Re: [urn] Feedback on draft-ietf-urnbis-semantics-clarif-03

Hi there,

I haven't seen any substantial feedback on what I wrote two weeks ago. 
Thus here's my attempt to rephrase this in order to get more people to 
think about it.

On draft-ietf-urnbis-semantics-clarif-03:

This currently updates RFC 3986. Of course we can do this, but RFC 3986 
is a full standard, and thus this draft needs to be crystal clear about 
what exactly is being updated. I don't think it currently does that; it 
does some hand-waving with respect to what fragments and queries are 
(without saying exactly what's wrong in RFC 3986). It does *not* talk 
about changes to equivalence and relative resolution, although 
draft-ietf-urnbis-rfc2141bis-urn-16 seems to attempt to change them.

Furthermore, it currently contains stuff that has nothing to do at all 
with the relation to RFC 3986, namely the introduction of new elements 
that are only relevant to the URN spec; these should be moved over to 
the other draft.

On draft-ietf-urnbis-rfc2141bis-urn-16:

This draft seems to rely on draft-ietf-urnbis-semantics-clarif-03, but 
does not reference it normatively.

Furthermore, it appears to redefine relative resolution and equivalence. 
This is problematic in several ways:

It's totally unclear what the intended effect of these redefinitions 
will be on existing code. Is existing, non-URN-specific code supposed to 
be changed? If yes, what's the strategy to make this happen? If no (thus 
it's for URN-specific code only), what's the point in attempting to 
change the generic framework defined in RFC 3986? Wouldn't it be much 
much simpler just to

- define the new URN-scheme-specific equivalence as such (as described 
in <https://greenbytes.de/tech/webdav/rfc3986.html#normalize-scheme>), and

- define the URN-specific reference resolution as something URN-specific 
tools can do, but not to pretend that existing URI processors will 
implement this?

Best regards, Julian

On 2016-04-27 17:02, Julian Reschke wrote:
> Hi there,
>
> I was asked off-list to review the current drafts, given my interest in
> RFC 3986 in the past.
>
> I was first confused about 2141bis seemingly making changes to 3986, but
> then realized that there's draft-ietf-urnbis-semantics-clarif-03 as
> well. I believe 2141bis needs to *normatively* reference this one.
>
> That said, I appreciate that these two are separated, because it's
> easier to understand what's going on with relation to 3986. However, the
> separation may need more work; this document IMHO contains stuff that
> should be in 2141bis, while there's stuff in 2141bis which would need to
> be here.
>
> Other than that see below comments inline (sorry for the format).
>
> Best regards, Julian
>
> -- snip --
>
> Uniform Resource Names (urnbis)                               J. Klensin
> Internet-Draft                                          February 5, 2016
> Updates: 3986 (if approved)
> Intended status: Standards Track
> Expires: August 8, 2016
>
>
>                       URN Semantics Clarification
>                draft-ietf-urnbis-semantics-clarif-03.txt
>
> Abstract
>
>    Experience has shown that identifiers associated with persistent
>    names have properties and requirements that may be somewhat different
>    from identifiers associated with the locations of objects.  This is
>    especially true when such names are expected to be stable for a very
>    long time or when they identify large and complex entities.  In order
>    to allow Uniform Resource Names (URNs) to evolve to meet the needs of
>    the Library, Museum, Publisher, and Information Science communities
>    and other users, this specification separates URNs from the semantic
>    constraints that many people believe are part of the specification
>    for Uniform Resource Identifiers (URIs) in RFC 3986, updating that
>
> Lack of clarity: this is intended to be standards track document
> updating a full internet standard. I don't think that what people
> believe about that spec is relevant; we should be able to agree upon
> what it says and what it doesn't say.
>
>    document accordingly.  The syntax of URNs is still constrained to
>    that of RFC 3986, so generic URI parsers are unaffected by this
>    change.
>
> ...that depends on whether resolution of a relative reference against a
> base URI is part of what a URI parser does (do we have a definiton of
> what a "URI parser" does?)
>
>
> 1.  Introduction
>
>    The Generic URI Syntax specification [RFC3986] covers both locators
>    and names and mixtures of the two (See its Section 1.1.3) and
>    describes Uniform Resource Locators (URLs) -- first documented in the
>    IETF in RFC 1738 [RFC1738] -- as an embodiment of the locator concept
>    and Uniform Resource Names (URNs), specifically those using the "urn"
>    scheme [RFC2141], as an embodiment of the names that do not directly
>    provide for resource location.  This specification is concerned only
>    about URNs of the variety described in RFC 2141 [RFC2141] and its
>    successors [RFC2141bis] (i.e., those that use the "urn" scheme).
>    URLs, other types of names, and any URI types that may not fall into
>    one of the above categories are out of its scope and unaffected by
>    it.
>
> I understand that historical context is useful, but do we really need
> half a paragraph to say: "this is about URIs using the 'urn' scheme"?
>
>    Experience with URNs since the publication of RFC 3986 has identified
>    several ways in which their inclusion under the 3986 scope has
>    hampered understanding, adoption, and especially extension
>    (specifically extensions of types that were anticipated, but not
>    defined, in RFC 2141).  The need for extensions to the URN concept is
>    now being felt in some communities, especially those that include
>    libraries, museums, publishers, and other information scientists.
>
>    In particular, the Generic URI Syntax specification goes beyond
>    syntax to specify the meaning and interpretation of various fields,
>    especially the "query" and "fragment" ones and the various syntax
>    forms and interpretations it allows for <hier-part>.  This
>
> Agreed for "fragment", not sure about "query". Could you elaborate a bit?
>
>    specification excludes URNs from those definitions of meaning and
>    interpretation so that RFC 3986 applies to their syntax only.  The
>    meaning --and any more specific syntax rules-- for those fields for
>    URNs are now defined in a URN-specific document [RFC2141bis].  URNs
>    remain members of the URI family and parsers for generic URI syntax
>    are not affected by this specification although parsers that make
>    assumptions based on other URI schemes obviously might be.
>
> I don't get the last sentence. If a parser makes assumptions on *other*
> schemes, how would it affect processing of "urn" URIs?
>
>    Neither this specification nor the successor to RFC 2141 [RFC2141bis]
>    discusses DDDS [RFC3401] resolution or conversion to (and
>    interpretation of) URCs [RFC2483] or, with the exception of providing
>    some syntax to cover some specific cases, URN "resolution" more
>    generally.  Any of those topics that do need to be addressed should
>    be covered in other documents.  The document also does not discuss
>    alternatives to URNs, either those that might use a different scheme
>    name within the RFC 3986 URI framework or those that might use a
>    different framework entirely.  In particular, some externally-defined
>    content or object identification systems could be represented either
>    by a URN namespace or through separate URI schemes.  This
>    specification does not offer advice on that choice other than to
>    suggest that the two options not be confused (or both used in a way
>    that would be confusing).
>
> (matter of taste: I think that long text about what spec does *not* do
> really distracts from what it is about; maybe it would be good to things
> like this (and the text about URN's history) to an appendix?)
>
>    This document updates RFC 3986 to make the distinction between syntax
>    and semantics clear for URNs and to isolate URNs from presumed URI
>    semantic requiremnts.  It is important to note that some readers of
>
> s/requiremnts/requirements/
>
>    RFC 3986 are convinced that the separation is clear in that
>    specification and therefore that no changes to that document are
>    needed.  For them, this specification is only a confirming
>    clarification.
>
> I understand that this is well-intended, but it is certainly very very
> confusing.
>
>    In the long term, as the expanded syntax and uses of URNs become
>    commonplace and RFC 3986 is updated, this specification is likely to
>    become of historical interest only, providing an extended rationale
>    for decisions made and adjustment of the boundary between URN
>    specifications and generic URI ones.
>
> ...
>
> 3.  The role of queries and fragments in URNs
>
>    Part of the concern that led to this document was a desire to
>    accommodate URN components that would be analogous to the query and
>    fragment components of generalized URNs but that might have different
>    properties.  For many cases, the analogy cannot be exact.  For
>    example, RFC 3986 ties the interpretation of fragments to media
>    types.  Since media type is a function of specific content, URNs that
>    are never resolved cannot have an associated media type, nor can URNs
>    that resolve to, for example, other URIs that may then not be
>
> FTR, RFC 3986 says: "If no such representation exists, then the
> semantics of the fragment are considered unknown and are effectively
> unconstrained. Fragment identifier semantics are independent of the URI
> scheme and thus cannot be redefined by scheme specifications."
>
>    resolved further.  Similarly, while the RFC 3986 syntax for queries
>    (and fragments) may be entirely appropriate for URN use, terminology
>    like "Service Request" (see Appendix B of the predecessor "URNs are
>    not..." draft [ServiceRequests] for additional discussion) may be
>    more suitable to the URN context than "query" (if, indeed, the
>    portion of the URN that is syntactically equivalent to a URI query is
>    where those requests belong).
>
> RFC 3986: "The query component contains non-hierarchical data that,
> along with data in the path component (Section 3.3), serves to identify
> a resource within the scope of the URI's scheme and naming authority (if
> any)." -- so what *exactly* does this specification try to change? Just
> the name of the component??
>
> 4.  Changes to RFC 3986
>
>    This specification removes URN semantics from the scope of RFC 3896.
>
> s/3896/3986/
>
>    It makes no changes to the generic URI syntax.  That syntax still
>    applies to URNs as well as to other URI types.  Even as regard to
>    semantics, it has no practical effect for URNs defined in strict
>    conformance to the prior URN specification [RFC2141] or the
>    associated registration specification [RFC3406].
>
> So what other effect *does* it have?
>
>    In particular (but without altering RFC 3986 in any way), the generic
>    URI syntax for "queries" (strings starting with "?" and continuing to
>    the end of the URI or to a "#"), and for "fragments" (strings
>    starting with "#" and continuing to the end of the URI) is unchanged.
>    For URNs, additional syntax is introduced to divide the URI "query"
>    into two parts, referred to as "q-components" and "r-components".
>
> ...I'd argue that this URN-specific syntax shouldn't be discussed in
> *this* specification.
>
>    The syntax and general semantics of "fragments" (specified in RFC
>    3986 as scheme-independent) are unchanged, but a somewhat liberal
>    interpretation may be needed in the context of URNs, so a fragment is
>    referred to as an "f-component" as a term of convenience to highlight
>    that distinction.  [RFC2141bis].
>
> From this paragraph it's entirely unclear what the actual change is.
>
> 5.  Actions Occurring in Parallel with this Specification
>
>    The basic URN syntax specification [RFC2141] was published well
>    before RFC 3986 and therefore does not depend on it.  The successor
>    to that specification [RFC2141bis], fully spells out, or references
>    documents that spell out, the semantics and any required within-field
>    syntax of URNs.  It uses great care about generic or implicit
>    reference to any URI specification and delegates further details to
>    specific namespaces.
>
>    [[CREF1: Note in Draft: Perhaps this section can be dropped
>    entirely.]]
>
> Actually, no. <draft-ietf-urnbis-rfc2141bis-urn-16#section-4.3>
> essentially updates <https://tools.ietf.org/html/rfc3986#section-5.2>.
> This specification needs to be clear about that, because that is
> actually the biggest change to RFC 3986, and it's not even mentioned here.
>
> So if there *was* agreement on that change (which is a separate,
> complex, discussion), it really really would need to be mentioned here.
>
>
> ....
>
> 8.  IANA Considerations
>
>    [[CREF2: RFC Editor: Please remove the first paragraph below before
>    publication.]]
>
>    This memo is not believed to require any action on IANA's part.
>
>    There is an existing (i.e. prior to the publication of this document)
>    registry for "Uniform Resource Identifier (URI) Schemes" that already
>    includes the "urn" scheme itself and a separate existing URN
>    Namespace registry.  None of those registrations have any specific
>    dependencies on generic URI specifications.
>
> Actually, the second paragraph could go as well...
>
> 9.  Security Considerations
>
>    This specification changes the semantics of URNs to make them self-
>    contained (as specified in other documents), relying on the generic
>    URI syntax specification for syntax only.  It should have no effect
>    on Internet security unless the use of a definition, syntax, and
>    semantics that are more clear reduces the potential for confusion and
>    consequent vulnerabilities.
>
> It seems that it's RFC 2142bis which defines these changes, no?
>
> 10.2.  Informative References
>
>    [DeterministicURI]
>               Mazahir, O., Thaler, D., and G. Montenegro, "Deterministic
>               URI Encoding", February 2014, <http://www.ietf.org/id/
>               draft-montenegro-httpbis-uri-encoding-00.txt>.
>
>               This is an expired document, cited for historical context
>               only.
>
> This reference doesn't seem to be used.
>
> ...
>
>    [URN-transition]
>               Klensin, J. and J. Hakala, "Uniform Resource Name (URN)
>               Namespace Registration Transition", Feburary 2016,
>               <https://datatracker.ietf.org/doc/draft-ietf-urnbis-ns-
>               reg-transition/>.
>
> This reference doesn't seem to be used.
>
>
> Appendix A.  Background on the URN - URI relationship
>
>    The Internet community now has many years of experience with both
>    name-type identifiers and location-based identifiers (or "references"
>    for those who are sensitive to the term "identifier" such as many
>    members of the library and information science communities..  The
>
> s/.././
>
>    primary examples of these two categories are Uniform Resource Names
>    (URNs [RFC2141] [RFC2141bis]) and Uniform Resource Locators (URLs)
>    [RFC1738]).  That experience leads to the conclusion that it is
>    impractical to constrain URNs to the high-level semantics of URLs.
>    The generic syntax for URIs [RFC3986] is adequately flexible to
>    accommodate the perceived needs of URNs, but the specific semantics
>    associated with the URI syntax definition -- what particular
>    constructions "mean" and how and where they are interpreted -- appear
>    to not be.  Generalization from URLs to generic Uniform Resource
>    Identifiers (URIs) [RFC3986], especially to name-based, high-
>    stability, long-persistence, identifiers such as many URNs, has
>    failed because the assumed similarities do not adequately extend to
>    all forms of URNs.  Ultimately, locators, which typically depend on
>    particular accessing protocols and a specification relative to some
>    physical space or network topology, are simply different creatures
>    from long-persistence, location-independent, object identifiers.  The
>    syntax and semantic constraints that are appropriate for locators are
>    either irrelevant to or interfere with the needs of resource names as
>    a class.  That was tolerable as long as the URN system didn't need
>    additional capabilities (over those specified in RFC 2141) but
>    experience since RFC 2141 was published has shown that they are, in
>    fact, needed.
>
> I don't believe this appendix is way too vague to be helpful.
>
> _______________________________________________
> urn mailing list
> urn@ietf.org
> https://www.ietf.org/mailman/listinfo/urn
>