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Programvareprosesser Software Process Kapittel 2 Carl-Fredrik Sørensen Letizia Jaccheri Ian Sommerville.

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1 Programvareprosesser Software Process Kapittel 2 Carl-Fredrik Sørensen Letizia Jaccheri Ian Sommerville

2 2 Programvareprosesser Temaer som dekkes –Programvareprosesser og modeller for programvareprosesser –Prosessaktiviteter –Plandreven versus agile/smidig –Modeller: Vannfallsmodellen, Rational Unified Process

3 3 Programvareprosessen En strukturert sett av aktiviteter som kreves for å utvikle programvare Alle prosesser innholder: –Spesifikasjon - definere hva systemet skal gjøre –Design og gjennomføring - definere hvordan systemet organiseres og implementeres –Validering - kontrollere at den gjør hva kunden ønsker på en riktig måte –Evolution - forandre systemet i respons til endrede kundebehov. Modell = abstrakt representasjon fra et synsvinkel –Tenk på Linux med 10 Millioner LOC

4 4 Prosess og model (hvem skal ut? ) The open library developer meeting OurToys Workshop Trondheim 2012 Modell Prosess

5 5 spesifikasjon utvikling evolusjon validering Den enkleste modellen

6 6 Prosess aktiviteter Aktiviteter i en programvareprosess –Tekniske –Samarbeidende –Ledelse

7 7 Modeller for programvareprosesser Aktiviteter –Spesifikasjon, design, utvikling, vedlikehold, men også designe et brukergrensesnitt, Produkter som er utfallet av en prosess aktivitet –Test dokument, design dokument, Roller som gjenspeiler ansvar for de menneskene som er involvert i prosessen –Arkitekt, systemeier, brukere, prosjektleder, utviklere, testere.. Pre-og post som beskriver det som skal være sant før og etter en prosess aktivitet er vedtatt eller et produkt produsert – f.e. spesifikasjon signert

8 8 The waterfall model 8

9 9 Mer om vannfallsmodellen Video Real Software Engineering by Glenn Vanderburg https://www.youtube.com/watch?v=NP9AIUT9nos 51 min.https://www.youtube.com/watch?v=NP9AIUT9nos Managing the Development of Large Software Systems, Dr. Winston Royce, he was the first who described the Waterfall model for software developmentManaging the Development of Large Software Systems SOFTWARE ENGINEERING Report on a conference sponsored by the NATO SCIENCE COMMITTEE Garmisch, Germany, 7th to 11th October 1968SOFTWARE ENGINEERING

10 10 Plan-drevne og smidige/agile prosesser Plan-drevne prosesser er prosesser hvor alle prosessaktiviteter er planlagt på forhånd og fremgang måles mot denne planen.  I smidige prosesser, er planlegging og utførelse inkrementell. Det er lettere å endre prosess og produkt for å reflektere endrede kravene fra kundene. Viktig!! Prøv å ha dette på minnet i gjesteforelesninger fra industrien

11 11 Inkrementell utvikling

12 Spesifikasjon Hvilke tjenester er nødvendig, og hva er begrensninger på systemets drift og utvikling. Prosess består av: –Feasibility study: er det teknisk og økonomisk mulig å bygge systemet? –Krav innhenting og analyse: hva krever interessenter fra systemet? –Kravspesifikasjon: definere kravene i detalj. –Kravvalidering: kontrollere gyldigheten av kravene spesifikasjon utvikling evolusjon validering

13 Design og implementering av programvare Fra spesifikasjon til et fungerende software system. Software design: Output - en programvarestruktur som realiserer spesifikasjonen Implementering: Output - en kjørbart program Design og implementering er nært beslektet og kan være sammenvevd Prosess består av: 1) Architectural design; 2) Interface design; 3) Component design; 4) Database design spesifikasjon utvikling evolusjon validering

14 Programvarevalidering Verifikasjon og validering (V & V) – mål er å vise at systemet oppfyller spesifikasjonen og oppfyller kravene (til kunden). 1.Review (statisk) 2.System testing (dynamisk) –Kjører systemet med testtilfeller fra spesifikasjonen av de virkelige data som skal behandles av systemet. Testing er den mest brukte V & V aktivitet. spesifikasjon utvikling evolusjon validering

15 15 Testingnivåer Komponent testing (skjer under utvikling) –Enkeltkomponenter testes uavhengig; –Komponenter kan være funksjoner eller objekter eller sammenhengende grupperinger av disse enhetene. Systemtesting –Testing av systemet som helhet. Testing av viktige egenskaper/krav er spesielt viktig. –Akseptansetesting: Testing med kundedata for å kontrollere at systemet oppfyller kundens behov.

16 Software evolusjon/vedlikehold Programvare er fleksibel (av natur) og kan endres Når krav endres gjennom skiftende forretningsbehov/ omstendigheter, må programvaren som støtter virksomheten, også utvikle seg og endre. avgrensning mellom utvikling og evolusjon (vedlikehold) blir stadig mindre relevant som færre og færre systemer er helt ny. spesifikasjon utvikling evolusjon validering

17 17 Rational Unified Process Inception (Innledning)Inception (Innledning): business case Elaboration (Utforming)Elaboration (Utforming): problem domain + system architecture Construction (Bygging)Construction (Bygging): system design, programming, testing Transition (Overgang)Transition (Overgang): Produsere, Distribuere produktet til interessenter, Drive support for produktet. iterativ og inkrementelliterativinkrementell

18 18 Nøkkelpunkter Programvareprosesser er aktivitetene involvert i å produsere et programvaresystem. Modeller av programvareprosesser er abstrakte representasjoner av disse prosessene. Generelle prosessmodeller beskriver organiseringen av programvareprosessene. Eksempler av disse generelle modellene inkluderer vannfallsmodellen, inkrementell utvikling og gjenbruksorientert utvikling.

19 19 Nøkkelpunkter Modeller og prosesser Planlegging og inkrementell planlegging Requirements engineering = Utvikle en spesifikasjon for en programvare/forretningsbehov. Design og implementering = transformere en kravspesifikasjon til et kjørbart programvaresystem. Programvarevalidering = sjekke at systemet er I overensstemmelse med spesifikasjonen og at det møter de virkelige behovene som brukere har av systemet. Programvareevolusjon = Endre eksisterende programvaresystemer slik at de møter nye eller endrede krav.

20 Programvareprosesser Repetisjon og flere detaljer

21 21 Software process models The waterfall model –Plan-driven model. Separate and distinct phases of specification and development. Incremental development –Specification, development and validation are interleaved. May be plan-driven or agile. Reuse-oriented software engineering –The system is assembled from existing components. May be plan-driven or agile.

22 22 Waterfall model phases There are separate identified phases in the waterfall model: –Requirements analysis and definition –System and software design –Implementation and unit testing –Integration and system testing –Operation and maintenance The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. In principle, a phase has to be complete before moving onto the next phase.

23 23 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. –In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work.

24 24 Incremental development benefits The cost of accommodating changing customer requirements is reduced. –The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model. It is easier to get customer feedback on the development work that has been done. –Customers can comment on demonstrations of the software and see how much has been implemented. More rapid delivery and deployment of useful software to the customer is possible. –Customers are able to use and gain value from the software earlier than is possible with a waterfall process.

25 25 Incremental development problems The process is not visible. –Managers need regular deliverables to measure progress. If systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system. System structure tends to degrade as new increments are added. –Unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. Incorporating further software changes becomes increasingly difficult and costly.

26 26 Reuse-oriented software engineering Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems. Process stages –Component analysis; –Requirements modification; –System design with reuse; –Development and integration. Reuse is now the standard approach for building many types of business system –Reuse covered in more depth in Chapter 16.

27 27 Reuse-oriented software engineering

28 28 Reuse: Types of software component Web services that are developed according to service standards and which are available for remote invocation. Collections of objects that are developed as a package to be integrated with a component framework such as.NET or J2EE. Stand-alone software systems (COTS) that are configured for use in a particular environment.

29 29 The requirements engineering process

30 30 A general model of the design process

31 31 Stages of testing Chapter 2 Software Processes 31

32 32 Testing phases in a plan-driven software process

33 33 System evolution

34 34 Software prototyping A prototype is an initial version of a system used to demonstrate concepts and try out design options. A prototype can be used in: –The requirements engineering process to help with requirements elicitation and validation; –In design processes to explore options and develop a UI design; –In the testing process to run back-to-back tests.

35 35 Benefits of prototyping Improved system usability. A closer match to users’ real needs. Improved design quality. Improved maintainability. Reduced development effort.

36 36 The process of prototype development

37 37 Prototype development May be based on rapid prototyping languages or tools May involve leaving out functionality –Prototype should focus on areas of the product that are not well- understood; –Error checking and recovery may not be included in the prototype; –Focus on functional rather than non-functional requirements such as reliability and security

38 38 Throw-away prototypes Prototypes should be discarded after development as they are not a good basis for a production system: –It may be impossible to tune the system to meet non-functional requirements; –Prototypes are normally undocumented; –The prototype structure is usually degraded through rapid change; –The prototype probably will not meet normal organisational quality standards.

39 39 Incremental delivery

40 40 Incremental delivery 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.

41 41 Incremental delivery problems Most systems require a set of basic facilities that are used by different parts of the system. –As requirements are not defined in detail until an increment is to be implemented, it can be hard to identify common facilities that are needed by all increments. The essence of iterative processes is that the specification is developed in conjunction with the software. –However, this conflicts with the procurement model of many organizations, where the complete system specification is part of the system development contract.

42 42 Boehm’s spiral model Process is represented as a spiral rather than as a sequence of activities with backtracking. Each loop in the spiral represents a phase in the process. No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required. Risks are explicitly assessed and resolved throughout the process.

43 43 Boehm’s spiral model of the software process

44 44 Spiral model sectors Objective setting –Specific objectives for the phase are identified. Risk assessment and reduction –Risks are assessed and activities put in place to reduce the key risks. Development and validation –A development model for the system is chosen which can be any of the generic models. Planning –The project is reviewed and the next phase of the spiral is planned.

45 45 Spiral model usage Spiral model has been very influential in helping people think about iteration in software processes and introducing the risk-driven approach to development. In practice, however, the model is rarely used as published for practical software development.

46 46 RUP iteration In-phase iteration –Each phase is iterative with results developed incrementally. Cross-phase iteration –As shown by the loop in the RUP model, the whole set of phases may be enacted incrementally.

47 47 Static workflows in the Rational Unified Process

48 48 Static workflows in the Rational Unified Process

49 49 RUP good practice Develop software iteratively –Plan increments based on customer priorities and deliver highest priority increments first. Manage requirements –Explicitly document customer requirements and keep track of changes to these requirements. Use component-based architectures –Organize the system architecture as a set of reusable components.

50 50 RUP good practice Visually model software –Use graphical UML models to present static and dynamic views of the software. Verify software quality –Ensure that the software meet’s organizational quality standards. Control changes to software –Manage software changes using a change management system and configuration management tools.

51 51 Key points We have seen models for the single phases: requirements, design, validation, evolution?? The Rational Unified Process is a generic process model that is organized into phases (inception, elaboration, construction and transition) but separates activities (requirements, analysis and design, etc.) from these phases.


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