I introduced a Virtuoso RDF View that maps the Musicbrainz relational database into RDF using the Music Ontology a couple of weeks ago. Now I will show some query examples evolving a special feature of these Virtuoso RDF Views: full text search on literals.
How RDF Views work
A Virtuoso RDF View can be seen as a layer between a relational database schemas and its conceptualization in RDF. The role of this layer is to convert relation data in its RDF conceptualization.
That is it. You can see it as a conversion tool or as a sort of lens to see RDF data out of relation data.
How full text search over literals works
Recently OpenLink Software introduced the full text feature of their Virtuoso’s SPARQL processor with the usage of the “bif:contains” operator (it is introduced into the SPARQL syntax like a FILTER).
When a user sends a SPARQL query using the bif:contains operator against a Virtuoso triple store, the parser will use the triple store’s full text index to perform the full text search over the queried literal.
With Virtuoso RDF View, instead of using the triple store’s full text index, it will use the relational database’s full text index (if the relational database is supporting full text indexes, naturally).
Some queries examples
In this section I will show you how the full text feature of the Virtuoso RDF Views can be used to increase the performance of a query against the Musicbrainz RDF View modeled using the Music Ontology
Note: if the system asks you for a login and a password to see the page, use the login name “demo” and the password “demo” to see the results of these SPARQL queries.
Example #1
A user remember that first name of the music artist is Paul, and he remember that one of the albums composed by this artists is Press Play. So this user wants to get the full name of this artist with the following SPARQL query:
sparql
define input:storage virtrdf:MBZROOT
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX mo: <http://purl.org/ontology/mo/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
SELECT ?artist_name ?album_title
FROM <http://musicbrainz.org/>
WHERE
{
?artist rdf:type mo:SoloMusicArtist .
?artist foaf:name ?artist_name .
?artist mo:creatorOf ?album .?album rdf:type mo:Record .
?album dc:title ?album_title .FILTER bif:contains(?artist_name, “Paul”) .
FILTER bif:contains(?album_title, “Press and Play”) .
};
Results of this query against the musicbrainz virtuoso rdf view
As you can notice with that query, the user will use the full text capabilities of Virtuoso over two different literals: the objects of these two properties foaf:name and dc:title.
Example #2
In this example, the user wants to know the name of the albums published by Madonna between 1990 and 2000. The answer to this question is returned by the following SPARQL query:
sparql
define input:storage virtrdf:MBZROOT
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX mo: <http://purl.org/ontology/mo/>
PREFIX dcterms: <http://purl.org/dc/terms/>
prefix dc: <http://purl.org/dc/elements/1.1/>
SELECT DISTINCT ?albums_titles ?creation_date
FROM <http://musicbrainz.org/>
WHERE
{
?madonna rdf:type mo:SoloMusicArtist .
?madonna foaf:name ?madonna_name .
FILTER bif:contains(?madonna_name, “Madonna”) .?madonna mo:creatorOf ?albums .
?albums rdf:type mo:Record .
?albums dcterms:created ?creation_date .
FILTER ( xsd:dateTime(?creation_date) > “1990-01-01T00:00:00Z”^^xsd:dateTime ) .
FILTER ( xsd:dateTime(?creation_date) < “2000-01-01T00:00:00Z”^^xsd:dateTime ) .
?albums dc:title ?albums_titles .
};
Results of this query against the musicbrainz virtuoso rdf view
Here the user will use the full text capabilities of the Virtuoso RDF Views to find artists with the name Madonna and he uses two filters on xsd:dateTime objects to find the albums that have been created between 1990 and 2000.
Examples #3
In this last example, the user wants to know the name of the members of the music group U2.
sparql
define input:storage virtrdf:MBZROOT
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX mo: <http://purl.org/ontology/mo/>
SELECT ?band_name ?member_name
FROM <http://musicbrainz.org/>
WHERE
{
?band rdf:type mo:MusicGroup .
?band foaf:name ?band_name .
?band_name bif:contains ‘”U2″‘ .
?band foaf:member ?members .
?members rdf:type mo:SoloMusicArtist .
?members foaf:name ?member_name .
};
Results of this query against the musicbrainz virtuoso rdf view
Here the user will use the full text feature to get the name of the music group, then the name of the members related to this (these) music group(s) will be returned as well.
Special operators of a full text search
Some full texts operators can be used in the literal parameter of the bif:contains clause. The operators are the same used in the full text feature of Virtuoso’s relational database. A list and a description of the operators can be found on that page.
I would only add that the near operator is defined as +/- 100 chars from the searched literal. And the wildcard ‘*’ operator should at least be placed after the third character of the literal. So, “tes*t” or “tes*” or “test*” are legal usages of the wildcard operator, but “*test”, “t*” or “te*st” are illegal usages of the operator.
Conclusion
Finally, as you can see, the full text feature available with the Virtuoso RDF Views is a more than essential feature that people should use to increase the performance of their SPARQL queries. The only two other options they have are: (1) using a normal “literal” that as to be well written and with the good cases; in one word this option render such queries useless and (2) they can use a FILTER with a regular expression with the “I” parameter that is far too slow for normal usages.
