Trying to create a set of entities & intents for things of the ilk "describe <something>" or "tell me about <something>" or "list instances of <something>". The <something>s are not known in advance. Consequently, I cannot exhaustively list the possible values for the entity.
My impression from (albeit very little) use and from the documentation is that the conversation API isn't good at this type of thing. Experience thus far says that it will recognize things that match the examples given for some entity, but I haven't seen that it can generalize to something like
without knowing the set of values for @target.
What am I missing?
Which services are you talking about? NLC is able to do this, and so is Conversation, by using wildcards. Either one of these can be trained to recognize intents with wildcard values in their training data. Just use an asterisk ( like this - "*" ) for the wildcard.
You don't have to train Conversation with every possible utterance, it learns from it's training data. So if you provided the service a series of utterances like "describe apples", "describe oranges", "describe fireflies", and "describe astrophysics", and then associated all of them with an intent of "#provide_description", then the Conversation service would indicte this intent for requests like "describe math".
Please also try to use real utterances for your training. I am not sure that your users will speak in two word sentences all of the time. Provide enough training data for each intent so the service is able to learn the various different ways people express the same intents.