Document Database Query Language

Recently I have noticed that Doctrine^[1], a PHP library focused on persistence services, has been working on ☞ defining a new query language for document databases.

So, I couldn’t stop asking myself is there a need for a (new) document query language?

To be able to answer this question, I thought I should firstly review what are the existing solutions/approaches.

1. CouchDB doesn’t allow running dynamic queries against the store, but you can define views with the help of Javascript-based mapreduce functions.
2. MongoDB allows dynamic and pretty complex queries, but it is using a custom query API.
3. RavenDB, the latest addition to the document database space, has chosen the route of Linq^[2] for defining indexes.
4. Terrastore supports predicate (XPath currently) and range queries offering a mapreduce-like solution. You can read more about these in the Terrastore 0.5.0 article
5. Last, but not least, XML databases are using XPath for querying.

Simply put, it looks like each solution comes with its own approach. While it will probably make sense to create a unified query language for document databases, I see only two possible solutions:

• either make all document databases sign up to use this query language (note: this might be quite difficult)
• or provide it through a framework that works will all of the existing document stores (note: this might not be possible)

But do not create a new query language in a framework that works only with a single document store.