Naming and Addressing: URLs
This is the overview materials related to the W3C
Addressing Activity, one of the activities of the
W3C Architecture domain.
URIs, or Uniform Resouce Identifiers, are the technology for naming and
addressing resources (pages, services, documents, etc.) on the web. It is
an extensible technology: there are a number of existing addressing
schemes, and more may be incorporated over time.
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A Beginner's
Guide to URLs
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The classic intro to URLs, by The NCSA
Mosaic team
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Schemes
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http:, ftp:, irc:, etc. Need to look one up? Thinking of suggesting a new
one?
The basic picture looks like this:
_______________________________________________________
| _________________ |
| | ftp: | |
| | gopher: | |
| | http: _______________ |
| | etc | | urn: | |
| |_____________|__| fpi: ? | |
| URLs | | |
| |_______________| |
| URNs |
|_______________________________________________________|
URIs
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URI
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Uniform Resource Idenifier. The generic set of all names/addresses that are
short strings that refer to resources. Full definition is given in
the URI spec.
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URL
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Uniform Resource Locator. The set of URI schemes that have explicit instructions
on how to access the resource on the internet. Full definition is given in
the URL specification.
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URN
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Uniform Resource Name.
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An URI that has an institutional commitment to persistence, availability,
etc. Note that this sort of URI may also be a URL. See, for example,
PURLs.
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A particular scheme which is currently (1991,2,3,4,5,6,7) under development
in the IETF (see discussion forums below), which
should provide for the resolution using internet protocols of names which
have a greater persistence than that currently assiated with internet host
names or organizations. When defined, a URN(2) will be an example of a URI.
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URC
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Uniform Resource Citation, or Uniform Resource Characteristics. A set of
attribute/value pairs describing a resource. Some of the values may be URIs
of various kinds. Others may include, for example, authorship, publisher,
datatype, date, copyright status and shoe size. Not normally discussed as
a short string, but a set of fields and values with some defined free formatting.
W3C has developed the PICS technology for resource
description.
See also: an index of web architecture
terms, a glossary of web terms.
This is a publication history, or bibliography collected
from IETF documents and W3C
Technical Reports as well as a record of events.
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April 1997
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38th IETF: URN WG meeting
(research notes)
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January 1997
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W3C Addressing Activity Statement updated for
W3C Advisory Committee meeting
[members only]
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December 1996
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San Jose IETF --
URL BOF
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Spring 1996
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2nd issue of W3J,
Key Specifications of the World Wide
Web includes URI specs.
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July 1995
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IETF URI Working Group is
closed.
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June 1995
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RFC 1808 released as Proposed
Standard
Relative Uniform Resource Locators R. Fielding
Abstract:
... When embedded within a base document, a URL in its absolute form may
contain a great deal of information which is already known from the context
of that base document's retrieval, including the scheme, network location,
and parts of the url-path. In situations where the base URL is well-defined
and known to the parser (human or machine), it is useful to be able to embed
URL references which inherit that context rather than re-specifying it in
every instance.
This one is both authoritative (i.e. it's been through the IETF proposed
standard process) and accurate on the matter of the syntax of URLs. Its grammar
is complete and consistent, and there are several clarifying examples.
On the other hand, it does not discuss any of the actual URL schemes (such
as HTTP, FTP, ...)
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December 1994
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(RFC 1738) released as Proposed
Standard:
Uniform Resource Locators
(URL) T. Berners-Lee, L. Masinter, M. McCahill
Abstract:
This document specifies a Uniform Resource Locator (URL), the syntax and
semantics of formalized information for location and access of resources
via the Internet.
This one is ratified as an IETF proposed standard, and it discusses each
of the URL schemes (known at that time), but its grammar has some mistakes,
and it doesn't cover several aspects of URL syntax, such as relative URLs
and fragment identifiers
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December 1994
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RFC 1737, Informational
Functional Requirements for Uniform Resource Names , K. Sollins,
L. Masinter
Abstract:
This document specifies a minimum set of requirements for a kind of Internet
resource identifier known as Uniform Resource Names (URNs). ...
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June 1994
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RFC 1630, Informational, is released:
Universal Resource
Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses
of Objects on the Network as used in the World-Wide Web T.
Berners-Lee.
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This documents the designer's intent, before it was revised by the standards
process. It was written by Tim Berners-Lee, but has only informational status
in the IETF. It discusses all aspects of URLs (relative, etc.) though it
has some mistakes in the grammar etc.
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March 94
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IETF
URI working group is formed
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1991
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Tim Berners-Lee's original writings on
Document Naming, part of
Design Issues for the Web
See also:
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www-talk
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A mailing list for technical discussion of web architecture and technology,
with a hypertext
archive (now searchable! Thanks EIT guys!)
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IETF Working Group
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This is where URL standardization used to takes place.
The area director for the IETF Applications Area maintains some
notes
on URL schemes
Roy Fielding maintains a
URI WG Archive,
and there is an
archive of the
uri mailing list.
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URN WG
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archive
You might also be interested in the discussion of extended fragement identifiers
for XML and the issue of
internationalization of URLs.
If you are new to the IETF, you should
probably do some background reading. I recommend:
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IETF - Uniform Resource
Identifiers (URI) Working Group
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by Roy Fielding.
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BIBLINK - Work Package
2 - Other Resources
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Decoupling the URL
Scheme from the Transport Protocol
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an idea from TimBL's design issues, independently discovered?
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Hypernews
on URNs
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By Daniel LaLiberte
at NCSA. Also,
hypernews
on URCs.
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The Augmented Knowledge
Workshop, Engelbart et. al., 1973
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URI background
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by Ron Daniel
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Stable Network
File URLs as a Mechanism for Uniform Naming
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by Terry Winograd
I found a draft of this dated Dec 1993, but it has since (Apr 97)
gone.
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DesignIssues: more on Axioms of Web Architecture,
Myth of Naming and Addressing, etc.
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Automated Link Maintenance
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Catalog Numbers
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URIs for publishing: URNs, Catalog numbers, citations...
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Catalogs: Resource Description and Discovery
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notes on PICS metadata infrastructure for resource description and catalogs
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Quality of Service
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on the tension between reliability and scalability
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the "me llamo" link
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idea: a link type where a document says "I call myself X". In combination
with a back-link service, it's a nifty URN idea.
Dan Connolly
last revised $Author: connolly $ on $Date $
Created 1993 by TimBL