The WebUmbrella Web-based access to distributed plasma-physics measurement data
To provide plasma-physics scientists with worldwide access to historical and current measurement data from the Textor-94 Tokamak experiment, we developed a new architecture: the "WebUmbrella." It uses HTTP to transfer data in (X)HTML, plain text, or other MIME-type documents. We provide a single point of access to our servers via HTTP redirection. Server implementations for several data stores are already present, and the first user tests are positive. In particular, we present one server implementation that provides access to already existing common object request broker architecture (CORBA) servers. It uses the Apache Web server and the Tomcat Servlets engine, and consists of Java Servlets that convert HTTP requests into CORBA requests for the existing interface. These developments are the aftermath of an earlier experience with CORBA interface definition language (IDL) interfaces between user clients and several data servers, which provide access to-the different data stores. The interfaces were developed in a telematics application program project, "Dynacore." After the evaluation of this demonstrator, we designed a new system to improve the service. Because of the positive experience, we inherited the data representation, the data-browsing features, and the single access point for clients to several data stores. We tried to eliminate the obligatory use of CORBA, as its added value did not weigh up against,the problems we faced using it: CORBA is difficult to understand for scientists inexperienced in object-oriented design and difficult to access with simple analysis tools like IDL or MATLAB. We also did not find a suitable CORBA implementation for Virtual Address eXtension/Virtual Memory System (VAX/VMS) with C/Fortran bindings. Finally, WebUmbrella's transport protocol, contrary to CORBA's, does not suffer from firewall and access problems.