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It expresses that the class with identity #id is only available as byte-code. This has two implications:

1. For byte-code classes JTransformer only generates PEFs at interface level
2. the class and all the related PEFs cannot be modified by program transformations.

The typical use of externalT/1 is therefore in the precondition of a conditional transformation, as a check that the class can be transformed.

#id: classT
ID of the byte-code class. This ID is NOT the ID of the externalTfact but just a reference to the fact representing the byte-code class.

Consider for example the class “java.lang.Object” that is part of the JDK as a pre-compiled, non-modifiable byte-code class. It would be represented as follows:

   packageT(#packageId, 'java.lang').               // Package 'java.lang'
   classT(#classId, #packageId, 'Object', ...).  // Class 'Object'
   externalT(#classId).                               // 'Object' is external

ast_relation('Java',externalT,[
     ast_arg(id,     mult(1,1,no ), id,   [classT]) 
]).