Development/Tutorials/Metadata/Nepomuk/QueryService
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Nepomuk Query Service
The Query service provides a D-Bus interfaces named org.kde.nepomuk.QueryService which is exported at nepomukqueryservice. This interface allows to issue queries using a simple user language (most importantly one can use AND and OR to combine terms and field:value terms to query certain fields. In the latter case value will be matched to a literal value or the label of a resource in case the property matching field has a non-literal range.)
Calling the query method will return the path to a new D-Bus object which provides the interface org.kde.nepomuk.Query. The latter interface allows to list the results and emits signals for new or removed results.
Normally one would use the libnepomukqueryclient library provided by kdebase/workspace to access this services.
Another possibility is the Nepomuk Query KIO slave named nepomuksearch. This will return results formatted as UDSEntries.
Using the nepomuksearch:/ kioslave
There are two search types available: the simple query syntax and a method to directly open SPARQL queries.
The legacy search method is to simply open
nepomuksearch:/<simple search query>
This is deprecated. Instead, to open a simple query you should open
nepomuksearch:/?query=<simple search query>
and to open a SPARQL query you should open
nepomuksearch:/?sparql=<sparql query>
Simple Search Syntax
The search syntax in Dolphin is as follows:
expression logicop...
logicop = and | or
expression = text | negation field operand value
operand = : | = | > | < | <= | >=
field: any ontology property
negation: + | -
The negation term is positive if unspecified.
Field refers to any ontology properties. Some common properties:
lastModified: resource modification date
contentSize: resource size
artist, album, title, year, genre, trackNumber, discNumber: music metadata
hasTag: search by tag
mimeType
fileExtension
rating: a 1 - 10 rating
Some examples:
nepomuksearch:/?query=nepomuk
search for the word nepomuk in the file name, content, comment, or other indexed field
nepomuksearch:/?query=contentSize>1000KiB
search for resources with a size greater than 1000KiB. Supported size postfixes: KB, KiB, MB, MiB, GB, GiB, TB, TiB. These are case sensitive
nepomuksearch:/?query=rating<2 or rating>8
nepomuksearch:/?query=-hasTag:nepomuk
search for resources WITHOUT the tag nepomuk
SPARQL syntax
Opening a SPARQL query is as simple as opening the URL
nepomuksearch:/?sparql=<sparql query>
The sparql query should have the variable ?r as one of the select variables. Simple ontology prefixes are possible: nie, nfo, rdf, rdfs, nrl, nao, xsd, pimo.
Examples:
nepomuksearch:/?sparql=select ?r where { ?r nie:hasTag <nepomuk:/nepomuk> }
select all resources tagged with "nepomuk"