I've just discovered, that DataparkSearch Engine has been compared with other open source search tools for crawling and indexing free music in the Volume 18, issue 1 of Journal of Telecommunications (2013), see it on Scribd.
Some points missed in the article:
- DataparkSearch has the RESTfull interface, though it's available only in the upcoming 4.54 version (you can try it in the latest snapshot).
- In addition to SQL-based storage for the index, DataparkSearch has its own storage, which is similar to nowadays NoSQL.
With these features, it's quite easy to integrate DataparkSearch with any other application or framework.