WWW Authoring: Glossary

Terms and Concepts

Contents

Client/Server
A sort of "division of labor" where one computer program requests services from another computer program (which is very often running on a separate computer). The program that is requesting services is called the client, and the one providing the service is called the server. In information retrieval systems, the client is freed from having to know the details about where the information is, and how it is organized (much as valet parking frees you from having to remember where you parked your car; you simply ask someone else to go get it for you).

With respect to the World-Wide Web, the client is a program that interacts directly with a user, allowing him or her to explore various network resources. Such a program is called a browser. The server is a program that manages a collection of documents, delivering them to the browser (and also supplying certain additional services) upon request.

Note: in casual usage, the terms client and server are sometimes used to refer to the computer that is running the client or server program, rather than the program itself.

Global Information Resources
A catch-all phrase describing the wide variety of services available on the Internet. These services include basic communication services, such as Telnet, FTP, and electronic mail. They also include Listservs (discussion groups that operate via electronic mail) and Usenet newsgroups (a type of discussion group which uses a more sophisticated distribution technique). More modern services are also included, such as Gopher, which was one of the first to try to remove the barrier for the user of having to know exactly where information was located and how it was stored, and the World-Wide Web, which goes even further and adds multimedia support. These are the most visible (and fastest-growing) segment of Internet services. Other services include miscellaneous auxilliary services, such as Archie (a search tool for finding files at anonymous FTP archive sites); Veronica (a search tool for finding Gopher items); whois, finger, and ph (tools for finding the addresses of individuals, much like a telephone book); and many others.
Home Page
The first document a browser fetches from the specified WWW server, or the default document when no specific document is requested. This is usually the primary page for a site; the term is used more frequently for personal pages than for institutions. This term is also used to denote the document that is initially displayed when a browser is first started. Colloquially: Any Web document.
HTML (HyperText Markup Language)
A markup language used to create hypertext documents. Special sequences of characters, known as "tags", are used to indicate what purpose various elements within the document serve (such as paragraphs, lists, headings, and so on), and how they should be displayed. A particular type of tag known as an "anchor" is used to create links to other documents.
Hypertext
Hypertext refers to a method of organizing textual information (on a computer) that goes beyond the flat, linear organization that is possible with paper documents. This is accomplished by having portions of the document become hyperlinks (or, simply "links") to other places within the document or to other documents. By selecting a link ("following" it), the reader is taken directly to a different set of information than he would have seen if he had simply proceeded to the next paragraph. Sometimes this is just additional information (such as the definition of a term), and the reader will then return to the original flow of the document. At other times, this can be used by the author of the document to create different flow paths for readers with different needs. In effect, a single set of documents (with one physical organization) can have a multitude of logical organizations corresponding to different audiences, all at the same time.
Internet
A vast collection of networks, providing a number of different services, including electronic mail, Usenet News, FTP, Telnet, Gopher, and WWW. (See also Global Information Resources.)
Multimedia
A term used to describe a document that contains more than just text. It includes still and moving images, sounds, and video (moving images and sound combined). Due to limitations of the browser or of the terminal device, it may not always be possible to provide all of these. In many cases, the browser may need to call upon "helper applications" to handle sound and/or video (or even still images in unusual formats).
Network
A set of computers interconnected by communication links. Each point of connection (essentially, each computer in the network) is called a node. The computer to which you currently have access is called the host.
Port Number
Port number is the UNIX port number through which a client communicates with a server. This is somewhat analogous to the channel number on cable television; different channels carry different information. The server decides which port to use to communicate. The port number needs to be specified in a URL, if it is not the default port for that service. The default port for HTTP services is 80, for Gopher is 70, for Telnet is 23, and for FTP is 20 and 21 (FTP opens two connections at once: one for data, and the other for commands).

The reason for using a non-standard port in the first place is often because more than one server program is being run on the same machine. This may be because one is a production server, while the other is a development or test server. Or the second server may be a private or restricted server. In any event, each server needs its own port.

Protocols and Standards
A mutually-agreed-upon set of rules about how something will be done (such as Robert's Rules of Order). In computerized communication, many different protocols are used to standardize the way various types of information are passed from one computer system to another. Specifically, a protocol defines the form and sequence of messages that are to be passed between communicating programs. Some protocols, such as TCP/IP, form the basis upon which more complex and sophisticated protocols are built. (TCP/IP stands for Transmission Control Protocol/Internet Protocol.) Different Internet services, such as Gopher, FTP, and electronic mail, use different protocols (all based on TCP/IP).

With respect to the Web, the primary protocols are: HTTP, for mediating the communication between the server and the client (browser); MIME, for negotiating how different types of documents (text, hypertext, images, sounds, video, compressed files, etc.) will be handled; and HTML, for creating actual hypertext documents and linking them together. However, it is important to note that most web browsers (and some servers) are actually capable of handling a variety of protocols.

Examples of various protocols include:

  • Transfer Protocols: These primarily specify how information is moved from place to place.
    • SMTP: (Simple Mail Transfer Protocol) The protocol used at Lehigh for electronic mail. (Note that other electronic mail protocols also exist.)
    • Telnet: A protocol for terminal emulation. Used when you want to log in to a remote computer.
    • FTP: (File Transfer Protocol) Used for moving files between computer systems. (Used at Lehigh to upload and download files between main systems, such as the Network Server, and PCs on Local Area Networks; also used to retrieve files from archive sites via "anonymous FTP".)
    • NNTP: (Network News Transfer Protocol) The protocol used by Usenet newsgroups (these are similar to bulletin boards).
    • Gopher: The protocol used by the Gopher system, which is a hierarchical menu-based information service for browsing the Internet.
    • WAIS: (Wide Area Information Server) The protocol used by WAIS, which is a tool for indexing and searching text databases remotely.
    • Z39.50: A protocol used primarily by libraries to standardize the exchange of information between bibliographic databases.
    • HTTP: (HyperText Transfer Protocol) The protocol used to transfer information between a World-Wide Web server and client.
  • Content Protocols: These primarily specify the format of information, and how information should be coded or interpreted.
    • SGML: (Standard Generalized Markup Language) A scheme for embedding special sequences of characters (these sequences are called "tags") into a document, in order to specify how the document should be displayed.
    • HTML: (Hypertext Markup Language) A particular version of SGML that is designed specifically for creating hypertext documents.
    • MIME: (Multimedia Internet Mail Extensions) A scheme for indicating what type of information is represented by the content of a message, so that the reciever can automatically handle different types of documents. (This scheme was originally developed to enable multimedia documents to be sent by electronic mail; the idea was co-opted to serve a similar purpose for web documents.)
    • VRML: (Virtual Reality Modelling Language) A proposal for a further extension of HTML to handle 3-dimensional models (which could be used for such things as architectural walk-throughs).
URL (Uniform Resource Locator)
An esoteric term for hyperlink. (See also hypertext.) URLs can invoke a TELNET session, retrieve files via anonymous FTP, read USENET news, retrieve Gopher menus, or load another HTML file via HTTP. The URL describes the type of information desired (or rather, the method used to get it), as well as identifiying where the information may be found (specifying both the machine to contact and the directory path to the information on that machine). A URL may sometimes include additional information, such as a search string.
World-Wide Web (WWW or simply, Web)
A global information retrieval system organized as hypertext documents with links to files (other hypertext documents) as well as other types of resources (such as Gopher, Telnet, FTP, etc.) all over the Internet.
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SDR, 11 Jun 1995.