Multimedia Glossary

UCS: Universal Character Set; Computers originated in the USA where English is the dominant language. Computers thus basically use a character set that is biased toward English (the ASCII character set). As computers became used in other cultures where other characters (such as ö, ë, ù, é in some European languages) are used, the basic set was extended to include these characters. This extended character set is known as ISO 8895. However, even this extended ASCII character set is not enough to cope with all the variety of characters found in the many different languages of the world. The UCS was formalized and contains thousands of characters used by communities all over the world (also see Unicode).

UDP: User Datagram Protocol; UDP is defined by RFC768 and is another protocol besides TCP that ensures safe transmission of data. UDP is a connectionless protocol (like CB radio) and each packet of information must contain its address. These kind of packets are called diagrams. UDP is much faster than TCP, but not reliable as it does no checking or error correction. It merely forwards data between upper-layer protocols.

Unicode: There are many languages in the world with many more characters than provided for in the ASCII set. The Unicode Standard (at http://www.unicode.org) is a subset of the International Standard ISO/IEC 10646-1:1993. Unicode 2.1 lists almost 40'000 characters, which are grouped into sets. Each set has a unique name. Unicode lists the characters, while the UTF-8 and UTF-16 systems map the characters for computer systems.

URC: Uniform Resource Characteristic; URC is a subclass of URI and used for the classification of web documents, much like the Dewey system in book libraries.

URI: Universal Resource Identifier; This is an identifier (an address) linked to each kind of resource that is made available on the Web, such as an HTML document, image, video clip, program, etc. There are subclasses of URI: URL, URC, URN; Example:
http://www.wacko.org/one/html4/index.html; This URI reads:
Use the HTTP protocol on the machine www.wacko.org. Follow the path /one/html4/ to the file (document) index.html.

URL: Universal Resource Locator; The URL is a subset of URI and is an identifier (an address) linked to each location available on the Web, such as a machine server, or software server. It has become customary to speak of URL's instead of URI's for web addresses.

URN: Universal Resource Name; URN is a subclass of URI and is intended to be a unique human name for an internet resource -- like a book's name.

User: A User is a person who uses the internet, and typically requests an HTML document from a user agent (i.e. typically a browser). The most common user is presently a person who browses through the Web by means of a web browser. However, HTML documents can be rendered in different ways such as in the audio medium. The user then does not browse the Web, but listens to the document.

User Agent: A User Agent is any device that interprets HTML (or other web-) documents. The most commonly used User Agents are presently Web browsers on computer screens. However, apart from other types of visual user agents (such as PDA screens, projectors and more) there are also non-visual User Agents, such as search robots, speech synthesizer and Braille readers. To indicate this wide variety of media that HTML caters for, it is thus more appropriate to talk of a User Agent than of a browser.

UTC: Unicode Technical Committee; The Unicode Technical Committee writes the technical specifications for Unicode.

UTF-8: UTF-8 is an 8-bit character set specified by Unicode Technical Committee. UTF-8 includes the first 128 characters of ASCII.

UTF-16: UTF-16 is a 16-bit (two bytes/two octets) character encoding system. It allows the definition of 65'536 characters. UTF-16 characters begin with a BOM (Byte Order Mark) to avoid possible confusion with UTF-8.

Multimedia Glossary: U