1. Chapter 13
Logical Architecture

2. Logical Architecture Large-scale organization of classes
Packages -
Subsystems
Layers
Tools - UML package diagrams

3. Layer Coarse grained Cohesive responsibility Strict or relaxed
E.g. User Interface or common services
Strict or relaxed
What are the pros and cons of each?
This class focuses on one layer – application (or domain) layer.

4. Software Architecture
Many definitions – fuzzy concept
“a set of significant decision about the organization of a software system.”
The framework or structure.
Key aspect: Large scale, big ideas
Motivation
Constraints
Organization
Patterns
Responsibilities
Connections

5. Design with Layers Organize layers using related responsibilities
Collaboration and Coupling
The Layers Pattern

6. Why? Separation of concerns Encapsulate complexity
Eliminate inter-twined code
Features and fixes are contained
Replaceable layer
Reusable function
Team organization
Up-front investment reduces maintenance costs.

7. Domain layer vs. Application Layer
Application layer organization
Create domain objects that encapsulate application logic (Domain Layer)
“Create software objects with names and information similar to the real-world domain and assign application logic responsibilities to them.”
Domain layer != Domain model
“Designing objects this way leads to the application logic layer being more accurately called the domain layer of the architecture – the layer that contains domain objects.”
Lowers the representational gap.”

8. Terminology Tier - current usage: physical nodes Layers
Partitions - parallel division of layers
See Figs 13.6 and 13.7

9. SSD, System Operations, Layers
When there is a UI layer:
SSD shows operations to the UI Layer
Do not couple UI objects directly to application/domain objects.
Do not put application data into UI objects.
Model (domain) vs UI (view) separation.

10. Summary Separation into layers is a common first step
In Architecture centric design, this flows from the software architecture