# Using a context free grammar to generate sample utterances for Amazon Alexa/Google Assistant?

I would like to get some opinions about using a context free grammar to generate sample utterances for Amazon Alexa/Google Assistant skills.

When developing these skills one has to provide a large number of sample utterances, i.e. sentences with which a user could try to invoke a particular feature of the skill. So when the skill is about ordering chocolate I would have to provide sentences like...

i would like to buy chocolate
i would like to order chocolate
we would like to buy chocolate
we would like to order chocolate


...and so on. the number of these sentences tends to grow almost exponentially, yet even with hundreds of them they still often become the bottleneck of the entire skill because users tend to come up with new formulations that weren't anticipated.

There are some tools available that can generate these sentences from simple patterns, i.e. this

{i|we} would like to {buy|order} chocolate


would produce the four variations given above. The drawback of this approach is that usually not all permutations of the pattern are valid (in most cases it is only a small subset of them) and one would thus need another "grammar" on top of these patterns to tell which are. The patterns are also not standardized and thus tied to one particular tool.

So I was looking for a better way to generate these sample utterances, and came across an approach that generates sentences from a context free grammar. This looks very promising to me, and in a small test script I was able to generate a large number of sentences from a very small grammar, with limitations on the sentences structure that I would have been able to include in the patterns of the existing tools.

I am however not a exactly an expert in Theoretical Computer Science and would like to ask a few questions before exploring this further:

• My understanding is that a CFG is basically a "pattern" in the form of a tree. It would thus work similar to the patterns described above, but with the additional benefit of having the rules about which permutations of variables are legal embedded in the pattern itself. Is that correct?
• If the CFG really is just a more complex pattern that would also mean that this approach (generating sentences from a CFG) can not produce grammatical variations of the generated sentences, e.g. it would not be able to generate pluralized forms like i would like to see _my_ shopping cart -> we would like to see _our_ shopping cart. Is that right?
• More generally: From the hierarchy of formal languages, is a CFG really the best solution to this problem, our should I experiment with other types of grammars?

As I've said, it is entirely possible that I am misunderstanding some fundamental things about CFGs here, I am really just looking for some external feedback on this idea before investing more time in it. Thanks!