1 Design Methods for Reactive Systems, R.J. Wieringa Part V: Communication Notations Jens Bæk Jørgensen, University of Aarhus

2 Where are we?

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

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

5 Data flow diagrams (DFDs): basic concepts zFlow: Instantaneous and reliable communication channel yCausal flow or semantic flow yTime-discrete or time-continuous flow zStores: Remembers the data written to it zProcess: Some system activity yData process yControl process yComposite process zStateless or stateful processes

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

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

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

9 Communication diagrams: heating controller; instance-level

10 Communication diagrams: components

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

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

13 Communication diagrams: flowdown

14 Context modelling: motivation

15 Context modelling: alternative system boundaries for the elevator controller

16 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

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

18 Requirements-level architectures: input sources

19 Requirements-level architectures: encapsulation versus layering

20 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

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

22 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

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

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

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