The subject of what kind of search and query operations should be provided in a hypertext system is still very much a research issue. So far, searching for a set of keywords or a regular expression in textual information, either in the whole hyperdocument or only in the current information node, is the only search operation offered by most systems.
In some sense searching the whole hyperdocument is not feasible in this course, because the course text plus everything reachable from it by following links is probably a very large part of World Wide Web. It is not (yet) feasible to perform a search on all information on all connected hyperdocuments at once. Many very large search engines exist for World Wide Web, but none of them are complete. It is simply not possible for a search engine to keep up with the rate of growth and change in the Web.
The search could however be limited to local information nodes, i.e. to the course text itself. The Tübingen version of Mosaic offers a "fish search" that makes it possible to perform a non-exhaustive search, possibly also limited in time, to find nodes that deal with specific words. (You can obtain this browser from the ftp server at ftp.win.tue.nl.) The "fish search" also exists in a server version, and is installed on the server of the computing science department of the TUE. (It can be reached at http://www.win.tue.nl/FishSearch.html.)
While the "fish search" searches through the nodes on the fly, there exist many so-called index databases that are (re)built periodically, and offer a search facility. The server containing this course text has such an index database and search engine which is updated every night. It can be used to find any information on this server.
For World Wide Web there exist some large index databases and search engines. At the expense of a lot of network bandwidth they download as many documents from the Web as they can find, and create an index-database for them. Some of the best search engines are Alta Vista, Excite and Lycos.
Queries about not only the information in the nodes but also about the network structure are subject for research. There are currently no systems that provide a user-friendly interface to ask queries that involve the network structure.