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The Extension Mechanism of the Reader Application of the dLibra SystemSince version 5.0, the dLibra system has had an extension mechanism for presenting publication content. For some document formats (for example, for the DjVu format), the reader must install appropriate browser extensions. In the Reader Application of the dLibra system, there are mechanisms for presenting some file types in a user-friendly form. The mechanisms are based on software compatible with HTML and on the default solutions of Internet browsers. . On the basis of the type and name of the main publication file, the Reader Application determines if extensions for the manner of content presentation are available for the given publication. If they are, the application displays the list of the available extensions to the reader (see the figure above), before displaying the content. The user can use the player built into the dLibra system or leave the handling to the browser (if the plugin is already installed). The Structure and Operation of Content Presentation ExtensionsEvery extension used for presenting content consists of two parts: files visible through the WWW, for example, JavaScript files or CSS sheets; those files are in the dlibra-webapp-5.0/formats/extension-name catalog; and files with extension configuration, for example, settings of the data formats which the given extension can display, VTL templates for generating HTML code, or a warning text; those files are in the dlibra-webapp/WEB-INF/formats/extension-name catalog. Below, we describe the extension used for presenting objects in the Zoomify format. It consists of the following files:
The settings.xml file contains the most important settings related to the functioning of the extension, such as:
When the user has chosen an extension for presenting content, the Reader Extension generates a warning which pertains to* the format – the content of the message.vm file is rendered with the use of the text labels from the messages_pl.xml and messages_en.xml files. Next, the user goes to the content, and the Reader Application displays the rendered content.vm template. In that template, references to a) the elements of the extension for the manner of content presentation which are visible from the WWW and b) the file with the publication content. From the level of the content.vm template, two variables are available for the person creating extensions for presenting content:
In the case of the presented extension, zoomifyZoomify, the page rendered while the publication content is being displayed contains the calling of the zoomifyViewer.swf script, where the arguments include the path to the main file of the publication. The box below contains the content of the content.vm template for the djvu_htm!5 html5 extension:
The Default Manner of Content PresentationThere are three files (message_pl.xml, message_en.xml i settings.xml) in the dlibra-webapp/WEB-INF/formats catalog. That is the configuration of the default handling of the manner of content presentation. Any changes in those files may prevent the Reader Application from functioning correctly. |