CS 425/625 Software Engineering Architectural Design

1
CS 425/625 Software Engineering Architectural
Design

• Based on Chapter 11 of the textbook SE-8 Ian
  Sommerville,
• Software Engineering, 8th Ed., Addison-Wesley,
  2006 and on the
• Ch11 PowerPoint presentation available at the
  books web-site
• www.comp.lancs.ac.uk/computing/resources/IanS/SE6/
  Slides/index.html
• October 15, 2008

2
Outline

• Introduction
• System Organization
• Modular Decomposition
• Control Styles
• Reference Architectures

3
Introduction.

• Architectural (high-level) design the process
  of establishing the subsystems of a larger
  software system and defining a framework for
  subsystem control and data communication
• Software architecture the output of the
  high-level design process
• Defining and documenting the software
  architecture provides support for
• Stakeholder communication
• System analysis
• Large-scale software reuse

4
.Introduction

• The overall system architecture influences the
  systems
• Performance
• Security
• Safety
• Availability
• Maintainability

5
..Introduction..

• Distinction between subsystem and module
• Subsystem larger part of the system with
  quasi-independent operation depends little on
  other subsystems services, contains other
  subsystems and modules as well as interfaces for
  communicating with other subsystems
• Module non-independent system component that
  provides services to other modules usually makes
  use of other modules services and contains
  simpler components

6
Introduction.

• Common high-level design activities
• System structuring (system organization)
  identification of sub-systems and their
  communication paths
• Modular decomposition identification of modules
  and module interconnection within each subsystem
• Control modeling determination of control
  connections between subsystems (modules)

7
.Introduction

• Types of architectural design models
• Static structural models
• Dynamic process models
• Interface models
• Relationship models
• Distribution models

8
System Organization..

• System organization (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
  systems structure
• The systems architecture can be shown using more
  specific structural models, e.g.
• Repository model
• Client-server model
• Layered model

9
.System Organization.

• The repository model shows a systems
  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 layered model (the abstract machine model)
  depicts the system as a series of layers, each
  layer representing an abstract machine and having
  assigned a subsystem

10
..System Organization

• Example of a structural model depicted using a
  block diagram a packing robot system Fig. 11.1,
  SE-8

11
System Organization..

• Example of repository model for system
  architecture a CASE toolset Fig. 11.2, SE-8

12
.System Organization.

• Example of client-sever architecture a movie and
  picture library Fig. 11.3, SE-8

13
..System Organization

• An abstract machine model a version management
  system Fig. 11.4, SE-8

14
Modular Decomposition..

• 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)
• Styles that may be used for decomposition
• Object-oriented decomposition a subsystem
  consists of several communicating objects
• Function-oriented pipelining functional modules
  are identified, together with data transfer paths

15
.Modular Decomposition.

• Partial object model of an invoicing system Fig.
  11.5, SE-8

16
..Modular Decomposition

• DFD of an invoicing system Fig. 11.6, SE-8

17
Control Styles..

• Control models emphasize control flow among
  subsystems
• Two general approaches
• 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
• Call-return model (top-down subroutine model)
• Manager model (applies to concurrent systems, in
  which several processes run in parallel)

18
.Control Styles.

• Two general approaches (continued)
• Event-based control each subsystem has control
  responsibilities they respond to events
  generated by the environment and/or other
  subsystems
• Broadcast models an event is dispatched to all
  subsystems
• Interrupt-driven models make use of interrupt
  handlers typical to RTS

19
..Control Styles...

• The call-return control model Fig. 11.7, SE-7

20
Control Styles..

• Example of a centralized control model an RTS
• Fig. 11.8, SE-7

21
.Control Styles.

• Control model with selective broadcasting Fig.
  11.9, SE-7

22
..Control Styles

• Example of interrupt-driven control model Fig.
  11.10, SE-7

23
Reference Architectures

• 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 architectural design
  various design models can (and usually need) be
  applied in combination

24
.Reference Architectures..

• Main categories
• Generic models models extracted from real
  systems that provide a common architectural
  framework for new applications within the domain
  (e.g., compiler design)
• 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)

25
..Reference Architectures.

• Generic repository model of a language processing
  system Fig. 13.13, SE-7

26
Reference Architectures

• Example of reference architecture the OSI model
  Fig. 11.11, SE-7