TERENA Guide to Network Resource Tools: Appendix
| ActiveX | ActiveX is a technology developed by Microsoft. With an ActiveX-enabled browser (i.e. Internet Explorer only) ActiveX controls can be downloaded as part of a Web document to add functionality to the browser (similar to Java applets). In particular ActiveX enables seamless viewing of Windows files of all types, e.g. spreadsheets, and in combination with other technologies such as Java and scripting languages, makes possible the development of complex Web applications. Currently it runs on 32-bit Windows platforms (Windows 95 and NT) only. |
| Aglet | An aglet is a Java object that can move from one host on the Internet to another. That is, an aglet that executes on one host can suddenly halt execution, dispatch to a remote host, and resume execution there. When the aglet moves, it takes along its program code as well as its state (data). A built-in security mechanism makes it safe for a computer to host untrusted aglets. |
| Avatar | A graphical image of a user, such as used in graphical real-time Chat applications, or, a graphical personification of a computer or a computer process, intended to make the computing or network environment a more friendly place. |
| Caching | Web documents retrieved may be stored (cached) for a time so that they can be conveniently accessed if further requests are made for them. Caching of files considerably speeds up retrievals, whether it is handled by the browser itself, a local proxy server, or a regional caching server for a wider community. The issue of whether the most up-to-date copy of the file is retrieved is handled by the caching program which initially makes a brief check and compares the date of the file at its original location with that of the copy in the cache. If the date of the cached file is the same as the original, then the cached copy is used. Web browsers normally maintain a cache of retrieved documents and this cache is used for retrievals where possible. In addition, the user may configure the browser to point to a caching server via the browser's options or preferences. File requests not able to be supplied from the browser cache would then be directed to the caching server. The caching server would supply the files from its cache if they were current, or pass on the request to the originating server if they were not. |
| Client-server | Client-server refers to a model of interraction between computers which is commonly used on the Internet. Users employ client software, such as a Web browser, to request information from servers. Servers, such as WWW servers, supply information in response to requests from clients. The client, which is normally installed on the user's computer, displays the information for the user. For instance when a Web document is retrieved from a remote server, the client will interpret the HTML tags and display the document appropriately. Some aspects of how documents are delivered and displayed may be determined by the user through configuration of the client's settings, for instance size and colour of font, whether images are displayed, whether cookies are accepted. In the client-server model, clients and servers have a special relationship derived from the common use of a well defined set of communicating conventions (protocol) . For example, Web browsers and servers use the WWW protocol, HTTP (Hypertext Transfer Protocol). Web browsers generally can use other Internet protocols as well. In this way they can also retrieve information from ftp servers, gopher servers, etc. The client-server model of processing is one of the cornerstones of the Internet's success. It is an efficient system which distributes the processing load between client and server, and also gives the user some control over their own interface to Internet information. |
| Cookies | Cookies provide a means for a Web server to induce a client to store information about itself which can subsequently be called up by the Web server when required. This might be information which the user has supplied about themselves, their preferences or their requirements via forms input. The oft-cited example is the shopping list which might be added to from time to time. Cookies are currently implemented by Netscape and Internet Explorer. More information : http://www.netscape.com/newsref/std/cookie_spec.html |
| Forms | The HTML standard provides support for forms in Web documents. Forms are a defined area of an HTML document such as a window or box into which the user is able to input data in order to have the data processed by another application, for instance to run a search on a database. The data keyed into the form is passed to a CGI (Common Gateway Interface) script which then passes it to the relevant application for processing. When the process is complete, the output is passed back, again using CGI, and the results presented to the user as some new HTML generated on the fly. |
| H.323 | ITU (International Telecommunications Union) standard for videoconferencing over local area networks and packet-switched networks generally. It is based on a recognised real-time standard and is commonly used with video over the Internet to ensure that users can communicate with each other, as long as they are using videoconferencing software which complies with the standard, e.g. Microsoft NetMeeting, Netscape Conference. The standard applies both to one-to-one and multi-party videoconferences. |
| HTML | WWW documents are normally written in Hypertext Markup Language (HTML), the native language of the WWW. HTML enables links to be specified, and also the structure and formatting of Web documents to be defined. HTML documents are written in plain text, but with the addition of tags which describe or define the text they enclose. For example, a link is defined by the ANCHOR <A> tag placed around the hyperlinked text. It specifies the URL of the 'linked to' document, e.g.
HTML is an evolving standard. Current work is focussed on extending accessibility features, multimedia objects, scripting, style sheets, layout, forms, math and internationalization. See the World Wide Web Consortium site for current information. |
| HTTP | HTTP (Hypertext Transfer Protocol) is the foundation protocol of the World Wide Web. It sets the rules for exchanges between browser and server. It provides for the transfer of hypertext and hypermedia, for recognition of file types, and other functions. |
| Hyperlink | Example of hyperlink in an HTML document:
When the HTML document is viewed with the Web browser, the tag information between angle brackets is not visible, but the words Web Search Tools are displayed in whatever format or colour is defined for links by the browser or the document's author (the browser default is often blue, underlined text but HTML authors may specify any colour or style). When the user selects these words, the document index.html will be displayed, having been fetched from the Web server www.terena.nl, where it was found in the path /gnrt/websearch. |
| Imagemap | Imagemaps, also known as active maps are graphics containing active link areas. Instead of the link being from a word or phrase in the document, it is embedded in a defined area of the imagemap. Clicking on that area fetches the referenced document. Imagemaps are often used to provide a graphical entry point to a Web site, though a text-based route through the site should always be given as an alternative. |
| ISDN | ISDN (Integrated Services Digital Network) is a system of digital telephone connections. It allows multiple digital channels to be operated simultaneously through a single, standard interface. The Basic Rate Interface (BRI) consists of two 64 kbps plus another lower rate channel to handle signalling. Primary Rate Interface (PRI) consists of 23 channels plus a signalling channel. ISDN is adequate for videoconferencing and other high bandwidth applications. The cost of an ISDN line is higher than a normal phone line, and special equipment is required. |
| JAVA | Powerful, cross-platform programming language developed by Sun Microsystems. Java applets (small applications) may be incorporated into Web documents and can be executed securely by any Java-capable browser irrespective of whether it is running on a PC, an Apple Mac or a Unix workstation. Both Netscape Navigator and Internet Explorer are Java-capable. Java is being used in many ways which enhance the functionality and interactivity of Web pages. |
| Javascript | Scripting language (originally called LiveScript) developed by Netscape Communications for use with the Navigator browser. JavaScript code forms part of the HTML page and can be used for example to respond to user actions such as button clicks or to run processes locally or validate data. JScript is the Microsoft equivalent of Netscape's JavaScript for use with Microsoft's Internet Explorer. |
| MIME | WWW's ability to recognise and handle files of different types is largely dependent on the use of the MIME (Multipurpose Internet Mail Extensions) standard. The standard provides for a system of registration of file types with information about the applications needed to process them. This information is incorporated into Web server and browser software, and enables the automatic recognition and display of registered file types. Users can add other file types and associated processing instructions to their browser's configuration options if they wish. |
| Plug-Ins | Browsers can display certain file types such as HTML and GIF as a standard part of their functioning. The display of other file types may be handled by additional software, either designed to work in conjunction with the browser for the display of a specific file type (a plug-in) or a stand-alone application which the browser can launch for viewing a file requiring that application (a helper application). With plug-ins there is closer integration with the functioning of the browser. Plug-ins are loaded when the browser is launched so can act instantly and non-intrusively when called upon, thus giving the browser the appearance of enhanced functionality. The idea of plug-ins was developed by Netscape but is also supported by Internet Explorer. Some plug-ins may be bundled with browser software, but many more from third party developers are available for downloading. Examples:
Further information on Netscape's plugins http://home.netscape.com/comprod |
| Proxy server | Where a high level of security of required, a proxy Web server may be used to provide a gateway between a local area network and the Internet. The local network is protected by firewall software installed on the proxy server. This software enables the proxy server to keep the two worlds separate. All outward HTTP requests from the local network pass through the proxy server and similarly all information retrieved comes back in via the proxy server and is then passed back to the client. Using the options or preferences, Web browsers can be configured to point to the proxy server. Proxy servers will normally maintain a cache of retrieved documents. |
| URL | The Uniform Resource Locator (URL) provides a way of uniquely specifying the address of any document on the Internet. This is the lynchpin of WWW's embedded linking. The typical URL specifies the method used to access the resource (the protocol), the name of the host computer on which it is located, and the path of the resource, e.g.
The protocol specified in this example is http (HyperText Transfer Protocol), the protocol of the World Wide Web. Other protocols can also by used within the WWW. |
| VRML | Virtual Reality Modelling Language (VRML) is an Internet standard
for the rendering of 3D graphics. VRML files can be viewed with plug-ins
such as Live3D.
|
| WYSIWYG | What You See Is What You Get. A graphical interface to a process which shows how the end-result will look as it is being produced, e.g. a WYSIWYG HTML editor generates HTML markup but displays the document as if viewed with a Web browser. |
gnrt@terena.nl
May 1997