As more and more websites start to embed RDFa content in their web application view, the need arises to provide a more extensive way for viewing and editing this semantic content independently from the remainder of the application. We present a JavaScript API that allows the independent creation of editing widgets for embedded RDFa, which adds a new edge to Web development in the context of the Semantic Web. As an addition, the API also provides sound update methods that allow on-the-spot model synchronization between client and server.
1 rdfapi-js is available at http://powl.svn.sf.net/viewvc/powl/trunk/rdfapi-js/ implication we would also like to mention is the redundancy of creating separate views for editing, because updating can often be solved with the proposed widgets. 2
The RDF-API for JavaScript implements the RDF JSON specication proposal from the Talis n2 Wiki 2 for data representation and allows for RDF manipulation methods. The RDF model is extracted by a modied version of the parser from the RDFa Javascript implementation 3 provided by the W3C.
The added methods can be grouped as follows: Statement modication: These methods are used to modify the content of the model. We have implemented methods for adding one or more statements to a model and for deleting one or more statements from the model.
Namespace management: Since RDFa incorporates the use of namespaces, methods on in-memory models for adding, deleting and applying namespaces are needed. The Talis RDF JSON specication proposal does not include namespace declarations, so we have added this to our object notication. We have implemented methods for adding and deleting namespaces as well as for converting models from qualied names to full URIs (and back) according to the current namespace declarations.
Model comparison and check: These methods are used to check the consistency
of a given model and to compare two models and produce a statement di for
the update service. At this time, we do not care about bnodes in the di, e.g.
by using blank node enrichment [
We complete the rdfapi-js by adding a small set of administration methods for counting, (X)HTML output and debugging. 3
We use rdfapi-js in our semantic wiki application OntoWiki [
The following steps describe an examplary editing process: 1. The complete page with RDFa markup and the link to the rdfapi-js and a control script are created on the server and transferred to the client. 2. The client receives the page and loads the rdfapi-js as well as the application control script through a script-link. 3. rdfapi-js parses the page and creates an in-memory model from the RDFa markup. 4. An onclick handler is added next to every RDFa Literal found in the page. 5. By clicking on the event handler, an editing widget is displayed as an overlay to the existing page (see Fig.1). 6. The user submits the new value to the widget. The widget modies the inmemory model by using statement modication methods of rdfapi-js. These API methods apply the changes to the in-memory model as well as modify the (X)HTML view. 7. The modied in-memory model triggers a new submit button which enables the user to submit the change request to the server. If pressed by the user, a statement dierence is calculated and transferred to the server via an asynchronous HTTP request to an update service. The current implementation sends two JSON models to the server, one with the statements which have to be deleted, another with the statements which have to be created on the server. The execution of these atomic add / delete actions is left to the server update interface.
Widgets are not limited to the editing of plain literals. According to the inmemory model, dierent widgets can be loaded (e.g. for dates or geo locations). The idea of such widgets is to achieve independence from the page template so that a growing widget library can enhance every application which uses rdfapi-js. 4
The presented API includes methods for customized client-side edit widgets to modify embedded RDFa. It tackles the synchronization of a locally changed RDF model with the model on the server. The main advantage is the separation of edit functions from the data view. Widgets can be created for dierent datatypes and properties. These widgets add new possibilities for exible user interaction. The API is included in OntoWiki, but can be used in other Semantic Web applications as well. Without making a promising statement, we have already considered to propose the API as a full alternative to an editing view. However, the problems that have to be overcome are numerous such as multiuser synchronization, security and user validation. Although solutions for these problems have to be provided, they are clearly out of the scope of this API, since these problems have to be solved on the server side.
Future work includes the improvement of the di computation algorithm
to support bnodes and the enhancement of the widget library with a set of
widgets for common attributes. The (X)HTML rollout of in-memory changes is
currently limited to plain literals and resource relations. This limitation has to
be resolved in order to support more complex RDFa markup. To generalize the
editing process, future work should include support for SPARUL [