Problems with the Query Language

taytor · #1 11-06-2008, 08:01 PM

Hi all,
I need to search for all blog's posts wrote from the same author. To do it I have to use SIOC ontology. So, when I wrote this query on Advanced search form:

* <http://rdfs.org/sioc/ns#User> *

I "found about 9.62 thousand" among which an author called Fred.
But if I search for:

* <http://rdfs.org/sioc/ns#User> "Fred"

the result is Search results for advanced “* <http://rdfs.org/sioc/ns#User> "Fred"”, found 0 .

Thank you in advance.

Richard Cyganiak · #2 11-07-2008, 12:15 PM

Hi Taytor! The problem is that sioc:User is a class, not a property. What you are looking for is the user's name:

* <http://rdfs.org/sioc/ns#name> "Fred"

Your first query, * sioc:User *, actually shouldn't return any results AFAICT, this might be a bug on our side. I will look into this.

Renaud Delbru · #3 11-07-2008, 12:26 PM

Hi Taytor,

yes, this is a known bug in the beta1 version.
When a triple pattern contains two wildcards, the position is not taken into account.
So, the queries

Code:

* <http://rdfs.org/sioc/ns#name> *

and

Code:

* * <http://rdfs.org/sioc/ns#name>

will return the same set of results.

The problem will be solved in beta2, which will be deployed in January. For the moment, we recommend to avoid the use of two wildcards in a single triple pattern.

Hope this help.

taytor · #4 11-07-2008, 12:41 PM

Quote:

Originally Posted by Richard Cyganiak

Hi Taytor! The problem is that sioc:User is a class, not a property. What you are looking for is the user's name:

* <http://rdfs.org/sioc/ns#name> "Fred"

Your first query, * sioc:User *, actually shouldn't return any results AFAICT, this might be a bug on our side. I will look into this.

Thanks, and how could I search for all blog's posts wrote from the same author? In fact User is not a property, but a class. If I would search a class with a property, how should I wrote the query?
In my case I have to search for all blog's post (ant posts could be from forums or from blogs) and they have to be wrote from a User named "user".

Renaud Delbru · #5 11-07-2008, 01:03 PM

To search all blog posts that mention triples about SIOC Users and about a resource with a certain sioc#name, you could use:

Code:

* <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User> AND * <http://rdfs.org/sioc/ns#name> "Fred"

This query shows documents that mention triples matching

Code:

* <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User>

and

Code:

* <http://rdfs.org/sioc/ns#name> "Fred"

You have to know that wildcards are not variables like in SPARQL, so the subject of the triples matching these patterns could be different. For example, the previous query will match the following document:

Code:

<http://example.org/user1> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User> .
<http://example.org/user2> <http://rdfs.org/sioc/ns#name> "Fred" .

As a side note, variables will be supported in beta2.

taytor · #6 11-07-2008, 01:13 PM

Thank you, now it works

Regards,
Sarah

Richard Cyganiak · #7 11-07-2008, 01:24 PM

Another approach is to make this a two-step process.

First, find out the URI (unique identifier) of authors called Fred. For this, you run the query I've given above, * sioc:name "Fred". Then, fetch the resulting RDF documents, load them all into a local RDF model, and find the URI of each author, e.g. by running this SPARQL query:

Code:

SELECT ?author WHERE {
    ?author sioc:name "Fred" .
}

This gives you the URIs of all SIOC authors named Fred. Then, for each one, you ask this query to Sindice:

Code:

* <http://rdfs.org/sioc/ns#has_creator> <xxx>

Where instead of xxx you use the author's URI. The result will be posts by that author.

Example query result for one author named Fred

taytor · #8 11-07-2008, 01:32 PM

Okay, but the last solution founds the posts of the author from an only blog, doesn't it?

Now I have noted that the query

Code:

* <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User> AND * <http://rdfs.org/sioc/ns#name> "Fred"

founds users named Fred but not the blog's posts wrote by this username.

Richard Cyganiak · #9 11-07-2008, 02:41 PM

Quote:

Originally Posted by taytor

Okay, but the last solution founds the posts of the author from an only blog, doesn't it?

Right. That's why you have to repeat the query for every author.

Quote:

Now I have noted that the query

Code:

* <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User> AND * <http://rdfs.org/sioc/ns#name> "Fred"

founds users named Fred but not the blog's posts wrote by this username.

Right. That's because the user's profile (which has his name and type) is one RDF document, and each post is another RDF document. Sindice searches are always on individual documents. You cannot ask for the name and the post in the same query, because in SIOC this information is not contained in the same document.

Renaud Delbru · #10 11-07-2008, 02:41 PM

To search all blog posts that mention triples about SIOC Users and about a resource with a certain sioc#name, you could use:

Code:

* <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User> AND * <http://rdfs.org/sioc/ns#name> "Fred"

This query shows documents that mention triples matching

Code:

* <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User>

and

Code:

* <http://rdfs.org/sioc/ns#name> "Fred"

You have to know that wildcards are not variables like in SPARQL, so the subject of the triples matching these patterns could be different. For example, the previous query will match the following document:

Code:

<http://example.org/user1> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/ns#User> .
<http://example.org/user2> <http://rdfs.org/sioc/ns#name> "Fred" .

As a side note, variables will be supported in beta2.

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