Filter content to extract from by an extractor by sampling a percentage of all the content in a repository

[diptanu]

Sometimes its useful to extract information only from a subset of the repository to run small scale experiments or for code synthesis for extraction before the extracted code is run against all the documents in the repository.

ExtractorBindng should have a sampling function based filter which allows extracting from N% of all the documents. And as documents come the binding should trigger extraction to maintain the watermark percentage.