Software Processes and Models

Software Processes Overview

• Software processes include activities for creating a software system.
• Software process models are abstract representations of these processes.

Software Process Descriptions

• Software process descriptions usually detail the activities and their ordering.
• Process descriptions may include products (outcomes), roles (responsibilities), and pre- and post-conditions (statements before/after activity).

Plan-Driven vs. Agile Processes

• Plan-driven processes plan all activities in advance, measuring progress against this plan.
• Agile processes use incremental planning, allowing easier adaptation to changing customer needs.
• Most practical processes combine elements of both approaches.

Software Process Models

• Waterfall Model: A plan-driven model with separate specification and development phases.
• Incremental Development: Specification, development, and validation are interleaved and can be plan-driven or agile.
• Reuse-Oriented Software Engineering: Systems are assembled from existing components and can be plan-driven or agile.
• Large systems often incorporate elements from multiple models.

The Waterfall Model

• A plan-driven model that has separate and distinct phases of specification and development
• It is appropriate to use when the requirements are well understood

Waterfall Model Phases

• Requirements analysis and definition: System services, constraints, and goals are established through user consultation.
• System and software design: Requirements are allocated to hardware or software systems, establishing an architecture.
• Implementation and unit testing: Software design is realized as programs or units; unit testing verifies specifications.
• Integration and system testing: Program units are integrated and tested to ensure requirements are met before delivery.
• Operation and maintenance: The system is installed and used; maintenance corrects errors, improves units, and enhances services.

Waterfall Model Problems

• A key drawback is the difficulty in accommodating changes once the process has started.
• Distinct project stages make it hard to adjust to changing customer needs.
• It is most suitable when requirements are well-understood and changes are limited.
• It's commonly used where a system is developed across multiple sites due to its plan-driven nature to coordinate work.

Incremental Development

• Specification, development and validation done concurrently in an iterative fashion

Incremental Development Benefits

• The cost of accommodating changing customer requirements is reduced since analysis and documentation is less.
• Customer feedback is more easily obtained.
• There is more rapid delivery and deployment of usable software.

Incremental Development Problems

• The process is not clearly visible.
• System structure can degrade as new increments are added, especially without refactoring

Reuse-Oriented Software Engineering

• It's based on integrating existing components or application systems (COTS).
• Process stages include: component analysis, requirements modification, system design and reuse, and development and integration.
• Reused elements are configured to meet user requirements.
• It's now standard for many business systems.

Types of Reusable Software

• Stand-alone application systems (COTS) configured for specific environments.
• Collections of objects developed as packages for integration with frameworks like .NET or J2EE.
• Web services developed according to service standards for remote invocation.

Reusable Software advantages

• Reduced costs and risks from less development from scratch
• Faster delivery and deployment

Reusable Software disadvantages

• Requirements may need to be compromised, so the system may not meet real user needs
• There is a loss of control over evolution of reused system elements

Process Activities

• Real software processes are sequences of technical, collaborative, and managerial activities.
• The goal is specifying, designing, implementing and testing a software system.
• The four basic activities are: specification, development, validation, and evolution differently organized based on chosen development processes
• For example in the waterfall model, they are in sequences, versus in incremental development they are interleaved.

Software Specification

• Software specification or requirements engineering establishes required services and constraints.
• Four main activities: feasibility study, requirements analysis, requirements specification, and requirements validation.

The requirements engineering process

• Has 6 steps
• Feasibility study towards requirements validation
• Requirements, models, and document are intermediate points.

Software Design and Implementation

• It's the process for converting system specifications into an executable system
• Involves software design to create a structure that realizes the specification
• Also involves implementation which translates this structure into an executable program
• These activities are closely related and interleaved.

Design Activities

• Architectural design: Identify system structure, components, relationships, and distribution.
• Database design: Design system data structures and database representation.
• Interface design: Define interfaces between system components.
• Component selection and design: Search for reusable components; if not found, design them.

System Implementation

• Software is implemented by programming or configuring an application.
• Design and implementation are interleaved for most software systems.
• Programming is an activity with no standard processes.
• Debugging is finding and fixing program faults.

Software Validation (V & V)

• Verification and validation ensures the system meets specifications and customer requirements.
• It includes checking, review, and system testing.
• System testing involves test cases from specifications that process real data.
• Testing is the most common V & V.

Stages of Testing

• Component testing: Testing individual components independently.
• System testing: Testing the system as a whole, focusing on emergent properties.
• Customer testing: Testing with customer data to meet customer needs.

Software Evolution

• Software is flexible and must change in response to evolving business requirements.

Key Points

• Design and Implementation includes transforming requirements specification into an executable software system
• Software Validation is the process of checking the system conforms to its specifications
• Software Evolution addresses the need to change existing software to meet new requirements