CS 5150 Software Engineering Lecture 2 Software Processes

Administration Project teams • Any announcement to class? • People who would like to form teams?

Administration Project teams When you have formed your team and reached agreement with your client, please send a message to cs5150-l@lists.cs.cornell.edu with the names of the team, the client's name, and the topic of the project. Letter "l"

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

Project Suggestion: iPhone Applications from CIT Registrar's services using iPhone Ron DiNapoli, Cornell Information Technologies

Project Suggestion: Paperless World Eliminate paper from credit card transactions Keith Cowing, Johnson School, Cornell University

Project Concept: Student Disability Services (SDS) Booking system for CULift service Michele D. Fish, Student Disability Services Center for Learning & Teaching

Project Suggestion: Online Surveys Online surveys for social science research Y. Connie Yuan, Assistant Professor, Department of Communication

Project Suggestion: Tickets for Military Non-profit organization to connect military members with people who have tickets to sporting events that they cannot attend Michael Merrell, Johnson School, Cornell University

Project Suggestion: Tracking system for HR A tracking and work flow system to handle the process of recruiting Brian Martinson, Director of Human Resources, Faculty of Computer and Information Science

Project Suggestion: Chinese Students Studying Overseas Robin W. Si, School of Hotel Administration, Cornell University Support for Chinese students who wish to study in the United States or other foreign countries

Project Concept: Cornell Cooperative Extension Cornell Collaborative Web Publishing Project Raj Smith, Department of Natural Resources and Cooperative Extension

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

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

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

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

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.

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 then defined in a manner that is understandable by both the client and the development staff.

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

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 individual program units are integrated and tested against the design by the development staff as a complete system.

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

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

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 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.

Iterative Processes: Requirements and Risk Mistakes in the requirements are the most expensive to correct. -> Integration of browser into operational system Requirements are hard to understand until there is an operational system • Especially with user interfaces Iterative software processes Create an outline system quickly, review it with clients, test it with users, improve the understanding of the requirements • Rapid prototypes • Throw away code

Iterative Development: Iterative Refinement (Evolutionary Development) Concept: Initial implementation for client and user comment, followed by refinement until system is complete. • Vaporware: user interface mock-up • Throw-away software components • Dummy modules • Rapid prototyping • Successive refinement Get something to evaluate as quickly as possible!

Iterative Refinement Evaluation Requirements Design Implementation

Iterative Refinement Evaluation Concurrent may be Activities continuous Concurrent Activities Initial Version Requirements Outline Description Intermediate Versions Design Implementation Final Version

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

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, that often requires the earlier stages to be revised. The Waterfall Model is not enough!

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.

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

Mixed Processes: Phased Development Combine sequential and iterative elements 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

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

Example: 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 detailed set of requirements. Write new compiler and run-time system incorporating graphics elements. Make minor adjustments to requirements as needed.

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.

CS 501 Project Presentations: Iterative Option Evaluation Requirements first presentation second presentation third presentation Implementation Design

CS 501 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