In Finland, a major research initiative FinnONTO [3] was carried out in 2003{2012 with the goal of providing a national level semantic web ontology infrastructure based on centralized ontology services. Since 2008, a prototype of such a system, the ONKI Ontology Service [8,7] has been used in a living laboratory experiment with more than 400 daily human visitors and over 400 registered domains using its web services, including the ONKI mash-up widget for annotating content in legacy systems and semantic query expansion. The FinnONTO infrastructure also includes the notion of creating and maintaining a holistic Linked Open Ontology Cloud KOKO that covers di erent domains, is maintained in a distributed fashion by expert groups in di erent domains, and is provided as a national centralized service. In 2013 the Ministry of Education and Culture and the Ministry of Finance decided to nance the deployment of ONKI and its key ontologies into a sustainable free national service Finto, created and maintained by the National Library of Finland. Finto was opened in public in January 2014, and the API services of ONKI were redirected to Finto in June. This paper summarizes, from a technical standpoint, major ideas and components underlying Finto and lessons learned during the deployment process. Issues encountered in ontology engineering regarding, e.g., concept analysis and linguistic aspects have been discussed in a separate paper [4].
ONKI/Finto supports publication of ontologies by providing a centralized place for nding, accessing, and utilizing
ontologies|the key functions of ontology libraries [
User groups Finto ontologies are used by both humans and machines. We indenti ed three human client groups, with slightly di erent needs in the user interface: full-time annotators (indexers working at, e.g., libraries and museums), users performing annotation as part of their other duties (e.g., journalists publishing articles), and ontology developers. The Finto user interface is designed to serve them all. For machine use and application developers, the service provides a variety of APIs and documentation for their usage.
Finto service utilizing Skosmos software The development of a successor system for ONKI started within the
FinnONTO Project. The rst step was a creation of ONKI Light [
Skosmos relies on a SPARQL endpoint (Apache Jena Fuseki with the jena-text index) as its back-end and is written
mainly in PHP. The main bene ts of using a SPARQL endpoint is that the data provided by the service is always up to
date. This allows fast update cycles in vocabulary development. Vocabularies are pre-processed using Skosify [
Machine access to concepts The ONKI system o ers machine access to ontologies not only by publishing Linked
Data, but also custom APIs more suited for integration to e.g. document and collection management systems. ONKI
provides three main APIs: a SOAP API, a HTTP API, and a JavaScript widget [
Ontologies in ONKI and Finto At the heart of ONKI/Finto lies the General Finnish Ontology YSO. The National Library took over the development of YSO in 2013. Since then, special attention has been paid to making YSO intuitive and user-friendly without losing the bene ts of machine-readable semantic data. The top-level ontology has been reworked, multilingual aspects have been re ned, and work is under way to link YSO to the Library of Congress Subject Headings (LCSH). The original OWL representation was changed to SKOS, with some extensions mainly from ISO 259644.
During the FinnONTO project, many YSO-based domain ontologies were created in collaboration with expert
organizations. YSO is used as the central hub or glue relating all the domain ontologies to one another while minimizing the
number of direct links between them. The aim here is to facilitate distributed development of the domain ontologies in the
expert organizations while allowing the domain ontology developers to worry only about links and changes to one other
ontology. Their content is aggregated into the single uni ed ontology KOKO [
The work on this harmonized cloud of interlinked ontologies was begun during FinnONTO and has now been continued at the National Library. The ultimate goal is to use KOKO to relate the annotations in the datasets of the various organizations facilitating interoperability and breaking down silos. KOKO has been in pilot use as an annotation vocabulary in, e.g., various museums and in the National Broadcasting Company YLE { i.e., in organizations that potentially deal with material from all possible domains.
In addition to YSO, KOKO and the YSO-based domain ontologies, a number of thesauri, classi cations and other controlled vocabularies have been published in Finto, including Medical Subject Headings5, Iconclass6, and Lexvo7 language codes. As of July 2014, 27 vocabularies are available and more are being prepared for publishing. Experiences during deployment The process of transitioning users from ONKI to Finto has generally been smooth. The ONKI name has already been used for several related but distinct initiatives, so the name Finto was chosen for the new service to avoid confusion. The Finto user interface has undergone multiple rounds of usability testing and is already well liked by users, but the implementation could be further improved in terms of speed and scalability. The bottleneck is usually the SPARQL endpoint, especially for non-exact label matches where the text index cannot always be used e ectively.
The transition from ONKI APIs to Finto was managed by testing the new wrapper implementations both internally and among major user organizations well in advance of their deployment. Nevertheless, there were some problems that had to be resolved after the transition, e.g., browser cache and SSL issues. Since Finto hosts newer versions of some ontologies including YSO and KOKO, users were simultaneously introduced to new versions, which caused some compatibility issues. The change from OWL to SKOS caused some API queries to break, and the new version of KOKO was also di erent both in terms of content and modeling. However, the transitioning problems were generally resolved in less than a week. In future, we expect similar migration issues as ontologies evolve and new versions are published, but the changes are likely to be incremental in nature.
In future, we expect some growth in the usage of the Finto service, as well as more systems integrated to use the API services. We also expect other organizations to deploy their own Skosmos instances for publishing their own vocabularies.