Process Modeling and Life Cycle

• Modeling the Process and Life Cycle

Meaning of a Process

• Involves a sequence of steps to accomplish tasks in the same order each time when providing services or producing a product
• Involves steps, activities, constraints, resources, and intended output
• A process involves a set of tools and techniques

Process Characteristics

• Prescribes all major process activities
• Uses resources subject to constraints like schedule, producing intermediate and final products
• Can be composed of subprocesses
• Each activity has entry and exit criteria to define its start and end
• Activities are organized sequentially
• Comes with guiding principles explaining goals of each activity
• Subject to constraints on activity, resource, or product
• Budget or schedule may limit activity time

Importance of Processes

• Imposes consistency and structure
• Guides understanding, control, examination and improvement effort
• Enables experience capture and knowledge transfer

Software Life-Cycle

• When a software is built using a process it can also be called a software life-cycle
• Encompasses development, implementation, delivery, use, and maintenance of a software product
• Software Development stages:
  • Requirement analysis and definition
  • System (architecture) design
  • Program (detailed/procedural) design
  • Writing programs (coding/implementation)
  • Unit testing
  • System testing
  • System delivery
  • Maintenance
• Each stage constitutes a process with activities described as a set
• Each activity involves constraints, output, and resources
• Requirement analysis and definition involves desired functions and features which becomes a set of requirements
• This produces budget, schedule, and standards about the notation used

Reasons for Modeling a Process

• To form a shared understanding of activities, resources, and constraints
• To identify process inconsistencies, redundancies, and omissions
• To evaluate activities for reaching process goals such as building high quality software and meeting the specified budget and schedule constraints

Software Development Process Models

• Waterfall model
• Prototyping
• V-model
• Phased development: increments and iteration
• Spiral model

Waterfall Model

• One of the first process development models
• Works well for well-understood problems with minimal requirement changes
• Each developmental stage is completed before the next one starts
• Easy to explain to customers
• Presents a high-level view and sequence of activities
• Major phases are marked by milestones
• There is a requirements analysis, system design, program design, coding, unit and integration testing, system testing, acceptance testing, operation, and maintenance
• Most software developments apply many iterations

Disadvantages of the Waterfall Model

• Doesn't guide handling changes during development
• Views software development as a manufacturing process
• Lacks iterative activities towards a final product
• Results in a long wait for the final product

Waterfall Model with Prototype

• Prototype is a partially developed product, which enables customer and developer to examine aspects of the proposed system and decide if it is suitable for the final product
• A system is built to implement a small portion of key requirements to ensure requirements are consistent, feasible and practical
• Parts of the design are prototyped to assess alternative design strategies
• Structures are evaluated to meet user requirements
• User interface prototype helps users understand

Waterfall Model with Prototype (Cont.)

• Addresses major requirements before system testing validation
• Validation ensures system implements all requirements
• Each function can be traced back to a requirement in specification
• Verification ensures function works correctly; checks implementation quality
• Shows feedback loops from each of those stages to each prior stage

V Model

• Is another variation of the waterfall model
• Analysis and design happen on the left, and testing and maintenance on the right
• Testing correlates to analysis and design activity
• Uses unit testing (coder & test team) to verify program design
• Uses integration testing (coder & test team) to verify system design
• Uses acceptance testing (customer) to validate requirements
• If issues arise, the V-Model's left side is re-executed for requirements, design, and code before re-enacting testing

Prototyping Model

• Allows constructing all or parts quickly to clarify issues
• Requires repeated requirements or design investigation by developers, users, and customers
• Includes loops for prototyping requirements, design, or the system, which will depend on the goals of prototyping
• Overall goal is to reduce risk and uncertainty

Phased Development: Increments and Iterations

• Cycle time is the time between writing the requirement documents and delivering the system
• Phased Development was introduced to reduce cycle time
• System delivered in pieces for phased functionality
• Allows two systems functioning in parallel - production release and development release
• The production release system is currently being used.
• The development release system is the next version

Incremental and Iterative Models

• Incremental development starts with small functional subsystem and adds functionality with each new release

• Iterative development starts with full system, then changes functionality with each new release

• Training begins early, even if some functions are missing

• Frequent releases mean developers can fix unanticipated problems quickly from the operational system

• A development team can focus on different expertise areas with different releases. For example one release can change the system from command-driven to a point-and-click interface

Spiral Model

• Views software development in light of risk
• Combines development activities with risk management to minimize and control risks
• Includes a budget, constraints, and alternatives for design and staffing with development
• Evaluates risks and prototype alternatives before producing a "concept of operation" document
• A "concept of operation" document specifies and scrutinizes requirements for completion
• "Concept of operation" is the product of the first iteration
• Requirements are the principal output of the second iteration
• Design forms the third iteration
• Testing forms the fourth.

Spiral Model (Cont.)

• Iteration involves risk analysis weighing requirements and constraints with prototypes for feasibility
• Project managers must decide how to minimize the risk and prototype interfaces and run tests to see which interface is preferred