1	Architectural Issues in Software Reuse: not only functionality, but packaging different kinds of component packaging different kinds of interactions between the components system model, components, connectors and control structure
2	Pipeline System model - mapping data streams to data streams Components - filters (computational, local processing) Connectors - data streams - ascii ds for unix pipelines Control Structure - data flow
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4	Data abstraction (OO) System model - localized state maintenance Components - managers: servers, objects, ADT Connectors - proc call with dynamic binding Control structure - decentralized, usually single thread
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6	Implicit invocation (event based) System model - independent reactive processes Components - processes that signal significant events without knowing recipients of signals Connectors - automatic invocation of processes that have registered interest in events Control structure - decentralized; indiv components are not aware of recipients of signal
7	Repository ( db and blackboard systems) System model - centralized data, usually richly structured Components - one memory, many purely computational processes Connectors - comput. units interact with memory by direct data access or procedure call Control structure - varies with type of repository; (depends on input data stream, as for db, predetermined or internal (depends on state of computation as for blackboards)
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9	Interpreter System model - virtual machine Components - one state machine ( the execution engine) and three memories (current state of execution machine, program being interpreted, current state of program being interpreted) Connectors - data access and proc call Control structures - state-transition for execution engine; input-driven for selection of what to interpret.
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11	Main program and subroutines System model - call and definition hierarchy Components - procedures Connectors - proc calls Control structure - single thread
12	Layered System model - hierarchy of opaque layers Components - composites - collections of procs Connectors - depends on structure of components; often proc calls; might also be client server Control structure - single thread
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14	Reconciling Architectual Mismatch
15	Solving the Mismatch Problem change A’s form to B’s form; in principle possible (but expensive) to completely rewrite one of the components to work with the other publish an abstraction of A’s form: APIs publish the procedure calls used to control a component. Open Interfaces -abstraction. Projections or views for databases
16	Solving the Mismatch Problem (cont.) transform from A’s form to B’s form on the fly: some distributed systems do this negotiate to find a common form for A and B: modems commonly negotiate to find their fastest common protocol make B multilingual: portable unix code will run on many processors
17	Solving the Mismatch Problem (cont.) provide B with import/export converters: standalone applications provide representation conversion services; extensions or external add-ons translate to and from foreign formats on demand
18	Solving the Mismatch Problem (cont.) introduce an intermediate form; external interchange representation, sometimes supported by Interface Description Languages (IDLs) can provide a neutral base. especially convenient when many components with different forms are involved. standard distribution forms (RTF, MIF, Postscript) another alternative
19	Solving the Mismatch Problem (cont.) attach an adapter or wrapper to A: ultimate wrapper may be the code that causes one machine to emulate another. maintain parallel consistent versions of A and B: possible, though delicate, for A & B to maintain their own forms and be extremely careful to make all changes to both forms
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