Topics

Special services

A few topics are reserved to a number of special services:

Topic	Description
System	Windows-defined topic name used to get information about the server.
$Sys_info	Used to get information about the supervision system which is not directly related to objects.

All other topic names are assumed to be object names. If you use object names that match the three special topics you will still be able to access them, but you will have to specify the area to which they belong as well as the object name.

Topic names and case-sensitivity

The topic names are in principle case-sensitive. However, the DDE protocol is not able to fully distinguish between topic names consisting of the same combination of letters in different cases (e.g., Flow_1 and FLOW_1).

In some cases, there is a workaround for this restriction, as shown in the following example. With a conversation to "Flow_1", any transaction intended for any combinations of different cases like FLOW_1, FLow_1 etc. will go to the topic Flow_1. When the conversation is closed, its history is forgotten and a new conversation to FLOW_1 or some other topic can be started. The problem is circumvented by accessing these topics one at a time. However, an advice loop is also a conversation and it is of no advantage to break an advice loop.

·   If you are using NETDDE, all topic names are converted to upper case. This means that the objects you want to access must have uppercase names, and the above-mentioned workaround will not work. You can, however, disable the case-sensitivity by changing the setting for CaseSensitive from 1 to 0 in the Registry. The branch is named HKEY_CURRENT_USER\7-Technologies\IGSS32\V7.00.00\DDE_HKLM.