RE: [wsbpel] Issue - 11 - Partial Schema Compliance

["Ugo Corda" <UCorda@SeeBeyond.com>]

Yaron,

How about saying that an uninitialized variable has always the complete set of elements as specified in the corresponding schema, only their values are null? That way the schema validation should be ok (except for possible constraints on the element values).

When I do the copy, the only case where the query yields zero nodes is when the query specifies a path that does not exist according to the schema. The copy operation is always a "find and replace", never insert. The copy operation will turn the value of an element either from null to the specified value, or from an old value to a new value.

Ugo

> -----Original Message-----
> From: Yaron Goland [mailto:ygoland@bea.com]
> Sent: Wednesday, August 06, 2003 11:20 AM
> To: wsbpel@lists.oasis-open.org
> Subject: [wsbpel] Issue - 11 - Partial Schema Compliance
> 
> 
> A related issue is what happens if the copy results in a non-schema
> compliant value?
> 
> For example:
> 
> Variable: Foo
> Part: P1
> Value: Uninitialized
> Schema:
> <foo>
>    <bar>INT</bar>
>    (<blah/>|<icky/>)
> </foo>
> 
> Now lets say that the programmer is building up the Foo 
> value. Some event
> has occurred which has told the programmer the value that bar 
> should have so
> naturally the programmer wants to execute:
> 
> <copy>
> 	<from something or another that contains the integer value>
> 	<to variable="Foo" part="p1" query="/foo/bar"/>
> </copy>
> 
> Assuming we use the idea that queries on to elements that 
> resolve to 0 nodes
> are inserts and assuming we accept that in cases where there 
> are no siblings
> of the insertion point then there is no need to use 
> beforeinsertionPoint or
> afterinsertionPoint since the insertion point is unambiguous 
> then the result
> would be:
> 
> <foo>
>    <bar>Whatever the INT value was that got copied in</bar>
> </foo>
> 
> But this result violates the schema for the Foo variable 
> which mandates the
> presence of either a blah or icky element in addition to the 
> bar element.
> Therefore the COPY would fail schema validation.
> 
> It looks to me like the way to get around this problem is to define a
> variable Temp whose schema is <ANY> and then build the legal 
> foo value there
> and when one has successfully put everything together then 
> one can copy that
> value into Foo. But doesn't that seem ham fisted to anyone? 
> In essence it
> means that all values are untyped until the last possible 
> moment when one
> has a big bang attempt to set the value and see if it is 
> schema compliant.
> 
> Another approach would be to define a temp variable whose schema was:
> 
> Variable: Temp
> Part: P1
> Value: Uninitalized
> Schema:
> <foo>
>    <bar>INT</bar>?
>    (<blah/>|<icky/>)?
> </foo>
> 
> This would allow one to build up the temp value incrementally 
> and still get
> schema validation. Then when one was done one could copy the 
> result into
> Foo.
> 
> But the level of sophistication this requires on the part of the
> programmers, e.g. the ability to take all of their typed 
> values, analyze
> them and figure out how to re-write their schemas so as to 
> allow for partial
> validation, seems way beyond the norm.
> 
> What I suspect will really happen is that programmers will 
> learn to define
> their temp variables as schema type <ANY>. They will build up 
> their values
> inside of the <ANY> variables and then when they are done 
> they will try to
> copy from the temp variable into the final location (Foo in 
> this case) and
> pray it works. If it doesn't they are probably out of luck since it is
> unlikely that they will be able to do much with the error message.
> 
> A workable programming model demands a way to build up values 
> incrementally
> with feedback on validity (e.g. error: the element you just 
> inserted does
> not exist in the schema).
> 
> What I think we need is a model where when manipulating 
> variables one can
> get some sort of automatic incremental validation and only 
> when trying to
> communicate the value externally through a Web Service 
> message will you get
> full validation where the value must be perfect or you get an error.
> 
> For example, in an incremental validation model the 
> programmer could execute
> the following assuming Foo is uninitialized:
> 
> <copy>
> 	<from something or another that contains the integer value>
> 	<to variable="Foo" part="p1" query="/foo/bar"/>
> </copy>
> 
> The result is that Foo would contain <foo><bar>Some 
> INT</bar></foo> which is
> 'partially' valid. E.g. it doesn't fully specify the schema 
> but it doesn't
> contradict it either.
> 
> However, in a partial schema validation model the following would be
> illegal:
> 
> <copy>
> 	<from something or another that contains the integer value>
> 	<to variable="Foo" part="p1" query="/foo/bark"/>
> </copy>
> 
> The reason being that /foo/bark/ does not exist in the schema 
> and so could
> never be valid.
> 
> The issue here is one of programming model friendliness. For 
> BPEL to be
> successful we need a programming model that programmers will 
> be comfortable
> with and I'm fairly confident that a model in which all variables stay
> untyped while they are being built up until the last possible 
> instant isn't
> one programmers are going to successfully use.
> 
> 	Just a thought,
> 
> 			Yaron
> 
> 
> -----Original Message-----
> From: Danny van der Rijn [mailto:dannyv@tibco.com]
> Sent: Wednesday, August 06, 2003 10:08 AM
> To: wsbpel@lists.oasis-open.org
> Subject: [wsbpel] Issue - 11 Query in <to> close should allow 
> assigning
> to new locations
> 
> 
> I would like to open discussion on this issue (and volunteer 
> to champion
> it).
> 
> The issue is that in section 14.3 dealing with assignment, 
> there is the
> following verbiage:
> 
> "For XPath 1.0, the value of the query attribute MUST be an absolute
> locationPath (with '/' meaning the root of the document fragment
> representing the entire part). It is used to identify the 
> root of a subtree
> within the document fragment representing the part. <b>The 
> location path
> MUST select exactly one node. If the location path selects 
> zero nodes or
> more than one node during execution, then the standard fault
> bpws:selectionFailure MUST be thrown by a compliant 
> implementation.</b>"
> (emphasis added)
> 
> This means that the only way to get an initialized value into 
> a variable is
> to receive a message from elsewhere.  This is, I believe, far too
> restrictive.  I propose that the wording be changed to
> 
>  "For XPath 1.0, the value of the query attribute MUST be an absolute
> locationPath (with '/' meaning the root of the document fragment
> representing the entire part). It is used to identify the 
> root of a subtree
> within the document fragment representing the part. <b>When 
> the expression
> is used inside a <from> element, the location path MUST 
> select exactly one
> node. If the location path selects zero nodes or more than 
> one node during
> execution, then the standard fault bpws:selectionFailure MUST 
> be thrown by a
> compliant implementation.  When the expression is used inside a <to>
> element, and it selects 0 nodes, then the expression should 
> be treated as
> the location that the value will have after it is inserted.</b>"
> 
> This probably isn't the best wording, and I'd love someone to 
> clean it up a
> bit, but I think you get the general idea.
> 
> Danny van der Rijn
> 
> 
> 
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