All the graphics proxies for which the data container provides data must be subscribed to it. This means that they are informed automatically of changes to data. The data container ensures that values can be changed or requested only by graphics proxies that are subscribed to it.

You do not need to know the details about communication between the data container and the graphics proxy if you only want to use a data container and a graphics proxy. You need to know the details if you want to program your own data container without using the data container wizard or if you want to implement your own graphics proxy.

The data container can tell its graphics proxies to request relevant changes to data from the data container - using the method NOTIFY.

For more information, see

To subscribe for data in the data container or to cancel a subscription a graphics proxy calls the methods SUBSCRIBE or UNSUBSCRIBE in the data container interface IF_DC_SUBSCRIPTION.

The graphics proxy also calls the method SUBSCRIBE if it wants to change its data selection (using the filter function) - that is, to resubscribe. In this case, if the current dataset is already distributed (that is, there is no normal distribution order) the graphics proxy is immediately instructed to read all its data (using the filters that are now new).

The data container uses its distribution methods DISTRIBUTE_CHANGES and RESTORE to call the method NOTIFY in the subscribed graphics proxies. The graphics proxies use this method to find out about the data changes of interest to them - they do this using the value change methods in the data container.

If the current dataset has already been distributed (that is, all the graphics display the current data) then the graphics proxies are not informed of the change.