Hi Aidan,

Thanks, very interesting, though I have not read the details yet.

I wonder if you have compared the actual query results you got from the different stores. As far as I know, Neo4J actually uses a very idiosyncratic query semantics that is neither compatible with SPARQL (not even on the BGP level) nor with SQL (even for SELECT-PROJECT-JOIN queries). So it is difficult to compare it to engines that use SQL or SPARQL (or any other standard query language, for that matter). In this sense, it may not be meaningful to benchmark it against such systems.

Regarding Virtuoso, the reason for not picking it for Wikidata was the lack of load-balancing support in the open source version, not the performance of a single instance.

Best regards,

Markus

On 06.08.2016 18:19, Aidan Hogan wrote:

Hey all,

Recently we wrote a paper discussing the query performance for Wikidata,
comparing different possible representations of the knowledge-base in
Postgres (a relational database), Neo4J (a graph database), Virtuoso (a
SPARQL database) and BlazeGraph (the SPARQL database currently in use)
for a set of equivalent benchmark queries.

The paper was recently accepted for presentation at the International
Semantic Web Conference (ISWC) 2016. A pre-print is available here:

http://aidanhogan.com/docs/wikidata-sparql-relational-graph.pdf

Of course there are some caveats with these results in the sense that
perhaps other engines would perform better on different hardware, or
different styles of queries: for this reason we tried to use the most
general types of queries possible and tried to test different
representations in different engines (we did not vary the hardware).
Also in the discussion of results, we tried to give a more general
explanation of the trends, highlighting some strengths/weaknesses for
each engine independently of the particular queries/data.

I think it's worth a glance for anyone who is interested in the
technology/techniques needed to query Wikidata.

Cheers,
Aidan


P.S., the paper above is a follow-up to a previous work with Markus
Krötzsch that focussed purely on RDF/SPARQL:

http://aidanhogan.com/docs/reification-wikidata-rdf-sparql.pdf

(I'm not sure if it was previously mentioned on the list.)

P.P.S., as someone who's somewhat of an outsider but who's been watching
on for a few years now, I'd like to congratulate the community for
making Wikidata what it is today. It's awesome work. Keep going. :)

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