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Subject: RE: [xdi] Rationale and semantics for the 3rd markup model

Ajay and Loren,


First, Ajay, I agreed with all your points below. I think your last sentence, "I would think [these terms] could be used to describe the independent (from the underlying data sources) model" captures the key distinction we are trying to decide on the best semantic term for, i.e., that the third model is independent from any specific schema that may be used either: a) by the underlying data sources (i.e., native database or directory schemas), or b) in conventional XML markup.


This jibes with what Loren suggests in his message: "How about the "Schema-less" or "Semantic" or "Self Describing" models?"


I think "schema-independent" is better than "schema-less", because there is still a schema involved (the native XDI schema). And although I understand Loren's suggestion of "Semantic", I think we should avoid this term to prevent confusion with the Semantic Web.


"Self-describing" is also a fascinating option. My first reaction was to say that any type of XDI markup is self-describing (indeed, I see it often said that XML markup is "self-describing"), so I didn't think its as good as "schema-independent" in capturing the essence of what distinguishes the third model. However the more I thought about it, the more "self-describing" might provide the right contrast to "inline" and "enveloped", because "self-describing" suggests that understanding the data does not depend on understanding another XML schema, and indeed that is the key distinguishing feature of the third model.


The only other suggestion I would make, along the lines of keeping it short and intuitive, is that a key benefit of schema-independence and self-description is "generalization". In other words, what the third model gives you is the ability to do generalized data sharing across any two applications or domains regardless of underlying schema. Following this logic, the third model could be called the "generalized model" or even just the "general model'.


So, we're narrowing it down to three candidates:


* Schema-independent

* Self-describing

* General


Preferences? Other thoughts?





From: Ajay Madhok [mailto:ajay@amsoft.net]
Sent: Tuesday, November 30, 2004 3:27 AM
To: 'Drummond Reed'; 'Loren West'; 'XDI TC'
Subject: RE: [xdi] Rationale and semantics for the 3rd markup model


Hi Loren and Drummond,


My two cents on the ‘Logical’ Model as I saw my name associated with it:


XDI is a paradigm shift that will allows us to replace EAI (Physical interconnection of systems to enable data aggregation and exchange) and other middleware (for Physical shuffling and translation of data between different systems) without having any semantic, procedural or structural knowledge of the underlying data sources. The end goal is a logical, abstract, distributed Data Service which does not have to deal with the context of each underlying data source.


This said, I do agree with you that the words I have used here – logical, abstract, distributed are ‘universally’ over-hyped and. I would think they could be used (at some risk of coming across as marketing fluff) to describe the independent (from the underlying data sources) model.


More on the call.








-----Original Message-----
From: Drummond Reed [mailto:drummond.reed@cordance.net]
Sent: Monday, November 29, 2004 11:19 PM
To: 'Loren West'; 'XDI TC'
Subject: RE: [xdi] Rationale and semantics for the 3rd markup model


I see your point, and I agree it means "logical" is probably not the best

name for the third XDI markup model, because "logical" could equally applies

to the abstract XDI model as a whole, not to any one markup model.


In that case I believe the single most distinguishing characteristic of the

third model is that it is independent of any XML schema OTHER than the XDI

schema. This is the biggest contrast with the other two models, which are

both XML-schema-centric. In which case the most precise label for the third

model would appear to be either "the independent model" or "the XDI schema






-----Original Message-----

From: Loren West [mailto:loren.west@epok.net]

Sent: Monday, November 29, 2004 12:44 PM

To: 'Drummond Reed'; 'XDI TC'

Subject: RE: [xdi] Rationale and semantics for the 3rd markup model


I'm not a big fan of the terms logical, physical, and abstract

because they don't communicate anything in and of themselves.

Sort of like the word "low" - it only makes sense when compared

to something "high".


If one model is logical, what is it compared to?  Illogical?

Physical?  And what is it that makes it more logical than the



ALL 3 models allow you to identify, describe, and exchange data

so none of them are any more or less XDI than the other.


I think it would be a mistake to say that the inline and enveloped

models are just a translation of a logical XDI model into XML

because it places emphasis on the model itself vs. the virtues

of identifying, describing, and exchanging data.


It suggests that you should understand the model first, then

understand it's translations into XML if that's how you want

to use XDI.  I fear we'll lose people if we try to get them

to understand the 3rd model in order to understand XDI.




-----Original Message-----

From: Drummond Reed [mailto:drummond.reed@cordance.net]

Sent: Monday, November 29, 2004 11:37 AM

To: 'XDI TC'

Subject: RE: [xdi] Rationale and semantics for the 3rd markup model





I think I get what you're saying - that the two applications that need to

exchange data may need to first establish context, and that's what this

"meta-context" is for.


But in that case, as you said on the last call, the application *is* XDI.

XDI is the context.


That's why it strikes me that most natural name for the third model is the

term Ajay uses - "the logical model" - because the goal of XDI is to provide

an abstract, logical model for identifying, describing, and exchanging data.

All forms of XDI markup, including inline and enveloped, serve to map data

to and from this logical model. But the first two do so from the context of

existing XML schemas. The third one does so from the context of the logical

model itself.




-----Original Message-----

From: Loren West [mailto:loren.west@epok.net]

Sent: Monday, November 29, 2004 11:12 AM

To: 'Drummond Reed'; 'XDI TC'

Subject: RE: [xdi] Rationale and semantics for the 3rd markup model


Hi Drummond,


This is the best description of the 3rd model yet.  It's still

a stretch of my imagination to think about an implementation of

software that could take advantage of this format, because

by the time I'm thinking about implementing software, I'm in

context, and I don't know how to handle out-of-context data.


I can imagine, however, a conversational application where

context is communicated in real-time - much like human conversation -

and data is retrieved and delivered based on ever changing context.


This would be a great way to communicate in that application.

With this said, I'd like to suggest a few more names for it:


Runtime model

Real-time model

Conversational model (I like this the best)






-----Original Message-----

From: Drummond Reed [mailto:drummond.reed@cordance.net]

Sent: Saturday, November 27, 2004 2:03 PM

To: xdi@lists.oasis-open.org

Subject: [xdi] Rationale and semantics for the 3rd markup model



I had an action item from Wednesday's XDI TC call (for which Marc is still

working on the minutes) as follows:


# Start a thread on the list to: a) solicit our collective rationale for

using each of the three XDI markup models, and b) out of this, develop

consensus on the name we should use for the third model.


The three XDI markup models were summarized in

http://lists.oasis-open.org/archives/xdi/200411/msg00041.html. The first two

models are both "XML-centric", i.e., in both cases XDI markup is added to

existing XML markup in order to gain the data sharing virtues of XDI while

still leveraging any existing investment in XML schema, tools, and



The only difference between first two models comes down to whether the

existing XML schemas being marked up with XDI are extensible or not:



directly inline with the existing XML. Thus the consensus on the call was to

call this XDI markup model "Inline".



added in an envelope wrapping the existing XML. The consensus on the call

was to call this XDI markup model "Enveloped".


Because these two models are so clear, most of the discussion on Wednesday's

call focused on the third model, and when and why an implementer would want

to use it. Three rationales were put forth:


  1) When richer resource description is needed than is available using XML

QNames (and thus is better provided by XRIs).


  2) When the data being marked up does not yet have an XML schema.


  3) When the data being aggregated in a single XDI document does not lend

itself to a particular XML schema because comes from many different data

sources and there is no single XML schema that makes sense for aggregating

all of it.


After the call, I realized the killer example of the third type of data is

when the resource being described is one as generalized as "person",

"organization", or "topic". It would be all but impossible to create a

single XML schema that can describe all the data that might be associated

with a person, an organization, or a topic. The reason is that these are

simply very general concepts, that can be reused in thousands or millions of

data sharing applications.


It dawned on me that this made perfect sense. The universe of XML schemas

today exist mostly to describe data in particular contexts, i.e., existing

applications and data stores that already have their own schema. Moving the

data in XML in this case is the first step in being able to share it with

other applications, domains, and Web services.


But the more generalized the data, the harder it becomes to completely

satisfy this need with conventional XML, because the data is less and less

"schema-specific" and conventional XML is designed to put data in a specific

schema context.


It is for these classes of applications, where data may be reused across

many (i.e., hundreds or thousands) of different XML schemas, that the real

demand for XDI arises. Of course all 3 markup models supply the solution:

XDI markup can identify and describe the data in a schema-independent

manner, so the same logical data can be identified and shared across many

different physical XML schema instances. But if the distinguishing criteria

of the first two models is that the data already exists and makes sense to

be used in the context of existing XML schemas, then the distinguishing

criteria of the third model is that either:


a) No XML schema currently exists to provide the data context, or

b) The context is so general that no single XML schema CAN exist to provide

sufficient context.


Although in the first case it can be argued that the easiest route to

establishing the context is to simply create a new conventional XML schema,

in the second case that's not an option. There is no such schema. The only

solution is a "generalized" or "universal" XML schema that exists to

describe things independent of any one specific XML schema context. That's

the third model.


Loren predicted that the right term for the third model would emerge once

the rationale for the third model was clear. I would summarize the

rationaled for using the third model as "the schema to use when you need

express and reuse data in a generalized, universal, XML-schema-independent

format". This would suggest the following names:


General model

Universal model

Independent model

Schema-independent model

Metaschema model

Abstract model (Victor's suggestion on the call)


Votes? Other suggestions?










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