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1、Chapter 6 Architectural design,Chapter 6 Architectural Design,Lecture 1,Chapter 6 Architectural design,Topics covered,Architectural design decisionsArchitectural viewsArchitectural patternsApplication architectures,Chapter 6 Architectural design,Software architecture,The design process for identifyi
2、ng the sub-systems making up a system and the framework for sub-system control and communication is architectural design.The output of this design process is a description of the software architecture.,Chapter 6 Architectural design,Architectural design,An early stage of the system design process.Re
3、presents the link between specification and design processes.Often carried out in parallel with some specification activities.It involves identifying major system components and their communications.,Chapter 6 Architectural design,The architecture of a packing robot control system,Chapter 6 Architec
4、tural design,Architectural abstraction,Architecture in the small is concerned with the architecture of individual programs.At this level,we are concerned with the way that an individual program is decomposed into components.Architecture in the large is concerned with the architecture of complex ente
5、rprise systems that include other systems,programs,and program components.These enterprise systems are distributed over different computers,which may be owned and managed by different companies.,Chapter 6 Architectural design,Advantages of explicit architecture,Stakeholder communicationArchitecture
6、may be used as a focus of discussion by system stakeholders.System analysisMeans that analysis of whether the system can meet its non-functional requirements is possible.Large-scale reuseThe architecture may be reusable across a range of systemsProduct-line architectures may be developed.,Chapter 6
7、Architectural design,Architectural representations,Simple,informal block diagrams showing entities and relationships are the most frequently used method for documenting software architectures.But these have been criticised because they lack semantics,do not show the types of relationships between en
8、tities nor the visible properties of entities in the architecture.Depends on the use of architectural models.The requirements for model semantics depends on how the models are used.,Chapter 6 Architectural design,Box and line diagrams,Very abstract-they do not show the nature of component relationsh
9、ips nor the externally visible properties of the sub-systems.However,useful for communication with stakeholders and for project planning.,Chapter 6 Architectural design,Use of architectural models,As a way of facilitating discussion about the system design A high-level architectural view of a system
10、 is useful for communication with system stakeholders and project planning because it is not cluttered with detail.Stakeholders can relate to it and understand an abstract view of the system.They can then discuss the system as a whole without being confused by detail.As a way of documenting an archi
11、tecture that has been designed The aim here is to produce a complete system model that shows the different components in a system,their interfaces and their connections.,Chapter 6 Architectural design,Architectural design decisions,Architectural design is a creative process so the process differs de
12、pending on the type of system being developed.However,a number of common decisions span all design processes and these decisions affect the non-functional characteristics of the system.,Chapter 6 Architectural design,Architectural design decisions,Is there a generic application architecture that can
13、 be used?How will the system be distributed?What architectural styles are appropriate?What approach will be used to structure the system?How will the system be decomposed into modules?What control strategy should be used?How will the architectural design be evaluated?How should the architecture be d
14、ocumented?,Chapter 6 Architectural design,Architecture reuse,Systems in the same domain often have similar architectures that reflect domain concepts.Application product lines are built around a core architecture with variants that satisfy particular customer requirements.The architecture of a syste
15、m may be designed around one of more architectural patterns or styles.These capture the essence of an architecture and can be instantiated in different ways.Discussed later in this lecture.,Chapter 6 Architectural design,Architecture and system characteristics,PerformanceLocalise critical operations
16、 and minimise communications.Use large rather than fine-grain components.SecurityUse a layered architecture with critical assets in the inner layers.SafetyLocalise safety-critical features in a small number of sub-systems.AvailabilityInclude redundant components and mechanisms for fault tolerance.Ma
17、intainabilityUse fine-grain,replaceable components.,Chapter 6 Architectural design,Architectural views,What views or perspectives are useful when designing and documenting a systems architecture?What notations should be used for describing architectural models?Each architectural model only shows one
18、 view or perspective of the system.It might show how a system is decomposed into modules,how the run-time processes interact or the different ways in which system components are distributed across a network.For both design and documentation,you usually need to present multiple views of the software
19、architecture.,Chapter 6 Architectural design,4+1 view model of software architecture,A logical view,which shows the key abstractions in the system as objects or object classes.A process view,which shows how,at run-time,the system is composed of interacting processes.A development view,which shows ho
20、w the software is decomposed for development.A physical view,which shows the system hardware and how software components are distributed across the processors in the system.Related using use cases or scenarios(+1),Chapter 6 Architectural design,Architectural patterns,Patterns are a means of represen
21、ting,sharing and reusing knowledge.An architectural pattern is a stylized description of good design practice,which has been tried and tested in different environments.Patterns should include information about when they are and when the are not useful.Patterns may be represented using tabular and gr
22、aphical descriptions.,Chapter 6 Architectural design,The Model-View-Controller(MVC)pattern,Chapter 6 Architectural design,The organization of the Model-View-Controller,Chapter 6 Architectural design,Web application architecture using the MVC pattern,Chapter 6 Architectural design,Layered architectur
23、e,Used to model the interfacing of sub-systems.Organises the system into a set of layers(or abstract machines)each of which provide a set of services.Supports the incremental development of sub-systems in different layers.When a layer interface changes,only the adjacent layer is affected.However,oft
24、en artificial to structure systems in this way.,Chapter 6 Architectural design,The Layered architecture pattern,Chapter 6 Architectural design,A generic layered architecture,Chapter 6 Architectural design,The architecture of the LIBSYS system,Chapter 6 Architectural design,Key points,A software arch
25、itecture is a description of how a software system is organized.Architectural design decisions include decisions on the type of application,the distribution of the system,the architectural styles to be used.Architectures may be documented from several different perspectives or viewssuch as a concept
26、ual view,a logical view,a process view,and a development view.Architectural patterns are a means of reusing knowledge about generic system architectures.They describe the architecture,explain when it may be used and describe its advantages and disadvantages.,Chapter 6 Architectural design,Chapter 6
27、Architectural Design,Lecture 2,Chapter 6 Architectural design,Repository architecture,Sub-systems must exchange data.This may be done in two ways:Shared data is held in a central database or repository and may be accessed by all sub-systems;Each sub-system maintains its own database and passes data
28、explicitly to other sub-systems.When large amounts of data are to be shared,the repository model of sharing is most commonly used a this is an efficient data sharing mechanism.,Chapter 6 Architectural design,The Repository pattern,Chapter 6 Architectural design,A repository architecture for an IDE,C
29、hapter 6 Architectural design,Client-server architecture,Distributed system model which shows how data and processing is distributed across a range of components.Can be implemented on a single computer.Set of stand-alone servers which provide specific services such as printing,data management,etc.Se
30、t of clients which call on these services.Network which allows clients to access servers.,Chapter 6 Architectural design,The Clientserver pattern,Chapter 6 Architectural design,A clientserver architecture for a film library,Chapter 6 Architectural design,Pipe and filter architecture,Functional trans
31、formations process their inputs to produce outputs.May be referred to as a pipe and filter model(as in UNIX shell).Variants of this approach are very common.When transformations are sequential,this is a batch sequential model which is extensively used in data processing systems.Not really suitable f
32、or interactive systems.,Chapter 6 Architectural design,The pipe and filter pattern,Chapter 6 Architectural design,An example of the pipe and filter architecture,Chapter 6 Architectural design,Application architectures,Application systems are designed to meet an organisational need.As businesses have
33、 much in common,their application systems also tend to have a common architecture that reflects the application requirements.A generic application architecture is an architecture for a type of software system that may be configured and adapted to create a system that meets specific requirements.,Cha
34、pter 6 Architectural design,Use of application architectures,As a starting point for architectural design.As a design checklist.As a way of organising the work of the development team.As a means of assessing components for reuse.As a vocabulary for talking about application types.,Chapter 6 Architec
35、tural design,Examples of application types,Data processing applicationsData driven applications that process data in batches without explicit user intervention during the processing.Transaction processing applicationsData-centred applications that process user requests and update information in a sy
36、stem database.Event processing systemsApplications where system actions depend on interpreting events from the systems environment.Language processing systemsApplications where the users intentions are specified in a formal language that is processed and interpreted by the system.,Chapter 6 Architec
37、tural design,Application type examples,Focus here is on transaction processing and language processing systems.Transaction processing systemsE-commerce systems;Reservation systems.Language processing systemsCompilers;Command interpreters.,Chapter 6 Architectural design,Transaction processing systems
38、,Process user requests for information from a database or requests to update the database.From a user perspective a transaction is:Any coherent sequence of operations that satisfies a goal;For example-find the times of flights from London to Paris.Users make asynchronous requests for service which a
39、re then processed by a transaction manager.,Chapter 6 Architectural design,The structure of transaction processing applications,Chapter 6 Architectural design,The software architecture of an ATM system,Chapter 6 Architectural design,Information systems architecture,Information systems have a generic
40、 architecture that can be organised as a layered architecture.These are transaction-based systems as interaction with these systems generally involves database transactions.Layers include:The user interfaceUser communicationsInformation retrievalSystem database,Chapter 6 Architectural design,Layered
41、 information system architecture,Chapter 6 Architectural design,The architecture of the MHC-PMS,Chapter 6 Architectural design,Web-based information systems,Information and resource management systems are now usually web-based systems where the user interfaces are implemented using a web browser.For
42、 example,e-commerce systems are Internet-based resource management systems that accept electronic orders for goods or services and then arrange delivery of these goods or services to the customer.In an e-commerce system,the application-specific layer includes additional functionality supporting a sh
43、opping cart in which users can place a number of items in separate transactions,then pay for them all together in a single transaction.,Chapter 6 Architectural design,Server implementation,These systems are often implemented as multi-tier client server/architectures(discussed in Chapter 18)The web s
44、erver is responsible for all user communications,with the user interface implemented using a web browser;The application server is responsible for implementing application-specific logic as well as information storage and retrieval requests;The database server moves information to and from the datab
45、ase and handles transaction management.,Chapter 6 Architectural design,Language processing systems,Accept a natural or artificial language as input and generate some other representation of that language.May include an interpreter to act on the instructions in the language that is being processed.Us
46、ed in situations where the easiest way to solve a problem is to describe an algorithm or describe the system dataMeta-case tools process tool descriptions,method rules,etc and generate tools.,Chapter 6 Architectural design,The architecture of a language processing system,Chapter 6 Architectural desi
47、gn,Compiler components,A lexical analyzer,which takes input language tokens and converts them to an internal form.A symbol table,which holds information about the names of entities(variables,class names,object names,etc.)used in the text that is being translated.A syntax analyzer,which checks the sy
48、ntax of the language being translated.A syntax tree,which is an internal structure representing the program being compiled.,Chapter 6 Architectural design,Compiler components,A semantic analyzer that uses information from the syntax tree and the symbol table to check the semantic correctness of the
49、input language text.A code generator that walks the syntax tree and generates abstract machine code.,Chapter 6 Architectural design,A pipe and filter compiler architecture,Chapter 6 Architectural design,A repository architecture for a language processing system,Chapter 6 Architectural design,Key poi
50、nts,Models of application systems architectures help us understand and compare applications,validate application system designs and assess large-scale components for reuse.Transaction processing systems are interactive systems that allow information in a database to be remotely accessed and modified
