System architecture

Every WissKI system consists of four layers: The ontology layer, consisting of the layer for the reference ontologies and the layer for the application ontologies, the data layer for data storage and the authorities layer for name authorities. Each layer comes with an API with well documented interfaces for import and export.

ontology layercake

The layers of the reference and application ontologies should be filled at the time when the WissKI system is installed. As stated, any ontology can be used as a reference ontology, but the use of the ECRM and the System Ontology is strongly recommended to benefit from all features of WissKI. The API current is able to import ontologies in OWL/XML, RDF/XML, N-Triples, Turtle, SPARQL + SPOG, Legacy XML, HTML tag soup, RSS 2.0 and Google Social Graph API JSON. Instance data can be exchanged using OWL-DL/XML or RDF/XML. Moreover the system supports LIDO as exchange format. The administrative information about the data such as its status or the rights involved is provided by the Open Archive Initiative Protocol for Metadata Harvesting (OAI-PMH) which serves as a data wrapper. Therefore every WissKI system is able to act as a data provider for every OAI-PMH harvesting institution e.g. the Europeana with hardly any additional effort by the user.

The preferred format for authority files is the Simple Knowledge Organization System (SKOS). SKOS is a common data model for sharing and linking knowledge organization systems such as thesauri using RDF. It is developed by the World Wide Web Consortium (W3C), and the specifications are currently in the stage of a candidate recommendation. Because it is a new standard not many thesauri are available in this format. For example the mentioned Getty thesauri and lists are provided as a proprietary XML-format. So as a byproduct we developed a tool to convert this format to SKOS. Since authority files can be huge, it is not feasible to use the OAI-PMH and to import them as a whole. One possibility is to access those files via a REST-API where only the requested data is submitted. The Getty Research Institute is currently working on a Web-API for their lists and thesauri. So the import and export mechanisms of WissKI support widely adopted standards and based on standardised vocabulary. Data exchange is not only possible between a WissKI installation and other systems but also between multiple installations of the WissKI system. Through the underlying ontology knowledge can be seamlessly integrated.

In the future a single WissKI installation should also be able to communicate automatically using these interfaces. This will enable the WissKI users to share digital objects, information and knowledge across the local system borders to support inter- and transdisziplinary research.