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CS 5150 Software Engineering

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Presentation on theme: "CS 5150 Software Engineering"— Presentation transcript:

1 CS 5150 Software Engineering
Lecture 3 Software Processes 2

2 Administration Project teams • Any announcement to class?
• People who would like to form teams? Project Suggestions on the web site Entrepreneurship experiment

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 Basic Process Steps in all Software Development
• Feasibility and planning • Requirements • System and program design • Implementation • Acceptance and release • Operation and maintenance In a lightweight process, these steps are repeated with each increment

5 Process Step: Feasibility
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.

6 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, customers, and users. The requirements may be developed in a self-contained study, or may emerge incrementally.

7 Process Step: System and Program Design
Design describes the system from the software developers' viewpoint System design: Establish a system architecture that matches the requirements to hardware or software systems. Program design: Represent the software functions in a form that can be transformed into one or more executable programs

8 Process Step: Implementation
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.

9 Process Step: Acceptance and Release
The system is tested against the requirements by the client, often with selected customers and users. Delivery and release The system is delivered to the client and released into production or marketed to customers.

10 Testing User testing A preliminary version of the user interface is tested by users. Their experience may lead to changes in the requirements or the design. Program testing The development team tests components individually (unit testing) or in combination (system testing) to find bugs, etc. Acceptance testing The client tests the final version of the system or parts of the system against the requirements.

11 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

12 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 Deliverables In a heavyweight process, each process step creates a deliverable, usually documentation, e.g., a requirements specification. In a lightweight process, the deliverables are incremental working code, with minimal supporting documentation.

13 Sequence of Processes Major alternatives
• Sequential: As far as possible, complete each process step before beginning the next. Waterfall model. • Iterative: Go quickly through all process steps to create a rough system, then repeat them to improve the system. Iterative refinement. • Incremental: An extension of iterative refinement in which small increments of software are placed in production. Agile development.

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

15 Iterative Refinement Evaluation Requirements Design Implementation

16 Incremental Development
Each iteration involves a team working through a full software development cycle including planning, requirements analysis, design, coding, unit testing, and acceptance testing. Each increment is completed in a fixed time period, e.g., four weeks. The size of an increment is based on team size, e.g., 5-10 people. Increment 1 Increment 2 Increment 3 Accept Increment 1 Accept Increment 2 Accept Increment 3

17 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!

18 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.

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

20 Discussion of Iterative Refinement
Concept: Initial implementation for client and user evaluation, but not for release, followed by refinement until system is complete. • User interface mock-up • Throw-away software components • Dummy modules • Rapid prototyping • Successive refinement

21 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: Start-up time of launching a complex application.

22 Incremental Development: Discussion
A simple system with basic functionality is brought quickly into production. Subsequent increments are based on experience gained from users of each previous release. Advantages Pay-back on investment begins soon. Requirement are more clearly understood in developing subsequent increments – minimize waste. • User feedback can be incorporated in later phases. Challenge A high-level team must establish overall architecture and coordinate increments

23 Incremental Development of Online Systems
When software is released online it is possible to divide it into small increments that are developed and released in quick succession. 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.

24 Mixed Processes In practice, many large projects create a process that is suitable for the specific development. For example: • A system may use a sequential process with iteration within the individual process steps. This is sometimes called a spiral development process. • User interfaces have to be tested with users. This forces iterative development, even within an underlying sequential process. • A phase 1 system may be developed by iteration and used as requirements for a phase 2, which is developed sequentially.

25 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.

26 Corporate Processes Large software development organizations have their own internal processes that are designed for their needs. For example: • (Internet commerce) divides most software development into phases of about four weeks elapsed time. • Lockheed Martin (government contactor) follows a process that fits with the way that the US government manages software contracts. • SAP (business software) emphasizes the functionality that is seen by their business customers. • Microsoft (PC software) places great emphasis on testing with a very wide variety of equipment and backward compatibility.

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. • If the market for the software is poorly understood, use an incremental process that gets operational software in front of customers as quickly as possible.

28 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 • Frequent releases, dividing large projects into phases • Early and repeated testing with users and customers. • Following a visible software process • Making use of reusable components

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

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

31 CS 5150 Project Presentations: Incremental Development
First release Second release Third release first presentation second presentation third presentation

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