Software Architecture. Paolo Ciancarini

Transcription

1 Software Architecture Paolo Ciacarii

2 Ageda Software Architecture: defiitios ad stadards The stadard IEEE 1471 ad its successors Architectural frameworks Architectural assets 2

3 What is the role of architecture??

4 Form vs fuctio: how may types of houses 4

5 What is Software Architecture? Software Architecture is like ay other architecture: it is about the fuctio - or purpose - ad the form - or structure It is about the gap betwee a curret system's desig ad its future desig It is about the evaluatio of the properties which gover the desig ad the evolutio of a system 5

6 What is the goal of Software Architecture? To uderstad the fudametal elemets of a system that cotribute to its utility, cost, effort to build, ad risk to use withi its eviromet I some cases, the fudametal elemets are physical or structural compoets of the system ad their relatioships Sometimes, the fudametal elemets are fuctioal or logical elemets I other cases, what is fudametal to the uderstadig of a system are its overarchig priciples or patters 6

7 Form ad fuctio What is the fuctio of a software system? The fuctio of a software system is its missio, as described by some use cases i some scaario What is the form of a software system? The form of a software system is a model of the system 7

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9 Views Logical view Addresses the static desig model Process view Addresses the desig's dyamic view Physical view Addresses how the software compoets are mapped oto the hardware ifrastructure Developmet view Represets the static orgaizatio of the software compoets i the developmet time eviromet 9

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11 What is software architecture? The software architecture represets the "sigificat decisios", where sigificace is measured by cost of chage Grady Booch Software architecture is the set of desig decisios which, if made icorrectly, may cause your project to be cacelled Eoi Woods 11

12 Architecture = desig decisios Software Architecture Software desig Decisios: Desig decisios Architectural decisios Requiremets costraits Requiremets Code etc. decisio: a choice that is bidig i the fial product

13 Hoare o software desig There are two ways of costructig a software desig: Oe way is to make it so simple that there are obviously o deficiecies, ad the other way is to make it so complicated that there are o obvious deficiecies. 13

14 Architectig software Architectural desig has o stoppig rule: there is o criterio that tells whe the architecture is fiished Solutios to architectural problems are ot correct or wrog: usually they are good or bad; solvig oe problem may very well result i a etirely differet problem elsewhere i the system Architectural desig ivolves trade-offs, such as those betwee speed ad robustess: as a cosequece, there is a umber of acceptable solutios, rather tha oe best solutio Architectural desig problems do ot have a well-defied set of potetial solutios: software architects caot exploit a set of ready-made solutios, but have to apply kowledge, practices, ad creativity to arrive at a satisfactory solutio 14

15 Role of architecture Software cocept Prelimiary requiremets aalysis Architecture sets system structure Desig of architecture ad system core Develop a versio First iteratio implemets system core A iterative lifecycle model Icorporate customer feedback Elicit customer feedback Deliver a versio Architecture plays a vital role i establishig the structure of the system, early i the developmet lifecycle

16 Role of architecture Visio Iceptio Developmet Deploymet Operatio Architecture is about decisios that affect the whole lifetime of the system Maiteace Alteratio Legacy operatio Death

17 Sigificat decisios The software architecture represets the "sigificat decisios", where sigificace is measured by cost of chage Example1: if the system is a idividual applicatio, ay decisio that could be made by implemetors should be deferred to them ad ot appear as part of the architecture Example2: if the scope of the architecture is a family of applicatios (a product lie), the ay decisio that relates oly to a sigle applicatio should be deferred to the applicatio architecture ad ot be part of the applicatio family architecture 17

18 Architecture = Desig? No! Do ot diluite the meaig of the term architecture by applyig it to everythig i sight. Mary Shaw

19 Defiitios A system is a collectio of parts the parts have relatios to each other ad form a whole that fulfils a desiged purpose

20 System (actually, software-itesive system ) System * * Software part istalled o * * acts with acts with Hardware part * * * * * * Most systems iclude also: - Natural elemets - Humas 20

21 System [IEEE 2000] A system is a collectio of compoets orgaized to accomplish a specific fuctio or set of fuctios A system exists to fulfill oe or more missios i its eviromet The term system ecompasses idividual applicatios, systems i the traditioal sese, subsystems, systems of systems, product lies, product families, eterprises, ad other etities of iterest 21

22 Two mai families of systems Iformatio systems, ecessary for eterprise busiess (eg. baks, e-commerce, egovermet) Embedded software systems, ecessary for egieerig domais (eg. automotive, aerospace) Iformatio systems ad their architectures are usually related to a eterprise orgaizatio, meaig that huma roles ad actios are icluded i the descriptio of the system Embedded sw systems ad their architectures are usually related to a system architecture (people are outside the system) 22

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24 Defiitio: Software architecture The software architecture of a system is the structure of the system, which comprises its software elemets, the exterally visible properties of those elemets, ad the relatioships betwee them The term also refers to the documetatio of a system's software architecture Documetig a software architecture facilitates the commuicatio betwee stakeholders, documets the early decisios about high-level desig, ad allows the reuse of its compoets across projects 24

25 Short history The basics of software architecture were itroduced by Dijkstra (1968) ad Paras (1970). They studied: The key role of the structure of a software system, ad How tricky the defiitio of the right structure for a give system is A great deal of research has bee coducted o software architectures startig from the 90s, maily focusig o: How to solve recurret architectural problems (patters) Which architectural forms are more commo (styles) Defiig laguages to describe software architectures (ADL) How to documet the architecture of a system (views) claimed to give rise to the defiitio of a disciplie See: Shaw ad Garla Software Architecture: Perspectives o a Emergig Disciplie,

26 Stadard: IEEE 1471 The mai stadard i the field of software architectures is the ANSI/IEEE : Recommeded Practice for Architecture Descriptio of Software-Itesive Systems better kow as IEEE 1471 stadard It is a recommeded practice the weakest type of IEEE stadards, whose adoptio ad iterpretatio are the resposibility of the usig orgaizatio It has bee adopted by ISO/IEC JTC1/SC7 as ISO/IEC 42010:2007, i 2007 most recet versio is ISO/IEC/IEEE 42010:

27 Defiitio: IEEE 1471 Ituitively, the architecture of a software system represets its iteral structure, i terms of the sigle compoets of which it is made up ad of the iteractios amog them Accordig to the stadard, the architecture of a software system is its basic orgaizatio, i terms of its compoets, of the iteractios amog compoets ad with the exteral eviromets, as well as of the basic, drivig, priciples for system desig ad evolutio 27

28 IEEE1471 Coceptual Model for Sw Architectures

29 Cosequeces of IEEE 1471 IEEE 1471's cotributios: It provides the defiitios ad a coceptual model for the descriptio of a software architecture It states that a architecture goal is to respod to specific stakeholders cocers about the software system beig described It asserts that architecture descriptios are iheretly multi-view, as o sigle view ca capture all stakeholders cocers about a architecture It separates the otio of a view from a viewpoit, which idetifies the set of cocers ad the represetatios/modelig techiques, etc. used to describe the architecture to address those cocers It establishes that a coformig architecture descriptio has a 1-to-1 correspodece betwee its viewpoits ad its views It ca be exteded to become a compay specific architectural model 29

30 Extedig

31 Evolutio of the stadard 2000: IEEE : ANSI 2007: ISO/IEC : ISO/IEC/IEEE 42010:2011 Systems ad software egieerig -- Architecture descriptio New versio: architecture frameworks & coformace 31

32 42010:

33 Architecture frameworks 33

34 Architecture framework A architecture framework icludes oe or more cocers, oe or more stakeholders havig those cocers, ay correspodece rules These are architecture frameworks recogized by the stadard: Krutche 4+1, Siemes 4 views method, Zachma framework, UKMODAF, TOGAF, RM-ODP, GERAM 34

35 Defiig a software architecture The defiitio of the architecture is a importat step of system desig (i.e., architectural desig) Its aim is the structural decompositio of a system ito sub-systems: Divide et impera approach: to develop sigle sub-etities is simpler tha to develop a etire system It allows to perform several developmet activities at the same time (differet etities ca be developed i parallel) It fosters the modifiability, the reusability, ad the portability of a system 35

36 Defiig the architecture The defiitio of the criteria for the idetificatio of sub-etities is a prelimiary step: A typical criterio is the fuctioal oe, i.e., a sub-etity may be idetified by mappig software fuctioalities to its parts: E.g., user iterface, database access, security maagemet High Cohesio ad Low Couplig amog compoets are key guidelies Each sub-system has to cotai cohesive compoets (e.g., modules providig services which are strictly related oe to each other) Miimize iteractios amog subsystems, that should result scarcely coupled 36

37 Software module A module is a piece of software that: Provides a abstractio (o data, o fuctio) Clearly separates the iterface from the body Usually makes sese at compilatio time rather tha at ru time The iterface specifies what the module is (the abstractio provided) ad how it ca be used The iterface is the cotract betwee a user ad the provider of the abstractio The body describes how the abstractio is implemeted Module Iterface (visible from outside) Body (hidde ad protected) 37

38 Mai elemets of a sw architecture Compoets Coectors Cofiguratios Architecture Architectural elemet Compoet +ame Cofiguratio +ame Coector +ame

39 Compoet A software compoet is a uit of compositio with cotractually specified iterfaces (icludig some ports) ad explicit depedecies Example: a web server A software compoet ca be deployed idepedetly ad is subject to compositio by third parties A compoet model defies rules (stadards) for amig, meta data, behavior specificatio, implemetatio, iteroperability, customizatio, compositio, ad deploymet of compoets Example: the CORBA compoet model

40 Coector A software coector specifies the mechaisms by which compoets trasfer cotrol or data Examples: procedure call, protocol, buffer, chael, stream A coector defies the possible iteractios amog compoets: the iterfaces of coectors are called roles, which are attached to ports of compoets

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42 UML compoet model Black box view White box view 42

43 Architectural cofiguratio A architectural cofiguratio is a coected graph of compoets ad coectors that describes the structure of a software architecture Example:

44 Simplicity Key architectural desig priciples Modularity Low couplig Separatio of cocers Abstractio Postpoig decisios Ecapsulatio Iformatio hidig Clear iterface High cohesio 44

45 Sources of Architecture Theft From a previous system or from techical literature Method A approach to derivig the architecture from the requiremets Ituitio The experiece of the architect From Mommy, Where Do Software Architectures Come From?, Philippe Kruchte 1st Iteratioal Workshop o Architectures for Software Systems, Seattle, 1995

46 Architecture goal: reuse of compoets 46

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48 Architectural assets Most elemets of a software architecture are derived from a previous system of the same kid, aother system with similar characteristics, or a architecture foud i techical literature 48

49 What Types of Architectural Asset are there? Referece Architecture Legacy Applicatio Patter Laguage Developmet Method Architectural Decisio Patter Compoet Architectural Style Desig Patter Architectural Mechaism Packaged Applicatio Referece Model Programmig Patter Compoet Library Architectural Patter Applicatio Framework

50 Patter [A patter is] a commo solutio to a commo problem i a give cotext. [UML User Guide] Patter types Architectural Patters Distributio patters Security Patters Desig Patters Programmig Patters Requiremets Patters Testig Patters Project Maagemet Patters Process Patters Orgaizatioal Patters

51 Architectural Patter A architectural patter expresses a fudametal structural orgaizatio schema for software systems. It provides a set of predefied subsystems, specifies their resposibilities, ad icludes rules ad guidelies for orgaizig the relatioships betwee them. [Buschma] Example: Patter: Layers Cotext A system that requires decompositio Problem High-level elemets rely o lower-level elemets ad the followig forces must be balaced: - Iterfaces should be stable - Parts of the system should be exchageable - Source code chages should ot ripple through the system Solutio 51 Structure the system ito layers

52 Architectural patter Layers ISO OSI 7-Layer Model Layer 7 Applicatio Provides applicatio facilities Layer 6 Presetatio Structures iformatio as required Layer 5 Sessio Maages the coectio Persoal Orgaizer Layer 4 Layer 3 Trasport Network Creates packets of data Routes packets of data <<layer>> Applicatio-Specific Persoal Orgaizer (from Applicatio-Specific) Layer 2 Data Lik Detects ad corrects errors Layer 1 Physical Trasmits bits <<layer>> Busi ess-specifi c Address Book (from Busiess-Specific) Calculator (from Busiess-Specific) <<layer>> Base Fil estore Maagemet (from Base) Memory Maagemet (from Base) Math (from Base)

53 Desig Patter A desig patter provides a scheme for refiig the subsystems or compoets of a software system, or the relatioships betwee them. It describes a commoly-recurrig structure of commuicatig compoets that solves a geeral desig problem withi a particular cotext. [Gamma] Observer Patter

54 Programmig Patter A idiom is a low-level patter specific to a programmig laguage. A idiom describes how to implemet particular aspects of compoets or the relatioships betwee them usig the features of the give laguage. [Buschma] // Swap the values of 2 variables temp = a; a = b; b = temp;

55 Architectural Style [A architectural style] defies a family of systems i terms of a patter of structural orgaizatio. More specifically, a architectural style defies a vocabulary of compoets ad coector types, ad a set of costraits o how they ca be combied. [Shaw] Cliet-server Supports the physical separatio of cliet-side processig (such as a browser) ad server-side processig (such as a applicatio server that accesses a database) Evet-based Promotes a publish-subscribe way of workig, applied strategically across large areas of the architecture Pipes-ad-filters A series of filters that provide data trasformatio, ad pipes that coect the filters. Examples iclude compilers, sigal processig

56 Patter Laguage A patter laguage defies a collectio of patters ad the rules to combie them. Patter laguages are ofte used to describe a family of systems IBM Patters for e-busiess A set of architectural patters that describe various web-based applicatios Icludes a patter selectio process that drives: Selectio of a busiess, itegratio or composite patter Selectio of applicatio patters Selectio of rutime patters Idetificatio of product mappigs *See 56

57 Referece Architecture A referece architecture is a architecture represetatio of a particular domai of iterest. It typically icludes may differet architectural patters, applied i differet areas of its structure Examples iclude JEE ad.net 57

58 Referece Model A referece model is a abstract represetatio of etities, their relatioships ad behavior, i a give domai of iterest, ad which typically forms the coceptual basis for the developmet of more cocrete elemets Examples: a busiess model, a iformatio model, or a glossary of terms IBM Iformatio FrameWork (IFW) IFW Iformatio Models (Bakig Data Warehouse) IFW Process & Itegratio Models IFW Foudatio Models Fiacial Services Data Model Fiacial Services Fuctio Model Fiacial Services Workflow Model Busiess Solutio Templates Applicatio Solutio Templates Busiess Object Model Busiess Process Model Bakig Data Warehouse Model Iterface Desig Model

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60 Example: automotive sw architecture (AUtOSAR) 60

61 Applicatio Framework A applicatio framework represets the partial implemetatio of a specific area of a applicatio Most widely-kow frameworks support user iterfaces Java Server Pages ASP.NET Cliet Server URL HTTP Iteret HTTP Web Server Scriptig cotaier Script

62 Architectural Mechaism Architectural mechaisms represet commo cocrete solutios to frequetly ecoutered problems. They may be patters of structure, patters of behavior, or both. [RUP] Ofte described as the mechaism for achievig X this elemet is uderpied by mechaism Y Examples Persistecy mechaism Error loggig mechaism Commuicatio mechaism Shoppig cart

63 Packaged applicatio A packaged applicatio is a Commercial-Off-The-Shelf (COTS) product available i the market that ca be bought "as is These applicatios are usually large graied, that is they provide a sigificat amout of capability (ad reuse) Examples Customer Relatioship Maagemet (CRM) applicatio (e.g. Siebel) Eterprise Resource Plaig (ERP) applicatio (e.g. SAP) The amout of required custom developmet is miimal Primary focus is o cofigurig the applicatio

64 Compoet & compoet library Compoet examples GUI widget (such as a table) Service Compoet library examples Class libraries (e.g. Java class library) Procedure libraries

65 Legacy Applicatio A legacy applicatio is a system that cotiues to be used because the owig orgaizatio caot replace or redesig it Usually o way to have past (regressio) tests Teds to be a focus o itegratio rather tha ew developmet Ofte results i a focus o eterprise applicatio itegratio (EAI)

66 Architectural Decisio [Architectural decisios are] coscious desig decisios cocerig a software system as a whole, or oe or more of its core compoets. These decisios determie the o-fuctioal characteristics ad quality factors of the system. [Zimmerma] Decisio ratioale may come from experiece, method or some other asset 66

67 A map of architectural cocepts 67

68 Summary: what is a software architecture? A architecture defies the form of software defies the fuctio of software focuses o sigificat elemets reuses ad coforms to a architectural style balaces the eeds of its stakeholders is iflueced by its eviromet iflueces its eviromet iflueces its developmet team

69 Quotatio Whether somethig is part of the architecture is etirely based o whether the developers thik it is importat. Architecture is a social costruct because it does t just deped o the software, but o what part of the software is cosidered importat by group cosesus. Marti Fowler 69

70 Self questios What is a software architecture? What is a architectural cocer? What is a architectural view? What is a compoet? What is a coector? What is a architectural framework? What is a architectural asset? 70

71 Suggested readigs Perry & Wolf, Foudatios for the study of software architecture, ACM Sw Eg Notes, 17:4(40-52), 1992 Cervates & Kazma, Desigig Software Architectures, AddisoWesley,

72 Refereces Shaw & Garla Software Architecture: Perspectives o a Emergig Disciplie, Pretice Hall, 1996 Bass, Clemes & Kazma, Software Architecture i Practice, 3 rd ed, Addiso Wesley, 2013 softarchpract.tar.hu 2 d ed Clemets, Documetig Software Architectures: Views ad Beyod, The SEI Series i Software Egieerig, 2010 Rozaski & Woods, Software Systems Architecture, Addiso-Wesley, 2012 Garlad, Large-Scale Software Architecture: A Practical Guide usig UML, Addiso-Wesley, 2005 Mistrik, Relatig System Quality ad Software Architecture, MorgaKaufma

73 Iterestig sites msd.microsoft.com/e-us/library/ee aspx stal.blogspot.com softwarearchitectureze.blogspot.com 73

74 Questios?