Jean Vincent Fonou Dombeu and Magda Huisman
Figure 3: Part of description logic representation of the domain ontology
The RDF formal representation of the domain ontology is created in the next subsection with Java Jena API and stored into a MySQL RDBMS.
5.3 Implementation and storage of the domain ontology in RDF
RDF and RDFS are the first standardized Web based languages( Sabou 2006; Kalyanpur 2006). RDF is a data model used to describe resources on the Web, whereas, RDFS is an improved version of RDF which provides facilities for the definition of basic ontology elements such as classes and hierarchy of classes, properties, domain and range of properties( Sabou 2006; Kalyanpur 2006). RDF uses statements in the form of < S, P, O > to represent an ontology. The meaning of a RDF statement is that a subject S has property P with value O. In a RDF statement, S and P are uniform resource identifiers( URIs), whereas, O is either a URI or a literal value( Wilkinson et al 2003).
In light of the above, the RDF syntax represents each class of an ontology as a resource which has properties with values. Thus, ontology will be represented in RDF with several statements. The RDF version of the domain ontology in Figure 1 was created with the Java Jena API( See step 5 in Figure 2).
Firstly, Jena API was downloaded, installed and configured in the Eclipse Java software development kit( SDK). Thereafter, the storable version of the domain ontology in RDF was created based on its semi‐formal representation established in the previous section. The bottom left part of Figure 2 shows a part of the generated RDF code of the domain ontology in Figure 1. The generated RDF code of the domain ontology was subsequently stored in a relational database with MySQL RDBMS. This was done by downloading and installing the MySQL RDBMS, configuring Jena and MySQL( instantiating and loading the MySQL driver, creating the connection, etc.), and store the RDF graph of the domain ontology in the database. The screenshot of MySQL nodes of the RDF store of the domain ontology is depicted at the bottom of Figure 2. Further information on the implementation of ontology with Jena API and MySQL is provided in( McCarthy, nd; Dickinson, nd). Finally, SPARQL queries are applied to query the stored RDF version of the domain ontology( See sample SPARQL query and output in step 4 in Figure 2). A detailed explanation of SPARQL can be found in the W3C Recommendation documentation( Prud’ hommeaux and Seaborne, 2008). The summary of the Semantic Web technologies applied in this study is provided in Table 2.
Table 2: Summary of semantic web technologies applied in this study
Semantic Web Technology Ontology
RDF Jena API MySQL SPARQL
Description Domain ontology for e‐Government monitoring of development projects in developing countries Semantic Web ontology language Java platform for developing, storing and querying ontology Relational Database Management Systems Semantic Web language for querying RDF ontology
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