Title: Overview - Software Lifecycles, Processes, Methods and Tools
1Overview - Software Lifecycles, Processes,
Methods and Tools
- Software lifecycle basics
- Software lifecycles
- build-and-fix
- waterfall
- rapid prototype
- incremental
- spiral
- Process improvement
- CMM ISO9000
- Methods and Tools
2Software Lifecycle
- A series of steps through which a software
product progresses - Lifetimes vary from days to months to years
- Consists of
- people!
- overall process
- intermediate products
- stages of the process
3Software Production Personnel
- Client
- individual or organization that wants a product
to be developed - Developer(s)
- (members of) an organization producing the
product - User(s)
- person who authorizes the client to contract the
developer - person(s) who will utilize software in operation
- internal software development client developer
- contract software development client ? developer
4What is a process?
- Device for producing a product (getting the job
done!) - Level of indirection
- Process description describes wide class of
instances - Humans create process descriptions to solve
classes of problems - Thus
- software processes are devices for creating and
evolving software products
5Intermediate Software Products
- Objectives
- Demarcate end of phases
- Enable effective reviews
- Specify requirements for next phase
- Form
- Rigorous
- Machine processible (highly desirable)
- Content
- Specifications, Tests, Documentation
6Phases of a Software Lifecycle
- Standard Phases
- Requirements Analysis Specification
- Design
- Implementation and Integration
- Operation and Maintenance
- Change in Requirements
- Testing throughout!
- Phases promotes manageability and provides
organization
7Requirements Analysis and Specification
- Problem Definition gt Requirements Specification
- determine exactly what client (and user) wants
and process constraints - develop a contract with client
- what task the product is to do
- Difficulties
- client asks for wrong product
- client is computer/software illiterate
- specifications may be ambiguous, inconsistent,
incomplete - Validation
- extensive specification reviews to check that
requirements satisfies client needs - look for ambiguity, consistency, incompleteness
- check for feasibility, testability
- develop system/acceptance test plan
8Design
- Requirements Specification gt Design
- develop architectural design (system structure)
decompose software into modules with module
interfaces - develop detailed design (module specifications)
select algorithms and data structures - maintain record of design decisions and
traeability - how the product is to do its task
- Difficulties
- miscommunication between module designers
- design may be inconsistent, incomplete,
ambiguous - Verification
- extensive design reviews (inspections with
checklists) to determine that design conforms to
requirements - check module interactions
- develop integration test plan
9Implementation and Integration
- Design gt Implementation
- implement modules and verify they meet their
specifications - combine modules according to architectural design
- how the product does its task
- Difficulties
- module interaction errors
- order of integration has a critical influence on
product quality and productivity - Verification and Testing
- extensive code reviews (inspections with
checklists) to determine that implementation
conforms to requirements and design - develop and test on unit/module test plan focus
on individual module functionality - test on integration test plan focus on module
interfaces - test on system test plan focus on requirements
and determine whether product as a whole
functions correctly
10Operation and Maintenance
- Operation gt Change
- maintain software after (and during) user
operation - integral part of process
- determine whether product as a whole still
functions correctly - Difficulties
- design not extensible
- lack of up-to-date documentation
- personnel turnover
- Verification and Testing
- extensive review to determine that change is
made correctly and all documentation updated - test to determine that change is correctly
implemented - test to determine that no inadvertent changes
were made to compromise system functionality
(check that no affected software has regressed)
11Build-and-Fix
Build First Version
Modify until Client is satisfied
Operations Mode
Retirement
12Waterfall (collapsed) - See Schach, pg. 66
Req. Change
Operations
Retirement
13Rapid Prototyping - See Schach, pg. 71
Req. Change
Operations
Retirement
14Incremental - See Schach, pg. 73
For each build Perform detailed design,
implement. Test. Deliver.
Operations
Retirement
15The Spiral Model Boehm,1988
16(Extremely) Simplified Spiral Model
Risk Assessment
Req. Change
Risk Assessment
Risk Assessment
Add a Risk Analysis step to each phase!
Operations
Retirement
17Capability Maturity Model (CMM) Watts
Humphrey,1989
- CMM is not a software lifecycle model ...
- but a strategy for improving the software process
regardless of the process model followed - Basic premise the use of new software methods
alone will not improve productivity and quality,
because software management is, in part, the
cause of problems - CMM assists organizations in providing the
infrastructure required for achieving a
disciplined and mature process - Includes
- technical aspects of software production
- managerial aspects of software production
18Capability Maturity Model (continued)
- Five maturity levels
- 1. initial ad hoc process
- 2. repeatable process basic project management
- 3. defined process process modeling and
definition - 4. managed process process measurement
- 5. optimizing process process control and
dynamic improvement - to move from one stage to the next, the SEI
provides a series of questionnaires and conducts
process assessments that highlight current
shortcomings
19ISO 9000
- Further attempt to improve software quality based
on International Standards Organization (ISO) - ISO 9000 series of five related standards
- within ISO 9000 standard series ISO 9000-3
focuses on software and software development - Basic features
- stress on documenting the process in both words
and pictures - requires management commitment to quality
- requires intensive training of workers
- emphasizes measurement
- Adopted by over 60 countries (USA, Japan,
European Union, ...) - To be ISO 9000 compliant, a companys process
must be certified
20Software Methods and Tools
- Methods provide a means or procedure for
accomplishing a task - Tools are devices for performing some task
- analytical tools
- software tools
- Methodology guides the proper use of methods and
tools - Process helps to enact a methodology
- Environments are a synergistic collection of
tools with process support
21Analytical Tools
- Problem solving techniques that help in software
development - cost-benefit analysis
- compare expected benefits against estimated costs
- stepwise refinement
- divide and conquer
- abstraction
- focus on some important property and ignore (for
the time being) irrelevant details - Analytical tools underlie many software
development methods
22Software Tools
- Software tools are an automated implement for
performing a task - Tools facilitate work because they are
- fast, immune to boredom and "cheating"
- Actual Software Tools are ...
- powerful, effective, convenient, natural,
reliable, robust - Most software development tools are not
- exceptions compilers, editors, loaders
- these have been polished, refined, and debugged
through long-term use and hence made reliable and
robust - these have been made natural and effective
through extended exposure and maintenance
23 Tool Obstacles
- Tool use obstacles
- developers tend to be like hammer and screwdriver
carpenters - tools are not powerful and/or effective
- tools are unreliable and/or unrobust
- comes with time and money
- tools are inconvenient and/or unnatural
- comes from successful use
- Tool building obstacles
- Short history of large-scale software development
- Limited success in
- developing software well
- exploiting tools successfully
- Few software techniques have had time and use
required to achieve tool status - No tools at all in some key areas (e.g.,
real-time analysis)
24Requirements Preview
- Requirements determine the What of a software
products functionality. - Requirements analysis and specification
transforms - informal product definition
- into
- formal requirements specification
- A step in between is transforming the product
definition into a natural language statement of
the systems functionality