2. Demystifying Architectural Styles Nikunj Mehta

3. 3/11/02Demystifying Architectural Styles2 Architectural Styles Characterize –Structure, i.e. external appearance –Supported interactions, i.e. software connectors –Topological constraints Various categories –Motion of data, e.g. batch sequential, data flow –Order of computation, e.g. subroutines, objects –Communication centric, e.g. client/server, events –Data centric, e.g. databases, blackboard, hypertext –Layered, e.g. interpreter

4. 3/11/02Demystifying Architectural Styles3 Why Research Architectural Styles? Design patterns are not enough –Styles support higher level reuse Component based software engineering –Avoiding COTS mismatches Model based software engineering –Avoiding model clashes Little is known about –Style similarities –Style primitives –Architectural primitives –Connector composition

5. 3/11/02Demystifying Architectural Styles4 Mystical Nature of Styles Stem from principles of encapsulation, and information hiding Invisible software connectors are key Origin of styles - a mystery –How is a style created? –How is a connector created? Codification of successful approaches One size fits all? How do we which styles is appropriate?

6. 3/11/02Demystifying Architectural Styles5 We Need… Style and architectural primitives Architectural composition techniques Tool-supported formal model Separation of behavioral, structural, compositional and interaction concerns Architectural prototyping framework Connector composition Architectural assembly language Welcome Alfa!

7. 3/11/02Demystifying Architectural Styles6 The Alfa Project Alfa – a bottom-up approach –Architecture needs composition Assembly language –Constructs and primitives for composition –Fine grain control over semantics –General but simple –Small set for analyzability and conceptual integrity –Style neutral and implementation agnostic Memories revived? –Assembly mnemonics and machine code –Start small, and then create languages and tools

8. 3/11/02Demystifying Architectural Styles7 Composition primitives Particles –Simplest architectural elements Portals –Entry/exit points for particles Jumpers –Interaction ducts –Softwire Links –Interaction path between particles

9. 3/11/02Demystifying Architectural Styles8 Behavioral primitives Fragment Controller –Locus of functional computation Transport Controller –Locus of interaction Portal Controller –Locus of message filtering/tagging

10. 3/11/02Demystifying Architectural Styles9 Interaction primitives Message –Communication container Call –Procedural invocation primitive Dispatcher –Dispatch messages and calls to controllers Thread –Schedule and control execution Queue –Buffer for holding messages and calls Semaphore, Monitor, Rendezvous –Synchronization

11. 3/11/02Demystifying Architectural Styles10 Architectural framework Compositional Aspects Behavioral Aspects

12. 3/11/02Demystifying Architectural Styles11 Composing Client Server Style

13. 3/11/02Demystifying Architectural Styles12 Lessons learned Architecture approaches should be composable Provide simple primitives that map consistently to implementation Data centric styles differ at fundamental level from communication centric styles Choose an architectural style that makes sense –Know which style is good for your context –Know the software connectors required Create architectural implementation framework