View
218
Download
0
Category
Tags:
Preview:
Citation preview
Systems Development Process set of activities, methods, best practices and deliverables that are used to develop and maintain information systems.
Process maturityas the development process matures, project costs decrease, timelines improve, productivity and quality increase.
Software development - The Process
Guiding principles
• Get the Owners and Users Involved
• Establish Phases and Activities
• Establish Standards for Development and Documentation
• Justify systems as Capital Investments
• Don’t be afraid to Cancel or Revise Scope
• Divide and Conquer
• Design for Growth and Change
Software development - The Process
3 Generic Phases• Definition (What)
– Customer contact
• role of system, scope
– Project Planning
• risk analysis, resources, cost estimation, schedules
– Requirement Analysis
• Development (How)– Design
– Coding
– Testing
• Maintenance– Correction of errors
– Adaptation
– Enhancements
• Preliminary Investigation Phase – establishes the project context, scope, budget, staffing, and schedule.
• Problem Analysis Phase – identifies and analyzes both the business and technical problem
domains for specific problems, causes, and effects• Requirements Analysis Phase
– identifies and analyzes business requirements that should apply to any possible technical solution to the problems.
• Decision Analysis Phase – identifies and analyzes candidate technical solutions that might solve
the problem and fulfill the business requirements. The result is a feasible, target solution.
Alternatively…
Alternatively (2)…• Purchasing Phase (optional)
– identifies and analyzes hardware and software products that will be purchased as part of the target solution.
• Design Phase – specifies the technical requirements for the target solution.
Today, the design phase typically has significant overlap with the construction phase.
• Construction Phase – builds and tests the actual solution (or interim prototypes of the
solution).
• Implementation Phase – puts the solution into daily production.
• Operation and Support Phase
– continues until the system is obsolete.
• Preliminary Investigation– “Is this project worth looking at?”– Define the scope of the project, the perceived problems,
opportunities, and directives that triggered the project. – Establish the project team and participants, the project budget,
and the project schedule.
• Problem Analysis– Gain an appropriate understanding of the business
problem domain– Determine if the system is worth developing– Learning the system terminology, history, culture, and
nuances of the organization (or department). – Address the causes and effects of the problems,
opportunities, and directives.
• Requirements Analysis– Identify the data, process, interface, and geographic
requirements for the users of a new system. – Specify these requirements without expressing
computer alternatives and technology details; at this point, keep analysis at the business level.
– Prioritize - requirements can be classified as ‘mandatory’, ‘desirable’, or ‘optional’.
• Decision Analysis– Define the candidate solutions– Evaluate each candidate for feasibility (next slide).– Recommend a feasible candidate as the target
system. – Feasibility analysis
• Purchasing– research the technology and marketplace– organize the business, technology, and relationship
requirements, and establishes the mechanisms that will be used to evaluate the technical alternatives.
– write the RFP. – receive proposals from vendors.– evaluate proposals.– make a recommendation to the system owners (and
usually the information system managers as well).– execute the final orders, contracts, licenses, and
service agreements.
• Design– transform the business requirements from the definition
phase into a set of technical design blueprints for construction.
– addresses how specific technologies will be used in the new system.
– design specs can include written documentation or prototypes
– existing systems must be integrated in the design.
• Construction– build and test a functional system that fulfills business and
design requirements
– implement the interfaces between the new system and existing systems
– system testing – unit and system testing
• Implementation– Install, deploy, and place the new system into
operation or production. – User training, manuals, loading files and databases
• Operations and System Support– ongoing maintenance of a system after it has been placed
into operation. This includes program maintenance and system improvements.
Systems Analysis– Organizational context and requirements (Enterprise Modeling)– Functional area context and requirements (Workflow diagrams)
– Analyze existing System• Physical analysis• Logical analysis
– New System requirement• Logical model of new system (Requirement specification)
( Functional requirements - DFDs)
– Documentation • Requirement specification Document
•
SystemEnvironment
System design– General design
• Logical design of alternatives (broad sketches)
• Evaluate and choose a solution approach
– Detailed design (Physical design)• Process design - program specification
(Program structure charts)
• Data design - logical structure of data and files (E/R Models)
• User interface design - Dialog and document flows
– Design Document
System Implementation
– Coding– Testing– Installation– Manuals, User training
Cross Life Cycle Activities
• Project Management– Schedules and cost, milestones
• Software Quality Assurance– creation of Standards– ensure conformation to those standards
• formal technical views
• documentation of errors
• testing strategy
Cross Life Cycle Activities
• Measurement– Time, Effort, Costs, Productivity, Quality
(Software Metrics)– enhanced estimates of new projects– baseline for process improvement– test effectiveness of new methods
Cross Life Cycle Activities
• Software Configuration Management– Controlled change
• customers change requirements• developers change technical approach• management modifies project approach
– Software configuration• Programs• Documents• Data structures
• Documentation• Fact Finding
• Effort Distribution
Development : Maintenance
40:60, 30:70
• Development Costs (Typical)Requirement : 10%
Design : 20%
Coding : 20%
Testing : 50% (often under-estimated. Can be reduced through better design and coding)
[Note: easy to test easy to maintain]
Software Engg. Paradigms ( Process models)
• Waterfall model (Classical life Cycle)
Planning
Reqt.Analysis
Design
Code
Test
Install
Maintenance
Feasibility Report
Requirements Specification Report
Design Document
Programs
Test Report
Installation Report
Waterfall Model
• old way of doing things• All projects go through these phases
But…• Sequential progress unrealistic, iterations expensive• Frozen requirements
• difficult to state all requirements at the beginning• requirements drift
• gap between users and designers, little communication with users
• working system unavailable till late in the project– also disastrous for errors at this stage
Reqt.Generationand refinement
Quick Design
Customer Evaluation of prototype
Refine Prototype Engineer Product
BuildPrototype
Software Engineering paradigms• Prototyping - a modeling paradigm
• Discard prototype
• Engineer prototype to production system
Prototyping: Problems• Customer impatient when prototype is rebuilt to production
system– Inefficient system often becomes the production system system
• (NOTE: Ideally prototyping is the mechanism for identifying requirements)– high risk innovation applications– promote send user participation– good candidates for prototyping:– user unable to specify requirements.– Do not know what they want/what they want is not what they
need– “I do not know what I want , but I will when I see it”
Software Engineering paradigms
• The RAD model (Rapid Application Development)
– linear sequential development,emphasizes very short development cycle
– component based construction– well-understood requirement, constrained scope– use of fourth generation techniques (4GLs)
Rapid Application Development
Business Modeling
Data Modeling
Process Modeling
ApplicationGeneration
Testing andTurnover
60 -100 days
Team 1 Team 2 Team 3
RAD
• 4GLs :– Enable developers to specify s/w characteristics at higher
level of abstraction. Tool automatically generates source code.
• Tools:– non-procedural languages for DB query,report
generation,data manipulation ,screen interaction, graphics,etc
– reduces development time for smaller applications– user and developer commitment to rapid-fire activities– inefficient code? Use where high performance is required?
– Use of reusable program components
OOD
Customerprototype
OOA
Browse libraryof reusablecomponents
CustomerEvaluation
Design/Implementation
Component Library
ComponentSpecification
ComponentDesign
Libraryentry
Coding
Testing
Software Engineering paradigms
• O-O Systems Development: reuse paradigm
O-O development
– Focus on reuse • Object Class library
– Focus on interoperability– Faster development,easier
maintenance,platform independence
Risk analysis based on initial requirements
PlanningPlanning Risk analysisRisk analysis
Customer evaluationCustomer evaluation EngineeringEngineering
Risk analysis based on customer reaction
Go, no-go decision
Toward a completedsystem
Initial software prototype
Next prototype level
Engineered system
Customerevaluation
Planning basedon customercomments
Initial requirementsgathering and projectplanning
Spiral Model
System development problems– Schedule and cost estimates often grossly inaccurate– Productivity has not kept pace with demand– Frequently poor quality systems are delivered– Existing systems are difficult to maintain
Type of Failure Reason for Failure Comment
QualityProblems
ProductivityProblems
Wrong problem addressedSystem conflicts withbusiness strategy
Wider influences are neglected Organisational culturemay be ignored
Analysis carried out incorrectly
Project undertaken for wrongreason
Users change their mind
External events change theenvironment
Implementation is not feasible
Poor project control
Team poorly skilled orinadequately resourced
Technology pull orpolitical push
New legislation
May not be known untilproject has started
Inexperienced projectmanager
Requirements drift
Recommended