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architeral design.pptx
- 2. Software architecture • The design process for identifying 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
- 3. Architectural design • An early stage of the system design process • Represents 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
- 4. Advantages of explicit architecture • Stakeholder communication – Architecture may be used as a focus of discussion by system stakeholders • System analysis – Means that analysis of whether the system can meet its non-functional requirements is possible • Large-scale reuse – The architecture may be reusable across a range of systems
- 5. Architectural design process • System structuring – The system is decomposed into several principal sub- systems and communications between these sub- systems are identified • Control modelling – A model of the control relationships between the different parts of the system is established • Modular decomposition – The identified sub-systems are decomposed into modules
- 6. Sub-systems and modules • A sub-system is a system in its own right whose operation is independent of the services provided by other sub-systems. • A module is a system component that provides services to other components but would not normally be considered as a separate system
- 7. Architectural models • Different architectural models may be produced during the design process • Each model presents different perspectives on the architecture
- 8. Architectural models • Static structural model that shows the major system components • Dynamic process model that shows the process structure of the system • Interface model that defines sub-system interfaces • Relationships model such as a data-flow model
- 9. Architecture attributes • Performance – Localise operations to minimise sub-system communication • Security – Use a layered architecture with critical assets in inner layers • Safety – Isolate safety-critical components • Availability – Include redundant components in the architecture • Maintainability – Use fine-grain, self-contained components
- 10. System structuring • Concerned with decomposing the system into interacting sub-systems • The architectural design is normally expressed as a block diagram presenting an overview of the system structure • More specific models showing how sub- systems share data, are distributed and interface with each other may also be developed
- 11. Packing robot control system Vision system Object identification system A rm cont roller Gripper controller Packaging selection system Packing system Conveyor controller
- 12. Cont… • System Structuring – The Repository Model – The Client Server Model – The Layered Model • Modular Decomposition – Data Flow diagram – Object Model • Control Styles – Centralized • Call return • Manager – Event based • Broadcasting • Interrupt Driven
- 13. The repository model • 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 explicitly to other sub-systems • When large amounts of data are to be shared, the repository model of sharing is most commonly used
- 14. Cont… • Disadvantages – Sub-systems must agree on a repository data model. Inevitably a compromise – Data evolution is difficult and expensive – No scope for specific management policies – Difficult to distribute efficiently
- 16. Repository model characteristics • Advantages – Efficient way to share large amounts of data – Sub-systems need not be concerned with how data is produced Centralised management e.g. backup, security, etc. – Sharing model is published as the repository schema
- 17. Client-server architecture • Distributed system model which shows how data and processing is distributed across a range of components • Set of stand-alone servers which provide specific services such as printing, data management, etc. • Set of clients which call on these services • Network which allows clients to access servers
- 18. Film and picture library Catalogue server Catalogue Video server Film clip files Picture server Digitized photographs Hypertext server Hypertext web Client 1 Client 2 Client 3 Client 4 Wide-bandwidth network
- 19. Client-server characteristics • Advantages – Distribution of data is straightforward – Makes effective use of networked systems. May require cheaper hardware – Easy to add new servers or upgrade existing servers • Disadvantages – No shared data model so sub-systems use different data organisation. data interchange may be inefficient – Redundant management in each server – No central register of names and services - it may be hard to find out what servers and services are available
- 20. Abstract machine model • 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, often difficult to structure systems in this way
- 21. Version management system Operating system Databasesystem Object management Version management
- 22. Control models • Are concerned with the control flow between sub- systems. Distinct from the system decomposition model • Centralised control – One sub-system has overall responsibility for control and starts and stops other sub-systems • Event-based control – Each sub-system can respond to externally generated events from other sub-systems or the system’s environment
- 23. Centralised control • A control sub-system takes responsibility for managing the execution of other sub-systems • Call-return model – Top-down subroutine model where control starts at the top of a subroutine hierarchy and moves downwards. Applicable to sequential systems • Manager model – Applicable to concurrent systems. One system component controls the stopping, starting and coordination of other system processes. Can be implemented in sequential systems as a case statement
- 24. Call-return model Routine 1.2 Routine 1.1 Routine 3.2 Routine 3.1 Routine 2 Routine 3 Routine 1 Main program
- 26. Event-driven systems • Driven by externally generated events where the timing of the event is outwith the control of the sub-systems which process the event • Two principal event-driven models – Broadcast models. An event is broadcast to all sub-systems. Any sub-system which can handle the event may do so – Interrupt-driven models. Used in real-time systems where interrupts are detected by an interrupt handler and passed to some other component for processing • Other event driven models include spreadsheets and production systems
- 27. Broadcast model • Effective in integrating sub-systems on different computers in a network • Sub-systems register an interest in specific events. When these occur, control is transferred to the sub-system which can handle the event • Control policy is not embedded in the event and message handler. Sub-systems decide on events of interest to them • However, sub-systems don’t know if or when an event will be handled
- 28. Cont... Sub-system 1 Event and message handler Sub-system 2 Sub-system 3 Sub-system 4
- 29. Interrupt-driven systems • Used in real-time systems where fast response to an event is essential • There are known interrupt types with a handler defined for each type • Each type is associated with a memory location and a hardware switch causes transfer to its handler • Allows fast response but complex to program and difficult to validate
- 31. Modular decomposition • Another structural level where sub-systems are decomposed into modules • Two modular decomposition models covered – An object model where the system is decomposed into interacting objects – A data-flow model where the system is decomposed into functional modules which transform inputs to outputs. Also known as the pipeline model • If possible, decisions about concurrency should be delayed until modules are implemented
- 32. Object models • Structure the system into a set of loosely coupled objects with well-defined interfaces • Object-oriented decomposition is concerned with identifying object classes, their attributes and operations • When implemented, objects are created from these classes and some control model used to coordinate object operations
- 33. Invoice processing system issue () sendReminder () acceptPayment () sendReceipt () invoice# date amount customer Invoice invoice# date amount customer# Receipt invoice# date amount customer# Payment customer# name address credit period Customer
- 34. Data-flow models • Functional transformations 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 for interactive systems
- 35. Invoice processing system Read issued invoices Identify payments Issue receipts Find payments due Receipts Issue payment reminder Reminders Invoices Payments
- 36. Thank you