## 2 Food Ontologies
### Agrovoc  
AGROVOC [19] is a large and mature multilingual thesaurus covering all areas of interest to the Food and Agriculture Organisation (FAO) of the United Nations. It includes terminology widely used in the practice of subject fields in agriculture, fisheries, forestry, food and related domains. The vocabulary consists of over 32,000 concepts, with up to 40,000 terms in 23 languages. AGROVOC was first developed in 1980 by FAO and the Commission of the European Communities, and is currently maintained by an active international community of experts and institutions. AGROVOC represents a great degree of consensus regarding terminology, and is used by specialized digital libraries and digital repositories for indexing and retrieving data. The structured and controlled vocabulary terms in AGROVOC allow for unambiguous identification of resources, standardization of indexing processes, and efficient searching. Since its existence, AGROVOC has gone through a series of improvements. It was first deployed using a relational database, but the managing community soon realized the limitation of this approach given the distributed nature of the contributors and the availability of the data to third parties only by means of database dumps or through Web services. Such process of information sharing imposed a huge burden on the developers and maintainers of the applications. In order to overcome this shortcoming, AGROVOC moved to linked data, which offered a standard model that is both human and machine-readable. Since 2003, several efforts attempted to convert the AGROVOC thesaurus into an ontology. [PERSON], [PERSON], and [PERSON] [23] sketched the first concepts to transform AGROVOC to ontology. This was a major milestone towards a proper representation of the AGROVOC vocabulary, but it came short of addressing important aspects related to query processing and completeness of domain-relevant entity types and relationship types. Later, in 2004, [PERSON] _et al._[24] developed an OWL-based ontology for AGROVOC, which was the best option available to share information through the World Wide Web. After that, several _ad-hoc_ solutions were added to the OWL structure to conveniently express terms in all the languages available in AGROVOC. The conversion of AGROVOC to OWL ontology offered a simplified mechanism to model multilingual resources, but was not efficient to deal with a thesaurus resource. In 2009, the World Wide Web Consortium (W3C) recommended the use of Simple Knowledge Organization System (SKOS) [25] for developing specifications and standards to support the use of thesauri and classification schemes within the framework of the Semantic Web. This was the right choice: to represent AGROVOC in SKOS, which is a vocabulary for Resource Description Framework (RDF) developed explicitly to support thesauri. SKOS offers much more flexible semantics compared to OWL and provides specific relationships between concepts and also relationships between their multilingual lexicalizations. AGROVOC is currently represented using SKOS-eXtention of Labels(SKOS-XL). The model was structured with concept schemes, where metadata descriptors about edited resources are provided. It also puts emphasis on multilingual and the natural language description of resources. Figure 2 shows an example of AGROVOC using RDF/SKOS. Old ontology editing tools suffered from several drawbacks, such as poor usability and lack of a collaborative environment supporting roles-based authentication, editorial workflow and multilingual search, among others, which led AGROVOC designers to develop their own editor called VocBench [26], a Web application specifically tailored to the AGROVOC Vocabulary. By using this tool, authenticated users can add or translate AGROVOC terms in their languages. VocBench is a distributed editing framework for thesauri, glossaries, authority lists, code lists, taxonomies and classifications.