Re: [Virtuoso-users] LOD Cloud Cache

[Kingsley I. <ki...@op...>]

On 2/20/14 2:44 PM, Timothy Lebo wrote:
> Virtuoso,
>
> I’m using the LOD Cloud Cache [1] as a sample of the LOD Cloud, and wanted to make sure that I was using it to its full potential.
> Thanks for such a useful resource.
> Could you comment on the following?
>
>
> A)
> What portion of Linked Data is in the cache?

You mean what portion of the datasets in the LOD Cloud pictorial are in 
this cache? If so, all the datasets we've been able to get our hands on 
over the years -- typically the larger ones.

> i.e., what methodology is used to load data into the cache?

We listen for new and interesting datasets an add them, basically.

>      Does it use crawls, load data dumps, use specific seed URIs or datasets?

No, this is quite a manual process, at this time.

>      Do the lists at http://datahub.io/group/lodcloud or http://datahub.io/dataset?tags=lod influence the loads?

A little, but no more than a ping from someone, or a dataset announced 
via Twitter, G+, or LOD mailing list.

>
> Unfortunately, http://lod.openlinksw.com/facet_doc.html mentions http://lod.openlinksw.com/void/Dataset, but that 404s.

Yes, and for good reason, it has 50 Billion+ triples, and we've opted to 
fill the DBMS up with data rather than more data about datasets in the 
DBMS :-)

>
>
> B)
> How often is new Linked Data added to the cache?
>

As per my comments above, as an when a dataset comes to our attention.

> C)
> Is the default graph the only graph that one needs to query to “query all of it”?

Yes.

> i.e., Can you verify http://lod.openlinksw.com/sparql's claim that:
> <http://lod2.openlinksw.com/sparql> sd:feature <http://www.w3.org/ns/sparql-service-description#UnionDefaultGraph>

Yes query without a Named Graph IRI scope. Even better, search using a 
text pattern via <http://lod.openlinksw.com/fct> and then look at the 
"Metadata" tab which always shows you:

1. Named Graphs with triples where the description subject (i.e., entity 
denoted by the URI in About: section) is in the subject role
2. Ditto but where the description subject is in the object role
3. Explicit Coreferences
4. Inferred Coreferences.



>
> (and, what’s the difference between http://lod.openlinksw.com/sparql and http://lod2.openlinksw.com/sparql?)

No difference, just admin artifact re. DNS.

>
>
> D)
> Is the following query an appropriate way to find out how many foaf:Person instances are in the cache?
> I get 141,721,466 people.
>
> select count(?s) where {?s a <http://xmlns.com/foaf/0.1/Person>}

Yes, but can also use "settings" to enable inference (there are some 
preset inference rules there plus the ability to enable owl:sameAs 
reasoning), which will increase the solution size.

>
>
> E)
> Is the following query an appropriate way to find out how many instances foaf:knows another?
> I get 84 “knowers”.
>
> select count(distinct ?s) where {?s <http://xmlns.com/foaf/0.1/knows> []}

Yes, but note my comments about reasoning and inference.
>
>
> Thanks so much for your time.
>
> Regards,
> Tim
>
>
> [1] http://lists.w3.org/Archives/Public/public-lod/2013May/0154.html
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-- 

Regards,

Kingsley Idehen	
Founder & CEO
OpenLink Software
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