The Ontology Explorer functionalities are subdivided between client-side and server-side. More precisely, inside the server-side, represented by a GWT Service, there is the basic structure of the application; it receives the information's requests effected by the client and then retrieves and returns such information, through Remote Procedures Call (RPC), in a proper format for the compilation in JavaScript. Regarding the client-side, instead, it manages the visualisation of the information and it is here that the benefits of AJAX are exploited, particularly thanks to the widgets furnished by GWT.
The Ontology Explorer's architecture defines a clear data flow: considering the loading of an ontology, the various steps of this procedure are:
the user, from the client-side, through the widgets that compose the OE interface, requests to the server information about a specific ontology ;
the server, after receiving the client request, uses the Protègè OWL-API to query the ontology. It then fills the necessary wrappers (data structure) with the data;
the server sends these wrappers to the client through the use of Remote Procedures Call (RPC);
the client, received these wrappers, analyses them and it visualizes the data correctly in the browser through the CSS.
The process just described is what happens to every information's request effected from the user.
The role of the GWT Service results of fundamental importance inside the Ontology Explorer's architecture. The GWT Service can be seen as the core of the tool. In fact this service, based on a particular servlet architecture (not HttpServlet but RemoteServiceServlet, that it is a Java's extension), is in charge of the management of all the information by the Ontology Explorer. The service attends for requests effected by the client and then search for the proper data to send an answer. These information are taken browsing and querying the ontology through the Protègè OWL-API.
Once retrieved the information, the service proceeds then to the parceling of these inside the wrappers and to dispatch them to the client-side for their visualisation.
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