Building a Sample Network

In this chapter we will walk you through the creation of a sample temporal constraint network. In the process, you will begin to become familiar with many of the important features of Tachyon.

Running Tachyon

If you are using X11:

From an Xterm prompt type xtach then press return. Tachyon does not need any startup parameters.

(See also ``Using the Master-Script'')

At this point, Tachyon's graphical user interface appears, and you can create a new temporal constraint network or reload a network created previously.

Loading a Sample Network

To familiarize yourself with the process of editing an existing temporal constraint network, you can use any of the sample networks in the Tachyon samples directory. We will use the Beatles network here.

1. From the File menu, choose Load... A Load File dialog opens.
2. Select Beatles from the file list (See above).
3. Choose OK. The Beatles event network should appear.
4. The current format of this network is in hours. From the ``Format'' menu, select ``(hours:minutes)''. This will make the network more meaningful for the next step.
5. Double-click on the first node (``Stage Opened''). The Node Information dialog box will appear.
6. Change the ``Early Start'' from -oo to 18:00.
   

   For more information about Events/Nodes see Section ``Using the Graphic Interface''

   
   

7. From the ``Solve'' menu, select ``Lock Current Values''. This will copy the current network for later restoration.

8. From the ``Solve'' menu, select ``Solve Current Network''. The last event ``Show Begins'' should appear as (20:35,+oo,20:35,+oo,e,+oo). This indicates that the show will not begin prior to 20:35, if the setup process begins at 18:00.

9. From the ``Solve'' menu, select ``Show Changes''. All events should be highlighted, since they were all modified during the network propagation step.

10. From the ``Solve'' menu, select ``Restore Locked Values''. The network should now contain values located in step 7.

You may now continue modifying events and solving the network using steps 6 - 10.

If you would like to change the color combinations refer to ``Configuration: Colors''

Creating a New Temporal Constraint Network

A temporal constraint network consist of a set of events and a set of constraints which affect those events. An event is any activity which consumes an amount of time. For example, 'Loading a truck' is an event.

For our first network we will create two events and a single constraint between them. This network will be used to design a 'widget'.

To create your first event, position your mouse on the Tachyon canvas. Press SHIFT+LEFT MB. An unnamed and unconstrained event (node) will appear where the mouse was positioned. The figure below shows the Tachyon user interface and the event that you should be seeing.

Double-click on the event (node). A Node Information Dialog box will appear which describes the event and allows you to modify the values.

Rename the node to something meaningful such as ``Write Widget Specs''.

Notice that the default time format is days (bottom right of Tachyon window). We will not change it for this example.

Next, do the following:

• Change Early Start to 0.
• Change Late Start to 5.
• Change Minumum Duration to 25.
• Change Maximum Duration to 30.
• Select the DONE button.

Create a second node (SHIFT+LEFT MB), and:

• Change Tag: to ``Build Prototype.''
• Change Minumum Duration to 20.
• Change Maximum Duration to 30.
• Select the DONE button.

For more information on the capabilities of the node dialog box see ``Node Information Dialog Boxes''.

The next step is to create a constraint between these two nodes. Position the mouse pointer onto the ``Write Widget Specs'' node. Press SHIFT+LEFT MB and keep it down while positioning the mouse pointer onto the ``Build Prototype'' node. Release the keys and the mouse button . At this point a constraint arrow (edge) will appear.

Double-click on the arrow. An Edge Information Dialog box will appear which describes the event and allows you to modify the constraint values.

• Press the ``Allen'' button. Additional constraint relationships will appear.
• Position the mouse to the ``Before'' box and press the LEFT MB.
• Position the mouse to the ``Meets'' box and press the LEFT MB.
• Position the mouse to the ``Display None'' cycle button and press the LEFT MB.
• Select the DONE button.

Selecting both ``Before'' and ``Meets'' creates a constraint between the events ``Write Widget Specs'' and ``Build Prototype'' that is satisfied only if ``Write Widget Specs'' is completed before or at the same time as ``Build Prototype'' starts.

After the ``Display'' cycle button was pressed the ``Display Relation'' should have appeared. This function controls whether or not the constraints label is displayed on the arrow.

For more information on the capabilities of the node dialog box see ``Edge Information Dialog Boxes''.

Now you have a very simple temporal constraint network. The next task that needs to be completed is to solve the network.

• From the ``Solve'' menu, select ``First Network solution''. This should modify the 6-tuple associated with each event, solving the network. The status line should indicate that the network was solved successfully.
  

• The ``Write Widget Specs'' 6-tuple should appear as (0,5,25,35,25,30).
  

• The ``Build Prototype'' 6-tuple should appear as (25,+oo,45,+00,20,30).).
  

For more information on 6-tuples, 8-tuples and Allen relations, see documents referenced in the Bibliography

If you were unable to complete this example network, please refer to support contacts.