An XML Driven Graphical User Interface and Application Management Toolkit

Abstract

In the past, the features of a user interface were limited by those available in the existing graphical widgets it used. Now, improvements in processor speed have fostered the emergence of interpreted languages, in which the appropriate method to render a given data object can be loaded at runtime. XML can be used to precisely describe the association of data types with their graphical handling (beans), and Java provides an especially rich environment for programming the graphics. We present a graphical user interface builder based on Java Beans and XML, in which the graphical screens are described textually (in files or a database) in terms of their screen components. Each component may be a simple text read back, or a complex plot. The programming model provides for dynamic data pertaining to a component to be forwarded synchronously or asynchronously, to the appropriate handler, which may be a built-in method, or a complex applet. This work was initially motivated by the need to move the legacy VMS display interface of the SLAC Control Program to another platform while preserving all of its existing functionality. However the model allows us a powerful and generic system for adding new kinds of graphics, such as Matlab, data sources, such as EPICS, middleware, such as AIDA [1], and transport, such as XML and SOAP. The system will also include a management console, which will be able to report on the present usage of the system, for instance who is running it where and connected to which channels. MOTIVATIONThe work on the JoiMint (Java Operator Interface and Management Integration Tool) application started at SLAC as a proof of principle study for the COSMIC[2] project. Special emphasis was given to keeping the functionality of the existing applications. An important aspect of these applications is the communication between the operator interface and the application on the mainframe itself. In this case the operator can configure the settings for the display. According to these settings the database will be queried to extract all necessary information and to retrieve the live data from the control system as well as all information to format and render the graphics.In a distributed computer environment the situation is more complex because all the communication between the client and the application preparing the graphic has to run over a protocol. Even more important is the necessary 'push' model for the graphics which has to be defined by the application while the rendering process is performed by the client tool.This was the starting point for the study of a graphical toolkit which will clearly separate the definition of a display from the rendering process and the data access from the graphic update. In addition, the study should show whether the m anagement of client applications can be integrated into such a toolkit. DEVELOPMENT ENVIRONMENTSince the toolkit should in the end also run as an Applet, the decision to use Java as the basic language for the development was obvious. Visual Café was chos...