Demystifying Architectural Styles Nikunj Mehta

3/11/02Demystifying Architectural Styles2 Agenda Architectural Styles The Alfa Project Architectural framework Composing Client Server Style Lessons learned

3/11/02Demystifying Architectural Styles3 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

3/11/02Demystifying Architectural Styles4 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

3/11/02Demystifying Architectural Styles5 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 to know which style is appropriate?

3/11/02Demystifying Architectural Styles6 We Need… Style and architectural primitives Architectural composition techniques Tool-supported formal compositional model Separation of behavioral, structural, compositional and interaction concerns Architectural prototyping framework Connector composition techniques An architectural assembly language Welcome Alfa!

3/11/02Demystifying Architectural Styles7 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

3/11/02Demystifying Architectural Styles8 Composition primitives Particles –Simplest architectural elements Link Entry Portal Exit Portal Particle Jumper Particle Portals –Entry/exit points for particles Jumpers –Interaction ducts –Softwire Links –Interaction path between particles

3/11/02Demystifying Architectural Styles9 Behavioral primitives Fragment Controller –Locus of functional computation Portal Controller Fragment Controller Transport Controller –Locus of interaction Portal Controller –Locus of message filtering/tagging

3/11/02Demystifying Architectural Styles10 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

3/11/02Demystifying Architectural Styles11 Architectural framework Compositional Aspects Behavioral Aspects

3/11/02Demystifying Architectural Styles12 Composing Client Server Style Client Protocol ConnectionServer Protocol

3/11/02Demystifying Architectural Styles13 Lessons learned Architecture approaches should be composable Provide simple primitives that map consistently to implementation Data-centric styles differ fundamentally from communication-centric styles Choose an architectural style that makes sense –Know which style is good for your context –Or compose your own architectural style –Know the software connectors required Create architectural implementation framework