In the design of the
Xanadu computer system, a tumbler is an address of any range of content or link or a set of ranges or links. According to
Gary Wolf in ''
Wired
''Wired'' (stylized as ''WIRED'') is a monthly American magazine, published in print and online editions, that focuses on how emerging technologies affect culture, the economy, and politics. Owned by Condé Nast, it is headquartered in San ...
'', the idea of tumblers was that "the address would not only point the reader to the correct machine, it would also indicate the author of the document, the version of the document, the correct span of bytes, and the links associated with these bytes." Tumblers were created by
Roger Gregory
Roger L. Gregory (born July 17, 1953) is an American lawyer who serves as the Chief United States circuit judge of the United States Court of Appeals for the Fourth Circuit.
Background
Gregory was born in Philadelphia, Pennsylvania but grew u ...
and
Mark Miller.
They were used in the Xanadu FEBE (Front End - Back End) protocol in a manner similar to the use of
URIs between web browsers and servers.
Concept and implementation
The idea behind tumblers comes from
transfinite number
In mathematics, transfinite numbers are numbers that are " infinite" in the sense that they are larger than all finite numbers, yet not necessarily absolutely infinite. These include the transfinite cardinals, which are cardinal numbers used to q ...
s.
A tumbler is a unique numerical address of any interesting artifact. It resembles an
IP address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
, but is much larger and has much more detailed structure. The structure looks like this.
1. < node >.0. < user >.0. < document >.0. < element >
The leading "1." is used in order to mark the start of a new address. The individual fields of the address are divided with ".0." so that they can be arbitrarily long. Each < element > has the format "n. n. ... . n", a hierarchy of subaddresses.
The last element denotes the type of data the tumbler refers to, for example:
# Text/Bytes
# Links
# Bitmaps etc.
The 9287th byte of this version of the document would be 1.2368.792.6.0.6974.383.1988.352.0.75.2.''0.1.9287'' and the 356th link would be 0.2.356 on the end instead.
A tumbler can be issued only once and never changes. The type of structure can grow at will, so the address space is infinite.
Nelson also introduces the concepts of direction and a "span", which is a part of a document that is semantically meaningful for the document. For example, one can speak of "2 chapters back" or "300 bytes forward".
See also
*
Purple Numbers, a proposal to address paragraphs in Web pages.
*
XPointer
*
Cross-reference
*
Impure name
References
External links
*
*
* ''(Xanadu project wiki, restructured in August 2005)''
* {{Cite web
, title = Theodor Holm Nelson's Homepage
, url = http://ted.hyperland.com/
, accessdate = January 13, 2004
Identifiers
Hypertext
Ted Nelson