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The Model-Driven System Builder

Giga System Builder Guide
Contents  >   3.  Tutorial

3.2 Modelling a System

 3.2.1  Modelling Properties
 3.2.2  Amending The Application
 3.2.3  Adding A Jar
 3.2.4  Adding the Vehicle Bean to the Jar
 3.2.5  Adding the Payment Bean to the Jar
 3.2.6  Adding the Congestion Charge Bean to the Jar
 3.2.7  Adding the Fine Bean to the Jar
 3.2.8  Siblings or Children
 3.2.9  Adding a Processing Unit with a Space
 3.2.10  Adding a Action
 3.2.11  Adding a Selection-Event
 3.2.12  Another Action and Another Selection-Event
 3.2.13  Adding the Lifecycle-Events
 3.2.14  Another Processing Unit
 3.2.15  Yet Another Processing Unit
 3.2.16  Adding a Service
 3.2.17  Calling a Service

3.2.1  Modelling Properties
In this section, we model the system, by fleshing out the .osm file. To start adding to the model, double-click on the .osm file in the Package Explorer window. This will open the file and show this:

Note that the CongestionChargeModel.osm window is selected. To ensure the Properties View is visible, right-click on and select 'Show Properties View'

The properties view is context sensitive and allows you to set the values of appropriate properties.

3.2.2  Amending The Application
Expand the model and you will see

Select the Application row. In the properties view you will see

In the properties view, amend the name of the application to 'CongestionChargeApp'. On pressing 'Enter' the model will change to

By the way, if you prefer to navigate by typing rather than using the mouse, once you have selected an element on the model, you can navigate up/down and open/close up the model using the up/down/left/right keys.
You can also use the Delete key to delete objects, and use Ctrl-Z and Ctrl-Y for Edit-Undo and Edit-Redo.

3.2.3  Adding A Jar
Now we are going to add some sub-elements to the Application. The sub-elements of Application are

  • Processing Unit (PU)
  • Jar

Let's add a Jar which will hold some Java beans. A Jar is used to hold common objects - Java beans - and any beans in it will be available to all PUs. A PU can also declare Java beans, but they will not be available outside the PU.

Right click on the Application row and select

New Child -> Jar

A new Jar 'jar1' is added to the model

In the properties view change the name of the Jar to 'BeanJar' and set the package to ''.

3.2.4  Adding the Vehicle Bean to the Jar
Now for the Vehicle bean.

To add a Java Bean, right click on the Jar row and select

New Child -> Java Bean

A Java Bean is added to the model

In the properties view change the name of the Java Bean to a 'Vehicle'.

Now we'll add 4 fields to the bean - they are 'children' of the bean. To do this, right-click on the Bean row and select

New Child -> Field

In the properties view set the names and types of the fields as follows

Field Type
make String.  ('String' is the default so you don't have to enter it.)
model String
licencePlate String
yearBuilt int

You can duplicate an item by holding down the control, selecting it with the mouse and moving and dropping it (while the '+' sign is showing) to another valid point in the diagram.

The model should now be:

3.2.5  Adding the Payment Bean to the Jar
Now add another bean to the Jar and name it 'Payment'. Add three fields

Field Type
recNo String
carRecord String
price int

3.2.6  Adding the Congestion Charge Bean to the Jar
Now add a third bean to the Jar and name it 'CongestionCharge'. Make it extend the Payment bean. This is done by using the dropdown on the 'Extends Object' property:

Add one field

Field Type
dateValid Date

3.2.7  Adding the Fine Bean to the Jar
Now add a fourth bean to the Jar and name it 'Fine'. Make it also extend the Payment bean.

Add one field:

Field Type
paid boolean

3.2.8  Siblings or Children
Note: Notice that as well as the option to add a 'New Child' you could also add a 'New Sibling'.

3.2.9  Adding a Processing Unit with a Space
Now add a Processing Unit below the application. Call it 'CongestionZoneProcessor' and give it package of ' This processing unit is going to contain a space into which the CongestionCharge and Vehicles are fed. So, create a space below the Processing Unit and call it 'CongestionZone'

3.2.10  Adding a Action
When a Vehicle enters the CongestionZone it will trigger an event which will call an Action. So we need an event in the Space and an Action that the event will call. Create an Action under the CongestionZoneProcessor and call it 'ProcessVehicle'. It should have an Input Object of Vehicle. and a Result Object of Fine.

3.2.11  Adding a Selection-Event
Add a SelectionEvent to the CongestionZone and set the Action to be ProcessVehicle. Also set the style to be 'subscriber' and the template- bean to be Vehicle

3.2.12  Another Action and Another Selection-Event
In the same way when a CongestionCharge enters the space an event will be triggered which will call and action. To model this create an Action called 'ProcessCharge'. It should take a 'CongestionCharge' as the Input Object. Leave the Result Object blank

Then create the selection-event that links the space to the action. Set the style to be subscriber and the template-bean to CongestionCharge.

3.2.13  Adding the Lifecycle-Events
Lifecycle events are used to adjust the objects . We need two lifecycle-events. The first will be used to filter out any vehicles made before the year 1972 before it enters the space. The second will be used to log the vehicles that once they enter the space. To do this select the 'CongestionZone' space and add a lifecycle-event sub-element. Name it 'removeOldCars'. Select the operations to be 'before-write'.

In a similar way create the second lifecycle-event. Set its name to be 'logVehicle' and its operation to be 'after-write':

3.2.14  Another Processing Unit
Add another Processing Unit and call it 'RoadUsers'. Give it a package of ''. This is going to simply feed the CongestionCharge and Vehicles in to the CongestionZone.

The next couple of steps will result in a helper class with a couple of methods on it which will make the implementation easier. Add an action to 'RoadUsers' and call it 'payCongestionCharge'. Make its inputObject be 'CongestionCharge'. Leave the resultObject blank.

Add a second action and call it 'driveVehicleIntoZone'. Make its inputObject be Vehicle. Again leave the resultObject blank.

Next add a bean to the Road Users Processing Unit. Name this bean 'Generator'. We will add some code to this bean to generate vehicles and congestionCharges and add them to the CongestionZone space. On the 'Generator' bean add two methods 'startGeneration' and 'stopGeneration'. Set these methods to be the 'Init Method' and 'Destroy Method' respectively. These will be used to start and stop the generation of the vehicles and congestionCharges.

3.2.15  Yet Another Processing Unit
Add another Processing Unit and call it 'DVLA'. Give it a package of ''. In Britain the DVLA is the Driving and Vehicle Licensing Authority. This Processing Unit is going to contain a service which will check the licencePlate on a vechicle. The service will be passed a String and will return either true or false depending on whether the licencePlate is valid.

3.2.16  Adding a Service
The current version of the GigaSystem Builder requires there to be a space in the same processing unit that contains the service. This space will be used as the transport mechanism for the service. So before we add a service to the DVLA Processing Unit we need to add a space. Call it the dvlaSpace. Then add a service to the DVLA Processing Unit and call the service 'LicenceService'. Also specify the space as 'dvlaSpace'

Now we need to add business method to the service. Call the businessMethod 'isLicenceValid'. The Return Type should be 'Boolean'. Also add to the business method a parameter called 'licence' and of type 'String'.

3.2.17  Calling a Service
Nearly there. One last thing to do. The service has been defined but nothing is making use of it yet. The Processing Unit that will call the LicenceService is the CongestionZoneProcessor. So, add a Service Call to this Processing Unit. Select the service to use. There should be only one

Right! That's it modelling over. Save your model and have a cup of tea. The next chapter will describe how to build the system and how to add the implementation code (the business logic).  

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