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Using Aliases


One of the main aims of TTCN is to specify behaviour descriptions so that the human reader can easily understand the TTCN specification of the test purpose.

The conformance standard requires that behaviour be expressed in terms of (N) and (N-1) ASPs. However, a behaviour tree consisting of mostly (N-1)-data requests and indications says very little to the reader. What is important are the PDUs embedded in these service primitives. If static chaining is used the reader will have no idea, without turning to the constraints, what PDU interactions are specified in the test.

The alias mechanism allows ASPs (and if necessary PDUs) to be renamed to reflect the different PDUs that they carry. The (N-1)-data request and indication may have several aliases, depending on which (N)-PDU they are carrying.

Figure 66 : Declaring aliases

In ISO/IEC 9646-3 aliases are defined as textual expansions. However, it is probably easier to think of alias identifiers as alternatives to ASP or PDU identifiers in the SEND and RECEIVE statements. The effect is exactly the same, i.e.

Figure 67 : Test Step dynamic behavior using aliases


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