Query implementation

A query engine needs to be implemented.

A query parser in oak-core should be able to handle xpath, sql2 and optionally other query languages. The jcr component must generate a valid query in one of those languages from JQOM queries and pass that statement along with value bindings, limit, offset, and name space mappings to the oak-core.

We need to:

• Define the oak-core API for handling queries. How are do we handle name space mappings, limit and offset
• Implement a query builder in the jcr component which takes care of translating JQOM queries to statements in string form
• Implement a query parser in oak-core and decide on a versatile AST representation which works with all query languages and which is extensible to future query languages.
• Implement the actual query execution engine which interprets the query AST