A number of books describing the Internet and the many tools available for locating and retrieving information have recently been published. A survey of these, including intended readership, price, etc. is available in a document by J. Quarterman. This survey is available as RFC 1432. RFC, in the tradition of technical, network-related documents, stands for ``Request for Comments''. One location among many where this file can be found is nisc.jvnc.net:pub/RFC/rfc1432.txt.
In the last two years or so, a number of so-called resource discovery tools have become widely used. Examples are WAIS (Wide Area Information Servers), Gopher, and WWW (World Wide Web). Some of these offer a command-line access mechanism on a machine to which you can login with telnet. However it is much more efficient to use the windowing potentials of such software. As examples, Lynx is a line-mode browser for WWW, and Mosaic is a widely-available window-based browser. Generally, the client-server paradigm is utilized: software sits on your machine, which handles your mouse- or key-controlled requests in your local windowing environment. This client communicates over the network with the remote server, as the need arises. There is compatibility between these tools, and often Mosaic (for example) is used to access remote sites using Gopher and to carry out free-text searches using WAIS. We will briefly describe these different tools.
Gopher offers a convenient way of accessing anonymous FTP accounts, connecting to remote sites, or receiving files. To use it, and assuming that the client software has been installed at your site, give the command xgopher. (This command may be different at your site.) Without a network address following this command, by default you will access a University of Illinois Gopher service. Navigation to various other sites is accomplished by clicking on the appropriate line in what you are shown. Further information on Gopher, including where to obtain client and server source code, is available in Anklesaria and McCahill (1993). A search tool which can be used in conjunction with Gopher is called Veronica.
A WAIS server offers an indexed set of files, so that full- and free-text retrievals may be carried out. A large number of source files (with extension .src) which specify the network access addresses of servers are in a Directory of Servers, available via anonymous FTP from think.com:wais/wais-sources.tar.Z. You or your system manager should retrieve all relevant source files. Further information on WAIS, including where to find source code for server and client ends of this system, is available in Fullton (1993, 1994). WAIS permits you to index, and thereafter search using free text, your own local text files or mail files. In fact, a wide range of file types can be used as input to WAIS. To display files which are not plain text files (Postscript files, for example) WAIS allows the specification of a filter program which permits display. Thus, if WAIS is informed at the indexing stage that the input files being indexed are of type PS, the information may be used subsequently by client software to direct retrieved files through the Ghostview X-terminal screen previewer. To register a WAIS-indexed collection of documents with the WAIS Directory of Servers, one uses the ``register'' parameter when indexing (which sends the source file to the appropriate registration addresses: firstname.lastname@example.org and email@example.com).
The WWW (World-Wide Web) is a cross-network hypertext system. It is often used via the user interface Mosaic of NCSA (National Center for Supercomputing Applications). The command mosaic (or Mosaic or xmosaic) may be the one available on your system for access to ``the web.'' A standard form of address and directory information, used by Mosaic, is referred to as a URL (Universal Resource Locator). There are now over 1000 URLs of potential interest to astronomers. Mosaic and the WWW are extremely useful tools for navigating the network, especially because they provide access to other network facilities (Gopher, Archie, FTP, telnet, etc.).
Using a URL via an appropriate browser such as Mosaic gives access to text and graphics, which often encompasses hypertext. This means that some text or graphical icons are ``clickable,'' and gives direct access to a new window of textual or image information. Hypertext is supported by a language (in appearance, not unlike a SGML or Standard Generalized Markup Language, or even LaTeX) called HTML or Hypertext Markup Language. Further details of Mosaic, including source codes for various workstation, PC, and Macintosh platforms, is available at NCSA: ftp.ncsa.uiuc.edu in directory /Web/xmosaic. A primer on HTML can be accessed at URL http://www.ncsa.uiuc.edu/General/Internet/WWW/HTMLPrimer.html.
An informal group of WWW enthusiasts, the AstroWeb Consortium, has been established to maintain a list of URLs of astronomical importance. Members include R. Jackson (ST ScI), D. Wells (NRAO), A. Koekemoer (Mt. Stromlo), D. Egret and A. Heck (Strasbourg), and H.-M. Adorf and F. Murtagh (ST-ECF). At the URL http://fits.cv.nrao.edu/www/astronomy.html these astronomical resources are grouped into the following categories: Observing Resources, Data Resources, Organizations, Software Resources, Publication-Related Resources, People-Related Resources, Various Lists of Astronomy Resources, Astronomical Imagery, and Miscellaneous Resources. A partial list of astronomical URLs is given in Appendix A.