[Monetdb-developers] RDF data management in MonetDB/SQL

wangx wangx at tju.edu.cn
Fri Jul 16 18:54:55 CEST 2010


Dear Lefteris,

  Thank you for your reply. Your explanation will help me much.
In addition, would you give me some guidelines on how to make the
6 different indices of the triple table be understood by the SQL/SPARQL
query optimizer and used accordingly. If I want to implement this
feature by myself, in which files the code should be added or modified. 
BTW, in the future, will you implement the MonetDB/SPARQL as a new 
supported front-end language? Will you consider to translate SPARQL to MAL 
directly, instead of through SQL to MAL (but this way you have to develop 
a SPARQL specific optimizer, instead of making use of the SQL optimizer)? 
Thank you so much.

Best regards, 
    Xin Wang

>From: Lefteris <lsidir at gmail.com>
>Reply-To: 
>To: wangx <wangx at tju.edu.cn>
>Subject: Re: [Monetdb-developers] RDF data management in MonetDB/SQL
>Date:Fri, 16 Jul 2010 10:29:53 +0200
>
>Hi,
>
>your understanding is in general correct. The availability of the six
>different indices of the triple table should be understood by the
>SQL/SPARQL query optimizer and used accordingly. However, the
>MonetDB/RDF module has not been announced yet, and that is because it
>has not finished yet. You are using a piece of code which is
>experimental and unfinished. As such, the only way to test Monet and
>its capabilities on RDF data is to manually write the SQL query in
>such a way that you use the correct order of the triple table on the
>correct join.
>
>In the future of course, this will be done by the optimizer and the
>user will only have to write simple SPARQL queries referring to the
>name of the graph, instead of the underlying storage schema, but until
>then I am afraid you will have to do it by hand. The good news is that
>if you are using RDF data and testing queries that have been published
>previously on papers as benchmarks, most likely someone else will have
>done already the translation to a correct SQL query (since most
>experiments on newly build engines that do not support SPARQL use this
>method).
>
>Hope this helps you a bit,
>
>lefteris
>
>2010/7/15 wangx
:
>> 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 writeSQLto query the shredded RDF data in the triples table, I
>> have two ways.The first way is toonly use spo table tomake self-joins.
>> The second way is touse 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". IfI use6 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
>> alreadybeen 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.
>>
>>  Best regards,
>> Xin Wang
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