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The classes RDFConsumer and RDFUtil integrates integrate dspace-rdf into DSpace. RDFConfiguration is used to centralize configuration properties that are use used by more than one class inside dspace-rdf. The class RDFizer contains the command line interface. To see the online help you have to use the following command:
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The package org.dspace.rdf.storage contains the classes to attach the Triple Store to the repository. The URIGenerator is an interface used to create URIs that are used to identify the repository resources in RDF. In the configuration (see below) you can define which class should be used. In cause of DS-1990 (
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The package org.dspace.rdf.providing contains the servlet to provide the converted data as serialized RDF. In the last days I added a second servlet, which is not part of the image yet. The LocalURIRedirectionService is used if you use the LocalURIGenerator. Linked Data distinguish distinguishes between non-information and information-resources. If a URI of a non-information resource is dereferenced it should forward to the URL of an information resource describing the non-information resource. With Handles or DOIs the resolver will perform the forward. For local URIs the LocalURIRedirectionService will do. The package org.dspace.rdf.providing.negotiation contains the classes for content negotiation. Linked Data uses content negotiation to serve the same information as html or different serializations of RDF under the same URI.
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The installation follows the normal installation of a DSpace source release. In addition you have to provide a Triple Store. You can use any Triple Store you like, if it support SPARQL 1.1 Query Language and SPARQL 1.1 Graph Store HTTP Protocol. If you do not have one yet, you can use Apache Fuseki. Download Fuseki from its official download page and unpack the downloaded archive. The archive contains several scripts to start fuseki. Use the start script appropriated for the OS of your choice with the options '--localhost --config=<dspace-install>/config/modules/rdf/fuseki-assembler.ttl'. Instead of changing into the directory you unpacked fuseki to, you may set the variable FUSEKI_HOME. If you're using Linux, unpacked fuseki to /usr/local/jena-fuseki-1.0.1 and istalled installed DSpace to /var/dspace this would look like this:
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Fuseki's archive contains a script to start fuseki automatically at startup as well.
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The configuration of Fuseki DSpace contains provides configures Fuseki it to provide a SPARQL endpoint that can be used to change the data of the Triple Store. You should not use this configuration and let Fuseki connect to the internet as it would make it possible for anyone to delete, change or add information to the Triple Store. The option --localhost tells fuseki to listen only on the loopback device. You can use Apache mod_proxy to make the read-only SPARQL endpoint accessible from the internet. A more detailed documentation on how this can be done will follow here one day. |
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In the folder [dspace-install]/config/modules/rdf/ you'll find more configuration files. The configuration files are writen written in RDF or more specific in Turtle. This behavior makes it easy to specify triples that should be part of the converted data and has some other advantages as well.
The files named [dspace-install]/config/modules/rdf/contstant-data-*.ttl are used to configure the StaticDSOConverterPlugin. Every triple specified in the file constant-data-general.ttl will be added to every resource created while conversion. For each DSpaceObject type except for Bundles and Bitstreams one file exists, that can be used to specify RDF that will be added to the converted data representing a resource of the appropriate DSpaceObject type. Bundles and Bitstreams gets converted as part of the Item they belongs belong to.
The files [dspace-install]/config/modules/rdf/metadata-*.ttl configure the MetadataConverterPlugin. This is the plugin that converts Item's metadata. The file metadata-prefixes.ttl can be used to specify prefixes (or namespaces) to be used in those serializations of RDF that support such mechanism (g.e. Turtle or RDF/XML). The file metadata-rdf-schema.ttl is not a configuration file. It contains the schema describing the vocabulary used for the configuration of the MetadataConverterPlugin. The file metadata-rdf-mapping.ttl contains several mappings between metadata fields and triples that should be created to represent the specified metadata field. It already contains some examples which should help until it is better documented. The triples that should be created while converting a metada field are specified using RDF reification. You can specify regular expresions to create some triple only for metadata fields those values fulfils the specified regular expression. Two more regular expressions can be used to manipulate field values before they will be used to generate Literals or URIs. The file metadata-rdf-mapping.ttl already contains examples on how to generate URIs and Literals using metadata field values. When the metadata-rdf-mapping.ttl is loaded simple inferencing is used to detect most of the types of its entities. So you do not need to type every resource. Typing (by using statements with the property 'rdf:type' or the turtle shortcut 'a') is necessary for ResourceGenerators and LiteralGenerators only as there is no way to distinguish them using inferencing. While links are what distinguish Linked Data from simple RDF, it is important to use ResourceGenerators and regular expresions to create links.
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Beside RDFUtil you can use the classes in the package org.dspace.rdf.providing.negotiation for content negotiation. I added content negotiation to JSPUI already, but it should be added to XMLUI as well. It would be even better to use content negotiation directly in Persistent Identifier Resolvers that support content negotiation. The resolver under at dx.doi.org supports content negotiation, but the DOIIdentifierProviders (currently contains a DOIIdentifierprovider for EZID and on for DataCite) must be extended before the content negotiation can be used.
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As soon as DS-1990 (
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<link rel="alternate" type="application/rdf+xml" href="http://demo.dspace.org/rdf/handle/123456789/123/rdf" /> <link rel="alternate" type="text/turtle" href="http://demo.dspace.org/rdf/handle/123456789/123/ttl" /> |
And of cause course a good English documentation is necessary as this document only give gives a little peak on how to configure and use dspace-rdf.
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