Correlation names
A correlation name is a field reference that identifies a well-defined starting point in the logical message tree and is used in field references to describe a standard part of the tree format.
When you access data in any of the four trees (message, environment, local environment, or exception list), the correlation names that you can use depend on the node for which you create ESQL or mappings, and whether the node creates an output message. For example, a Trace node does not alter the content of the message as it passes through the node, but a Compute node can construct a new output message.
You can introduce new correlation names with SELECT expressions, quantified predicates, and FOR statements. You can create non-correlation names in a node by using reference variables.
Correlation names in nodes that do not create an output message
Most message flow nodes do not create an output message; all ESQL expressions that you write in ESQL modules or in mappings in these nodes refer to just the input message. Use the following correlation names in the ESQL modules that you write for Database and Filter nodes:
You cannot use these correlation names in the expression of any mapping for a Mapping node.
Correlation names in nodes that create an output message
If you are coding ESQL for a Compute node, the correlation names must distinguish between the two message trees involved: the input message and the output message. The correlation names in ESQL in these nodes are:
For a description of how to use *, see Using anonymous field references.