Re: [wsbpel] Issue 13 - Updated Proposed Resolution]

[Alex Yiu <alex.yiu@oracle.com>]

Hi, Rania and Paco,

Thanks for following up this discussion.

Before going into the discussion again, I would to recap my viewpoint on this issue again:
---------------------------------------------------------------
There are two cases of resolution:
(1) Leave the spec unchanged. And, we use XPath function call to incorporate
functionality (like XQuery) for now, as we proposed in previous email.
(2) Relax the syntax WITHOUT defining binding of XQuery (or a similar language)
in the same BPEL spec cycle.

(1) [new proposal] is simple and easy to understand.
It has ZERO changes and impact to the existing spec.
Fewer language portability issues.
(2) [current proposal] open a flood gate of undefined semantics.
It implies a lot of language portability issues.
---------------------------------------------------------------

I understand that the proposal of Issue 13 is a pure syntax relaxation.
*In theory*, it may look like orthogonal to the semantics of language binding.
IMHO, opening up syntax without proper semantics examples would be like openning up a flood gate.

XPath 1.0 is a very simplistic language, compared with XQuery. XPath is simply used as an one-line expression in BPEL currently. And, it does not have: assignment or multiple-output semantics.

IMHO, most of programming languages that need to span multiple lines or multple XML elements (instead of one line of attribute string) will quite likely have similar features comparable to XQuery: e.g.: assignment, multiple-output, or even transactional / serializable.

Regarding to the interop , the complexity of binding for a multiple-line language (e.g. XQuery) is an order of magnitude bigger than the binding for XPath. XPath binding simply is not rich enough to provide guidelines for vendor to bind a multiple-line language with BPEL in a relatively consistent way.

Don't get me wrong. I DON'T want to define binding between BPEL and ALL languages. It is just we need to have an example of language binding for BPEL that has scale of complexity similar to XQuery, not just XPath 1.0, if we decide to relax the syntax. Then, I would feel more comfortable about that.

Regarding to WSDL analogy, we have SOAP binding as an example to illustrate how WSDL can be bound to a particular protocol. That is prefectly fine. IMHO, SOAP semantics is rich enough to cover different aspects of WSDL. However, if the WSDL spec only had an example of SMTP binding without using SOAP env, then I would feel very uncomfortable about that.

The core issue is: whether XPath 1.0 binding is rich enough to provide guidelines for a language of XQuery. I guess the answer is no.

Paco said in one of latest emails: "leave further the problem of how to best bind XQuery out of the TC discussions." If that is the direction that we adopt, different vendors will just have their proprietary bindings between XQuery and BPEL. I think that would be a shame for language portability, because both BPEL are XQuery are standardized, while binding between them are not portable or standardized.

I hope I can convince you guys and rest of the BPEL community.

Thanks!!!




Regards,
Alex Yiu

rkhalaf wrote:

Hi Alex,

The proposal for issue 13 was to relax the syntax in order to "gear up for using other
languages for querying that may have a structured syntax" (quoting from the proposed resolution).  It is not to figure out how to explicitly deal with XQuery/X; therefore, as Yaron already mentioned the discussion below is out of scope for issue 13.

The specification currently forces any expressions to be strings because they must be in an attribute, where moving it to an element gives more flexibility and makes it easier to   add support for other languages. Already the specification lets you choose an expression/query language at the top level - so you could make up your own language that only uses strings and define some fancy binding/usage and have a  valid process. We are just saying that instead now it's an element instead of an attribute so the expressions in the language that you choose to use don't have to be just strings.  Of course, you may want to just stick with the default XPath and you're fine.

I understand your concern about how XQuery/X should be used, and there are issues in its use with BPEL as there are with the use of any other language. With XPath as the default with clearly defined usage, the specification is clear about what you would be able to interoperate with.   Working out the issues with any additional expression/query languages is open, and orthogonal to this syntactic change.

To clarify further, consider the parallel with WSDL  bindings: the SOAP binding was defined in the specification , but one could define ones own bindings, publicise them and use them. Example there are the Java and EJB bindings used in WSIF.  The same thing would apply here. The parallel is that you would not disallow bindings in WSDL just because you haven't defined the full bindings to all languages.

Regards,
Rania




Alex Yiu wrote:

Hi, all,

I hope I am not too late to join this discussion. :-)

In general, I am all for bringing the capability of XQuery to the BPEL world. It can potentially do some simple data transformation and merging multiple data documents into one document.

I hope this email may bring a new prospective on how to leverage power of XQuery or other similar languages in BPEL, other than XPath 1.0 or 2.0.

I see the current syntax changes is the first step to allow more generic syntax for Query and Expression Language (from attribute to element).  However, this is just the first step from my viewpoint. There are a lot of not-resolved-yet issues in the semantics space with this inline-oriented proposal. Using this syntax change to introduce XQuery power to BPEL may create more issues. IMHO, we may NOT be ready for it yet.

At the end of this email, I would suggest a potentially cleaner way to introduce XQuery into BPEL.

Unresolved Issues include:

    * Language Binding Issue between BPEL and the
      target-Query/Expr-language:

        * Variable Binding Issue: how variables in BPEL are exposed
          into the XQuery world? What is the name of variables? Are
          variable names shared between BPEL world and XQuery world?
          Can XQuery handle WSDL 1.1 MessageType directly?
        * Namespace Sharing Issue: the XQuery language has two styles:
          human-readable XQuery language and not-so-human readable
          XQueryX (XML version of XQuery). It would be treated as Text
          or CData Node in XML for plain XQuery, while XQueryX will
          wrap around target data element and attribute with
          <xqx:tagName> and <xqx:attributeName> (unlike the literal
          style of <from> element in BPEL). One way or the other,
          there is no easy way to effectivly share XMLNS declaration
          between BPEL and XQuery world. That sort of defeats the
          purpose of embedding XQuery syntax directly into BPEL.


Some of  the true power of XQuery actually are classified into two following aspects:

    * Result Data Model: The primary Data Model of XQuery is a data
      sequence. This data sequence length can be unbounded / stream
      and data items in that sequence can be of same types or
      different types. BPEL Data Model is much restrictive than that.
      Hence, there is a mismatch in Data Models. We need to enrich our
      BPEL Data Model to fully leverage XQuery.
    * Transform Multiple XML Data Sequence into one single result XML
      Data Sequence: by just allowing embedding XQuery syntax as
      element content, we do not define / solve how to refer multiple
      variables and variable binding issue listed above.


Basically, before we resolve the above issues, I don't think we are ready to embed a language, which can be used in a relatively complicated way like XQuery, directly into BPEL. I don't want gives people the illusion all the XQuery binding issues is resolved by just introducing these syntax changes.  Also, I don't want open up this syntax gateway which individual vendors tried to solve the above issues in their proprietary ways. That is a big portability issues.

However, we can still leverage XQuery in BPEL without placing the XQuery or XQueryX syntax directly into a BPEL document. Because, XQuery already allows developers to define a XQuery-based function. That is a more well-defined interface for separating:

    * Syntax
    * Datatypes
    * XML namespace
    * variable namespace

It also encourages better encapsulation and  components reuse. The same XQuery function can be used within BPEL or other XML-related components within same application. If the XQuery logic needs to be used multiple time within the same BPEL or multiple BPEL, they can now be re-used with this function-oriented approach. (On the other hand, the inline-approach would encourage users to copy XQuery fragments everywhere in BPEL)

http://www.w3.org/TR/xquery/#FunctionDeclns

E.g.:
In an XQuery file:
--------------------------------------------

declare function local:summary($emps as element(employee)*)   as element(dept)*
{
  for $d in fn:distinct-values($emps/deptno)
  let $e := $emps[deptno = $d]
  return
     <dept>
        <deptno>{$d}</deptno>
        <headcount> {fn:count($e)} </headcount>
        <payroll> {fn:sum($e/salary)} </payroll>
     </dept>
};

--------------------------------------------
And, this XQuery file / component is deployed together with the BPEL components in the same application.

In BPEL, we can do the following:

<assign>
   <from expression="local:summary(myBPELVar)" />
   <to ... />
</assign>
<switch>
   <case condition="local:total(PO,Discount) > 500">
       ...
   </case>
</switch>

Note:

    * We use "expression" as opposed to "query" here.
    * The expression / query language does not need to change to
      XQuery. It can stay with XPath 1.0 or XPath 2.0
    * This function call business is nothing in XML-world. And, we
      don't need to reinvent the wheel and invent anything brand-new
      (e.g. variable binding semantics). We can borrow a lot of
      definition from other specificiations. E.g.:

        Function Call in XPath 1.0:
        http://www.w3.org/TR/xpath#section-Function-Calls
        Function Call in XPath 2.0:
        http://www.w3.org/TR/xpath20/#id-function-calls
        Function Call in XQuery 1.0:
        http://www.w3.org/TR/xquery/#id-function-calls

        Function Declaration in XQuery 1.0:
        http://www.w3.org/TR/xquery/#FunctionDeclns

    * I would even say, this approach is ALREADY allowed by BPEL
      implicitly as of today. Because, BPEL allows XPath expression,
      which in turn allows this kind of function-call already. We just
      need to make the expression available to assign statement in BPEL.
    * This function-call approach will allow users to switch the
      implementation choice of language with minimal impact BPEL
      document itself. E.g. changing from XQuery 1.0 to XQuery 2.0
    * The development overhead of this approach is very minimal. One
      seperate XQuery file for ALL XQuery logic and one extra line of
      function signature declaration for each XQuery logic.




I hope this proposal make senses to you guys.


Thanks!


Regards,
Alex Yiu




Yaron Goland wrote:

The question is what will cause the least amount of effort for users? To
take an existing language that they are familiar with and routinely use and
then create a sub-set of it for use in join-conditions or to create an
entirely new language specifically for join conditions and now force users
to learn two languages with potentially unrelated and inconsistent syntaxes?

I personally favor the former. I also think that if we are to finish this
spec in a reasonable amount of time we should avoid creating new query
languages.

    Just my two cents,

        Yaron

 

-----Original Message-----
From: Maciej Szefler [mailto:mbs@fivesight.com]
Sent: Wednesday, January 07, 2004 9:55 AM
To: ygoland@bea.com; 'Assaf Arkin'
Cc: 'rkhalaf'; wsbpel@lists.oasis-open.org
Subject: RE: [wsbpel] Issue 13 - Updated Proposed Resolution]


Consistency should be reserved for areas where there is some
common domain.
As Assaf points out join conditions have nothing to do with XML node
selection, so why would we try to adopt an expression language aimed
squarely at XML node selection crippling it so that it no
longer does what
it was intended to do? It makes no sense to me. If anything
it makes things
confusing.

Would a structured XML representation such as "<and><link
name="foo"/<link
name="bar"></and>" satisfy your objection to creating multiple sets of
grammars?

-maciej

-----Original Message-----
From: Yaron Goland [mailto:ygoland@bea.com]
Sent: Wednesday, January 07, 2004 10:08 AM
To: 'Assaf Arkin'
Cc: 'rkhalaf'; wsbpel@lists.oasis-open.org
Subject: RE: [wsbpel] Issue 13 - Updated Proposed Resolution]

This has nothing to do with XML manipulation, this has to do
with the need
to have a consistent expression/query language used
throughout BPEL. If
someone is moving to a new expression/query language for all other
expressions in BPEL they should not be forced to use a different
expression/query language just for join conditions. That is why join
condition must have the same syntax flexibility that is
available to all
other expressions/queries.

  

-----Original Message-----
From: Assaf Arkin [mailto:arkin@intalio.com]
Sent: Monday, January 05, 2004 7:00 PM
To: ygoland@bea.com
Cc: 'rkhalaf'; wsbpel@lists.oasis-open.org
Subject: Re: [wsbpel] Issue 13 - Updated Proposed Resolution]


Yaron Goland wrote:

    

Imagine a prefix style XML manipulation language is
      

introduced that does
    

things like "and(foo,bar)". No tool in its right mind is
      

going to say to the
    

user 'well you can use the prefix style everywhere in BPEL
      

but this one
    

single place, join conditions, where you have to use an
      

infix "foo and bar"
    

style.'


      

You're right.

I've read the spec over and over and over and I still don't
understand
what XML manipulation has to do with join conditions. I don't
see node
selection, there's no context node or any variable/function
you can use
to operate on nodes. No operators are allowed unless they deal with
binary values. If nodes are non-existent, then where does XML
manipulation come into play?

So while I agree with the logic you presented, I still fail
to see how
it applies to join conditions.

arkin


    

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