Tutorial: building a model from scratch

This tutorial shows how to build a simple model of a CD radio player in the model editor. It is a simplified version of the CDRadioPlayer example project that you explore in Tutorial: exploring the CD radio player. If you have not read What is being modelled yet, read it first.

Fig. 6 A CD radio player. Source: Wikimedia Commons.

Note

The cluster diagrams in this tutorial come from an earlier version of this guide. Their colours differ slightly from the colours in the interface. For example, test results are light green there. The model also differs from the example project: it is simpler and uses other names. To compare your model with the diagrams, enable the diagram on the cluster pages (see Settings).

All steps are done in Editor mode. Remember that nothing is stored until you press Save in a form.

1. Create the model

1. Start the interface with an empty database (see Starting the interface).

2. On the landing page, click and create the root cluster CDRadioPlayer.

3. On the cluster page of CDRadioPlayer, add two functions with in the Functions table: PlayCD and PlayRadio. These are the main functions of the device.

A root cluster cannot contain hardware. The hardware goes into the subclusters that you create next.

2. CD reader and radio receiver

Each component of the device gets its own cluster with a function, the hardware that realizes it, and a test.

1. In the Clusters table of CDRadioPlayer, click and create the cluster CDReader. Select both Add default hardware? and Add default function?, and name the function ReadCD. The interface creates the hardware CDReader, which realizes ReadCD.

2. Make ReadCD a subfunction of PlayCD. Open the page of PlayCD, click in the Subfunctions table and select CDReader.ReadCD. Reading the CD is part of playing a CD.

3. In the Diagnostic tests table of CDReader, create the test Test_ReadCD. Select Add default test result? to create Test_ReadCD_Result, and enter a cost.

4. On the page of Test_ReadCD, open the tested items of Test_ReadCD_Result and select the function ReadCD. The result now indicates whether the CD can be read.

Fig. 7 The CDReader cluster.

Create the cluster RadioReceiver in the same way, with the function ReceiveRadio (a subfunction of PlayRadio) and the test Test_ReceiveRadio.

Fig. 8 The RadioReceiver cluster.

3. Audio system

Both playing a CD and playing the radio need the audio system. Create the cluster AudioSystem like the previous clusters, with the function GenerateAudio and the test Test_AudioSystem. Make GenerateAudio a subfunction of both PlayCD and PlayRadio.

Fig. 9 The AudioSystem cluster.

4. Power system

The power system provides power to all parts of the device. The power comes from a battery or from the wall socket. A power board selects one of these sources and distributes the power.

1. Create the cluster PowerSystem in CDRadioPlayer, with the hardware PowerSystem and the function ProvidePower.

2. In the Observables table of PowerSystem, create the direct observable PowerLED. The LED shows whether there is power.

3. On the page of ProvidePower, click in the Observed by table and select PowerLED.

Power board

1. In PowerSystem, create the cluster PowerBoard with default hardware and the function DistributePower. Add the test Test_DistributePower, whose result indicates DistributePower.

2. Make DistributePower a subfunction of ProvidePower.

3. The CD reader, the radio receiver and the audio system need power. On the page of DistributePower, click in the Required for table. Add ReadCD, ReceiveRadio and GenerateAudio one by one, without operating modes.

Fig. 10 The PowerBoard cluster. The diagram does not show the required for relations to ReadCD, ReceiveRadio and GenerateAudio.

Operating mode: battery or wall power

The device runs on battery power or on wall power. Model this with an operating mode selector:

• In the Operating mode selectors table of PowerSystem, create the selector Select_Power with the operating modes BatteryPower and WallPower.

The selector is placed in PowerSystem. Then its modes are available for required for relations between the functions in all clusters inside PowerSystem (see Required for).

Battery, AC-DC converter and power cable

The battery supplies the power board in the mode BatteryPower. In the mode WallPower, the power cable supplies the AC-DC converter, and the converter supplies the power board.

1. In PowerSystem, create three clusters with default hardware and a default function:

   • Battery with the function SupplyBatteryPower;

   • ACDCConverter with the function ConvertACtoDC;

   • PowerCable with the function SupplyWallPower.

2. Make the three functions subfunctions of ProvidePower.

3. Add the required for relations, with the operating modes:

   Function	Required for	Operating mode
   SupplyBatteryPower	DistributePower	BatteryPower
   ConvertACtoDC	DistributePower	WallPower
   SupplyWallPower	ConvertACtoDC	(none)

4. Add a test with a default result to each cluster: Test_Battery, Test_ACDCConverter and Test_PowerCable. These tests check the hardware, not the function. So in the tested items, select the hardware node of the cluster (for example Battery) instead of its function.

Fig. 11 The Battery cluster. The test result indicates the hardware.

Fig. 12 The ACDCConverter cluster.

Fig. 13 The PowerCable cluster.

The complete power system looks like this:

Fig. 14 Overview of the PowerSystem cluster. The operating mode selector, the required for relations and the contents of the subclusters other than their main functions are not shown.

5. Check the model

• Check the dependencies on the required-for matrix of CDRadioPlayer. The overview diagram does not show them.

• Run the validator and solve the reported problems.

• To inspect the complete model, download it as a yEd graph with (see Downloading the graph and Bayesian network).

6. Diagnose a failure

Open the The diagnoser from the CDRadioPlayer cluster and try this scenario:

1. The device runs on batteries. Set the operating mode of Select_Power to BatteryPower.

2. The power LED does not light up. Set PowerLED to NOk.

3. Click Compute. The diagnoser shows the most likely broken hardware and suggests tests.

4. Perform the suggested tests and enter their results. For example, Test_DistributePower gives NOk and Test_Battery gives Ok. Then the power board is the most likely cause.

The exact ranking of the tests depends on their costs, the fault rates and the balance setting. Your model may therefore suggest the tests in another order.

Next steps

• Add custom faults and states, and their CPTs.

• Analyse the diagnosability of the design in Design for diagnostics.

• For larger models, model the system in Capella and import it (see Modelling in Capella).