All applications and media files used by UJML applications are invoked using URLs. In most cases, relative URLs will be used, but it will sometimes be necessary to use an absolute URL. 

UJML applications can either be run from the file system (referred to as standalone applications) or using the Apache Tomcat application server (referred to as appserver applications). The absolute URL used to invoke the application will determine whether the application is being run in standalone mode or appserver mode. If an application includes JSP resources, then it must be run in appserver mode. 

UJML source files are application files written in UJML, an XML-based programming language. UJML source files typically have a .ujml file extension. The compiler processes these files into a proprietary byte code format that is understood by the UIE Player. The byte code format is typically specified using the .ujbc extension. The URL should request the byte code from the server or file system using the .ujbc extension (for example, using http://{host}:{port}/{context}/{filename}.ujbc). 

JSP files are compiled into byte code using a URL of the form http://{host}:{port}/{context}/compile/{filename}.jsp. This URL notifies the application server that byte code should be returned, rather than UJML source code. It is also possible to compile UJML source code using an application server with a URL of the form http://{host}:{port}/{context}/compile/{filename}.ujml.