Design
Figure 6-1. Example of iterative floor plan design. Three successive versions show how we minimize walking distance and take advantage of sunlight.
Overview
Figure 6-2. The activities of system design (UML activity diagram).
Why is Design so Difficult?
The Purpose of System Design
System Design
How to use the results from the Requirements Analysis for System Design
Section 1. Design Goals
Relationship Between Design Goals
Typical Design Trade-offs
Nonfunctional Requirements give a clue for the use of Design Patterns
Textual Clues in Nonfunctional Requirements
Section 2. System Decomposition
Services and Subsystem Interfaces
Figure 6-4. Subsystem decomposition for an accident management system (UML class diagram, collapsed view). Subsystems are shown as UML packages. Dashed arrows indicate dependencies between subsystems.
Figure 6-3. Subsystem decomposition (UML class diagram).
Choosing Subsystems
Definition: Subsystem Interface Object
Figure 6-28. Analysis model for the MyTrip route planning and execution.
Figure 6-29. Initial subsystem decomposition for MyTrip (UML class diagram).
Figure 6-32. Revised design model for MyTrip (UML Class diagram, associations omitted for clarity).
Figure 6-35. Subsystem decomposition of MyTrip after deciding on the issue of data stores (UML class diagram, packages collapsed for clarity).
Coupling and Coherence
Figure 6-5. Example of coupling reduction (UML object diagram and Java declarations). This figure shows a parse tree for the expression “a + b + c”. The left column shows the interface of the OpNode class with sharing through attributes. The right column shows the interface of OpNode with sharing through operations. Figure 6-6 shows the changes for each case when a linked list is selected instead.
Figure 6-6. Example of coupling reduction (UML object diagram and Java declarations). This figure shows the impact of changing the parse tree representation of Figure 6-5 to a linked list. In the left column, with sharing through attributes, four attributes need to change (changes indicated in italics). In the right column, with sharing through operations, the interface remains unchanged.
Figure 6-7. Decision tracking system (UML class diagram). The DecisionSubsystem has a low coherence: The classes Criterion, Alternative, and DesignProblem have no relationships with Subtask, ActionItem, and Task.
Figure 6-8. Alternative subsystem decomposition for the decision tracking system of Figure 6-7 (UML class diagram). The coherence of the RationaleSubsystem and the PlanningSubsystem is higher than the coherence of the original DecisionSubsystem. Note also that we also reduced the complexity by decomposing the system into smaller subsystems.
Partitions and Layers
Properties of Layered Systems
Subsystem Decomposition into Layers
Layer and Partition Relationships between Subsystems
Figure 6-12. An example of open architecture: the OSF/Motif library (UML class diagram, packages collapsed). Xlib provides low-level drawing facilities. Xt provides basic user interface widget management. Motif provides a large number of sophisticated widgets. The Application can access each of these layers independently.
Figure 6-10. An example of closed architecture: the OSI model (UML class diagram). The OSI model decomposes network services into seven layers, each responsible for a different level of abstraction.
Figure 6-11. An example of closed architecture (UML class diagram). CORBA enables the access of objects implemented in different languages on different hosts. CORBA effectively implements the Presentation and Session layers of the OSI stack.
Virtual Machine
Virtual Machine (Dijkstra, 1965)
Closed Architecture (Opaque Layering)
Open Architecture (Transparent Layering)
Software Architectures
Repository Architecture
Examples of Repository Architecture
Client/Server Architecture
Figure 6-18. Client/server architecture (UML class diagram). Clients request services from one or more Servers. The Server has no knowledge of the Client. The client/server architecture is a generalization of the repository architecture.
Figure 6-19. The World Wide Web as an instance of the client/server architecture (UML object diagram).
Design Goals for Client/Server Systems
Problems with Client/Server Architectures
Peer-to-Peer Architecture
Model/View/Controller
Example of a File System based on MVC Architecture
Sequence of Events
Figure 6-22. Pipe and filter architecture (UML class diagram). A Filter can have many inputs and outputs. A Pipe connects one of the outputs of a Filter to one of the inputs of another Filter.
Figure 6-23. An instance of the pipe and filter architecture (Unix command and UML activity diagram).
Summary
Email: d-russomanno@memphis.edu
Other information: ECE 3220
Download presentation source