Echelon LNS DDE Server - Manual (Page 64)

Address Components
When a DDE client sends out a request to begin a DDE conversation, all
DDE servers running on the PC see the message. In order to direct the
message to a specified point on a particular server, the client addresses the
message using a three-part DDE address with application, topic, and item
components.
Application
The name of the server to which the message is directed.
For example, to address a message to the LNS DDE Server,
the client may specify LNSDDE as the application. This
name is case insensitive. By default, the DDE application
name is LNSDDE for the LNS DDE Server, but this name
can be changed on the Server Settings tab of the Server
Configuration dialog described in Chapter 3.
Topic For the specified application, the type of information that the
client is interested in receiving or sending. A server
categorizes the services it provides by topic. The LNS DDE
Server recognizes several topics depending upon your
network configuration. The topic names and how they are
constructed are described later in this chapter.
The names are made up of several individual parts, some of
which are case sensitive, and others that are case
insensitive.
Item Within the context of the specified topic, the name of the
specific piece of information that the client wants to send or
receive. For example, to tell the LNS DDE Server that it
wants the value of the network variable named status on
the device named monitor, the client specifies
monitor.status as the item. The format of an item
depends on the topic it is part of, and is in general, case-
sensitive. This corresponds with the convention for device
names, network variable names, configuration property
names, and message tag names in an LNS database. The
client application must be able to specify the device, network
variable, configuration property, and message tag names
with exactly the same case as they are defined in the LNS
database.
Topics
The topic is specified using either a standard or custom format. The
standard topic format includes Network_name, Subsystem_path, and
Topic_type components. The custom topic format includes Topic_name
and Topic_type components.
4-2 Topics and Items