Dealing with resources is just a point of view. Reading the documentation, it seems very easy to model it in a resource-oriented way; in fact, what they call "objects" (articles, keywords, etc) are essentially resources, which are created from the original resource (the text you submit).
You could just POST the text, get back a bunch of links to the resources and then GET the ones you're interested in.
Assuming that certain "objects" are more expensive than others to generate, a resource-based view with lazily-generated representations could be more efficient than wasting resources without knowing if the client needs them or not.
They are not created in any persistent way. They are entirely ephemeral to that specific request.
What's expensive is the analysis of the original text, not creation of the objects. If you want to do what you are saying you would need to create and store objects server side in order not to have to re-do the analysis the second time around. There's no point in that.
You could just POST the text, get back a bunch of links to the resources and then GET the ones you're interested in.
Assuming that certain "objects" are more expensive than others to generate, a resource-based view with lazily-generated representations could be more efficient than wasting resources without knowing if the client needs them or not.