Software Project Management Lecture 2 Software Development Models

Overview Introduction Technical plan Software process models Selecting process model(s) Software project management

Definitions Software Process Software Process Model (Humphrey 1990) the set of activities, methods, and practices that are used in the production and evolution of software Software Process Model one specific embodiment of a software process architecture (Humphrey 1990) Software project management

Why Modelling? To provide a common understanding To locate any inconsistencies, redundancies and omissions To reflect the development goals and provide early evaluation To assist the development team to understand any special situation Software project management

Project Analysis Methodologies Technologies Object-Oriented Development (OOD) Structured System Analysis and Design Method (SSADM) Jackson Structured Programming (JSP) Technologies application-building environments knowledge-based system tools Software project management

Project Characteristics data oriented or control oriented system? general package or application specific? a particular type of system for which specific tools have been developed? safety-critical system? nature of the hardware/software environment? Software project management

Project Risks Product uncertainty Process uncertainty Resource uncertainty Software project management

Considerations for Project Approach Control systems Information systems General applications Specialized techniques Hardware environment Safety-critical systems Imprecise requirements Software project management

Technical Plan Contents Constraints Approach Implementation Implications Software project management

Technical Plan - Constraints Character of the system to be developed Risks and uncertainties of the project User requirements concerning implementation Software project management

Technical Plan - Approach Software Project Management Technical Plan - Approach Selected methodology or process model(s) Development methods Required software tools Target hardware/software environment The technical plan is typically a mixture of models. Eg prototyping to resolve some requirements plus V-model for production. Software project management

Technical Plan - Implementation Development environment Maintenance environment Training Software project management

Technical Plan - Implications Software Project Management Technical Plan - Implications Project products and activities effect on schedule duration and overall project effort Financial report used to produce costings Software project management

Software Process Models Waterfall Model V Model Spiral Model Prototyping Model Software project management

Software Process Models (cont’d) Phased Development Model incremental development model iterative development model Operational Specification Model Transformation Model Software project management

Waterfall Model Requirements Analysis System Design Coding Testing Maintenance Software project management

Waterfall Model (cont’d) classical one-shot approach effective control limited scope of iteration long cycle time not suitable for system of high uncertainty Software project management

V Model Maintenance Requirements Analysis User Acceptance Testing System Design System Testing Unit and Integration Testing Program Design Coding Software project management

V Model (cont’d) Additional validation process introduced Relate testing to analysis and design Loop back in case of discrepancy Software project management

Spiral Model (adapted from Boehm 1987) Cumulative cost Progress through steps Determine objectives, alternatives and constraints Evaluate alternatives; identify and resolve risks Risk analysis Risk analysis Risk analysis Prototype Prototype Prototype Requirements plan Concept of operation Software requirements System product design Detailed design Development plan Requirements validation Coding Integration and Test plan Design validation Unit testing Develop and verify next-level product Plan next phases Integration and Test Acceptance test Software project management

Spiral Model (cont’d) Evolutionary approach Iterative development combined with risk management Risk analysis results in “go, re-do, no-go” decision Software project management

Spiral Model (cont’d) Four major activities Planning Risk analysis Software Project Management Spiral Model (cont’d) Four major activities Planning Risk analysis Engineering Evaluation Software project management

Prototyping Model Goals meet (some) user requirements at an early stage reduce risk and uncertainty verify a design or implementation approach Should always answer specific questions; goals must be identified Software project management

Classification of Prototype Software Project Management Classification of Prototype Throw-away After users agree the requirements of the system, the prototype will be discarded. Evolutionary Modifications are based on the existing prototype. Incremental Functions will be arranged and built accordingly. Software project management

Prototyping Model User YES satisfaction Build prototype NO User feedback Software project management

Benefits of Prototyping Learning by doing Improved communication Improved user involvement Clarification of partially-known requirements Software project management

Prototyping Sequences Requirements gathering Quick design Prototype construction Customer evaluation Refinement Loop back to quick design for fine tuning Product engineering Software project management

Benefits of Prototyping Software Project Management Benefits of Prototyping Demonstration of the consistency and completeness of a specification Reduced need for documentation Reduced maintenance costs Feature constraint Production of expected results for testing real system Reduced maintenance costs in the sense that users are less likely to ask for changes after the system goes into its operation. However, when asked for changes, the system is difficult to maintain because the software is usually not well structured. Software project management

Drawbacks of Prototyping Users sometimes misunderstand the role of the prototype Lack of project standards possible Lack of control Additional expense Machine efficiency Close proximity of developers Software project management

Forms of Prototypes Mock-ups Simulated interaction Partial working model Software project management

Prototype Products Human-computer interface System functionality Software project management

Prototype Changes Three categories Cosmetic (35%) Local (60%) Software Project Management Prototype Changes Three categories Cosmetic (35%) screen layout Local (60%) screen processing Global (5%) multi-parts processing design review Software project management

Phased Development Reduce cycle time Two parallel systems: operational system (Release n) development system (Release n+1) Two approaches incremental iterative Software project management

Incremental Model Break system into small components Implement and deliver small components in sequence Every delivered component provides extra functionality to user Software project management

Incremental Model (cont’d) Arrange requirements in increments Design and develop increment Requirements Analysis NO System OK? Validate increment Integrate increment YES Software project management

Iterative Model Deliver full system in the beginning Enhance functionality in new releases Software project management

Iterative Model (cont’d) Design system version n n = n+1 NO System complete Develop system version n Validate system version n YES Software project management

Combined Incremental and Iterative Model Every new release includes extra functionality enhancement of existing functionality Popularly used in software industry Software project management

Ranking the Increments Rank by value to cost ratio V = value to customer (score 1 -10) C = cost (score 1- 10) Value to cost ratio = V/C Example: Table 4.1 Software project management

Advantages of Phased Development Early feedback Less possible requirement changes Early benefits for users Improved cash flow Easier to control and manage Software project management

Advantages of Phased Development (cont’d) Capture early market Facilitate early training Can be temporarily abandoned Increase job satisfaction Software project management

Disadvantages of Phased Development ‘Software breakage’ Reduced productivity Software project management

Operational Specification Model Executable or translatable specification Use executables to demonstrate system behaviour Resolve requirement uncertainties in early stage Merging functionality and system design Software project management

Transformational Model Transform a specification into delivered system Requires automated support Relies on formal specification method Software project management

Software Project Management References Boehm, B. (1987) A sprial model of software development and enhancement, Software Engineering Project Management, p.128–142. Hughes, B. and Cotterell, M. (1999) Software Project Management, 2nd ed., McGraw Hill. Humphrey, W. (1990) Managing the Software Process, Addison-Wesley. Pfleeger, S.L. (1998) Software Engineering Theory and Practice, Prentice Hall Software project management