Software Processes - Software Engineering - Lecture Notes, Study notes of Software Engineering

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SE Fundamentals:

1. Software Processes

Topics covered  Basic software process models (1, 2, 3)  Process activities  Coping with change & additional software process models (4, 5)  The Rational Unified Process (6)

Software process descriptions  When we describe and discuss processes, we usually talk about the activities in these processes such as specifying a data model, designing a user interface, etc. and the ordering of these activities.  Process descriptions may also include:  Products, which are the outcomes of a process activity;  Roles, which reflect the responsibilities of the people involved in the process;  Pre- and post-conditions, which are statements that are true before and after a process activity has been enacted or a product produced.

Plan-driven and agile processes  Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan.  In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements.  In practice, most practical processes include elements of both plan-driven and agile approaches.  There are no right or wrong software processes.

1 The waterfall model

Waterfall model phases  There are separate identified phases in the waterfall model:  Requirements analysis and definition  System and software design  Implementation and unit testing  Integration and system testing  Operation and maintenance  The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. In principle, a phase has to be complete before moving onto the next phase.

2 Incremental (exploratory) development

Incremental development benefits  The cost of accommodating changing customer requirements is reduced.  The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model.  It is easier to get customer feedback on the development work that has been done.  Customers can comment on demonstrations of the software and see how much has been implemented.  More rapid delivery and deployment of useful software to the customer is possible.  Customers are able to use and gain value from the software earlier than is possible with a waterfall process.

3 Reuse-oriented software engineering  Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems.  Process stages  Component analysis;  Requirements modification;  System design with reuse;  Development and integration.  Reuse is now the standard approach for building many types of business system  Reuse covered in more depth in Chapter 16.

Reuse-oriented software engineering

Software specification  The process of establishing what services are required and the constraints on the system’s operation and development.  Requirements engineering process  Feasibility study

• Is it technically and financially feasible to build the system?  Requirements elicitation and analysis
• What do the system stakeholders require or expect from the system?  Requirements specification
• Defining the requirements in detail  Requirements validation
• Checking the validity of the requirements

The requirements engineering process

A general model of the design process

Design activities  Architectural design, where you identify the overall structure of the system, the principal components (sometimes called sub-systems or modules), their relationships and how they are distributed.  Interface design, where you define the interfaces between system components.  Component design, where you take each system component and design how it will operate.  Database design, where you design the system data structures and how these are to be represented in a database.