Software Processes Lecture 3

The Software Process

• Structured set of activities required for software system development.
• Key activities include:
  • Specification: Defining system requirements.
  • Design and Implementation: Organizing and creating the system.
  • Validation: Ensuring the system meets customer expectations.
  • Evolution: Adapting the system to changing customer needs.
• Software process models provide an abstract representation of these processes from various perspectives.

Software Process Descriptions

• Descriptions typically focus on activities like data modeling and user interface design along with their sequence.
• Elements included in process descriptions:
  • Products: Outcomes of activities.
  • Roles: Responsibilities of individuals involved.
  • Pre- and post-conditions: True statements before and after activities.

Plan-Driven and Agile Processes

• Plan-driven Processes: All activities are pre-planned, measuring progress against the plan.
• Agile Processes: Planning is iterative and adaptable, accommodating changing requirements.
• Most practical processes blend both approaches; no universally right or wrong processes exist.

Software Process Models

• Waterfall Model:
  • Plan-driven with distinct phases for specification and development.
• Incremental Development:
  • Interleaved phases of specification, development, and validation, adaptable to changes.
• Integration and Configuration:
  • Systems assembled from existing configurable components, can be plan-driven or agile.
• Most large systems use a combination of these models.

Waterfall Model Phases

• Phases include:
  • Requirements analysis and definition
  • System and software design
  • Implementation and unit testing
  • Integration and system testing
  • Operation and maintenance
• Main disadvantage is resistance to change once a phase is completed.

Waterfall Model Problems

• Inflexible stage partitioning complicates responses to customer requirement changes.
• Best for projects with well-understood and stable requirements.
• Commonly applied in large systems engineering projects with multiple sites due to its organized nature.

Incremental Development Benefits

• Reduced costs for adapting to changing customer requirements.
• Less re-analysis and documentation compared to waterfall model.
• Enhanced customer feedback opportunities through demonstrations.
• Faster delivery and deployment of actionable software benefits customers earlier.

Incremental Development Problems

• Lack of visibility in the process; challenges in measuring progress without regular deliverables.
• System structure may degrade with frequent increments without proper refactoring.
• Costs to incorporate further changes may rise as system complexity increases.

Integration and Configuration

• Based on reusing existing components or COTS (Commercial-off-the-shelf) systems.
• Configurable components adapt behavior to user requirements.
• Reuse is a standard approach for building business systems.

Types of Reusable Software

• Stand-alone application systems (COTS) for specific environments.
• Collections of objects developed as packages for integration with frameworks like .NET.
• Web services developed to standards for remote invocation.

Reuse-Oriented Software Engineering

• Key stages include:
  • Requirements specification
  • Software discovery and evaluation
  • Requirements refinement
  • Application system configuration
  • Component adaptation and integration

Advantages and Disadvantages of Reuse

• Advantages include reduced costs and risks from less new software development.
• Faster system delivery and deployment.
• Inevitably leads to requirement compromises; systems may not fully meet user needs.
• Potential loss of control over lifecycle of reused components.

Process Activities

• Real software processes are interleaved sequences of technical, collaborative, and managerial actions aimed at specifying, designing, implementing, and testing a system.
• Basic activities: specification, development, validation, evolution, organized differently based on the development approach (sequential in waterfall, interleaved in incremental).