SYSC 3100 - System Analysis and Design Basic Concepts Software lifecycles and Requirement Engineering

Questions How do you build things? How do you think software is built today? Are they the same?

Objectives Describe the software life-cycle Explain the development styles for a small selection of development models. Waterfall V Incremental.

Life cycle A structured set of activities required to develop a software system Specification; Design; Validation; Evolution. A software life cycle is an abstract representation of a development process. It presents a description of a process from some particular perspective.

Software Life Cycles A software life cycle has a number of: Distinct activities: “requirements”, “analysis”, “design”, “implementation”, “testing”, “operation” Products: requirements, analysis, design and testing documents, user manual, … Rules for completing a phase and transitioning to the next phase

Software Life Cycles Well-known models for a software life cycle: The Waterfall model The V model Incremental software development The Rational model (Rational Unified Process)

The waterfall model Requirements definition System and Software Design System’s services, constraints and goals System and Software Design System architecture, software system functions Implementation and Unit Testing Set of programs or program units Integration and System Testing Units and programs are integrated and tested The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase. Operation and Maintenance

Waterfall Model Problems Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process. Few business systems have stable requirements. The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.

Unit and Integration Testing The V model Requirements Acceptance Testing System Analysis System Testing Unit and Integration Testing System Design A variant of the Waterfall model Implementation

Incremental delivery Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality. User requirements are prioritised and the highest priority requirements are included in early increments. Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.

Incremental development

Incremental development advantages Customer value can be delivered with each increment so system functionality is available earlier. Early increments act as a prototype to help elicit requirements for later increments. Lower risk of overall project failure. The highest priority system services tend to receive the most testing.

(Rational) Unified Software Development Process A modern process model derived from the work on the UML and associated process. Inception is concerned with determining the scope and purpose of the project establishes the business case for the system Elaboration focuses requirements capture and determining the structure/architecture of the system develops an understanding of the problem domain Construction: System design, programming and testing Transition: product installation and rollout

1 2 3 4 5 6 7 8 9 10 Size of square relative to time spent on workflow Inception Elaboration Construction Transition Project Phases 1 2 3 4 5 6 7 8 9 10 Iterations within each phase Requirements Analysis Design Implementation Test Workflows