1 Design Methods for Reactive Systems, R.J. Wieringa Part V: Communication Notations

2 Outline zData flow diagrams (DFDs) zCommunication diagrams zContext modelling zRequirements-level architectures

3 Where are we?

4 Data flow diagrams (DFDs): heating controller example A collection of communicating data stores and processes

5 Data flow diagrams (DFDs): hierarchical structuring; tank control process Data process specification: Lower-level DFD

6 Data flow diagrams (DFDs): basic concepts (1) zFlow: Instantaneous and reliable communication channel

7 Data flow diagrams (DFDs): basic concepts (2) zStores: Remembers the data written to it

8 Data flow diagrams (DFDs): basic concepts (2) zProcess: Some system activity yData process yControl process yComposite process zStateless or stateful processes zSyntax:

9 Data flow diagrams (DFDs): control process specification; STD for heater control process Note consistency with DFD

10 Communication diagrams: basics zDFDs instance-level; communication diagrams possibly type-level zUsed to represent requirements-level architectures z”Language”

11 Communication diagrams: heating controller example Nodes ~ components Edges ~ communication channels

12 Communication diagrams: heating controller; instance-level

13 Communication diagrams: components

14 Communication diagrams: decomposition

15 Communication diagrams: decomposition and closely coupled components

16 Communication diagrams: decomposition and closely coupled components; elevator controller

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

18 Communication diagrams: flowdown

19 Context modelling: motivation

20 Context modelling: alternative system boundaries for the elevator controller

21 Contex modelling: context boundary

22 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

23 Context modelling: structuring the context

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

25 Context modelling: structure in the context of a directive system

26 Context modelling: structure in the context of manipulative system

27 Requirements-level architectures: architectures in general We now move from modelling what is given to designing the SuD

28 Requirements-level architectures: input sources

29 Requirements-level architectures: encapsulation versus layering

30 Requirements-level architectures: architectural styles zData flow style: yNot applicable to reactive systems zVon Neumann style yStrict separation of data storage and data processing yDatabase and application programs zObject-oriented style yProcessing and storage encapsulated in objects

31 Requirements-level architectures: comparison with implementation-level architectures

32 Requirements-level architectures: main decomposition approaches zFunctional decomposition yeach system function is allocated to a different component zSubject-oriented decomposition yeach group of subject domain entities corresponds to a system component

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

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

35 Requirements-level architectures: mixed architecture

36 Requirements-level architectures: communication-oriented decomposition

37 Requirements-level architectures: evaluation criteria

38 Summary zData flow diagrams (DFDs) zCommunication diagrams zContext modelling zRequirements-level architectures