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Subject: RE: [xri] Feedback requested on terms used in Metadata spec

Hi all,
I am terribly sorry for belated reply.
I still am a bit mixed up, I guess.
Here is my understanding:
(1) $ is a metadata character describing that following character is
     describing the metadata type.
(2) Something like $d is a metadata describing the string (data) that
     follows '*' after it. The extent that this metadata is effective is
     within the cross reference parens. I.e., ($v*2.3) means that string
    '2.3' is actually of type version. 
(3) '($v*2.3)' is significant in resolution and as treated as opaque string.
      If there is nothing that match the entire identifier, it will be an error.
     '($d*2006-01-01T23:45:42Z)' is significant in resolution and is not
      treated as opaque string, but some computation will be done at the
     resolver so that the concrete identifier for then most current version
     of the object is returned.
      '($- comment)' is insignificant in resolution and is ignored.
     '($l*fr)' is insignificant in resolution and is ignored.
Am I right?

From: Drummond Reed [mailto:drummond.reed@cordance.net]
Sent: Tuesday, January 17, 2006 5:44 AM
To: 'Chasen, Les'; 'Schleiff, Marty'; Sakimura, Nat; 'Wachob, Gabe'; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec

Les has a good point. From an XRI resolution standpoint, resolution is always left to right. So I think it is safe that $d and $v namespaces *always* create a datetime or version space for the resource identified by the XRI for their immediate parent.




From: Chasen, Les [mailto:les.chasen@neustar.biz]
Sent: Monday, January 16, 2006 12:14 PM
To: Drummond Reed; Schleiff, Marty; Sakimura, Nat; Wachob, Gabe; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec


I think a simple rule is missing, normal left to right resolution rules still apply.  The meta-data cross reference is a sub-segment under the authority to the left.  So if presented with this XRI =sakimura*($v*2.3)*(+email) a resolver will look for a ($v*2.3) iname under =sakimura.  It will then look for a (+email) iname under =sakimura*($v*2.3).  To me this means that we are looking for version 2.3 under the sakimura authority not look for 2.3 of +email … it is all left to right.


Note:  We have not done any service end point matching here.  (+email) is not a legal service type in the latest resolution draft.  In this example it is just an iname.


- Les



I-Name:  =les.chasen 


From: Drummond Reed [mailto:drummond.reed@cordance.net]
Sent: Monday, January 16, 2006 1:54 PM
To: 'Schleiff, Marty'; 'Sakimura, Nat'; 'Wachob, Gabe'; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec


First, this is a great thread – I encourage all XRI TC members to read it as it gets to the heart of the revisions being made to XRI Metadata 2.0 Working Draft 08.


Nat: Marty already answered the first point I was going to make that under the proposed new ABNF for XRI metadata, language tags are now completely unambiguous because the identifier being described is *inside* the cross-reference. So as Marty illustrates, instead of…




…you would have…




The same is true for identifier types. Whereas under XRI Metadata 2.0 Committee Draft 01, if we'd had $t, we would have had…




…and it might have been ambiguous which string was an OID and which was a Case Exact String, under Working Draft 08 you would have…




…and it will not be ambiguous at all.


I was very happy about that realization, and it produces wonderfully clean ABNF. However it's true that with $d datetime identifiers and $v version identifiers, the XRI metadata is only telling you that the cross-reference is a datetime or a version number. How the datetime or version number cross-reference applies to the XRI as a whole is up to the identifier authority.


As Marty points out, XRI authorities do have a clean way to specify in an XRI that a datetime or version applies to a specific portion of the XRI, and that again would be to use cross-reference syntax to explicitly group the related identifiers as he illustrates…




While this is certainly valid, I don't think it will prove as useful as simply using datetime and version cross-references to create namespaces. For example, with…




…it doesn't really matter whether "($d*2002-10-10T11:00:00Z)" is interpreted as "describing" "=sakimura" or "(+email)" because the net effect will be exactly the same: you have an XRI that includes exactly one datetime space that can be compared with any other XRI with the same datetime space to determine an ordered relationship. For example, in the following two XRIs, you will know that the first one comes before the second one in time:





The same is true of versions – you know unambiguously that the second XRI below is a later version than the first:





I believe that with datetimes and versions this is all that is necessary, but of course I'm too close to the subject at this point to see it objectively, so please do point out other use cases that this approach may not meet.






From: Schleiff, Marty [mailto:marty.schleiff@boeing.com]
Sent: Monday, January 16, 2006 9:22 AM
To: Sakimura, Nat; Drummond Reed; Wachob, Gabe; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec


Hi All,


Here's how I look at it: Metadata is data that describes data, not objects.


So, "$d" (the metadata) describes "2002-10-10T11:00:00Z" (the date/time value). And in "($v*2.3)", the "$v" metadata describes describes "2.3" to let us know it's a version number.


Here's a thought that I think should be an XRI foundational principle: An XRI is an identifier/name for some object. The purpose of XRI is to NAME objects, not DESCRIBE objects. I admit that many names have descriptive meaning; however, I think that's just incidental and up to the whims of the naming authority. 


Drummond and I figured out that we often violate this "principle" when we talk about metadata. For example if we have a document called "pays", we often say that "($l*fr*pays)" lets us know that pays is a French document. However, what the metadata REALLY says is that the letters p-a-y-s constitute a French word, or a word with French pronunciation.


When we include metadata in an XRI, it doesn't really describe the object. Instead, it just becomes part of the XRI and becomes part of the object's name.


So, in "=sakimura*(+email)*($d*2002-10-10T11:00:00Z)*(+personal)", there is an object (or namespace) called "=sakimura*(+email)*($d*2002-10-10T11:00:00Z)", and within that namespace there is an object called "(+personal)".


With language (as with all metadata) Drummond and I claim the intended "target" of the metadata is within the same cross reference, which would clarify the multi-lingual example as: "=sakimura*($l*za*chinese_string)*($l*ja*japanese_string)*some_string".


For the email example where you would like to interprete it as ("me" at 2002-10-10T11:00:00Z)'s email,we think you would use more cross references to clarify, resulting in an XRI like: "(=sakimura*($d*2002-10-10T11:00:00Z))*(+email)".


I still feel kinda new to XRI land, so I hope all my examples actually yield valid XRI syntax.


The point about metadata that drummond and I still argue about is what to do when some portion of an XRI is the target for multiple sets of metadata. I don't think we have to worry about this for $v and $t; it's more of a problem for $l and $t. For example, if the target of the metadata is both case-exact-string (a type) and French (a language). Drummond says this is a case for nesting cross references, as in "($l*fr*($t*ces*pays))". I don't like that because I can't tell if the "$t" and the "ces" should have French pronunciation, or just the "pays". Also, I'm struggling to figure out if "($l*fr*($t*ces*pays))" is equivalent to "($t*ces*($l*fr*pays))". Instead, I favor adding yetta 'nuther metadata tag, "$m" for "multi", which would somehow indicate that multiple metadata clauses describe the same target; however, I can't yet figure out the ABNF for how to do it. Because I'm losing the arguement with Drummond, I'd like to hear other's comments (if I were winning that arguement, I might not risk inviting your possibly contentious views;-).



Marty.Schleiff@boeing.com; CISSP
Associate Technical Fellow - Cyber Identity Specialist
Computing Security Infrastructure
(425) 957-5667



From: Sakimura, Nat [mailto:n-sakimura@nri.co.jp]
Sent: Monday, January 16, 2006 6:37 AM
To: Drummond Reed; Schleiff, Marty; Wachob, Gabe; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec

I sort of understand the situation. However, IMHO, having unambiguous rule about what that version or date metadata points has its merit in a way that by just looking at it, you will be able to tell what that cross reference is pointing to. i.e., you do not have to worry about whether the date is describing (+email) or (+personal) in the following example.




Always needing to ask the authority about which interpretation is right is an overhead for implementations. Besides, an authority may start mixing up the uses and may well screw up.


This pain point become even more accute when we are talking about multilingual XRI.

Think of this:




If I had to ask the authority (in this case =sakimura?) whether the child or parent that the language metadata describes, then I will not be able even to show the XRI correctly on screen when I am offline. If I know 'a priori' that the metadata describes the immediately preceding, then I will be able to show it without making a query to the authority. Moreover, on the way of resolving the next authorities from left to right, if I got stuck with the permission problems, I will be out of luck - I will never know how to represent the above string on screen.


Besides, is there a syntax to know which way the metadata is describing?


The reason I think that the metadata should describe something on the left is because it will be restricting what precedes. This follows the pattern of restriction from left to right. e.g.,




actually will be the vector of email addresses that I had during my life. *($d*2002-10-10T11:00:00Z) constrains it to this particular date. You could argue that it could have been




and the date is describing the email. However, I would like to interprete it as ("me" at 2002-10-10T11:00:00Z)'s email. Let me do one more: If the metadata were to describe something on its right, then to describe "me" on a particular date, I would have to do:




I think this is not quite right.




From: Drummond Reed [mailto:drummond.reed@cordance.net]
Sent: Monday, January 16, 2006 5:26 PM
To: Sakimura, Nat; 'Schleiff, Marty'; 'Wachob, Gabe'; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec

Nat, there is no inherent "problem" with this approach if that is what the XRI authority intended. What Marty and Dave and I found, however, was that for every use of a date cross-reference describing its parent node, another example can be created in which it described its child node.


So we concluded that the only thing that can be stated unambiguously is that:


1) A $d cross-reference describes an identifier representing a date (which is contained in the cross-reference)


2) The XRI authority that assigns the $d cross-reference is responsible for interpretation of what it "describes" outside of the cross-reference.


In other words, we don't need to define in the Metadata spec that a metadata cross-reference describes the node before it or the node after it, only that it defines a date (or version, or language, or type) and can be compared with other XRIs that are otherwise identical except for the same cross-reference.


So let me turn the question around: do you see anything wrong with this approach?




From: Sakimura, Nat [mailto:n-sakimura@nri.co.jp]
Sent: Sunday, January 15, 2006 6:37 PM
To: Drummond Reed; Schleiff, Marty; Wachob, Gabe; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec


Sorry, I still do not quite follow, I guess, but my feeling is that it is very useful if one can determine what the metadata really describes. For example, for version, it is nice to be able to determine that in





*($d*2002-10-10T17:00:00Z) is describing =GabeW*resume and not job.

The version metadata in this case actually describes the immediately preceding segment "resume". Although it just explains "resume", this in turn means that it is describing "=GabeW*resume".


What is the problem of this approach?





From: Drummond Reed [mailto:drummond.reed@cordance.net]
Sent: Thursday, January 12, 2006 12:30 PM
To: 'Schleiff, Marty'; 'Wachob, Gabe'; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec

Do not listen to that man behind the giant aluminum curtain at Boeing. Those questions he keeps asking just happen to have about 30 years of thought and experience behind them and he has completely resculpted the contour of XRI metadata because he has asked the hard questions long enough and insisted on clear, clean, even answers with little (preferably no) ambiguity.


Gabe, here's an answer your question about the application of the RDF S-P-O pattern (that's subject-predicate-object for anyone who's not an RDF disciple). As Marty explained, the solution we realized for making XRI metadata both simple and unambiguous was by including the subject (the identifier being described) as part of the cross-reference.


For example, if we wanted to express that the identifier "pays" was the French word and not the English word, the S-P-O triple would be:


Subject = "pays"

Predicate = "$l"

Object = "fr"


…with the resulting XRI being…




…which when used as a cross-reference in the context of another resource might be something like…




What threw off our analysis of the underlying pattern being the S-P-O pattern was the fact that the very simple XRI metadata cross-references we have been using for quite a while actually fit this pattern even though they were only two "levels" deep. Example:




…which when used in context (to choose a particular very real example from the XRI Resolution 2.0 spec) would be…




In this use of XRI metadata, the identifier "$v" directly describes the identifier "2.0". In RDF terms, what we realized was that this was just like the metadata in the following XML snippet:




If you analyze this tag from an RDF perspective, what you get is:


Subject = "car"

Predicate = fontstyle (implicit)

Object = "strong"


In other words, it's implicit in the semantics of the tag <strong> that it's a font style. You could make this much more explicit as follows:


            <font style="strong">car</font>


Marty and I realized that $v and $d both followed this implicit predicate pattern. So "$v*2.0" from an S-P-O perspective is:


Subject = "2.0"

Predicate = $v

Object = version number (implicit)


And "$d*2002-10-10T17:00:00Z" from an S-P-O perspective would be:


Subject = "2002-10-10T17:00:00Z "

Predicate = $d

Object = XML datetime (implicit)


Marty then suggested that $v and $d, besides their "implicit" numeric version and XML datetime formats, respectively, could also have other formats defined explicitly without conflicting with the implicit default. Examples:




Subject = "b.e.c"

Predicate = $v

Object = "alpha" (explicit)




Subject = "2005"

Predicate = $d

Object = "year" (explicit)


So (I realize this is a very long answer to your question), the S-P-O pattern applies strictly to the identifier that is the subject of the cross-reference, i.e., the final subsegment of the cross-reference (ALWAYS).


What it ducks is the question of what the entire XRI metadata cross-reference describes – if it does describe anything explicitly. In other words, under the above use of the S-P-O pattern, the S-P-O only operates within the XRI metadata cross-reference. The mere inclusion of an XRI metadata cross-reference in an XRI does not explicitly tell you what it describes.


Marty and I did discuss a way to make that ambiguous, which again would be by using cross-references. For example, in your question about whether the date cross-reference in…




...describes your resume or your job, one easy way to make this unambigous is…





It sure is unambiguous to me what describes what in these identifiers.


However, other than suggesting/specifying the use of cross-references when you really want to make it unambiguous what a XRI metadata cross-reference refers to, I'm in favor of just tightly defining the XRI metadata cross-reference syntax and letting identifier authorities use these within other XRIs as needed.







From: Schleiff, Marty [mailto:marty.schleiff@boeing.com]
Sent: Wednesday, January 11, 2006 4:57 PM
To: Wachob, Gabe; Drummond Reed; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec


Hi Gabe (& All),


Now you're asking me really hard questions. I think you need to understand that when Drummond and I work together, it's mostly him doing the work. I have three unofficial roles in the collaboration: 1) repeatedly ask stupid questions about a particular concept until Drummond gets enough practice answering in various ways, and can figure out the best way to describe it in a spec; 2) think up bizarre use cases to test out our ideas; and 3) continually pester him and try to convince him that there are some places where an xref doesn't make sense. For good answers, I think we'll have to wait for Drummond to chime in.


I'm apparently guilty of trying to constrain the specs too much. I don't like the concept of it being up to the issuer to decide how to interpret the target of the metadata. In and XRI containing ".../pays/pays/(l*fr)/pays/pays/...", to which part(s) should the metadata apply? I.e., which part(s) should have French pronunciation? The ambiguity drove us to putting it into the xref, e.g., ".../pays/pays/($l*fr*pays)/pays..."


Your "left" / "right" idea is an interesting approach we hadn't thought of (at least I hadn't thought of it - maybe Drummond had).



 Marty.Schleiff@boeing.com; CISSP
Associate Technical Fellow - Cyber Identity Specialist
Computing Security Infrastructure
(425) 957-5667



From: Wachob, Gabe [mailto:gwachob@visa.com]
Sent: Wednesday, January 11, 2006 4:29 PM
To: Schleiff, Marty; Drummond Reed; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec


    Are you saying that metadata XREFs should have a way of saying "the thing identified to the left of me" vs. "the thing identified to the right of me" ? So, in the pattern of:

 xri-metadata       = "$" predicate [ “*” object ] “*” subject

  you might have:

=GabeW*resume*($v*left*1.2) -- indicating version 1.2 of my resume


=GabeW*resume*($v*right*2002-10-10T17:00:00Z)*job -- indicating my job as of 10/10/02?


  I guess I'm confused about the concept of having a *choice* about what the metadata applies to.. I don't quite understand how/why these metadata xrefs "apply" to parts of the XRI. In that sense, I guess I'm saying that I don't understand how the subject is *part* of an XRI. It would seem to me that the subject has to be explicit if you are to have the Subject-Predicate-Object model.


Can we state succinctly what it means when such a S-P-O triple appears in an XRI? What inference do we draw by its mere presence? Isn't it just a convenient way to qualify everything to the right of the metadata XREF, and nothing more?




From: Schleiff, Marty [mailto:marty.schleiff@boeing.com]
Sent: Wednesday, January 11, 2006 4:19 PM
To: Wachob, Gabe; Drummond Reed; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec

Hi Gabe (& All),


Drummond and I have discussed/debated at length how to express the portion of an XRI to which metadata applies. We determined that the only way to clearly associate metadata with the intended subject of the metadata is to include the subject and metadata within the same xref. How metadata associates with portions of the XRI outside the metadata xref is up to the XRI issuer. This is one of several concepts for which we're interested in reactions from the rest of the TC. There are other issues, but rather than point them out, I'll be interested to see if you recognize them on your own.


Marty.Schleiff@boeing.com; CISSP
Associate Technical Fellow - Cyber Identity Specialist
Computing Security Infrastructure
(425) 957-5667



From: Wachob, Gabe [mailto:gwachob@visa.com]
Sent: Wednesday, January 11, 2006 12:54 PM
To: Drummond Reed; xri@lists.oasis-open.org
Subject: RE: [xri] Feedback requested on terms used in Metadata spec

I guess I'm partial to the RDF-mindset, but I'm thinking that it is an odd fit to make that tight a connection to the S-P-O model since its not clear what the actual *subject* is in all cases - to wit, isn't the subject the thing outside the metadata cross-reference? Doesn't the Metadata XREF explicitly describe/refer to something *outside* the metata XREF?


If we *could* mesh this with RDF concepts, that'd would be interesting.


Otherwise, I don't have a strong preference between the other four items. They all seem pretty isomorphic to me, without having thought about this very deeply.




From: Drummond Reed [mailto:drummond.reed@cordance.net]
Sent: Wednesday, January 11, 2006 11:45 AM
To: xri@lists.oasis-open.org
Subject: [xri] Feedback requested on terms used in Metadata spec

I'm happy to report that Marty and I, after a series of in-depth work sessions (abetted by Dave McAlpin when he's been in town), believe we have wrestled the metadata dragon most of the way to the ground.


The "dragon" is a tighter, more consistent ABNF for all forms of XRI metadata as well as a much cleaner set of rules about what it describes.


Without going into all the gory detail, what XRI Metadata 2.0 Working Draft 08 will recommend is a very simple ABNF for "tagging" an identifier with XRI metadata, which can then be used as a cross-reference inside another XRI. The important clarification we will be making is that this metadata only describes the "subject" identifier (the identifier being described, to borrow term from RDF). For example, in the XRI…




…the metadata "$v" only describes the identifier "2.3". It tells you it’s a version number. That's it. From the identifier above, it would be a pretty obvious conclusion that the identifier authority intended the cross-reference "($v*2.3)" to identify a version namespace for the resource identifier by "filename". However in the following XRI…




…it may not be quite as clear – does the identifier "($v*2.3)" create a version namespace for "filename" or for "anotherfile"?


The answer is: that's up to the identifier authority and out of scope for the XRI Metadata spec. The scope of the Metadata spec is limited to defining well-known semantics and syntax for a limited set of broadly useful identifier metadata (versions, dates, languages, types, and annotations).


With that explained, here's what we'd like feedback on: the semantics of the actual production names used in the ABNF – which (per our experience with XRI syntax) we'd like to match up with the terms used in the text of the Metadata spec itself.


Following are four "versions" of the ABNF that are all identical structurally but different in the production names for the first two of the three productions in the proposed syntax. (Marty and I both like the term "subject" for the third component -- the identifier being described -- since this is consistent with RDF and SAML and other similar uses.)


We'd just like to know which of these (if any) are preferred by other members of the TC, since semantics is not something that can be determined by fiat. Please send a reply email to the list with a comment about your preference if you have one (or a different suggestion if you feel something else altogether would work better).




=Drummond and Marty


Example 1 ("tag" wording)

 xri-metadata        = "$" metadata-tag [ “*” metadata-tag-value ] “*” subject

 metadata-tag        = ( alpha / xref )

 metadata-tag-value  = ( xri-subseg / xref )

 subject             = ( xri-subseg / xref )

Example 2 ("attribute" wording)

  xri-metadata       = "$" attribute [ “*” attribute-value ] “*” subject

  attribute          = ( alpha / xref )

  attribute-value    = ( xri-subseg / xref )

  subject            = ( xri-subseg / xref )

Example 3 ("property" wording)

  xri-metadata       = "$" property [ “*” property-value ] “*” subject

  property           = ( alpha / xref )

  property-value     = ( xri-subseg / xref )

  subject            = ( xri-subseg / xref )

Example 4 ("RDF" wording)

  xri-metadata       = "$" predicate [ “*” object ] “*” subject

  predicate          = ( alpha / xref )

  object             = ( xri-subseg / xref )

  subject            = ( xri-subseg / xref )


Examples of the five types of XRI metadata:


($t*ces* john%20henry%20doe)





How these examples parse to the ABNF above:


First production

Second production









*number (default – can be omitted)



*XMLdatetime (default – can be omitted)



*string (default – can be omitted)





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