Patterns, Styles, and DSSAs
Patterns, styles, and DSSAs differ in their scope and application-domain knowledge.
- Program design patterns
Smaller scope and shallower domain knowledge. - Architectural patterns
Broader scope and greater architectural knowledge. - Architectural styles
Wider scope and less domain specificity than architectural patterns. - DSSAs
Broad system scope with deep application-domain knowledge.
Domain-Specific Software Architectures
A Domain-Specific Software Architecture (DSSA) is an assemblage of software components that are:
- Specialized for a particular type of task or domain.
- Generalized for effective use across that domain.
- Composed in a standardized structure (topology) for building successful applications.
DSSAs are useful when an architecture already exists for the domain in which a new application is being developed.
DSSAs provide extensive reuse of:
- Knowledge
- Previous development
- Architectural solutions
Architectural Patterns
An architectural pattern is a set of architectural design decisions that:
- Applies to a recurring design problem.
- Is parameterized for different software development contexts.
Architectural patterns are similar to DSSAs but are applied at a lower level and within a narrower scope.
State-Logic-Display: Three-Tiered Pattern
The State-Logic-Display pattern separates an application into three parts:
Display
Provides the user interface.
Logic
Contains the application’s business logic.
State
Stores and manages the application’s data.
The pattern can be used in:
- Business applications
- Multi-player games
- Web-based applications
Model-View-Controller
Model-View-Controller (MVC) separates:
- Information
- Presentation
- User interaction
Model
Encapsulates information.
View
Encapsulates display choices and presents information to the user.
Controller
Encapsulates interaction semantics and handles user input.
When model data changes, the view and controller can be notified.
When the user generates an event, the controller can update the model when required.
Sense-Compute-Control
The Sense-Compute-Control pattern is used for structuring embedded control applications.
The computer:
- Reads sensor values.
- Computes control outputs.
- Sends controls to actuators.
- Repeats the process.
Problems with Sense-Compute-Control
The Sense-Compute-Control approach can become computationally demanding because all information is processed centrally.
Behavioral Module Solution
A solution is to implement the system as a set of behavioral modules (horizontal slices).
Each module processes only some of the available information.
This approach was associated with Rodney Brooks in the 1980s at MIT.
Behavior-Based Approach
A behavior-based approach divides a system into multiple behavioral modules, where each module is responsible for a specific behavior.
Each behavioral module:
- Receives relevant sensory or input information.
- Processes the information independently.
- Proposes an action based on its behavior.
An Action Selection Mechanism (ASM) selects or coordinates the proposed actions from the behavioral modules to determine the system’s overall action.
This approach allows different behaviors to operate as separate modules rather than processing all information centrally.
