Operator instance naming conventions

You use operator instance names for debugging and visualization purposes. They are especially useful with operators with multiple output streams because they provide a uniform way to refer to the operator instance.

When you invoke an operator in Streams Processing Language (SPL), give a name to that operator instance. This name is mandatory only when the invoked operator has no output streams.

When you run an application, all the operators must have unique names. If the application has user-defined parallelism, the names of the operators in a parallel region contain the channel numbers that apply to each of the operators. For example, if a parallel region is a single primitive operator with the logical name of Operator1, the operators in each channel are named Operator1[i] where i is the channel number. If the parallel region is a composite operator, the channel number is displayed after the name of the composite operator, but before the enclosed name of the operator. For example: Composite1[i].Operator1.

If an instance name is not specified, the SPL compiler automatically assigns the output stream names as valid operator instance names. For example, operator FileSource in line 5 of the following sample has an instance name of Numbers. Operator instance names are expanded when the operator is not inside a main composite operator. In this case, the operator instance name is appended to the name of the enclosing composite operator instance to form a fully qualified operator instance name.

The following example uses a Filter operator to generate two output streams that are based on the attribute value (attribute number) of the input stream (Numbers). The operator instance is named FilteredNumbers (line 10), which is semantically related to this specific invocation of the operator Filter.

01: namespace example;
02:
03: composite Main {
04:   graph
05:     stream<int32 number>  Numbers = FileSource() {
06:       param file   : "input.dat";
07:     }
08:     
09:     (stream<int32 number> Higher10;
10:      stream<int32 number> Lower10) as FilteredNumbers = Filter(Numbers) { 
11:       param filter : number > 10;
12:     }
13: }