Tumbler (Project Xanadu)

Tumblers were proposed by Ted Nelson in "Literary Machines" as a means to address every bit ever written, or a particular span of bits in any text ever written.

A tumbler is a unique numerical address of an interesting artefact. The address resembles an IP address, but is much larger and has much more detailed structure. The structure looks like this.

1. < node >.0. < user >.0. < document >.0. < element >

The "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 arbitratily long. Each < element > has the format "n. n. ... . n", a hierarchy of subaddresses.

The last element denotes the special kind of element, for example:

1. Text/Bytes 2. Links 3. Bitmaps 4. etc.

Address area	Tumbler Address	Comment
Node	1.2368.792.6	This is the computer with the number 2368.792.6
User	1.2368.792.6.0.6974.383.1988.352	This is user 6974.383.1988.352 on the above computer.
Document	1.2368.792.6.0.6974.383.1988.352.0.75	The user's document number 75.
Version	1.2368.792.6.0.6974.383.1988.352.0.75.2	Version 2 of the document.

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.

Tumblers are only issued once and never changed again. The structure can grow at will, the address space is practically infinite.

Nelson also introduces the concept of "spans", and the idea of direction. One can speak of "2 chapters back" or "300 bytes forward".

See also

• Purple Numbers, a proposal to address paragraphs in Web pages.

External links

• "Tumbler Arithmetic". Udanax.com&#0153;. Retrieved May 22. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)CS1 maint: extra punctuation (link)
• "The Xanadu model". Retrieved January 13. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
• "Definitions". Sunless Sea. Retrieved January 30. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help) (Xanadu project wiki, restructured in August 2005)
• Theodor Holm Nelson (December 1999). "Xanalogical Structure. Needed Now More than Ever: Parallel Documents, Deep Links to Content, Deep Versioning, and Deep Re-Use". ACM Computing Surveys. 31 (4).
• "Theodor Holm Nelson's Homepage". Retrieved January 13. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)