Process Models

Dr. Noman Islam

Software Development as Social Learning

Software Process: Definition and Importance

• Definition and Purpose of Software Process
• A software process is a series of predictable steps that helps create a timely, high-quality result.
• It provides stability, control, and organization to the software development activity.
• Importance of Agile Software Engineering
• A modern software engineering approach must be agile and demand only necessary activities and controls.
• The quality, timeliness, and long-term viability of the product are the best indicators of the efficacy of the process.

Defining a Software Process

Generic Process Model and Process Flow

• Generic Process Framework
• The generic process framework defines five framework activities: communication, planning, modeling, construction, and deployment.
• Additional umbrella activities include project tracking and control, risk management, quality assurance, and configuration management.
• Process Flow and Execution
• Process flow describes how framework activities and actions are organized with respect to sequence and time.
• Types of process flow include linear, iterative, evolutionary, and parallel execution.

Defining a Framework Activity

Components of a Framework Activity

Process Models Overview

• Types of Process Models
• Linear process flow: A straightforward, sequential approach with no branching or iteration.
• Parallel process flow: Multiple tasks executed simultaneously to improve efficiency.
• Evolutionary Process Models
• Iterative process flow: A cyclical approach with continuous improvement and refinement.
• Incremental process flow: Releasing small, working increments of the project regularly.

Project Communication and Planning

• Communication in Small Projects
• Simple projects may require minimal communication, such as a phone call with the stakeholder.
• Key communication tasks include discussing requirements and taking notes.
• Framework Activity Adaptation
• The nature of the project affects the framework activity, requiring adjustments to process models.
• As project complexity increases, communication and planning become more critical.

Organizing Project Requirements

Choosing a Task Set for Requirements Gathering

What is a Process Pattern?

Process Pattern Template

Pattern Initiation and Context

• Initial Context and Conditions
• Prior to pattern initiation, organizational activities, entry state, and existing software engineering information or project information must be established.
• Examples include: collaborative communication, successful task patterns, and known project scope and business requirements.
• Pattern Requirements and Constraints
• The specific problem to be solved by the pattern must be clearly defined.
• Software engineering information or project information that is available before pattern initiation must be transformed as a consequence of successful pattern execution.

Pattern Implementation and Outcome

• Pattern Implementation and Transformation
• The pattern describes how to implement the solution successfully, modifying the initial state of the process and transforming existing software engineering information or project information.
• Examples include: software project planning, communication, and deployment activities.
• Pattern Outcome and Resulting Context
• Upon pattern completion, organizational activities, exit state, and developed software engineering information or project information must be established.
• Examples include: successful project completion, known project scope and business requirements, and transformed software engineering information or project information.

Process Assessment and Improvement

• Importance of Process Assessment
• Ensures the software process meets basic criteria for success, including timeliness, customer needs, and long-term quality characteristics.
• Requires solid software engineering practice, such as those outlined in Part 2 of this book.
• Approaches to Software Process Assessment
• Standard CMMI Assessment Method for Process Improvement (SCAMPI) - a five-step process assessment model with five phases: initiating, diagnosing, establishing, acting, and learning.
• SEI's CMMI - describes the characteristics of a software process and the criteria for a successful process in detail.

Formal Techniques for Assessing Software Process

• Understanding Current State and Improving Process
• Assessment attempts to understand the current state of the software process with the intent of improving it.
• Formal techniques, such as prototyping, are available for assessing the software process.

CMM-Based Appraisal for Internal Process Improvement

• CMM-Based Appraisal for Software Organizations
• Provides a diagnostic technique for assessing the relative maturity of a software organization.
• Uses the SEI CMM as the basis for the assessment [Dun01].
• Other Software Process Assessment Standards
• SPICE (ISO/IEC15504) defines a set of requirements for software process assessment.
• ISO 9001:2000 for Software applies to any organization that wants to improve the overall quality of its products, systems, or services [Ant06].

Prescriptive Process Models in Software Engineering

• The Edge of Chaos in Software Development
• Prescriptive process models strive for structure and order, but may be inappropriate for a software world that thrives on change.
• The edge of chaos is a natural state between order and chaos, where structure and surprise coexist [Kau95].
• Philosophical Implications for Software Engineering
• Too much chaos can make coordination and coherence impossible, while too much order can lead to a lack of creativity and self-organization [Roo96].
• Software organizations have exhibited significant shortcomings in capitalizing on experiences gained from completed projects [NASA].

Software Process Models Overview

• Prescriptive Process Models
• Define a set of process elements, such as framework activities, software engineering actions, and tasks, to ensure project consistency.
• Prescribe a predictable process work flow, including quality assurance and change control mechanisms.
• Limitations of Prescriptive Models
• May not accommodate changing project requirements or uncertain project scope.
• Can be inflexible and difficult to adapt to new or unexpected situations.

Waterfall Model and V-Model

• Waterfall Model
• A systematic, sequential approach to software development that begins with customer specification of requirements and progresses through planning, modeling, construction, and deployment.
• Suitable for projects with well-defined and stable requirements, such as adaptations or enhancements to existing systems.

V-Model Overview and Application

• Refining Problem Requirements
• Basic problem requirements are progressively refined into detailed and technical representations as the team moves down the left side of the V.
• This process involves modeling and communication activities to ensure a clear understanding of the problem and its solution.
• Quality Assurance Actions
• The team performs a series of tests (quality assurance actions) to validate each model created as they move down the left side of the V.
• These actions are essentially verification and validation actions applied to earlier engineering work.

Waterfall Model Limitations and Criticisms

• Sequential Flow and Iteration Challenges
• Real projects rarely follow the sequential flow proposed by the waterfall model.
• The model can accommodate iteration, but it does so indirectly, leading to potential confusion and difficulties in making changes.

Challenges with Waterfall Model

• Difficulty in Stating Requirements Explicitly
• The waterfall model requires explicit requirements, which can be challenging for customers to provide, especially at the beginning of a project.
• This can lead to 'blocking states' where team members must wait for others to complete dependent tasks, resulting in wasted time.
• Linear Nature of Waterfall Model
• The waterfall model follows a linear sequential process, which can be inappropriate for fast-paced and changing software work.
• This can lead to delays and difficulties in accommodating changes and updates to the software.

Incremental Process Models

Incremental Development Process

Evolutionary Process Models

• Characteristics of Evolutionary Process Models
• Evolutionary process models produce an increasingly more complete version of the software with each iteration, reflecting changing business and product requirements.
• These models are particularly useful in situations where tight market deadlines make completion of a comprehensive software product impossible.

Evolutionary Process Models

• Characteristics of Evolutionary Models
• Iterative development of increasingly more complete versions of the software
• Accommodate a product that evolves over time
• Examples of Evolutionary Process Models
• Prototyping
• Other process models (not specified in the text)

The Prototyping Paradigm

• Key Steps in the Prototyping Paradigm
• Communication: Define overall objectives and identify known requirements
• Quick plan and construction of a prototype, followed by modeling and a quick design
• Benefits of Prototyping
• Assists stakeholders to better understand what is to be built when requirements are fuzzy
• Quote: "Plan to throw one away. You will do that, anyway." - Frederick P. Brooks

Prototyping in Software Engineering

• Prototype Construction and Deployment
• A quick design leads to the construction of a prototype, which is deployed and evaluated by stakeholders.
• Feedback from stakeholders is used to refine requirements and iterate the prototype to satisfy their needs.
• Prototype Evaluation and Refining Requirements
• The prototype serves as a mechanism for identifying software requirements, and its working version provides a feel for the actual system.
• Stakeholders and software engineers can collaborate to build something immediately, but it's essential to define the rules of the game at the beginning.

Challenges and Best Practices in Prototyping

• Common Challenges in Prototyping
• Stakeholders may demand that a prototype be made into a production product, compromising quality.
• Software engineers may make implementation compromises to get a prototype working quickly, leading to less-than-ideal choices becoming an integral part of the system.

The Spiral Model Overview

Spiral Model Key Characteristics

Spiral Model Overview

Adaptability and Iterations in Spiral Model

• Adaptability Throughout Software Life Cycle
• The spiral model can be adapted to apply throughout the entire life cycle of an application, from concept development to maintenance.
• This allows for continuous improvement and adjustments to the project plan based on customer feedback.

Spiral Model- Characteristics and Advantages

Challenges and Limitations

• Potential Drawbacks of the Spiral Model
• May be difficult to convince customers of controllable evolutionary approach
• Requires considerable risk assessment expertise

Concurrent Development Model Overview

Concurrent Process Model Representation

• Modeling Activity States
• The modeling activity may be in one of the following states: Under review, Baselined, Under revision, Awaiting changes, Under development, Inactive, or Done.
• Each state represents an externally observable mode of behavior.

Concurrent Modeling Overview

• Transition of Software Engineering Activities
• The modeling activity transitions from inactive to under development state upon completion of communication activity.
• Customer requirements changes trigger transitions among states.
• Process Network Definition
• Concurrent modeling defines a process network where each activity exists simultaneously.
• Events generated at one point trigger transitions among states.

Evolutionary Process Models Limitations

Prioritizing Speed over High Quality

Specialized Process Models

• Component-Based Development
• Incorporates characteristics of the spiral model, with iterative approach to software creation.
• Constructs applications from prepackaged software components with well-defined interfaces.

Component-Based Development Model

• Research and Evaluate Components
• Available component-based products are researched and evaluated for the application domain in question.
• Consideration of component integration issues is also a crucial step in this process.
• Benefits of Component Reuse
• Software reuse leads to a reduction in development cycle time and project cost.
• Component reuse becomes a key part of a software engineering culture.

Formal Methods Model and Its Challenges

Aspect-Oriented Software Development Overview

• Localized Software Characteristics and Components
• Localized software characteristics are modeled as components (e.g., object-oriented classes) and constructed within the context of a system architecture.
• Components may provide or require one or more aspect details relating to a particular aspect, such as user interface, distribution, persistency, security, and transaction aspects.
• Crosscutting Concerns and Aspectual Requirements
• Crosscutting concerns are concerns that cut across multiple system functions, features, and information, often referred to as crosscutting concerns.
• Aspectual requirements define those crosscutting concerns that have an impact across the software architecture.

Aspect-Oriented Software Development Process

• Aspect-Oriented Process Characteristics
• The evolutionary model is appropriate as aspects are identified and then constructed.
• The parallel nature of concurrent development is essential because aspects are engineered independently of localized software components.

Asynchronous Communication in Software Process

• Aspect-Oriented Software Development
• Applies to engineering and construction of aspects and components.
• Importance of Asynchronous Communication

Process Models for Software Development

• Process Management
• Objective: Define, execute, and manage prescriptive process models.
• Tools provide a road map and template for software engineers and managers.
• Unified Process
• Use case driven, architecture-centric, iterative, and incremental software process.
• Draws on best features of traditional software process models and agile development principles.

Unified Process Key Features

Unified Process Phases and History

Inception Phase Overview

Elaboration Phase Activities

• Communication and Modeling
• Refine and expand preliminary use cases to include five different views of the software: use case, requirements, design, implementation, and deployment models.
• Create an executable architectural baseline, representing a first cut of the system, to demonstrate architecture viability.
• Plan Review and Modification
• Carefully review the plan to ensure scope, risks, and delivery dates remain reasonable.
• Make necessary modifications to the plan at the culmination of the elaboration phase.

Unified Process Construction Phase

Unified Process Transition and Production Phases

• Transition Phase: Software Deployment and Feedback
• Software is given to end users for beta testing and user feedback reports defects and necessary changes.
• Support information (e.g., user manuals, troubleshooting guides) is created for the release.
• Production Phase: Ongoing Software Support
• Ongoing use of the software is monitored, and support for the operating environment is provided.
• Defect reports and requests for changes are submitted and evaluated.

Personal Software Process (PSP) Overview

PSP Framework Activities and Postmortem

Personal Software Process (PSP) Overview

• Identify Errors Early and Understand Error Types
• PSP emphasizes the need to record and analyze the types of errors you make, so that you can develop strategies to eliminate them.
• This is accomplished through a rigorous assessment activity performed on all work products you produce.
• Benefits of PSP Adoption
• PSP leads to significant improvement in software engineering productivity and software quality.
• However, PSP adoption is hindered by human nature and organizational inertia.

Team Software Process (TSP) and Self-Directed Teams

TSP Framework Activities

Adapting Process Models with Process Technology

The Software Process: Understanding and Modeling

Product and Process Duality

• The Pendulum Swing Between Product and Process
• The software community constantly shifts focus between product and process issues, causing confusion and failure to solve the problem.
• This dichotomy is harmful and does not recognize the dual nature of product and process.

Duality of Product and Process

• Viewing Artifacts as Both Product and Process
• Derives a sense of self-worth from activities resulting in reusable representations or instances.
• Increases satisfaction from reuse of products by oneself or others.
• Consequences of One-Sided View
• Reduces opportunities for reuse and job satisfaction.
• Obscures context and ways to use artifacts.

Software Engineering Process Models

• Generic Process Model for Software Engineering
• Encompasses framework and umbrella activities, actions, and work tasks.
• Can be described by different process flows and patterns.
• Prescriptive Process Models and Sequential Paradigms
• Suggest different process flows, but perform the same generic framework activities.
• Have applicability in situations with well-defined and stable requirements.

Incremental Process Models Overview

Software Process Models and Activities