The NLM Webinfo system provides both pre-computed and user-selectable graphical and textual summaries of past access to the HyperDOC multimedia service (note that the numbers provided by Webinfo apply only to the HyperDOC server, and not to the other NLM World Wide Web servers to which it may point; these other servers may or may not provide their own statistical summary services).
HyperDOC relies upon the network information retrieval technology known as World Wide Web. Invented by physicist Tim Berners-Lee and his colleagues at CERN in Geneva, Switzerland, Web technology is now fostered by multiple organizations, including the Internet Society and its Internet Engineering Task Force (IETF), the International World Wide Web Conference Committee (IW3C2), the (largely commercial) World Wide Web Consortium, the University of Illinois' National Center for Supercomputer Applications (NCSA), the NSF/NCSA World Wide Web Federal Consortium, and numerous other institutions and individuals working in the commercial, academic, and government sectors.
You can envisage your trip through the Web as if you were travelling on the head of a pin, piercing various documents as you view them, trailing a thread behind you as a record of your path. Most WWW browsers offer "forward" and "back" commands which allow you to travel linearly along this thread. HyperDOC provides a further method of traversing the information it offers. The information it offers is organized hierarchically, with each document attached to a single "parent" document (the topmost parent being the home page document you are examining currently).
The extensive cross-referencing which WWW allows can be viewed as a web which is cast over the hierarchical tree-like structure. At the bottom of most documents you will be offered the option to move to the parent document. In the case of documents which represent fragments of a larger document, you may be offered additional options as well, such as the ability to move to a neighboring fragment.
There are numerous software tools for both providing and viewing WWW documents, designed for various platforms. NCSA has introduced a particularly powerful and easy-to-use multi-protocol, multi-platform browser known as Mosaic.
Note that you may encounter problems when displaying the images offered by HyperDOC. Due to differences between the perceived brightness of different monitors, images which appear fine on one monitor may appear too light or too dark when seen on another monitor. Hardware manufacturers are currently working on techniques for automatically correcting for this effect, although this work is likely to take years to come to fruition. In the interim, brightness differences can often be compensated for by means of using a quantity known as the gamma factor (the supplemental technical description tells you more about gamma, as well as providing a simple means for measuring the gamma value of your monitor).
Note that unless explicitly stated otherwise, all images associated with HyperDOC are created for monitors with a gamma of 2.6. If the gamma of your monitor differs from this value, you can often correct for this discrepancy by setting up your external image display programs to compensate. For example, many users on X workstations employ the program xv, which accepts a command-line argument for a gamma correction (refer to the documentation for the viewer you are using).
Unfortunately, none of the currently available World Wide Web browsers that we are aware of will perform a gamma correction for in-line images (images appearing within hypertext). We hope that groups such as NCSA will respond to this problem. It is likely that if in-line image gamma correction becomes widely available within Web browsers, we will modify the gamma of all images in HyperDOC to a value of one.
Many people associated with universities and large industrial concerns have access to the Internet. An important practical limitation in making network-accessible information widely available is the problem of providing Internet access to non-institutional end-users working in their homes or offices.
This situation is likely to change dramatically in the next few years. Companies offering inexpensive Internet access are appearing frequently, and software publishers are preparing kits which will make it easy to connect to the network over ordinary telephone lines using many types of computers in popular use. For parties interested in telephone-based access, there is an electronic mailing list known as PDIAL ("Public Dialup Internet Access List").
Another avenue toward rapid Internet access in homes and offices is the use of the digital telephony standard known as Integrated Services Digital Network (ISDN). The Combinet BBS service offers an automated system which provides information about the availability of ISDN in your area (after logging in, enter your area code and three-digit telephone prefix).