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ontologies for Knowledge modeling in construction planning • vito getuli
layers: (a) backends for ontology storage, (b) middleware for the services offered by the tool suite, and (c) client applications that access the ontology middleware and provide end-user applications. The KAON tool suite is completely implemented in Java and can be extended with plug-ins that provide to developer a flexible tool. The ontology editor is called OIModeler and is composed by a graphical user interface for managing the ontology. 1.4 Ontology visualization When an ontology is developed, its visualization is very useful and helps working with the ontology itself. Different visualizations for ontologies have been presented in the last couple of years. While some of them are implemented as standalone applications, most visualizations are provided as plugins for ontology editors like ProtĂŠgĂŠ. With reference to (Lohmann, Negru, Haag, & Ertl, 2014) in this paragraph an overview of the main approaches for ontology visualization is provided. A lot of approaches use graphs as the method to visualize ontologies since they seem to be the natural way to represent the structure of the concepts and relationships in a domain of knowledge. The graphs are, very often, rendered in force-directed or sometimes in hierarchical layouts, resulting in a very comprehensive visualization. However, only few visualizations methods show complete ontologies, while most focus just on certain aspects. OWLViz, OntoTrack and KCViz depict only the class hierarchy of ontologies. Likewise, GLOW represents the class hierarchy but uses a radial tree layout and hierarchical edge bundles to display additional property relations. There are few applications able to provide the developer with a more comprehensive graph visualizations that represent all key elements of ontologies and not only the class hierarchy and their relationships. For instance, TGViz and NavigOWL use very simple graph visualizations where all nodes and links look the same except for their color. This is different in GrOWL and SOVA, which define more elaborated notations using different symbols, colors, and node shapes. In addition, some applications have been presented able to depict a 3D graph visualization of the ontologies. In this regard, we can cite OntoSphere, or tools that use hyperbolic trees to visualize ontologies, such as OntoRama and Ontobroker. Differently from all those applications that use common node-link diagrams to represent ontologies; there are various applications that apply other diagram typologies to visualize ontologies.
