Echelon LonBridg Server - Manual (Page 31)

LonBridge Server User’s Guide 25
retrieves the id attribute; you can also view the id attribute in the devices.xml
file (see Instances Directory on page 16).
Expressions
Expressions are used in the where attribute of the <get> message. The
conditional operators include:
• and
• or
• >
• >=
• ==
• !=
Operators are processed from left to right. However, you can use parentheses to
group conditions.
Tracers
A tracer is a special attribute that you can use to identify a specific message, so
that the LonBridge application can filter the message response from other
responses it receives. A tracer is any attribute that includes an underscore (_)
prefix. You can use tracers for LonBridge API messages (called message tracers )
or for a LonBridge device class file (called node tracers ).
Example for a message tracer:
<lon _mytracename="Turn on a light">
<o43.get _mytraceid="34"
_mytracetimestamp="090803121356"/>
</lon>
...
<lon _mytracename="Turn on a light">
<o43.is brightness="100" _mytraceid="34"
_mytracetimestamp="090803121356"/>
</lon>
Subsequent queries do not return the same tracers:
<lon>
<o43.get/>
</lon>
...
<lon>
<o43.is brightness="100"/>
</lon>
Errors
The LonBridge Server reports errors using the <error> element. The <error>
element contains a message that describes the error. There are no fixed
attributes for the <error> element.