As per Relevance of the word document, we have this rfc below:
Network Working Group L.
Request for Comments: 2718 Xerox
Category: Informational H.
Maxware,
D.
WebTV Networks, Inc
R.
UUNET
November 1999
Guidelines for new URL
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
A Uniform Resource Locator (URL) is a compact string
of the location for a resource that is available via the Internet
This document provides guidelines for the definition of new
schemes
1.
A Uniform Resource Locator (URL) is a compact string
of the location for a resource that is available via the Internet
RFC 2396 [1] defines the general syntax and semantics of URIs, and
by inclusion, URLs. URLs are designated by including a ":"
and then a "specific-part>". Many URL schemes are
defined
This document provides guidelines for the definition of new
schemes, for consideration by those who are defining and
or evaluating those definitions
The process by which new URL schemes are registered is defined in
2717 [2].
Masinter, et al. Informational [Page 1]
RFC 2718 Guidelines for new URL Schemes November 1999
2. Guidelines for new URL
Because new URL schemes potentially complicate client software,
schemes must have demonstrable utility and operability, as well
compatibility with existing URL schemes. This section
these criteria
2.1 Syntactic
New URL schemes should follow the same syntactic conventions
existing schemes when appropriate. If a URI scheme that has
links in content accessed by that scheme does not share syntax with
different scheme, the same content cannot be served up
different schemes without rewriting the content. This can already
a problem, and with future digital signature schemes, rewriting
not even be possible. Deployment of other schemes in the
could therefore become extremely difficult
2.1.1 Motivations for syntactic
Why should new URL schemes share as much of the generic URI
(that makes sense to share) as possible? Consider the following
o If fragment syntax isn't shared between two schemes, (e.g. "<
href="#foo">"), you can't move individual completely
referential documents between schemes without rewriting
embedded references within the document. In the Web, the
syntax is a property of the media type, and evaluated by
client
o If fragment syntax is not shared between different media types
the same capability (e.g. HTML, XML, Word, or image types such
GIF, JPEG, PNG) then you can't have a URI reference that
evolve to superior media types as they become available, or
likely work properly today with content negotiation
o If relative syntax (to the extent of understanding the URI
relative, and what part of the URI string is relative) isn'
shared between two schemes, (e.g. ""), you can'
move sets of documents that are internally self
between schemes without rewriting the embedded URIs
o If the ".." syntax as a path component in relative URI's isn'
shared between schemes, you can't easily have sets of
sets and refer to them between schemes without rewriting
embedded references
Masinter, et al. Informational [Page 2]
RFC 2718 Guidelines for new URL Schemes November 1999
o If the "/" syntax (to the extent of understanding that the
refers to a path relative to the current naming authority,
section 2.1.1) isn't shared, you can't have multiple sets
documents easily be moved up or down in a relative hierarchy
names and share a common set of documents between them,
rewriting the content, shared either in that scheme or
schemes. The best example is a site that has a common set
GIF's, JPEG and PNG images, and you want to reorganize the
changing the depth of a subtree from one depth to another, or
one directory to another where the depth isn't the same
o If naming authority syntax (e.g. what comes after "//" in most
schemes, see section 2.1.1) and relative path syntax is shared,
the extent of understanding that the URI has a naming authority
and what part of the URI string is the naming authority vs. path),
isn't shared between two schemes, you can't share identical
spaces and serve them up via different schemes. (The
authority syntax is a property of the scheme). The fact
HTTP, and FTP have the same syntax, for example, has often
exploited by sites transitioning from ftp archive service to
archive service so that the URL's can be identical between
except for the scheme; the same content can be served via
schemes simultaneously
2.1.2 Improper use of "//" following ":"
Contrary to some examples set in past years, the use of
slashes as the first component of the specific-part> of a
is not simply an artistic indicator that what follows is a URL
Double slashes are used ONLY when the syntax of the URL's
specific-part> contains a hierarchical structure as described in
2396. In URLs from such schemes, the use of double slashes
that what follows is the top hierarchical element for a
authority. (See section 3 of RFC 2396 for more details.)
schemes which do not contain a conformant hierarchical structure
their specific-part> should not use double slashes
the ":" string
2.1.3 Compatibility with relative
URL schemes should use the generic URL syntax if they are intended
be used with relative URLs. A description of the allowed
forms should be included in the scheme's definition.
applications use relative URLs extensively. Specifically
o Can the scheme be parsed according to RFC 2396 - for example,
the tokens "//", "/", ";", or "?" are used, do they have
meaning given in RFC 2396?
Masinter, et al. Informational [Page 3]
RFC 2718 Guidelines for new URL Schemes November 1999
o Does the scheme make sense to use it in relative URLs like
RFC 2396 specifies
o If the scheme syntax is designed to be broken into pieces,
the documentation for the scheme's syntax specify what
pieces are, why it should be broken in this way, and why
breaks aren't where RFC 2396 says that they usually should be
o If the scheme has a hierarchy, does it go left-to-right and
slash separators like RFC 2396?
2.2 Is the scheme well defined
It is important that the semantics of the "resource" that a
"locates" be well defined. This might mean different
depending on the nature of the URL scheme
2.2.1 Clear mapping from other name
In many cases, new URL schemes are defined as ways to
other protocols and name spaces into the general framework
URLs. The "ftp" URL scheme translates from the FTP protocol
while the "mid" URL scheme translates from the Message-ID field
messages
In either case, the description of the mapping must be complete
must describe how characters get encoded or not in URLs,
describe exactly how all legal values of the base standard can
represented using the URL scheme, and exactly which modifiers
alternate forms and other artifacts from the base standards
included or not included. These requirements are
below
2.2.2 URL schemes associated with network
Most new URL schemes are associated with network resources
have one or several network protocols that can access them.
'ftp', 'news', and 'http' schemes are of this nature. For
schemes, the specification should completely describe how URLs
translated into protocol actions in sufficient detail to make
access of the network resource unambiguous. If an
of the URL scheme requires some configuration, the
elements must be clearly identified. (For example, the 'news
scheme, if implemented using NTTP, requires configuration of
NTTP server.)
Masinter, et al. Informational [Page 4]
RFC 2718 Guidelines for new URL Schemes November 1999
2.2.3 Definition of non-protocol URL
In some cases, URL schemes do not have particular
protocols associated with them, because their use is limited
contexts where the access method is understood. This is the case
for example, with the "cid" and "mid" URL schemes. For these
schemes, the specification should describe the notation of
scheme and a complete mapping of the locator from its source
2.2.4 Definition of URL schemes not associated with data
Most URL schemes locate Internet resources that correspond to
objects that can be retrieved or modified. This is the case
"ftp" and "http", for example. However, some URL schemes do not
for example, the "mailto" URL scheme corresponds to an
mail address
If a new URL scheme does not locate resources that are
objects, the properties of names in the new space must be
defined
2.2.5 Character
When describing URL schemes in which (some of) the elements of
URL are actually representations of sequences of characters,
should be taken not to introduce unnecessary variety in the
in which characters are encoded into octets and then into
characters. Unless there is some compelling reason for
particular scheme to do otherwise, translating character
into UTF-8 (RFC 2279) [3] and then subsequently using the %
encoding for unsafe octets is recommended
2.2.6 Definition of
In some contexts (for example, HTML forms) it is possible
specify any one of a list of operations to be performed on
specific URL. (Outside forms, it is generally assumed to
something you GET.)
The URL scheme definition should describe all well-
operations on the URL identifier, and what they are supposed
do
Some URL schemes (for example, "telnet") provide
information for hooking onto bi-directional data streams,
don't fit the "infoaccess" paradigm of most URLs very well;
should be documented
Masinter, et al. Informational [Page 5]
RFC 2718 Guidelines for new URL Schemes November 1999
NOTE: It is perfectly valid to say that "no operation apart
GET is defined for this URL". It is also valid to say
"there's only one operation defined for this URL, and it's
very GET-like". The important point is that what is defined
this type is described
2.3 Demonstrated
URL schemes should have demonstrated utility. New URL schemes
expensive things to support. Often they require special code
browsers, proxies, and/or servers. Having a lot of ways to
the same thing needless complicates these programs without
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
than (for instance) a proxy gateway
2.3.1 Proxy into HTTP/
One way to provide a demonstration of utility is via a gateway
provides objects in the new scheme for clients using an
protocol. It is much easier to deploy gateways to a new service
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
can find the referenced object
o If not, is there a way in which the user can find any object
this type, and "run his own proxy"?
o Are the operations mappable one-to-one (or possibly
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
Masinter, et al. Informational [Page 6]
RFC 2718 Guidelines for new URL Schemes November 1999
2.4 Are there security considerations
Above and beyond the security considerations of the base mechanism
scheme builds upon, one must think of things that can happen in
normal course of URL usage
In particular
o Does the user need to be warned that such a thing is
without an explicit request (GET for the source of an IMG tag,
instance)? This has implications for the design of a
gateway, of course
o Is it possible to fake URLs of this type that point to
things in a dangerous way
o Are there mechanisms for identifying the requester that can
used or need to be used with this mechanism (the From: field in
mailto: URL, or the Kerberos login required for AFS access in
AFS: URL, for instance)?
o Does the mechanism contain passwords or other security
that are passed inside the referring document in the clear (as
the "ftp" URL, for instance)?
2.5 Does it start with UR
Any scheme starting with the letters "U" and "R", in particular if
attaches any of the meanings "uniform", "universal" or "unifying"
the first letter, is going to cause intense debate, and generate
heat (but maybe little light).
Any such proposal should either make sure that there is a
consensus behind it that it will be the only scheme of its type,
pick another name
2.6 Non-
Some issues that are often raised but are not relevant to new
schemes include the following
Masinter, et al. Informational [Page 7]
RFC 2718 Guidelines for new URL Schemes November 1999
2.6.1 Are all objects accessible
Can all objects in the world that are validly identified by a
be accessed by any UA implementing it
Sometimes the answer will be yes and sometimes no; often it
depend on factors (like firewalls or client configuration)
directly related to the scheme itself
3. Security
New URL schemes are required to address all security
in their definitions
4.
[1] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
[2] Petke, R. and I. King, "Registration Procedures for URL
Names", BCP 35, RFC 2717, November 1999.
[3] Yergeau, F., "UTF-8, A Transformation Format of Unicode and
10646", RFC 2279, January 1998.
Masinter, et al. Informational [Page 8]
RFC 2718 Guidelines for new URL Schemes November 1999
5. Authors'
Larry
Xerox
Palo Alto Research
3333 Coyote Hill
Palo Alto, CA 94304
URL: http://purl.org/NET/
EMail: masinter@parc.xerox.
Harald Tveit
Maxware,
N-7005
Phone: +47 73 54 57 00
EMail: harald.alvestrand@maxware.
Dan
WebTV Networks, Inc
305 Lytton
Palo Alto, CA 94301
Phone: +1-650-614-6071
EMail: djz@corp.webtv.
Rich
UUNET
5000 Britton
P. O. Box 5000
Hilliard, OH 43026-5000
Phone: +1-614-723-4157
Fax: +1-614-723-8407
EMail: rpetke@wcom.
Masinter, et al. Informational [Page 9]
RFC 2718 Guidelines for new URL Schemes November 1999
6. Full Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Masinter, et al. Informational [Page 10]
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