COHOWeb reuses many of the ideas and the software from the previous WWW-based data system, OMNIWeb, which was brought on line in December 1994. However, COHOWeb represents the second generation of WWW-based interactive data retrieval and browsing systems. From NSSDC's experience in creating OMNIWeb, COHOWeb goes a step beyond in the integration of retrieval and browsing into a single interface rather than as separate activities. Not only does COHOWeb provide a new interface to NSSDC's COHO data, but it also allows public access to data previously accessible only via CD-ROM and ftp.
Underneath this view is the Common Gateway Interface (CGI) layer that actually processes the user's requests, accesses the data, and generates HTML output displayed on the browser. It is composed of a number of Perl scripts, C programs, and other utility programs. The interaction of CGI scripts, HTML documents, and the data has the effect of a seamless interaction with the system through the WWW.
A control panel of graphic buttons appears near the bottom of every "page." The control panel in conjunction with the "back" button on WWW browsers allows the user to navigate the COHOWeb system.
Figure 1. COHOWeb System Diagram
The Data Selector is a form that allows users to register their user names and select spacecraft. When submitted, the corresponding CGI program verifies the input and generates the Data Explorer form with the parameters specific to the spacecraft selected in the Data Selector form.
COHOWeb provides the user with a capability to query any spacecraft's data sets for specific variables, such as plasma speed and magnetic field intensity, over any time period from the Data Explorer and view time series plots of the selected variables. The plots are created with the Interactive Data Language (IDL) graphical data analysis package and displayed as HTML documents with inline GIF images. Figure 2 is an example of a typical plot covering the time period of January 1, 1975, to April 14, 1975.
Figure 2. Sample Plot from COHOWeb
Also from the Data Explorer the user may retrieve the data as an ASCII data file, a machine-independent Common Data Format (CDF) file, or a raw binary file for various platforms. With this interface the user may retrieve data in any format that is most appropriate, whether as a GIF or PostScript file to use in a journal article, an ASCII file to import into a spreadsheet program, or as binary data to read from a data analysis package.
To collect ideas and user opinions on how COHOWeb could be further improved, there is a forms-based feedback mechanism available from the control panel. The inclusion of the feedback form is based on the philosophy that the best designer of any computer system is the user. Further enhancements to the COHOWeb system will be driven primarily by user requests.
The COHOWeb News section contains important announcements about the COHOWeb system. It was created to allow the user to see quickly updates, enhancements, and other changes to the system.
OMNIWeb and COHOWeb represent a framework from which to model data systems providing interactive access to data via the World Wide Web. There is a trend to put more than HTML hypermedia documents onto the WWW, and NASA is very aggressive in developing many such interactive systems (OMNIWeb, COHOWeb, SkyView, and StarTrax) that go far beyond authoring a simple HTML document. COHOWeb and systems like it are radically shifting the paradigm with which researchers currently acquire data. Not only does it offer instant access to data but also has the added feature of supporting browsing as part of the data selection process. The WWW, which was originally conceived for document delivery, has evolved into a network-based data retrieval and display tool.