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 book’s web-site:
October 21, 2009

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 system’s:
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 system’s structure
The system’s 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 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 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 , 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 , SE-7]

26. …Reference Architectures
Example of reference architecture: the OSI model [Fig , SE-7]