1. A computer-implemented method comprising: automatically generating, at a local rule engine, 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, the rule engine vocabulary defining a data type of a result; serializing the rule engine vocabulary in a schema document that, when received at the external rule engine, allows a rule to be defined by the external rule engine 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 to provide the result corresponding to the data type; receiving, at the local rule engine, the result specified according to the result description as the output of the external rule engine; and outputting the result.