fragment_downloaded_cb({"url":"tutorial.html#ontologies","fragment":"Ontologies\nIn the RDF world, an \"ontology\" defines the characteristics of\nthe data that a RDF database can hold. RDF triples that fit in its\nview of the world are accepted, while data that does not is rejected.\nTracker defines all its ontologies on top of the RDF Schema, which\nprovides the basic blocks to define classes (i.e. the types of\nthe resources being stored) and the properties that each of these\ncan have.\nBasic types and literals have their own builtin classes (e.g.\nxsd:string for string literals), properties can point to either\none of these builtin classes (e.g. the rdfs:label property points\nto string literals), or any other class defined in the ontology.\nThis ability to \"define the type\" of properties allows to define\nthe structure of the data:\nThe ontology is defined via RDF itself, and Tracker makes it part\nof the data set, there are thus full introspection capabilities\nbuiltin:\nIt is even possible to use these introspection capabilities while\nquerying the stored data:\nTo learn more about how ontologies are done, read the documentation about\ndefining ontologies. Tracker also provides a stock\nNepomuk ontology, ready for use.\n"});