9.2 Usage scenarios

Typically, a project will use a single file using the same format as a manifest file that defines alternative configurations that can be loaded. This file is loaded at program startup using rdf_attach_library/1. Users can now list the available libraries using rdf_list_library/0 and rdf_list_library/1:

1 ?- rdf_list_library.
ec-core-vocabularies E-Culture core vocabularies
ec-all-vocabularies All E-Culture vocabularies
ec-hacks            Specific hacks
ec-mappings         E-Culture ontology mappings
ec-core-collections E-Culture core collections
ec-all-collections  E-Culture all collections
ec-medium           E-Culture medium sized data (artchive+aria)
ec-all              E-Culture all data

Now we can list a specific category using rdf_list_library/1. Note this loads two additional manifests referenced by resources encountered in ec-mappings. If a resource does not exist is is flagged using [NOT FOUND].

2 ?- rdf_list_library('ec-mappings').
% Loaded RDF manifest /home/jan/src/eculture/vocabularies/mappings/Manifest.ttl
% Loaded RDF manifest /home/jan/src/eculture/collections/aul/Manifest.ttl
<file:///home/jan/src/eculture/src/server/ec-mappings>
. <file:///home/jan/src/eculture/vocabularies/mappings/mappings>
. . <file:///home/jan/src/eculture/vocabularies/mappings/interface>
. . . file:///home/jan/src/eculture/vocabularies/mappings/interface_class_mapping.ttl
. . . file:///home/jan/src/eculture/vocabularies/mappings/interface_property_mapping.ttl
. . <file:///home/jan/src/eculture/vocabularies/mappings/properties>
. . . file:///home/jan/src/eculture/vocabularies/mappings/ethnographic_property_mapping.ttl
. . . file:///home/jan/src/eculture/vocabularies/mappings/eculture_properties.ttl
. . . file:///home/jan/src/eculture/vocabularies/mappings/eculture_property_semantics.ttl
. . <file:///home/jan/src/eculture/vocabularies/mappings/situations>
. . . file:///home/jan/src/eculture/vocabularies/mappings/eculture_situations.ttl
. <file:///home/jan/src/eculture/collections/aul/aul>
. . file:///home/jan/src/eculture/collections/aul/aul.rdfs
. . file:///home/jan/src/eculture/collections/aul/aul.rdf
. . file:///home/jan/src/eculture/collections/aul/aul9styles.rdf
. . file:///home/jan/src/eculture/collections/aul/extractedperiods.rdf
. . file:///home/jan/src/eculture/collections/aul/manual-periods.rdf

9.2.1 Referencing resources

Resources and manifests are located either on the local filesystem or on a network resource. The initial manifest can also be loaded from a file or a URL. This defines the initial base URL of the document. The base URL can be overruled using the Turtle @base directive. Other documents can be referenced relative to this base URL by exploiting Turtle's URI expansion rules. Turtle resources can be specified in three ways, as absolute URLs (e.g. <http://www.example.com/rdf/ontology.rdf>), as relative URL to the base (e.g. <../rdf/ontology.rdf>) or following a prefix (e.g. prefix:ontology).

The prefix notation is powerful as we can define multiple of them and define resources relative to them. Unfortunately, prefixes can only be defined as absolute URLs or URLs relative to the base URL. Notably, they cannot be defined relative to other prefixes. In addition, a prefix can only be followed by a Qname, which excludes . and /.

Easily relocatable manifests must define all resources relative to the base URL. Relocation is automatic if the manifest remains in the same hierarchy as the resources it references. If the manifest is copied elsewhere (i.e. for creating a local version) it can use @base to refer to the resource hierarchy. We can point to directories holding manifest files using @prefix declarations. There, we can reference Virtual resources using prefix:name. Here is an example, were we first give some line from the initial manifest followed by the definition of the virtual RDFS resource.

@base <http://gollem.science.uva.nl/e-culture/rdf/> .

@prefix base:           <base_ontologies/> .

<ec-core-vocabularies>
        a lib:Ontology ;
        a lib:Virtual ;
        dc:title "E-Culture core vocabularies" ;
        owl:imports
                base:rdfs ,
                base:owl ,
                base:dc ,
                base:vra ,
                ...

<rdfs>
        a lib:Schema ;
        a lib:Virtual ;
        rdfs:comment "RDF Schema" ;
        lib:source rdfs: ;
        lib:schema <rdfs.rdfs> .