Software Processes and Models

• Software processes are structured activities for developing a software system.

Software Processes

• Specification involves defining what the system should do.
• Design and implementation involves defining the organization of the system and implementing it.
• Validation means checking that the system does what the customer wants.
• Evolution means changing the system in response to changing customer needs.
• Software process model is an abstract representation of a process.
• The abstract representation presents a description of a process from some particular perspective.
• Plan-driven processes plan all process activities in advance and measure progress against that plan.
• Agile processes incrementally plan, thus making it easier to change the process to reflect changing customer requirements.
• Most practical processes include elements of both plan-driven and agile approaches.
• There are no right or wrong software processes.

Software Process Models

• The waterfall model has separate and distinct phases of specification and development along with being a plan-driven model.
• Incremental development interleaves specification, development, and validation and can be plan-driven or agile.
• Integration and configuration assembles the system from existing configurable components and can be plan-driven or agile.
• Most large systems are developed using a process that incorporates elements from all the software process models.

Waterfall model phases

• Requirements analysis and definition
• System and software design
• Implementation and unit testing
• Integration and system testing
• Operation and maintenance
• A main drawback is difficulty accommodating change after the process is underway.
• In principle, a phase needs to be complete before advancing to the next phase.
• Inflexible partitioning of a project into distinct stages makes it difficult to respond to changing customer requirements.
• The model is appropriate when the requirements are well-understood and changes will be fairly limited during the design process.
• Few business systems have stable requirements.
• The model is mostly used for large systems engineering projects where a system is developed at several sites.

Incremental Development Benefits

• The costs of accommodating changing customer requirements is reduced.
• The amount of analysis and documentation that has to be redone is much less than is required in the waterfall model.
• Gaining Customer feedback is easier on the development work that has been done.
• Customers can comment on demonstrations of the software and see how much has been implemented.
• Rapid delivery and deployment of useful software to the customer is possible.
• Customers can use and gain value from the software earlier than is possible with a waterfall process.

Incremental Development Problems

• The process is not visible.
• Managers need deliveries to measure progress.
• If systems are developed quickly, creating documents that reflect every version of the system is not cost-effective.
• System structure tends to degrade as increments are added.
• Without time and money spent on refactoring the software, regular change tends to corrupt a system's structure.
• Incorporating further software changes becomes increasingly difficult and costly.

Integration and Configuration systems

• Based on software reuse, systems are integrated from existing components or application systems sometimes called Commercial-off-the-shelf (COTS) systems.
• The reused components can be configured to adapt their behaviour and functionality to a user's requirements.
• Reuse is a standard approach for building many types of business system.
• Reduced costs and risks with less software being developed from scratch.
• Faster delivery and deployment of system
• Requirements compromises are inevitable, so the system may not meet real needs of users.
• The process can cause loss of control over evolution of reused system elements.

Process Activities

• Real software processes involve inter-leaved sequences of technical, collaborative, and managerial activities with the overall goal of implementing/testing a software system.
• The four basic process activities of specification, development, validation, and evolution are organized based on the development processes being used.
• These are organized in sequence in the waterfall model, whereas they are interleaved in incremental development

Software Specification

• This establishes required services and the constraints on the system's operation and development.

Requirements engineering process

• Requirements elicitation and analysis answers what the system stakeholders require or expect from the system.
• Requirements specification defines the requirements in detail.
• Requirements validation checks the validity of those requirements.

Software Design

• Involves designing a software structure that realises the specification.

Implementation

• Implementation translates this structure into an executable program.
• Design and implementation are closely related and may be inter-leaved.

General Model of The Design Process

• Architectural design identifies the overall structure of the system, the principal components and how they are distributed.
• Database design involves designing the system data structures and their representation in a database.
• Interface design defines interfaces between system components.
• Component selection and design means searching for reusable components otherwise design how the components will operate.

System Implementation

• Software is implemented by either developing a program or programs or by configuring an application system.
• Design and implementation are interleaved activities for most types of software systems.
• Programming is an individual activity with no standard process.
• Debugging is the activity of finding and correcting program faults.

Software Validation

• Validation is intended to show a system conforms to its specifications and meets the customer's requirements.
• The process involves review processes and system testing.
• System testing entails executing the system with test cases derived from the specification of the real data to be processed by the system.
• Testing is the most commonly used validation activity.

Stages of Testing

• Component testing individually tests the components. -May involve using functions or objects of coherent groupings of these entities.
• System testing tests the system as a whole.
• Emergent properties are important.
• Customer testing uses customer data to check if the system meets the customer's needs.

Software Evolution

• Software is flexible and can change.
• Software evolution takes place when you change existing software systems to meet new requirements.
• Software must evolve to stay useful. As requirements change through changing business circumstances, software must also evolve and change.
• There has been less differentiation between development and evolution, as fewer systems are completely new.

Coping with change in projects

• Change anticipation includes anticipating possible changes before major rework is needed. -A prototype system may be developed to show some key features of the system to customers.
• Change tolerance designs the process, so that it can accommodate changes at a relatively low cost.
• Change requires rework, so the costs of change include rework as well as implementing new functionality.
• Incremental development is required.
• Proposed changes may be implemented in increments that have not yet been developed.
• Otherwise, a single increment may have to be altered.
• Processes should include activities such as prototyping and incremental delivery to cope with change.

Coping with change in system and software

• System Prototyping approach supports change anticipation.
• System prototyping quickly develops a version of the system or part of the system to check the customer's requirements and the feasibility of design decisions.
• Incremental delivery supports both change avoidance and change tolerance.
• Incremental delivery is an evolutionary strategy, where system increments are delivered to the customer for comment and experimentation.

Explore structured activities for software development, including specification, design, validation, and evolution. Learn about plan-driven and agile processes, and software process models. There are no right or wrong software processes.