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Demystifying Architectural Styles
Nikunj Mehta
3/11/02 Demystifying Architectural Styles 2
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
3/11/02 Demystifying Architectural Styles 3
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
3/11/02 Demystifying Architectural Styles 4
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?
3/11/02 Demystifying Architectural Styles 5
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!
3/11/02 Demystifying Architectural Styles 6
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
3/11/02 Demystifying Architectural Styles 7
Composition primitives
• Particles– Simplest architectural
elements
• Portals– Entry/exit points for
particles
• Jumpers– Interaction ducts – Softwire
• Links– Interaction path between
particles
Fragment
OutputPortal
Jumper
InputPortal
Transport
3/11/02 Demystifying Architectural Styles 8
Behavioral primitives
• Fragment Controller– Locus of functional
computation
• Transport Controller– Locus of interaction
• Portal Controller– Locus of message
filtering/taggingFragment
OutputPortal
Jumper
InputPortal
Transport
3/11/02 Demystifying Architectural Styles 9
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
3/11/02 Demystifying Architectural Styles 10
Architectural frameworkArchitectureManager
ArchitectureManager()getInstance()createParticle()createParticle()createMessage()createCall()stopParticle()shutParticle()removeParticle()startParticle()pauseParticle()linkParticles()linkParticles()unlinkParticles()joinMessageProcessing()
-$manager
FragmentController
FragmentController()getType()
TransportController
TransportController()handleMessage()getType()
ParticleController
HALT_READY : int = 5HALTED : int = 1REMOVE_READY : int = 4state : int = HALTEDSUSPENDED : int = 3READY : int = 2
getType()startParticle()stopParticle()pauseParticle()removeParticle()shutParticle()removeThyself()isActive()messageArrived()ParticleController()setDispatcher()getDispatcher()getOwner()sendMessage()
Dispatcher
dispatchMessage()stateChanged()
dispatcher
Particle
FRAGMENT : int = 1TRANSPORT : int = 2
Particle()Particle()handleMessage()getType()getController()getInputPortals()getOutputPortals()
owner
#controller
PortalController
jumperChanged()setPortal()
Portal
INCOMING : int = 1OUTGOING : int = 2direction : int
Portal()Portal()getDirection()getOwner()setJumper()removeJumper()getJumper()setPortalController()handleMessage()forwardMessage()
-owner
jumper
#controller
DefaultPortalController
DefaultPortalController()DefaultPortalController()handleMessage()
portal
Call
PARAMS : int = 0RESULT : int = 1EXCEPTION : int = 2resultAvailable : boolean = false
Call()setResult()getResult()getParams()setException()getException()
Message
SYSTEM_STOP : int = 1SYSTEM_START : int = 2SYSTEM_SHUT : int = 3SYSTEM_PAUSE : int = 4SYSTEM_REMOVE : int = 5MIN_TYPE_VALUE : int = 1024type : intpayload : Object
Message()Message()Message()getType()getPayload()
<<creates>>
<<creates>>
output
0..n
<<uses>>
inputs
0..n
<<uses>>
PooledAsynchronousDispatcher
countOfWorkers : int = 0DEFAULT_POOL_SIZE : int = 5
PooledAsynchronousDispatcher()PooledAsynchronousDispatcher()PooledAsynchronousDispatcher()PooledAsynchronousDispatcher()createWorkerThreadPool()startThreadPool()interruptThreadPool()isAliveThreadPool()stateChanged()
Dispatcher
dispatchMessage()stateChanged()
CircularQueue
DEFAULT_CAPACITY : int = 5emptySlots : intqueue[] : Objectcapacity : inthead : inttail : int
CircularQueue()CircularQueue()getLength()enqueue()dequeue()isFull()isEmpty()
Thread(from lang)
Queue
getLength()enqueue()dequeue()
isFull()isEmpty()
AsynchronousDispatcher
keepWorking : boolean = truewaiting : boolean = trueid : String
AsynchronousDispatcher()AsynchronousDispatcher()AsynchronousDispatcher()AsynchronousDispatcher()getWaitingLength()addToBuffer()getMessage()dispatchMessage()createWorkerThread()stateChanged()run()toString()
#worker
#queue
workers
1..n
<<uses>>
LinkedList(from util)
DynamicQueue
DynamicQueue()getLength()enqueue()dequeue()isFull()isEmpty()
Compositional Aspects Behavioral Aspects
3/11/02 Demystifying Architectural Styles 11
Composing Client Server
Style
P rotoco l
P rotoco lP rotoco l
Client
C on n
C on n
P rotoco l
Server
C on n
C on n
P rotoco l P rotoco l
C on n
C on n
Server
Server
C lient
C on n
C on n
P rotoco lP rotoco l
P rotoco lP rotoco l
P rotoco lP rotoco l Protocol
Con
nect
ion
Client
3/11/02 Demystifying Architectural Styles 12
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