The SQL repository allows applications to query repository items based on attributes of their attributes, sometimes referred to as subproperties.
Continuing our book example, subproperty querying means that you can write repository queries like:
Get me all the books that were written by authors living in NY
This query could be represented, using RQL in a <query-items> tag, as follows:
<query-items item-descriptor="book">author.state="NY"</query-items>
