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Subject: Re: [wsbpel] Issue 11 - why <copy create="yes"> is instrincally interwinedwith XPath


This "create" feature is defined in the BPEL base spec, not in an expression-language-specific binding extension specification outside of this TC.

We MUST provide a clear boundary and direction on how this feature works with other expression languages by using some pure XML terminologies and NOT relying terminologies from a particular expression language.

Mentioning a BPEL-base feature in the spec by just showing a definition of its behavior in XPath ... then hand-waving about what should happen in other expression languages ... ask implementators  to make their own best guess how this BPEL feature should behave in other expression languages ... That is just plain violating the fundamental direction of BPEL spec,  IMHO.

Paco wrote:
"The fact is that many activities already depend on the use of a query language, and that usually means that the execution semantics cannot be fully determine until one language is selected"

Could you actually give some examples to support your claim above?

One key thing to differientiate: "execution details in one expression language" and "execution semantics of the BPEL" are two different things.

Without knowing which expression language is used, of course, we would not know the execution details of an expression language after the execution enters from the BPEL world to the expression language world.

However, the overall execution semantics of BPEL is well-known without picking a particular expression language, including the pre-condition and post-condition of executing expression language. (e.g. the  post condition of executing <assign>/<copy>/<to> must always returns on XML node regardless of which expression language is picked).

As far as I understand, the way that we specify <assign>/<copy> today is expression language-independent. We define its semantics based on expression-language terms.

In our definition of <copy> today, we do NOT need to mention: descendants "//" or  predicate "[]", which are the essential parts of this "create" feature.

(I was trying to mention some political sensitive terms in this email thread. It seems to me that I have no choice but to touch those hidden land-mines)

If Paco's claim about the fundamental direction and charter of  BPEL TC is true, then one can define a specific feature which we say only how it works in Java / BPELJ in this OASIS TC?  Leave C# binding for other people to specify?

For example:
<variable name="x" ... objectType="anObjectClass"? dataBinding="uri"? />
Add an objectType attribute to allow pointing to an Object Class (And in our spec, we just specify its semantics when it is pointing to a Java class, do not mention what happen in C#.) And, add "dataBinding" attribute to point to a XML-to-Object mapping (And, in our spec, we just define what its means in the JAXB binding world).

Note: I am not saying I am going to define object-features in BPEL. But, if Paco's claim is true and particularly after passing this "create" proposal, then we have precedent cases and putting the above definition in BPEL spec becomes reasonable and legal

Alex Yiu

Francisco Curbera wrote:
I think we all understand that binding each query language requires
clarifying many language specific issues; I just don't see how that
argument plays against the "create" proposal. Alex made specific
observations about how the particular XPath binding should be clarified; I
don't see anything substantial that would prevent the proposal from being
refined to deal with them.

If, for example, we need to clarify that only XPath expressions that
returns a single node are valid, then, well, we have to do that using XPath
specific language - I don't get what is the big deal. The fact is that many
activities already depend on the use of a query language, and that usually
means that the execution semantics cannot be fully determine until one
language is selected, even if the overall general behavior of the activity
is common across languages.

As I sadi before, I think this proposal is our best chance to get something
reasonable done for issue 11. IMO, the only acceptable alternative would be
to close with no change.


                      Alex Yiu                                                                                                          
                      <alex.yiu@oracle.        To:       chris.keller@active-endpoints.com                                              
                      com>                     cc:       wsbpel@lists.oasis-open.org, Alex Yiu <alex.yiu@oracle.com>                    
                                               Subject:  Re: [wsbpel] Issue 11 - why <copy create="yes"> is instrincally interwined     
                      05/10/2005 12:58          with XPath                                                                              


It is of course possible to come up with a similar semantics in some other
non-XPath languages. (I need to stress that I use the word "similar" and
"some", not "same" and "all")

But, the question is: How does one come up with one single, portable and
universal description which is applicable to all programming languages that
we can think of?

The BPEL base specification MUST  provide a universal, clear and
expression-language-independent description to state:
      what are the expected behavior of this "create" feature
      what expression language patterns are supported and what are not
      supported with this feature.

Without this description, this "create" feature is basically NON-portable
to other expression language.

For javascript, we basically need to re-describe the semantics in some sort
of Javascript terminology by saying something like:

      getElement(“a”) should return one node, while getElement(“b”,10)
      returns zero node.
      [Disclaimer: I am no Javascript expert. My terminologies used above
      are probably wrong. Let me switch to Java and XQuery for other

Chris, few questions for you (some of them are already stated in my
previous email) before we move forward:

How do you resolve "Parent Location Ambiguity" problem that I stated in my
previous email without referencing to any XPath terminology? How do you
resolve that problem with an expression-language independent description?

Even if we stay within the pure XPath world, it was not clearly enough
stated that which XPath expression patterns are supported and which are not
supported. If not supported, why?

Can we support "/abc//def/ghi[3]", as long as "/abc//def" returns one
element node? If not, why?
Do we support "/abc/def/ghi[@abc='fff'][3]"?
Do we support "/abc/def[@abc='fff']/ghi[3]"? If not, why?

And, how do you describe what XPath expression patterns are supported or
not supported without hardwiring your proposal to XPath terms and concepts?
And, did you already use quite a few of XPath terms in your proposal  to do

Instead of covering the infinite universe of programming languages, could
you come up with a single, universal but clear description to at least
cover the following cases?

(1) someone uses Java with JAXB embedded within BPEL:


How do we say:
"javaVariableForCollectionType.getBooks().getBook().get(3)" return null
javaVariableForCollectionType.getBooks().getBook()" return a non-null
java.util.List object?
WITHOUT referencing to Java terminologies?

(2) someone uses XQuery embedded within BPEL

{ (for $b in $collectionTypeVar1/book
  where $b/price > 200
  order by $b/price ) }[3]

Is the "where" and "order by" clause in XQuery supported, when this
"create" feature is used?

Please note: XPath does not have the order-by capabilities, while XQuery

Another important note:

NOT All programming languages have the same XML capabilities. Even within
one programming language, there may be multiple ways to access XML data.

Example #1: There are other ways to expose XML data in Java other than
JAXB. How about just pure DOM API?

Example #2: Javascript with E4X extension has more XML capabilites than the
original javascript.
Here is an example of E4X syntax: "order.item.*[1]". Is that supported?


Alex Yiu

Chris Keller wrote:
      Hi Alex,

      <to variable=”x” part=”y”>
         <query create=”yes” queryLanguage=”jscript”>

      A context for this script execution would know create was turned on
      and then it would create the 10th element called “b” under “a” if it
      did not exist and return the new “b” element.  If create was not
      turned on it could throw a fault.

      Thereby the “create” could be applied to a non-xpath language if the
      binding makes it so.

      - Chris

      From: Alex Yiu [mailto:alex.yiu@oracle.com]
      Sent: Monday, May 09, 2005 9:46 PM
      To: wsbpel@lists.oasis-open.org
      Cc: Alex Yiu
      Subject: Re: [wsbpel] Issue 11 - why <copy create="yes"> is
      instrincally interwined with XPath

      Hi all,

      As I mentioned in the last conf call, here are details on why <copy
      create="yes"> is instrincally interwined with XPath - i.e. no
      feasible way to define this feature in an expression-language
      independent fashion.

      Summary of why <copy create="yes"> is a bad idea:
            It is intrinsically XPath dependent (more details are provided
            below), while BPEL  itself should be expression language
            <copy> itself is somewhat schema-aware [See
            mismatchedAssignmentFailure], while "create" version of <copy>
            is not:
                  As the new node will just always be appended to the
                  parent, regardless of the related schema design, as the
                  current proposal stands.
                  The current form <copy> itself is the pure replacement
                  logic, one can compare the XSD type info associated with
                  from-node and to-node, when XPath 2.0/XQuery 1.0 data
                  model is used. If mismatched, it can trigger
                  mismatchedAssignmentFailure fault. However, for the
                  "create" version, this feature is lost. That creates some
                  hidden and profound asymmetry, which are surprising to
            The create version of <copy> in the standard is NOT
            schema-aware, it is almost useless. And, customers immediately
            force vendors to do add sort of schema tricks. It defeats the
            whole point of standardization. It is a very slippery slope.
            Bad for standardization.

      Details of XPath-Only / XPath-Dependent Concern

      Parent Location Ambiguity

      The proposal says: "Newly created nodes are always appended as the
      next child of a parent."
      However, it does not address one big ambiguity issue: Where is the

      Consider this example:

          <def id="d1"> <ghi id="g1"> </def>
          <def id="d2"> <ghi id="g2"> </def>

      /abc/def/ghi[1] points to "g1"
      /abc/def/ghi[2] points to "g2"

      Now, if someone tries to use this "create" feature to copy to
      "/abc/def/ghi[3]", which <def> is the parent? "d1" or "d2"????

      One thing the proposal SHOULD say is: by "popping off" the
      bottom-most-XPath-child axis token in XPath expression parse tree,
      (i.e. "/abc/def/ghi[3]" => "/abc/def"), the resultant XPath
      expression must be evaluated to be ONE single element node. Then, it
      solves the ambiguity of parent location. This is a MUST-HAVE

      Please note that: I underlined some of the terms above. Because,
      those terms are extremely XPath specific. This MUST-HAVE
      clarification make this feature become completely XPath-specific.

      If one wants to standardize the "create" feature in BPEL spec, ONE
      MUST give the equivalent, crispy clear and portable terms of
      underlined text for other expression languages and data-modeling
      technologies. E.g. XQuery 1.0, XPath 2.0, Java (with or without JAXB
      ... and with or without SDO), C#, Javascript (with or without XML
      extension), SQL, SQL/XML ... (I consider that mission-impossible).

      "Fuzziness" of XPath Expression Subset Definition

      Also, its current attempt to define the subset of XPath expressions
      are supported by this feature is no where clear enough to be put on
      the BPEL spec. As of now, it just tries to excludes 3 cases of XPath:
      (1) must use abbreviation form (2) must not use "//" (3) must use
      position predicate

      For (1), the proposal does not provide a real good reason on why
      restricting to abbreviation form only.
      For (2), why we cannot support XPath "/abc//def/ghi[3]"? As long as
      "/abc//def" returns one elment node?
      For (3), is this Xpath "/abc/def/ghi[@abc='fff'][3]" supported? How
      about "/abc/def[@abc='fff']/ghi[3]"? The proposal does NOT say it

      Loosely (or arbitrarily) clipping off some XPath features off the
      support domain does NOT create a portable behavior of this "create"

      I strongly urge that whoever wants to standardize this feature
      (outside of this BPEL TC) should come up with a restricted form of
      EBNF Grammar for XPath expression subset. Then, that grammar will
      clearly state what XPath subset are supported and what are NOT.  That
      restricted EBNF Grammar needs to be based on the non-terminal in EBNF
      Grammar of XPath 1.0
      (e.g. http://www.w3.org/TR/xpath#predicates )

      Implementation experiences say it even louder ...

      As I mentioned before, we (Oracle) have a similar implementation
      extension feature. We NEVER have the intention to standardize this
      XPath-only extension feature in BPEL spec. Because BPEL is supposed
      to expression language independent and BPEL spec is NEVER the right
      place to standardize a feature which fudges and breaches the clean
      border line between BPEL and expression language.

      That is: The semantics of a BPEL construct (<copy create="...">)
      relies on certain features and behavior of underlying expression
      language.  And, we cannot find a proper portable description of those
      features and behaviors across a wide spectrum of expression languages
      that can be put into the BPEL spec.

      Also, in our implementation experience of similar features, we need
      to play around with XPath parser implementation to achieve that
      functionality. And, that implementation will be NEVER portable to
      other expression languages. That again further illustrates that this
      "create" feature is by definition XPath-concept dependent.

      As far as I know some other vendors have similar extension features
      as well, they have no plan to standardize this XPath-only feature
      either. Hence, I am not alone in that crowd.


      Alex YIu


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