Methods and apparatus for querying a relational data store using schema-less queries
The invention provides, in one aspect, a method of searching an RDF triples data store of the type in which the triples are maintained in accord with a first storage schema. The method includes inputting a first query specifying RDF triples that are to be identified in the data store. That first query assumes either (i) that the triples are stored in a schema-less manner (i.e., with no storage schema) or (ii) that the triples are maintained in accord with a second storage schema that differs from the first. The method further includes generating, from the first query, a second query that specifies those same RDF triples, yet, that reflects the first storage schema. That second query can be applied to the RDF triples data store in order to identify and/or retrieve the desired data.
1. A method to extract data in a data store comprising:
performing, by a computer system programmed with code stored in a memory and executing by a processor of the computer system that transforms the computer system into a machine:
receiving a first query specifying one or more resource description framework (RDF) triples to be identified in a data store, where the first query is either schema-less or reflects a second storage schema;
extracting data, represented by one or more tokens in the first query and included within context-specific grammar events represented by the one or more tokens, from the context-specific grammar events to generate a second query that specifies one or more RDF triples to be identified in the data store responsive to the first query and that reflects the first storage schema, wherein the events represent any of a declaration and a constraint specified in the first query;
where the second query comprises:
a single SQL SELECT statement with a WHERE clause containing three or more logical conditions limiting triples to be considered for retrieval from the RDF triples data store, where each logical condition specifies one or more RDF triples according to a Boolean condition; and
applying the single SQL SELECT statement second query to the data store for identification of the one or more specified RDF triples responsive to the first query.
2. The method of claim 1 , wherein the RDF triples store uses a hashed with origin schema.
3. The method of claim 1 further comprising:
performing, by the computer system programmed with code stored in the memory and executing by the processor of the computer system that further transforms the computer system:
examining the first query for the one or more tokens that represent data to be used in generating the second query;
dispatching context-specific grammar events containing the data represented by the tokens in the examined first query, to be used in generating the second query; and
wherein:
each of the events represents any of a declaration and a constraint specified in the first query, and
the constraint specifies RDF triples to be identified.
4. The method of claim 3 , wherein dispatching events further comprises generating any of a logical condition event, a selection term declaration event, and a triple declaration event.
5. The method of claim 3 , wherein the first language is any of SQL-like and XML-like.
6. The method of claim 3 , further comprising generating the output query as an SQL Select statement.
7. The method of claim 3 , wherein the RDF triples are stored in a hashed with origin schema.
8. The method of claim 7 where generating a logical condition event comprises generating an event containing data which, when applied to a relational database via the second query, identifies RDF triples according to a Boolean condition.
9. The method of claim 7 , where generating a selection term declaration event comprises generating an event containing data which, when applied to the relational database via the output query, identifies RDF triples including a specified term.
10. The method of claim 7 , further where generating a triple declaration event comprises generating an event containing data which, when applied to the relational database via the output query, identifies RDF triples according to a specified subject, predicate and object.
11. The method of claim 1 wherein the first query is schema-less in a first language and the second query is an output query in a second language, the method further comprising:
performing, by the computer system programmed with code stored in the memory and executing by the processor of the computer system that further transforms the computer system:
generating the second query comprising:
examining the schema-less first query in the first language for the one or more tokens;
dispatching the context-specific grammar events to be used in generating the second query,
populating portions of the second query according to at least the context-specific grammar events; and
extracting data, represented by the tokens and contained within the context-specific grammar events, from the context-specific grammar events to generate the second query in the second language, comprising the populated portions, wherein the second query represents a schema of a relational database storing RDF triples;
wherein each of the events represents any of a declaration and a constraint specified in the first query, and
wherein the constraint specifies RDF triples to be identified.
12. The method of claim 11 , where generating a logical condition event comprises generating an event containing data which, when applied to the relational database via the output query, identifies RDF triples according to a boolean condition.
13. The method of claim 11 , where generating a selection term declaration event comprises generating an event containing data which, when applied to the relational database via the output query, identifies RDF triples including a specified term.
14. The method of claim 11 , further where generating a triple declaration event comprises generating an event containing data which, when applied to the relational database via the output query, identifies RDF triples according to a specified subject, predicate and object.
15. The method of claim 1 wherein dispatching context-specific grammar events further comprises generating any of a logical condition event, a selection term declaration event, and a triple declaration event.
16. The method of claim 1 , further comprising generating the second query as an SQL Select statement.
17. The method of claim 1 , wherein the RDF triples are stored in a hashed with origin schema.