CS 425625 Software Engineering Architectural Design Based on
CS 425/625 Software Engineering Architectural Design Based on Chapter 10 of the textbook [Somm 00] Ian Sommerville, Software Engineering, 6 th Ed. , Addison-Wesley, 2000 and on the Ch 10 Power. Point presentation available at the book’s web-site: www. comp. lancs. ac. uk/computing/resources/Ian. S/SE 6/Slides/index. html October 08, 2003 1
Outline n n n 2 Introduction System Structuring Control Modeling Modular Decomposition Domain-specific Architectures
Introduction…. n n n Architectural (high-level) design = the process of establishing the subsystems of a larger software system and defining a framework for subsystem control and communication Software architecture = the output of the high-level design process Defining and documenting the software architecture provides support for: u Stakeholder communication u System analysis u Large-scale software reuse 3
. Introduction… n The overall system architecture influences the system’s: u Performance u Safety u Security u Availability u Distributability u Maintainability 4
. . Introduction. . n Distinction between subsystem and module: u Subsystem = larger part of the system with quasiindependent operation; depends little on other subsystems’ services, contains other subsystems and modules as well as interfaces for communicating with other subsystems u Module = non-independent system component that provides services to other modules; usually makes use of other modules’ services and contains simpler components 5
…Introduction. n Common high-level design activities: u System structuring: identification of subsystems and their communication paths u Control modeling: determination of control connections between subsystems u Modular decomposition: identification of modules and module interconnection within each subsystem 6
…. Introduction n Types of architectural design models: u Static structural models u Dynamic process models u Interface models u Relationship models 7
System Structuring…. . n n System structuring is focused on identifying subsystems and their communication links Communications between subsystems involve both data and control Block diagrams can be used for describing the system’s structure The system’s architecture can be shown using more specific structural models, e. g. : u u u 8 Repository model Client-server models Abstract machine models
. System Structuring…. n n n 9 The repository model shows a system’s architecture centered around a shared database The client-server model is a distributed, network model that describes how operations and data are distributed across several processing units. Some of these units are servers, other are clients The abstract machine model (the layered model) depicts the system as a series of layers, each layer representing an abstract machine and having assigned a subsystem
. . System Structuring… n 10 Example of a structural model depicted using a block diagram: a packing robot system [Fig. 10. 1, Somm 00]
…System Structuring. . n 11 Example of repository model for system architecture: a CASE toolset [Fig. 10. 2, Somm 00]
…. System Structuring. n 12 Example of client-sever architecture: a movie and picture library [Fig. 10. 3, Somm 00]
…. . System Structuring n 13 An abstract machine model: a version management system [Fig. 10. 4, Somm 00]
Control Modeling…. . n n Control models emphasize control flow among subsystems Two general approaches: u Centralized control: a single subsystem (central controller) has the control responsibility of the entire system; it may defer control to other subsystems but the control must be returned to the central controller Ø Ø 14 Call-return model (top-down subroutine model) Manager model (applies to concurrent systems, in which several processes run in parallel)
. Control Modeling…. . n Two general approaches (continued): u Event-based control: each subsystem has control responsibilities; they respond to events generated by the environment and/or other subsystems Ø Ø 15 Broadcast models: an event is dispatched to all subsystems Interrupt-driven models: make use of interrupt handlers; typical to RTS
. . Control Modeling. . . n 16 The call-return control model [Fig. 10. 5, Somm 00]
…Control Modeling. . n 17 Example of a centralized control model: an RTS [Fig. 10. 6, Somm 00]
…. Control Modeling. n 18 Control model with selective broadcasting [Fig. 10. 7, SE-6]
…. . Control Modeling n 19 Example of interrupt-driven control model [Fig. 10. 8, Somm 00]
Modular Decomposition. . n n n Modular decomposition means dividing each subsystem in modules and identifying interconnections between modules Models described previously can be applied here as well (a subsystem is, in fact, a system, and the distinction between a subsystem and a module is relative) Models that may be used for decomposition: u u 20 Object-oriented model: a subsystem consists of several communicating objects Data-flow model (pipeline model): functional modules are identified, together with data transfer paths
. Modular Decomposition. n 21 Partial object model of an invoicing system [Fig. 10. 9, Somm 00]
. . Modular Decomposition n 22 DFD of an invoicing system [Fig. 10, Somm 00]
Domain-specific Architectures… n n 23 A domain-specific architecture is characteristic to a particular application domain; it proposes a common architectural structure that can be used across applications within that particular domain Note that, generally, in software architectural design various design models can (and usually need) be applied in combination
. Domain-specific Architectures. . . n Main categories: u Generic models: models extracted from real systems that provide a common architectural framework for new applications within the domain (e. g. , compiler design) u Reference models: more abstract models that communicate commonly used domain and design concepts; derived from studying the application domain (e. g. , the Open Systems Interconnection [OSI] reference model) 24
. . Domain-specific Architectures. n 25 Generic repository model of a language processing system [Fig. 10. 12, Somm 00]
…Domain-specific Architectures n 26 Example of reference architecture: the OSI model [Fig. 10. 13, Somm 00]
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