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Lecture 4 Prototyping

CS 540 – Quantitative Software Engineering. Lecture 4 Prototyping. Software Requirements Process. Requirements Elicitation Requirements Analysis Use Cases Requirements Specification Prototype/Modeling Requirements Management. Software Prototyping Process.

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Lecture 4 Prototyping

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  1. CS 540 – Quantitative Software Engineering Lecture 4 Prototyping

  2. Software Requirements Process • Requirements Elicitation • Requirements Analysis • Use Cases • Requirements Specification • Prototype/Modeling • Requirements Management

  3. Software Prototyping Process • Software prototyping is the process of creating an incomplete model of the future full-featured software • Process: • Identify basic requirements • Develop Initial prototype • Review with customers users • Revise and enhance

  4. Types of Software Prototypes • Throwaway prototype: process of creating a rapid model (demonstration or marketing) • Evolutionary prototype: build a system then refine • Incremental: final product built as separate prototypes

  5. Serial development is costly The Longer You Wait for Feedback, the more costs are sunk.

  6. Applications • Feasibility (must use) • Human Interface testing • Increases user involvement • Reduce time and cost • DSDM (Dynamic systems development method) • Business prototypes (automation/mechanization) • Usability prototypes • Performance and Capacity • Proof of concept

  7. Benefits of Automation New Cost of Work Cost of System Operation System Administrator Cost of Work Today Technician Technicians Cost of System Hardware $1b/yr Software Training Developer Technology Standards Reuse Tools Processes

  8. Project A: Order Reading and Analysis Software Size of Prototyping Effort: 12K lines of C Code (10% of final system module) Purpose:   Find a method for order reading and analysis, applicable to variable formats. Duration and Staff of Prototype: Four people for eight months.

  9. Prototyping Results 1. Final requirements based on prototype results.  2. Alerted developers' to the possibility of a having a tunable system.  3. Early evaluation of functional decomposition and performance showed bottlenecks in the dispatcher. 4. Eliminated the possibility of reusing code from another project.  5. Prototype was thrown away due to decomposition and performance problems.

  10. Project B: Outside Plant Data Base System Size of Effort: 5% of 500K line of source code. Purpose: To evaluate database structures for an outside plant data and to experiment with approaches to handling multiple future states of equipment usage. Duration:   Three people for 15 months.

  11. Experience: • A data base structure using hyper graph theory was invented. • An algorithm for handling both time-driven and event-driven assignments was invented • The prototype became the basis for the production code. • UNIX flat files were used to model loop plant by way of a directed graph. • The prototype showed database portability from Unix to the Mainframe.

  12. Comparison 30% 45% 25% TRADITIONAL PROTOTYPE BASED Systems Engineering & Prototype Systems Engineering 20% Final Development Design, Develop, Test, Install 80% Deployment Final Development, Deployment 40% 40% REDUCTION

  13. Prototypes • Plan to build a prototype • Document feedback from customer for the prototype. • Manage the feedback into the software product

  14. Prototyping with Reuse • Application level development • Entire application systems are integrated with the prototype so that their functionality can be shared • For example, if text preparation is required, a standard word processor can be used • Component level development • Components are mutually independent • Individual components are integrated within a standard framework to implement the system • Framework can be a scripting language or an integration platform.

  15. Prototyping Benefits • Misunderstandings between software users and developers are exposed • Missing services may be detected and confusing services may be identified • A working system is available early in the process • The prototype may serve as a basis for deriving a system specification • The system can support user training and system testing

  16. Prototyping Approaches E v o l u t i o n a r y D e l i v e r e d p r o t o t y p i n g s y s t e m Prospectus E x e c u t a b l e P r o t o t y p e + T h r o w - a w a y S y s t e m S p e c i f i c a t i o n P r o t o t y p i n g

  17. Prototyping Objectives • The objective of evolutionary prototyping is to deliver a working system to end-users • The development starts with those requirements which are best understood. • The objective of throw-away prototyping is to validate or derive the system requirements • The prototyping process starts with those requirements which are poorly understood

  18. Evolutionary Prototyping • Must be used for systems where the requirements specification cannot be developed in advance • Based on techniques which allow rapid system iterations • Verification is impossible as there is no specification • Validation means demonstrating the adequacy of the system

  19. Evolutionary Prototyping Flow

  20. Evolutionary Prototyping Advantages • Accelerated delivery of the system • Rapid delivery and deployment are sometimes more important than functionality or long-term software maintainability • User engagement with the system • Not only is the system more likely to meet user requirements, they are more likely to commit to the use of the system

  21. Evolutionary Prototyping Technologies • Specification, design and implementation are inter-twined • The system is developed as a series of increments that are delivered to the customer • Techniques for rapid system development are used such as CASE tools and 4GLs • User interfaces are usually developed using a GUI development toolkit

  22. Evolutionary Prototyping Challenges • Management problems • Existing management processes assume a waterfall model of development • Specialist skills are required which may not be available in all development teams • Maintenance problems • Continual change tends to corrupt system structure so long-term maintenance is expensive • Contractual problems

  23. Prototypes as Specifications • Some parts of the requirements may be impossible to prototype • E.g., safety-critical functions • An implementation has no legal standing as a contract • Non-functional requirements cannot be adequately tested in a system prototype

  24. Incremental Development • System is developed and delivered in increments after establishing an overall architecture • Requirements and specifications for each increment may be developed • Users may experiment with delivered increments while others are being developed • These serve as a form of prototype system • Intended to combine some of the advantages of prototyping • More manageable process • Better system structure

  25. Incremental Development Flow

  26. Throw-away Prototypes • Used to reduce requirements risk • The prototype is developed from an initial specification, delivered for experiment then discarded • The throw-away prototype must NOT be considered as a final system • Some system characteristics may have been left out • There is no specification for long-term maintenance • The system will be poorly structured and difficult to maintain

  27. Throw-away Prototyping

  28. Rapid Prototyping Techniques • Various techniques may be used for rapid development • Dynamic high-level language development • Database programming • Component and application assembly • These techniques are often used together • Visual programming is an inherent part of most prototype development systems

  29. Dynamic High-level Languages • Languages which include powerful data management facilities • Need a large run-time support system. Not normally used for large system development • Some languages offer excellent UI development facilities • Some languages have an integrated support environment whose facilities may be used in the prototype

  30. Choice of Prototyping Language • What is the application domain of the problem? • What user interaction is required? • What support environment comes with the language? • Different parts of the system may be programmed in different languages • Example languages • Java, Smalltalk, Lisp, Prolog, Perl, Tcl/TK

  31. Database Programming Languages • Domain specific languages for business systems based around a database management system • Normally include a database query language, a screen generator, a report generator and a spreadsheet • May be integrated with a CASE toolset • The language + environment is sometimes known as a “4GL” • Cost-effective for small to medium sized business systems

  32. Prototyping with Reuse • Application level development • Entire application systems are integrated with the prototype so that their functionality can be shared • For example, if text preparation is required, a standard word processor can be used • Component level development • Components are mutually independent • Individual components are integrated within a standard framework to implement the system • Framework can be a scripting language or an integration platform. .

  33. Key points • A prototype can be used to give end-users a concrete impression of the system’s capabilities • Prototyping is becoming increasingly used where rapid development is essential • Throw-away prototyping is used to understand the system requirements • In evolutionary prototyping, the system is developed by evolving an initial version to the final version

  34. Visual programming • Scripting languages such as Visual Basic support visual programming • the prototype is developed by creating a user interface from standard items and associating components with these items • A large library of components exists to support this type of development • These may be tailored to suit the specific application requirements

  35. Visual programming with reuse

  36. Problems with visual development • Difficult to coordinate team-based development • No explicit system architecture • Complex dependencies between parts of the program can cause maintainability problems

  37. User interface prototyping • It is impossible to pre-specify the look and feel of a user interface in an effective way • UI development consumes an increasing part of overall system development costs • User interface generators may be used to ‘draw’ the interface and simulate its functionality with components associated with interface entities • Web interfaces may be prototyped using a web site editor

  38. Mindset • Prototyping is critical system parts that cannot be effectively pre-specified • Rapid prototyping focus on partial functionality • Prototyping techniques include the use of tools, very high-level languages and database programming • Users must be involved in prototype evaluation

  39. Growing from Prototype to Model

  40. Software Prototyping: Review • Types: Throwaway, Evolutionary, Incremental • Advantages and Disadvantages • When to Use • Methods: DSDM, Evolutionary, Operational, SCRUM • Tools: Screen Generators, design, tangible architect, Visual Basic, REE, LYMB • Simulation technologies

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