Architecture Styles

Intro

• It is a pattern of component types and their interactions.
• Define constraints: how things are allowed to interact.
• Architectural pattern is synonym for style.
• Defining features:
  • Component types: e.g data store, processes etc.
  • Component layout: e.g. which process is allowed to access data store.
  • Connectors: e.g how are they connected ? RPC, Data stream ?
  • Constraints: On components - e.g. data store cant modify itself, On connections - no P2P communication allowed.

Data Centred

• Characterised by the access/update of a central data store.
• The data store can be passive (e.g. a file) or be active (e.g. blackboard)
• Good for integration and extensibility. There is a low coupling - only the data is shared.
• E.g. Transactional DB, Blackboard, CASE Tools.

Blackboard

• If the current state of the central data is the main trigger for processes to execute, then the repository can be a blackboard.
• A common knowledge base, the "blackboard", is iteratively updated by a diverse group of specialist knowledge sources, starting with a problem specification and ending with a solution.
• Each knowledge source updates the blackboard with a partial solution when its internal constraints match the blackboard state.
• In this way, the specialists work together to solve the problem.
• Invocation of a KS is triggered by the state of the blackboard.

Data Flow Architectures

• Characterized by viewing the system as a series of transformations on successive pieces of input data.
• Orderly motion of data. Explicit pattern of data flow.
• No direct interactions b/w components.
• Objectives: Modifiability - plug in/out components. Reusability - sequence of components plugged together.