In the course of exploring the potential of linked open data for public procurement in the work package LOD2 for a Distributed Marketplace for Public Sector Contracts we have created the Public Contracts Ontology providing means of expression for describing public contracts in RDF to enable seamless exchange of semantically annotated data across distributed data sources.
The ontology’s design was informed by the schemas used in existing non-RDF data sources of public contracts, such as the European Union’s TED that has a strong influence on the content tracked in public contracts data in country-specific systems in the EU member states. It covers stages of public procurement from request to tender to contract award; i.e. pre-award and pre-realization phases. The central notion of the ontology is a contract (pc:Contract class) to which other information from the procurement process, such as from requests to tender or public notices, is attached.
Public Contracts Ontology reuses parts of several established vocabularies and ontologies, such as GoodRelations for modelling price specifications, so that it meshes well with other data on the schema level. Other vocabularies are aligned with the ontology via mappings, for example Call for Anything vocabulary expressing demands. Integration on the instance level is also encouraged and the ontology promotes linking to external datasets, such as Common Procurement Vocabulary, a classification of products or services requested in a contract, or companies tendering for a contract that are described in business registers.
Given the flexible nature of linked data vocabularies accompanied with the design decision for the Public Contracts Ontology, it has an open, extensible architecture that is ready to cater for the specificities in various context of exchanging public contracts data, such as in different national implementations. This aspect of the ontology was put to use in a small module for the Czech Republic that adds ways to express country-specific features of public contracts.