[April 30, 2000] "The idea behind displets is to create a generic rendering browser that can load and activate little independent software modules tailored to create specific visualization objects. The rendering browser would then activate these modules depending on the content of the document, and deliver all kinds of required rendering needs. Displets (display applets) are little software modules, designed to be fully interoperable and to be activated by a generic display module.
Release 3: "This release is a completly new implementation of the Displets. The main news is the adoption of JavaBeans standard for displet implementation. The new architecture is able to work with existing JavaBeans and now Displets can do everithing a JavaBeans can do. The displets of this release didn't simple create a static image to diplay the associated tag, but can have their own behaviour... First the XML document is read and transformed by a normal XML parser into a internal tree representation using DOM. Then one or more layers of XSL stylesheets are applied to the DOM tree through the use of an XSL processor. This transforms the tree, at the end of all these passages, into another DOM tree that has an important property: for every element name in the tree there exist an available Java class, called displets, that provides the rendering. The XMLC application will then activate all the Java classes of the required displets, creating a tree of runnable Java objects. The Java classes are free to be of any type, but using the newly introduced concept of JavaBeans it is easy to create sophisticated and interoperable displets: the use of JavaBeans Containers and Components, which can be easily organized in hierarchies, nicely fits with the hierarchical nature of DOM trees and XML documents. XMLManager is an Applet we have developed to use our XMLC engine inside Internet Browsers The main advantage of this approach is that the browser itself does not have a fixed and limited set of visualization objects, but can load and activate any Java class for the purpose of specialized rendering needs. This means that there is no limit to the number of different notations and sophisticated graphic objects that can be satisfied by the XMLC approach. Furthermore, since the XML elements transform into JavaBeans objects, it is easy to add complex and behaviors during the lifetime of the visualization, providing support for hypertext jumps, animations, interactions with the reader, and in general all the computational capabilities of the Java language. The kind of currently supported notations is the topic of the next sections..."
References:
"Visualization of UML Sequence Diagrams through Displet." By Emanuele Bandini, et al. Bologna, 30th june 1999. "The Unified Modeling Language (UML) is a modelling language to express designs through graphical notation. The Sequence Diagrams are a particular model that describe how groups of objects collaborate in some behavior. The eXtended Markup Language (XML) is a new W3C markup meta-language useful for exchanging structured information. Displets are an University of Bologna proposal for extending HTML documents using Java. We have implemented a displet useful for rendering UML Sequence Diagrams in a XML document conformed to an our Data Type Definition (DTD)." Also in Postscript format.
"Active Documents in XML." By Luca Bompani, Paolo Ciancarini, and Fabio Vitali. Department of Computer Science, University of Bologna. "In this paper we introduce XMLC, a generic, modular XML browser that can display any kind of notation required for XML documents, and we also discuss the use of XMLC for active documents. Currently, XML tools are either meant to display text-oriented documents (belonging to one of the myriad document types expressed in XML DTDs) or to rely on XML comfortable syntax for their run- time parameters. To overcome these limitations we have created a generic, modular XML browser called XMLC. Each XML element is associated to a special rendering module, called displet, that creates the visual representation of the element [CRV98]. But the power of displets goes beyond the simple visualization of XML documents. The solution taken within the XML family is to map (or rewrite) the source XML document (containing elements meaningful to the author) into a different XML document containing elements meaningful for the program that has to perform the application. Thus, a document containing elements such as section, titles, formulas, sentences, etc., all meaningful to its human author, will be rewritten into a new document containing elements such as blocks, paragraphs, inline styles, white regions, and so on, all meaningful to a displaying or printing program. 3 Figure 1: The general architecture of the XMLC prototype The XML document is read and transformed by a normal XML parser into a internal tree representation using DOM. Then one or more layers of XSL stylesheets are applied to the DOM tree through the use of an XSL processor. This transforms the tree, at the end of all these passages, into another DOM tree that has an important property: for every element name in the tree there exist an available Java class, called displets, that provides the rendering. TBJava A prototype that allows XMLC to execute Toolbook books within an Internet browser has been implemented [BOMPANI98]. TBJava translates Toolbook books in XML documents, and displays and activates them in an XMLC applet within a browser... Displets provide an exciting working environment for XML. Since they support but are not limited to traditional text documents, any kind of different applications can be foreseen. Currently XMLC is a prototype, and thus is not comparable in speed to other, professional applications. We are planning a new implementation of the XSL engine that should considerably increase the speed of the application. Furthermore, we are continuously enriching the set of displet classes, and are going to provide soon some support for XLinks." [cache]
