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INTERNET-DRAFT                                    Larry Masinter
<draft-masinter-url-process-00.txt>                  Dan Zigmond
January 4, 1997                             Harald T. Alvestrand
expires June 4, 1997

               Guidelines and Process for new URL Schemes

Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time.  It is inappropriate to use Internet-Drafts
   as reference material or to cite them other than as ``work in
   progress.''

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet-Drafts
   Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net
   (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East
   Coast), or ftp.isi.edu (US West Coast).

   Issues:
        Registration process isn't really there.

Abstract

   A Uniform Resource Locator (URL) is a compact string representation
   of the location for a resource that is available via the Internet.
   [RFC URL-SYNTAX] defines the general syntax and semantics of URLs.
   This document provides guidelines for the definition of new URL
   schemes and describes the process by which they are registered.

1. Introduction

   In addition to specifying the general syntax for Uniform Resource
   Locators, RFC 1738 defined a number of generally useful URL schemes
   and promised that a mechanism for registering new schemes would be
   established.  Several new URLs have been proposed since that time,
   but the procedure for standardizing these schemes has never been
   fully defined.  This document describes the current practice and
   offers some guidance for authors of new schemes.

   One process for defining URL schemes is via the Internet standards
   process: new URL schemes should be described in standards-track
   RFCs.  The Internet Assigned Numbers Authority (IANA) maintains a
   registry of all URL schemes defined in this way.

2. Guildelines for new URL schemes

   Because new URL schemes potentially complicate client software, new
   schemes must have demonstrable utility and operability, as well as
   compatibility with existing URL schemes. This section elaborates
   these criteria.

2.1 Syntactic compatibility

   New URL schemes should follow the same syntactic conventions of
   existing schemes when appropriate.

2.1.1 Use of initial "//" for Internet host addresses

   Many proposed new URL schemes seem to use "://" as a kind of
   indicator that what follows is a URL. However, the use of the top
   level "//" is indicative of an Internet host address, and not a top
   level marker.

2.1.2 Compatibility with relative URLs

   URL schemes should use the generic-URL syntax if they are intended
   to be used with relative URLs.  A description of the allowed
   relative forms should be included in the scheme's definition.
   Many applications use relative URLs extensively.

   o Can it be parsed according to RFC URL-SYNTAX - that is, if the tokens
     "//", "/", ";", "?" and "#" are used, do they have the meaning
     given in RFC URL-SYNTAX?

   o Does it make sense to use it in relative URLs like those RFC
     URL-SYNTAX specifies?

   o If something is designed to be broken into pieces, does it
     document what those pieces are, why it should be broken in this
     way, and why the breaks aren't where URL-SYNTAX says that they
     usually should be?

   o If it has a hierarchy, does it go left-to-right and with slash
     separators like RFC URL-SYNTAX? If not, why not?

2.1.3 Does it start with "ur"?

   Any scheme starting with the letters "U" and "R", in particular if
   it attaches any of the meanings "uniform", "universal" or
   "unifying" to the first leter, is going to cause intense debate,
   and generate much heat (but maybe little light).

2.2 Is the scheme well defined?

   It is important that the semantics of the "resource" that a URL
   "locates" be well defined. This might mean different things
   depending on the nature of the URL scheme.

2.2.1 Clear mapping from other name spaces

   In many cases, new URL schemes are defined as ways to translate
   other protocols and name spaces into the general framework of
   URLs. The "ftp" URL scheme translates from the FTP protocol, while
   the "mid" URL scheme translates from the Message-ID field of
   messages.

   In either case, the description of the mapping must be complete,
   must describe how character sets get encoded or not in URLs, must
   describe exactly how all legal values of the base standard can be
   represented using the URL scheme, and exactly which modifiers,
   alternate forms and other artifacts from the base standards are
   included or not included.

   In all cases, encoding rules must be made clear: What octets are
   put into the URL, and if other octets need to be represented, what
   convention is used to represent them?  Any departure from the %xx
   convention needs special justification.

2.2.2 URL schemes associated with network protocols

   Most new URL schemes are associated with network resources that
   have one or several network protocols that can access them. The
   'ftp', 'news', and 'http' schemes are of this nature.  For such
   schemes, the specification should completely describe how URLs are
   translated into protocol actions in sufficient detail to make the
   access of the network resource unambiguous.  If an implementation
   of of the URL scheme requires some configuration, the configuration
   elements must be clearly identified. (For example, the 'news'
   scheme, if implemented using NTTP, requires configuration of the
   NTTP server.)

2.2.3 Definition of non-protocol URL schemes

   In some cases, URL schemes do not have particular network protocols
   associated with them, because their use is limited to contexts
   where the access method is understood. This is the case, for
   example, with the "cid" and "mid" URL schemes. For these URL
   schemes, the specification should describe the notation of the
   scheme and a complete mapping of the locator from its source.

2.2.4 Definition of URL schemes not associated with data resources

   Most URL schemes locate Internet resources that correspond
   to data objects that can be retrieved or modified. This is the
   case with "ftp" and "http", for example. However, some URL schemes
   do not; for example, the "mailto" URL scheme corresponds to an
   Internet mail address.

   If a new URL scheme does not locate resources that are data
   objects, the properties of names in the new space must be clearly
   defined.

2.2.5 Definition of operations

   In some contexts (for example, HTML forms) it is possible to
   specify any one of a list of operations to be performed on a
   specifc URL. (Outside forms, it is generally assumed to be
   something you GET.)

   The URL scheme definition should describe all well-defined
   operations on the URL identifier, and what they are supposed to
   do.

   Some URL schemes (for example, "telnet") provide location
   information for hooking onto bidirectional data streams, and don't
   fit the "infoaccess" paradigm of most URLs very well; this should
   be documented.

   NOTE: It is perfectly valid to say that "no operation apart from
   GET is defined for this URL". It is also valid to say that "there's
   only one operation defined for this URL, and it's not very
   GET-like". The important point is that what is defined on this type
   is described.

2.3 Demonstrated utility

   URL schemes should have demonstrated utility.  New URL schemes are
   expensive things to support. Often they require special code in
   browsers, proxies, and/or servers.  Having a lot of ways to say the
   same thing needless complicates these programs without adding value
   to the Internet.

   The kinds of things that are useful include:

      o Things that cannot be referred to in any other way.

      o Things where it is much easier to get at them using this scheme than
        (for instance) a proxy gateway.


2.3.1 Proxy into HTTP/HTML

   One way to provide a demonstration of utility is via a gateway
   which provides objects in the new scheme for clients using an
   existing protocol. It is much easier to deploy gateways to a new
   service than it is to deploy browsers that understand the new URL
   object.

   Things to look for when thinking about a proxy are:

   o Is there a single global resolution mechanism whereby any proxy can
     find the referenced object?
   o If not, is there a way in which the user can find any object of this
     type, and "run his own proxy"?
   o Are the operations mappable one-to-one (or possibly using
     modifiers) to HTTP operations?
   o Is the type of returned objects well defined?
      * as MIME content-types?
      * as something that can be translated to HTML?
   o Is there running code for a proxy?

2.4 Are there security considerations?

   Above and beyond the security considerations of the base mechanism
   a scheme builds upon, one must think of things that can happen in
   the normal course of URL usage.

   In particular:

   o Does the user need to be warned that such a thing is happening
     without an explicit request (GET for the source of an IMG tag,
     for instance)?  This has implications for the design of a proxy
     gateway, of course.

   o Is it possible to fake URLs of this type that point to different
     things in a dangerous way?

   o Are there mechanisms for identifying the requester that can be
     used or need to be used with this mechanism (the From: field in a
     mailto: URL, or the Kerberos login required for AFS access in the
     AFS: url, for instance)?

   o Does the mechanism contain passwords or other security
     information that are passed inside the referring document in the
     clear (as in the "ftp" URL, for instance)?

2.7 Does it start with UR?

Any scheme starting with the letters "U" and "R", in particular if it
attaches any of the meanings "uniform", "universal" or "unifying" to the
first leter, is going to cause intense debate, and generate much heat (but
maybe little light).

Any such proposal should either make sure that there is a large consensus
behind it that it will be the only scheme of its type, or pick another
name.

2.5 Non-considerations

   Some issues that are often raised but are not relevent to new URL
   schemes include the following.

2.5.1 Is it an URL, an URN or something else?

   This classification has proved interesting in theory, but not
   terribly useful when evaluating schemes.

2.5.2 Are all objects acessible?

   Can all objects in the world that are validly identified by a
   scheme be accessed by any UA implementing it?

   Sometimes the answer will be yes and sometimes no; often it will
   depend on factors (like firewalls or client configuration) not
   directly related to the scheme itself.

3. Revision process

NOTE: THIS SECTION IS ENTIRELY TBD. REVIEW COMMITTEE? PRIVATE URLS?

   URL schemes will have either a standards track RFC, or else they
   will be a registration at IANA. where include the whole draft.  URL
   schemes will have a review panel, appointed by IETF AD, who may not
   reject a URL scheme but who may provide a 2 sentence recommendation
   about the use of the URL scheme.  Conflicting registrations are
   possible for non-standard URL schemes, and the order in the IANA
   list of conflicting registrations will be determined by a random
   number generator.

4. Security considerations

   New URL schemes are required to address all security considerations
   in their definitions.

5. IANA considerations

   This document requires IANA to register URL schemes according to
   the process outlined in section 3.

6. References

 [URL-SYNTAX]
    Berners-Lee, Fielding, Masinter, "Uniform Resource Locators",
    <draft-fielding-url-syntax-03>, will be RFC.

7..Author's Addresses

   Larry Masinter
   Xerox Corporation
   Palo Alto Research Center
   3333 Coyote Hill Road
   Palo Alto, CA 94304
   Fax: +1-415-812-4333
   EMail: masinter@parc.xerox.com

   Dan Zigmond
   Wink Communications
   1001 Marina Village Parkway
   Alameda CA 94610
   Fax: +1-510-337-2960
   Phone: +1-510-337-6359
   Email: dan.zigmond@wink.com

   Harald T. Alvestrand
   UNINETT A/S
   Postboks 6683 Elgeseter 7002
   Trondheim, Norway
   Tel: +47 73 59 70 94
   EMail: Harald.T.Alvestrand@uninett.no


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