1. A computer-implemented method comprising: automatically generating a rule engine vocabulary comprising a context description and a result description that respectively define an input to and an output of an external rule engine; serializing the rule engine vocabulary in a schema document that, when received at the external rule engine, allows a rule to be defined based on the context description and the result description; transmitting the schema document to the external rule engine; transmitting a context specified according to the context description as the input to the external rule engine, for evaluation by the rule; receiving a rule-evaluated result specified according to the result description as the output of the external rule engine; and outputting the result.