project will include these basic processes, in some shape or form, but: They may be formal or informal They may be carried out in various sequences

15 CS 5150 15 Sequence of Processes Major alternatives Iterative: Go quickly through all process steps to create a rough system, then repeat them to improve the system. Iterative refinement. Sequential: As far as possible, complete each process step before beginning the next. Waterfall model. Phased: Divide the project into a number of phases. Implement each phase in turn and put it in production immediately.

16 CS 5150 16 Iterative Refinement Requirements Design Implementation Evaluation

17 CS 5150 17 Iterative Development: Iterative Refinement (Evolutionary Development) Concept: Initial implementation for client and user evaluation, followed by refinement until system is complete. Vaporware: user interface mock-up Throw-away software components Dummy modules Rapid prototyping Successive refinement

18 CS 5150 18 Iterative Processes: Requirements and Risk Mistakes in the requirements are the most expensive to correct. Requirements are hard to understand until there is an operational system, particularly with user interfaces Create an outline system quickly, review it with clients, test it with users, improve the understanding of the requirements Example: Integration of browser into operational system

19 CS 5150 19 Sequential Development: The Waterfall Model Requirements System design Testing Operation & maintenance Program design Implementation (coding) Acceptance & release Requirements Design Implementation Feasibility study

20 CS 5150 20 Discussion of the Waterfall Model Advantages: Process visibility Separation of tasks Quality control at each step Cost monitoring at each step Disadvantages: Each stage in the process reveals new understanding of the previous stages, which often requires the earlier stages to be revised. The Waterfall Model is not enough!

21 CS 5150 21 Sequence of Processes A pure sequential model is impossible Examples: A feasibility study cannot create a proposed budget and schedule without a preliminary study of the requirements and a tentative design. Detailed design or implementation usually reveals gaps in the requirements specification. The plan must allow for some form of iteration.

22 CS 5150 22 Modified Waterfall Model Requirements System design Testing Operation & maintenance Program design Implementation (coding) Acceptance & release Waterfall model with feedback This is better Feasibility study

23 CS 5150 23 Phased Development A simple system with basic functionality is brought quickly into production (Phase 1). Subsequent phases are based on experience gained from users of each previous phase. Advantages Pay-back on investment begins soon. Requirement are more clearly understood in developing subsequent phases. User feedback can be incorporated in later phases.

24 CS 5150 24 Phased Development Online When software is released online it is possible to divide it into small phases that are developed and released in quick succession. Example: divides most software development into phases of about four weeks elapsed time. This approach is excellent for continual enhancement of a system within an established architecture. It is not possible for shrink wrapped software, embedded systems, or similar environments.

25 CS 5150 25 Mixed Processes: User Interface Development User interfaces have to be tested with users. This forces iterative development, even within an underlying sequential process. A common model is to combine iterative refinement of user interfaces within an overall sequential process. (Iteration within the steps of a sequential process is sometimes called a spiral development process.)

26 CS 5150 26 Examples of Mixed Processes: Iterative Refinement + Waterfall Model: Problem: Add graphics package to a programming environment Phase 1: Iterative refinement Extend current environment with a preprocessor and run-time support package. Test with users. Make several new versions until users are pleased with function. Throw the code away. Phase 2: Modified waterfall Use the results of Phase 1 as the basis for a formal set of requirements. Write new compiler and run-time system incorporating graphics elements. Make minor adjustments to requirements as needed.

27 CS 5150 27 Modern Developments in Software Processes Changes during the software development process are expensive. If the requirements are poorly understood, or expected to change, select a process that keeps flexibility. Iterative refinement, phased implementation. For big software systems with many inter-related components, avoid major changes to the design of a system during development. Sequential process, such as the modified waterfall model.

28 CS 5150 28 Modern Developments in Software Processes Agile software development is a variant of iterative refinement that stresses rapid iterations with a flexible approach to requirement and design. Extreme programming is an approach that concentrates on selected techniques of software development, e.g., coding by teams, design and code reviews, and typically releases software in a sequence of small phases.

29 CS 5150 29 Observations about Software Processes Completed projects should have the basic process steps but... the development process is always partly evolutionary. Risk is lowered by: Prototyping key components Dividing into phases Following a visible software process Making use of reusable components Conclusion It is not possible to complete each step and throw it over the wall.

30 CS 5150 30 CS 5150 Project Presentations: Iterative Option Requirements Design Implementation Evaluation first presentation second presentation third presentation

31 CS 5150 31 CS 5150 Project Presentations: Sequential Option Requirements System design Testing Operation & maintenance Program design Implementation (coding) Acceptance & release 1. Requirements 2. Design 3. Implementation Feasibility study If you follow a sequential process the three presentations should be as shown.

32 CS 5150 32 CS 5150 Software Engineering Project Suggestions

33 CS 5150 33 Project Suggestion: eCommons Harvesting from Web sites for the Cornell academic repository John Saylor, Cornell University Library

34 CS 5150 34 Project Suggestion: iPhone Application for Pet Nutrition Stephanie Specchio, College of Veterinary Medicine Ron DiNapoli, Cornell Information Technologies

35 CS 5150 35 Project Suggestion: Field of Mars Social networking and e-commerce site for athletics and fitness Jonathan and Aleda Schaffer Johnson School, Cornell University

36 CS 5150 36 Project Concept: Legal Information Institute Spaeth database of Supreme Court statistics User contributed queries Tom Bruce, Director Legal Information Institute

37 CS 5150 37 Project Concept: FSAE Race Car Controller area network for FSAE race car Cangming Liu FSAE Race Team

38 CS 5150 38 Project Concept: Risk Management and Public Safety Personal Protection Equipment & Training Assessment Tool Curtis Baker, Risk Management and Public Safety Information Services [former CS 5150 student]

39 CS 5150 39 Project Suggestion: Civitas electronic voting system Civitas electronic voting system Michael Clarkson Computer Science Department

40 CS 5150 40 Project Suggestions from Electrical and Computer Engineering GPS Sensor Array Management Brady O'Hanlon Aerobic Exercise Monitor John Belina

41 CS 5150 41 Project Suggestion: SNAP Social Network Applied Perception (SNAP) Search Engine Stephen Purpura, Cornell Information Science

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