WWW Names and Addresses, URIs, URLs, URNs, URCs

Addressing is one of the fundamental technologies in the web. URLs, or Uniform Resouce Locators, are the technology for addressing documents on the web. It is an extensible technology: there are a number of existing addressing schemes, and more may be incorporated over time.

Background and Discussion

Design Issues

TimBL's original discussion of design issues involved

A Beginner's Guide to URLs

by the NCSA SDG writers (originally by Marc Andreesen?). Nice short intro, though it's not precisely accurate nor up to date.

www-talk

A mailing list for technical discussion of web architecture and technology, with a hypertext archive (now searchable! Thanks EIT guys!)

IETF Working Group

This is where URL standardization used to takes place. For current status, see Roy Fielding's URI WG Archive, and the archive of the uri mailing list.

The group is being broken into smaller peices:

URN WG mailing list archive

Resource Discovery and Reliable Links

Connolly's notes on the subject. Should become part of Collaboration and Knowledge Representation.

Hypernews on URNs

By Daniel LaLiberte at NCSA. Also, hypernews on URCs.

URI background

by Ron Daniel

UR* Terms

This is my personal view and explanation. -- TimBL

URI: Universal Resource Idenifier. The generic set of all names/addresses which are short strings which refer to objects. (Originally UDI in some www documents) See URI spec ..
URL: Uniform Resource Locators. Term introducted by the IETF in forming the URI working group to point out that currently available URIs are mainly addresses rather than names. Exactly what consitutes a locator as opposed to a name is basically lack of persistence, but this is a much discussed point and impossible to define precisely. In practice, the set of schmes referring to existing protocolls, listed in the URL specification .
URN: Uniform Resource Name. 1. Any URI which is not a URL. 2. A particular scheme which is currently (1991,2,3,4) under development by the IETF, 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(1) will be an example of a URI.


	 _______________________________________________________
	|							|
	|	 _______________	 _______________	|
	|	|  ftp:		|	|  urn:		|	|
	|	|  gopher:	|	|  fpi: ?	|	|
	|	|  http:	|	|  path:	|	|
	|	|  etc		|	|		|	|
	|	|_______________|	|_______________|	|
	|		URLs			URNs		|
	|_______________________________________________________|
				   URIs

URC: Uniform Resource Citation. A set of attribute/value pairs describing an object. 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.
URC is a mechanism of resource description, which can be seen as an instance of the general problem of knowledge representation.

Schemes

And where they are defined/proposed.

lifn: BFD -- Buld File distribution. Isomorphic to cid:
cid:: Content-ID. Syntax ala news: Where is it defined???
data:: originally proposed by Masinter on www-talk. related to INSERT spec
file: Host-specific file names URL RFC
ftp: File Transfer protocol URL RFC
hdl:: CNRI handle system
http: Hypertext Transfer Protocol URL RFC HTTP spec
irc:: PICS service spec
gopher: The Gopher protocol URL RFC
mailto: Electronic mail address URL RFC
md5: MD5 is a cryptographic checksum. Anybody using it as a URI scheme?
news: USENET news URL RFC
nntp: USENET news using NNTP access URL RFC
prospero: Prospero Directory Service URL RFC
STANF: Stable Network Filenames
telnet: Reference to interactive sessions URL RFC
wais: Wide Area Information Servers URL RFC
mid:: Message-ID. Where is it defined?
path:: path spec
uuid:: identifies OLE/COM objects and classes, as well as DCE objects, interfaces, etc. related to INSERT spec
whois++: Distributed directory service. @@need to find spec.

Specifications

URLs

Relative Uniform Resource Locators (RFC 1808) (34950 bytes), R. Fielding, June 1995,: A Uniform Resource Locator (URL) is a compact representation of the location and access method for a resource available via the Internet. 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 document defines the syntax and semantics for such Relative Uniform Resource Locators.
Uniform Resource Locators (URL) (RFC 1738) (51348 bytes), T. Berners-Lee, L. Masinter, M. McCahill, Editors, December 1994.: This document specifies a Uniform Resource Locator (URL), the syntax and semantics of formalized information for location and access of resources via the Internet.

Historical

URL specification: March, 1994. This specification does not necessarily describe WWW practice.
Contents list of hypertext document for browsing and reference: Availability of the spec in other forms
Oustanding Issues
Change History
Requirements

URI (RFC 1630)

Universal Resource Identifiers (URIs) is the name for a generic WWW identifier. The URI specification simply defines the syntax for encoding arbitrary naming or addressing schemes, and has a list of such schemes. See:

URI specification: Contents list and list of available forms

The specification of URIs as used by WWW is to be distributed with informational status in the Internet community. It is also published as RFC 1630:

RFC 1630 -- "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. June 1994.

URN

There is an effort to define Uniform Resource Names, which are URI schemes that improve on URLs in reliability over time, including authenticity, replication, and high availability.

Functional Requirements for Uniform Resource Names (RFC 1737) (16337 bytes), K. Sollins, L. Masinter, December 1994.: This document specifies a minimum set of requirements for a kind of Internet resource identifier known as Uniform Resource Names (URNs). URNs fit within a larger Internet information architecture, which in turn is composed of, additionally, Uniform Resource Characteristics (URCs), and Uniform Resource Locators (URLs). URNs are used for identification, URCs for including meta-information, and URLs for locating or finding resources. It is provided as a basis for evaluating standards for URNs. The discussions of this work have occurred on the mailing list uri@bunyip.com and at the URI Working Group sessions of the IETF.
The Path URN Specification: D. LaLiberte, M. Shapiro, 07/26/1995 The Path URN Specification, plain text
Stable Network File URLs as a Mechanism for Uniform Naming: Terry Winograd. Early draft version 12/2/93 -- Fire away!

Connolly
TimBL
last update by $Author: connolly $ on $Date: 1995/12/21 22:09:14 $