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

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 that?

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 has.

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 neutual.
  • <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 users.
  • 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 parent?

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 clarification.

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 clearly.

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

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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