[Monetdb-developers] RDF data management in MonetDB/SQL
wangx at tju.edu.cn
Thu Jul 15 20:49:54 CEST 2010
Hi MonetDB developers,
I have a question about RDF data management in MonetDB/SQL. The comment of sql.rdfshred says "shredding an RDF data file from location results in 7 new tables (6 permutations of SPO and a mapping) ... We can then query with SQL queries the RDF triple store by quering tables gid_spo, gid_pso etc., ...". In my option, if the spo table is considered the triples table, the other 5 tables (sop, pso, pos, osp, ops) (except the mapping table) can be viewed as indexes of the triples table spo.
When I write SQL to query the shredded RDF data in the triples table, I have two ways. The first way is to only use spo table to make self-joins. The second way is to use all 6 tables to make joins. I noticed that "MonetDB/SQL Reference Manual" says that "The heart is the MonetDB server, which comes with the following innovative features. ... Index selection, creation and maintenance is automatic". If I use 6 tables (as indexes) explicitly to make joins, it seems that I write the query plan by myself. However, I think this work should be done by the SQL optimizer using statistics from the system catalog. I wondered if these tables have already been specified as indexes in the internal code, or if there is a way to specify it so that the optimizer can use them as indexes to generate query plans. I am not sure if my understanding is correct. I will appreciate any help from developers. Thank you in advance.
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