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Design Methods for Reactive Systems, R.J. WieringaPart V: Communication Notations

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Outline

Data flow diagrams (DFDs)Communication diagramsContext modellingRequirements-level architectures

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Where are we?

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Data flow diagrams (DFDs): heating controller example

A collection of communicating data stores and processes

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Data flow diagrams (DFDs): hierarchical structuring; tank control process

Data processspecification:

Lower-levelDFD

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Data flow diagrams (DFDs): basic concepts (1)

Flow: Instantaneous and reliable communication channel

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Data flow diagrams (DFDs): basic concepts (2)

Stores: Remembers the data written to it

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Data flow diagrams (DFDs): basic concepts (2)

Process: Some system activity Data process Control process Composite process

Stateless or stateful processesSyntax:

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Data flow diagrams (DFDs): control process specification; STD for heater control process

Note consistency with DFD

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Communication diagrams: basics

DFDs instance-level; communication diagrams possibly type-level

Used to represent requirements-level architectures ”Language”

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Communication diagrams: heating controller example

Nodes ~ componentsEdges ~ communication channels

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Communication diagrams: heating controller; instance-level

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Communication diagrams: components

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Communication diagrams: decomposition

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Communication diagrams: decomposition and closely coupled components

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Communication diagrams: decomposition and closely coupled components; elevator controller

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Communication diagrams: allocation of functions to components (allocation table)

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Communication diagrams: flowdown

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Context modelling: motivation

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Context modelling: alternative system boundaries for the elevator controller

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Contex modelling: context boundary

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Context modelling: context diagram for the training information system

We need not only worry about the system boundary,but also about the context boundary … see guidelines

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Context modelling: structuring the context

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Context modelling: structure in the context of a information-provision system

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Context modelling: structure in the context of a directive system

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Context modelling: structure in the context of manipulative system

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Requirements-level architectures: architectures in general

We now move from modelling what is given to designing the SuD

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Requirements-level architectures: input sources

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Requirements-level architectures: encapsulation versus layering

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Requirements-level architectures: architectural styles

Data flow style: Not applicable to reactive

systems

Von Neumann style Strict separation of data

storage and data processing Database and

applicationprograms

Object-oriented style Processing and storage

encapsulated in objects

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Requirements-level architectures: comparison with implementation-level architectures

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Requirements-level architectures: main decomposition approaches

Functional decomposition each system function is allocated to a different component

Subject-oriented decomposition each group of subject domain entities corresponds to a

system component

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Requirements-level architectures: functional decomposition, object-oriented style; the ticket system example

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Requirements-level architectures: subject-oriented decomposition, object-oriented style; the ticket system example

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Requirements-level architectures: mixed architecture

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Requirements-level architectures: communication-oriented decomposition

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Requirements-level architectures: evaluation criteria

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Summary

Data flow diagrams (DFDs)Communication diagramsContext modellingRequirements-level architectures