Using the idea of six degrees of separation to get to any person on the planet, I came up with the idea to use a word cloud that would represent the top N words in all documents.
When you click on a word, (say “alpha”) the resulting word cloud would represent the top N words for all the documents with “alpha” in it.
As you click, bravo -> charlie, etc. the list of documents gets smaller and smaller, until just your required document remains.
This has several advantages, you don’t need to distinguish between words and numbers or need to “understand” the meaning of a word or interpret the user intent.
More importantly, the user doesn’t need to know the relevant words or vocabulary, since they’re all represented in the UI.
Enhancements include allowing for negative words, as-in, exclude documents with this word.