Expression rules are comprised of If expressions and Then and/or Else expressions. The Platform reads the information defined in the If expression to determine whether it is true or false. Depending on the results of the evaluation, the Platform runs the defined Else action or the defined Then action.
The following syntax rules are defined below:
o Use
the Boolean AND operator (&&) between multiple functions or multiple
actions in a single expression. For example,
Then: SetAlarmSeverity=10 &&
SetAlarmState="ESCALATED" && SetState("Operations",
"suspended")
o If your data item names contain colons (for example, in SNMP data items), you MUST use the escape sequence, $C, when using these data item names in an expression. For example, when you want to refer to a data item named 'Temp:12' in an expression rule, you need to use 'Temp$C12' in the rule for the data item to resolve to its current value. When updating that data item through an action, you need to use the actual data item name as a string variable: SetDataItem("Temp:12", 20).
o Converting non-string values to string
o Creating IF comparisons with Boolean and non-Boolean values
o Expression Variable namespaces
o Historical data functions (GetData and GetDataN) require statistical functions (must be enabled for these functions to be available)
o Matching parameter values with supported parameter data types
o Supported functions for If expression and Then and Else expressions
o Use correct case for string comparisons and enumerated list values
o Use values returned by the Platform