This chapter defines many of the terms commonly heard when talking about the Web.
- anchor
- An element in an HTML
document that points to one of:
- another document
- a specific location in another document
- a specific location in the current document
- An element that denotes a specific location in a document, pointed to by
another anchor.
When the document is displayed in a browser,
clicking on an anchor (of the first type) causes the browser to display the
document and/or the location that it points to. - attribute
- A value that is associated with an element
but is not part of the content of the element (that is,
text or sub-elements). For example, the
URL part of an anchor
is an attribute; you would use an attribute to specify the alignment of an
image. In an HTML
file, the attributes are actually located inside the element's start-tag, but
when you're editing in HoTMetaL, you view and edit attributes using the
Edit SGML Attributes...
command.
- browser
- A networked program that communicates with Web servers, used for retrieving and displaying documents from the
World Wide Web. Compare this
with editor.
Some well-known browsers are Mosaic,
Netscape, Lynx, and Cello.
- CERN
- The European Laboratory for Particle Physics in Geneva, where the World Wide Web was `invented'. For more information, see http://www.cern.ch/.
- CGI
- An acronym for Common Gateway Interface. This is a feature of Web servers that allows HTML clients such as browsers
to communicate over the web with scripts installed on the server. HTML forms are often
processed by such scripts. `
CGI scripts' can be written in any programming language that will
run on the server.
- clickable image map
- See image map.
- client
- A program, such as a browser,
that uses HTML
and communicates with a
Web server.
- DNS
- Domain Name System. This is the way in which the network turns a host or
Internet domain (e.g., sq.com) into an Internet IP address for use with TCP/IP.
- editor
- A program, such as HoTMetaL, used to create, or change the content of,
HTML
documents. Compare this with
browser.
- element
- Elements are the structural building blocks of HTML documents. Blocks of text in HTML
documents are surrounded by elements according to their function in the
document: for example, headings, lists, paragraphs, and anchors are all
surrounded by specific elements.
- firewall
- In networking, a firewall is a computer that prevents an intruder from
accessing all the computers on a network if he or she manages to break into one
computer someplace. The firewall usually sits between your inside network and
the outside Internet. For more information, see Cheswick & Bellovin's
approachable book Internet Firewalls: Repelling the Wily
Hacker.
- form
- A group of elements (enclosed by a FORM
element) in an
HTML
document, which generate graphical controls such as text entry boxes, radio buttons, and check
boxes when the document is displayed in a browser. The user can enter
information in a form and use the browser to submit it to a program on a
Web server.
- FTP
- The File Transfer Protocol; one of the schemes that can be specified in a
URL. This has traditionally been one of the most important of
the network services. It lets you pick up a copy of a file from a remote
computer, provided that you can connect to that computer (with
TCP/IP, for example).
- GIF
- The unofficial standard graphics format used in
HTML documents. This format is owned by CompuServe. See
also PNG.
- gopher
- A line-mode Internet protocol that predates the Web. Web browsers
can normally communicate with gopher servers.
- home page
- The top-level document on an organization's Web server, usually containing introductory information and links
to other relevant pages.
- hot image; hot spot; hot text
- Hot text is text in a hypertext
document (such as an HTML
document) that is a link to some other file; a hot image is an image that is a
link to some other file; a hot spot is hot text, or a region in an image map.
- HTML
- The HyperText Markup Language. This is the usual format for documents
that are `published' on the Web.
HTML is an application of SGML.
- HTML browser
- See browser.
- HTTP
- The HyperText Transfer Protocol. This is used to transfer
HTML documents over the
network, between a
Web server and an HTML browser, while you wait. The HTTP
protocol is implemented by a number of Web servers.
- HTTP server
- See Web server.
- hypertext
- Text that contains links to other documents. HTML documents are examples of hypertext.
- ICADD
- The International Committee for Accessible Document Design. Techniques
created by ICADD and documented in ISO
12083 specify how to automatically transform
SGML files (including HTML files) into input to a Braille, large print, or
synthesized voice system. All HTML documents created
by HoTMetaL are ICADD-ready and can readily be
converted to these formats using ICADD techniques.
- IETF
- The Internet Engineering Task Force, responsible for the technical
management of the Internet. The IETF coordinates the
development of the HTML
standard.
- image map; image map file
- An image map is an image that is divided into
regions, each of them associated with a URL. Clicking in a region causes the file referred to by the
associated URL to be accessed. An image map is also
called a clickable image map. An
image map file is a file that defines the regions in an
image map and assigns them to URLs.
- interlaced GIF
- A GIF
file that is first displayed in the browser at a low resolution, and then in
successively higher resolutions, until the whole image has been downloaded. This
is sometimes referred to as progressive display. Not
all browsers support this feature.
- ISO
- The International Organization for Standardization (`ISO'
is not an exact acronym).
- ISO 8859/1 character set
- This is the character set for `special' or `accented' characters
supported by HTML. This character set is also called
`ISO Latin 1'. It includes
characters required for most western European languages: Dutch, English,
French, German, Italian, Irish, the `Iberian' languages, and the `Nordic'
languages. This character set is one of several in the ISO
8859 standard: others support, for example, eastern European languages and
Cyrillic-based languages. Only ISO 8859/1 is
currently supported by HTML, however.
- line-mode browser
- An HTML
browser that can be used on a `dumb terminal' such as a VT100
or a PC with communications software. The most common
are
Lynx and a program called www from
CERN.
- link
- See anchor.
- Lynx
- A common line-mode
HTML
browser. Lynx can be used
over a dial-up line or if you don't have a windowing system.
- mailto
- A scheme that causes
a browser to send a form to a particular e-mail address, or generate a
mail-editing window.
- markup
- Special codes in a document that specify how parts of it are to be
processed by an application. In a word-processor file, markup specifies how the
text is to be formatted; in an HTML document, the markup specifies the text's structural
function (heading, title, paragraph, etc.).
- MIME
- The Multipurpose Internet Mail Extensions (RFC 1510):
extensions that allow e-mail messages to contain audio, video, and multiple
files. It is also the format that Web
servers and browsers
use to transfer files. The
MIME content type of a file
tells a browser how to process it. The content type for HTML
files is `text/html'.
- Mosaic
- One of the most widespread HTML browsers.
- NCSA
- The National Center for Supercomputing Applications, located at the
University of Illinois at Urbana-Champaign, Illinois. The NCSA
is an (indirectly) U.S. government-funded body that
exists to try and make powerful computers more accessible to researchers. Mosaic was originally written at NCSA.
- Netscape
- A popular Web browser.
- page
- A single HTML
document (which can be longer than one screen).
- PNG
- Portable Network Graphics; pronounced `ping'. A graphics format intended as a replacement for GIF,
on account of patent infringements involving the compression algorithm used with
GIF. PNG is a `lossless'
format; some of its advantages over GIF are better (24-bit) color support, compression, and anti-aliasing and
transparency capabilities.
- progressive display
- See interlaced GIF.
- proxy server
- If you have a firewall
at your site, you can't normally connect directly to a server on the Internet. You need an agent, a proxy server running
on the firewall, to make the connection for you. To you, inside the firewall, it
pretends to be the server that you're attempting to connect to; on the outside,
it pretends to be the client, and talks to the real server, thus letting you
talk to a server outside the firewall (or vice versa).
- relative URL
- A URL
that is missing some information (such as the scheme or network location), which a browser is expected to inherit from the URL
of the document that contains the relative URL.
- scheme
- The part of a URL
that tells an HTML
client such as a browser
how to retrieve the file specified in the
URL.
- server
- See Web server.
- SGML
- An international standard for describing the markup of structured documents. The basic idea behind SGML is that information can be made independent of particular hardware
and software. This is done by storing all documents as text-only files (with
references to documents in other formats, such as graphics, when required), and
using markup that describes the structure of documents,
rather than their physical appearance. SGML is
described by the ISO 8879 standard (
1986). HTML
is an application (a particular instance) of SGML.
- tag
- An element in an
HTML file begins with a start-tag
(e.g., `<PRE>') and (usually) ends with an end-tag
(e.g., </PRE>). In the HoTMetaL display tags are represented by tag icons
at the beginning and end of an element. Sometimes tags are called `commands',
but this isn't correct.
- TCP/IP
- Transmission Control Protocol/Internet Protocol. This is the low-level
protocol used by much of the Internet. It's really two protocols; IP packets are sent over a network that itself uses TCP.
Other common variations include SLIP (pronounced
`slip'; Serial Line/Internet Protocol), and PPP
(Point to Point Protocol).
- transparent GIF
- A GIF
image that has had one color (usually the dominant background color) designated
as `transparent', so that when the image is displayed in a browser, the image's
background is colored with the browser's
background color. The desired effect is an image that does not have a
rectangular boundary.
- URI
- Uniform Resource Identifier. This is a generic name for any of a class of
ways of identifying resources on the Internet. Three types of
URIs are URCs (Uniform Resource
Classification), URLs (see the next entry), and URNs (Uniform Resource Name). Implementations of URCs
and
URNs are still in an experimental stage. The basic idea is that a
resource (e.g., a document) is identified by a URN, a
kind of `public identifier' in the SGML sense.
The URN is resolved into a URC,
which is a collection of information about the resource (it could include, for
example, the price of obtaining the resource, and one or more
URLs).
- URL
- Uniform Resource Locator. A URL is the address
of a file, written in a format that can be interpreted by a Web server, which then retrieves the file. A URL
consists of a filename and, usually, a scheme that tells how the file is to be
retrieved. For most files on Web servers, the scheme
http is used.
- W3O
- The WWW Organization. This has been set up at
MIT, modelled after the X Consortium that promotes X
Windows. W3O is a not-for-profit organization that
provides sample code. For more information, see http://www.w3.org/.
- Web, the
- An informal name for the World Wide
Web.
- Web server
- A networked program that responds to requests from local or remote
computers for HTML
files. You give the Web server a file name (in the form of a
URL) and it gives you back the file (which can be in any
format, text or binary) over the same network connection.
- World Wide Web
- This is a generic term for the collection of Web servers and browsers
that literally spans the world. Usually abbreviated WWW.
- WWW
- The World Wide Web.