Almost parallel to the dedicated client-server systems of the ADS and ESIS, several general purpose network information systems were developed, notably Gopher, WAIS, and the World Wide Web. We call them general purpose systems, because their design allows them to be employed for the presentation of a wide variety of information, across scientific disciplines. The capabilities, of the hypertext based World Wide Web system in particular, are so versatile, that there is much less need for dedicated client-server systems.
The same remarks regarding continuity and stability apply with respect to astronomical information systems employing these general purpose client-server systems, as they were made concerning the dedicated systems of the ADS and ESIS in the previous section. The End-User should not have to worry about whether a particular system or service will still be here tomorrow, nor about what it will look like by then or how it should be operated. Of course, we are only just discovering the technology of network information systems, and both information providers and information seekers will have to explore the technology to find out about its capabilities. Changes are inevitable, as new information or new capabilities are added to the systems. However, when new systems are initiated, with the intent of providing a lasting service, changes to a system once in existence should be of an evolutionary nature rather than revolutionary, otherwise the End-User will loose track.