Repositories and the Semantic Web
The most sites on the Internet are oriented towards human consumption. While HTML may be a good format to create websites it is not a good format to export data in a way a computer can work with. Like the most software for repositories DSpace supports OAI-PMH as an interface to export the stored data. While OAI-PMH is well known in the field of repositories it is rarely known elsewhere (e.g. Google retired its support for OAI-PMH in 2008). The Semantic Web is an approach to publish data on the Internet together with information about its semantics. The W3C released standards like RDF or SPARQL for publishing structured data on the Web in a way computers can easily work with. The data stored in repositories is particularly suited to be used in the Semantic Web, as metadata is already available. It doesn’t have to be generated or entered manually for publication as Linked Data. For most repositories, at least for Open Access repositories, it is quite important to share their stored content. Linked Data is a rather big chance for repositories to present their content in a way it can easily be accessed, interlinked and (re)used.
To my knowledge, EPrints is currently the only repository software capable to export its content as RDF. Nevertheless, the software ignores some important conventions regarding Linked Data, meaning it rather provides RDF than Linked Data.
The main topics of my thesis were how metadata and digital objects stored in repositories can be woven into the Linked (Open) Data Cloud and which characteristics of repositories have to be considered while doing so. As main part of my thesis I created a software independent concept on how to provide repository contents as Linked Data. In addition, I implemented it as a DSpace extension. There are some last steps left to be done before it can be used in a productive environment. I would be glad to contribute it to a future release of DSpace as soon as it's ready.
German native speakers can find my thesis here: http://www.pnjb.de/uni/diplomarbeit/repositorien_und_das_semantic_web.pdf
dspace-rdf
dspace-rdf is an extension for DSpace that adds capabilities to convert contents stored in DSpace into RDF, to store the converted data in a Triple Store and to provide it as serializations of RDF. The Triple Store must support SPARQL 1.1 and can be used to provide the converted data over a read-only SPARQL endpoint. dspace-rdf can currently be found on my github repositoriy, but I would be glad to contribute it to a future version of DSpace.
Installation and Configuration
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 DSpace to /var/dspace this would look like this:
export FUSEKI_HOME=/usr/local/jena-fuseki-1.0.1 ; $FUSKI_HOME/fuseki-server --localhost --config /var/dspace/config/modules/rdf/fuseki-assembler.ttl
Fuseki's archive contains a script to start fuseki automatically at startup as well.
The configuration DSpace contains configures Fuseki 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.
config/modules/rdf.cfg
The file [dspace-install] is the main configuration file of dspace-rdf. It contains information on how to connect to the triple store, which URL should be used
RDFizer
Development / API
TODOs
dspace-rdf is realized as a new module of DSpace as it contains a webapp and everyone should be able to decide whether it should be deployed or not. The webapp is used to provide the data in serializations of RDF (RDF/XML, Turtle, N-Triples and N3-Notation).
