1. BTS530: Major Project Planning and Design
Architectural Patterns / Principles
References and Material From:
Applying UML and Patterns, 3rd Edition, chapters 26 and 13

2. Architectural Patterns/Principles
Layers
Separation of Concerns
Model-View Separation Principle

3. Layers The Layers Pattern:
Organize large-scale logical structure of a system into discrete layers of responsibilities
lower layers are low-level general services, higher layers more application specific
collaboration and coupling is from higher to lower layers
lower to higher coupling is avoided
Benefits
helps isolate application logic from UI for reusability
isolates source code changes—eases maintainability
keeps coupling between areas of concern (e.g. layers) low
lower layers contain reusable functions
some layers can be distributed….etc…
Applying UML and Patterns P. 203

4. Applying UML and Patterns Fig. 13.4

5. Separation of Concerns
responsibilities of objects in a layer should be strongly related to each other and not mixed with responsibilities of other layers
=>UI objects should not do application logic
=>application object should not do DB logic
Applying UML and Patterns P. 203

6. Model-View Separation
Do not connect or couple non-UI objects directly to UI objects.
Do not put application logic (e.g. tax calculations) in the UI object methods. UI object should only:
initialize UI elements
receive UI events (e.g. mouseclick)
delegate requests for application logic on to non-UI objects (e.g. facades)
Applying UML and Patterns P. 209

7. Model-View Separation
domain object should not have direct knowledge of UI objects, at least as view objects
E.g. Sale should not directly send a message to a GUI window ProcessSaleFrame asking it to display something
Relaxation of this principle: Observer pattern—domain objects send messages to UI objects viewed only in terms of an interface such as a PropertyListener.
Applying UML and Patterns P. 209/210

8. Applying UML and Patterns Fig. 13.8