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

["Chris Keller" <chris.keller@active-endpoints.com>]

One nice advantage of the variable typing (even with lax intermediate
validation) is that bpel editors can supply additional functionality if
they know what the variable is supposed to be.  But allowing the
variable to be out of sync momentarily with the schema (until use) seems
like a pretty worthwhile idea in support of complex mappings.  

If some users feel the variables should never be invalid against their
schemas then maybe a global process option could be introduced like
validateVariables="always | onExternal" (ala suppressJoinFailure) to
give the user control over this behavior.

-----Original Message-----
From: Danny van der Rijn [mailto:dannyv@tibco.com] 
Sent: Wednesday, August 06, 2003 6:04 PM
To: wsbpel@lists.oasis-open.org
Subject: Re: [wsbpel] Issue - 11 - Partial Schema Compliance

if we only validate when dealing with external services, i'm not sure i
see
much of a point of strongly typing the variables.  not that i'm
necessarily
thinking that that's a bad idea, mind you..

danny

----- Original Message ----- 
From: "Chris Keller" <chris.keller@active-endpoints.com>
To: "'Danny van der Rijn'" <dannyv@tibco.com>;
<wsbpel@lists.oasis-open.org>
Sent: Wednesday, August 06, 2003 2:58 PM
Subject: RE: [wsbpel] Issue - 11 - Partial Schema Compliance


> I'd vote for the validation "only when dealing with external
services".
> But in addition we should add a new function like
> bpws:validateVariable('x').  This could return a Boolean, which would
be
> true if valid and false if not (or we could have it return a new bpel
> type, which gave more info on what was invalid).  In this way users
can
> build valid messages via assigns and then decide if and when they may
> need to test the data (e.g. they can put it in a switch with a throw
if
> the data is invalid).  But they should never receive or send out bad
> data so that validation should be mandatory.
>
> -----Original Message-----
> From: Danny van der Rijn [mailto:dannyv@tibco.com]
> Sent: Wednesday, August 06, 2003 5:26 PM
> To: wsbpel@lists.oasis-open.org
> Subject: Re: [wsbpel] Issue - 11 - Partial Schema Compliance
>
> I was going to raise this as a separate issue, and was just beginning
to
> write it up.  Not sure if it should be a separate issue at this point
or
> not, since its existence as an issue depends on a solution to the
> insertion
> issue.
>
> I think that yaron's example can be easily fixed by saying that schema
> validation occurs after all <copy> elements of an <assign> activity
have
> been completed, and not after each <copy> clause.  So the example
turns
> into
> something like:
>
> <assign>
>   <copy>
>     <from something or another that contains the integer value>
>     <to variable="Foo" part="p1" query="/foo/bar"/>
>   </copy>
>   <copy>
>     <from something or another that contains the Icky value>
>     <to variable="Foo" part="p1" query="/foo/icky"/>
>   </copy>
> </assign>
>
> however, if the validation boundary (more on this in a sec) is arrived
> at,
> and there is a validation problem, a new standard fault needs to be
> thrown:
>
> invalidVariableContent - Thrown when the content of a variable fails
> validation
>
> it would be nice if the fault could include information about which
> variable
> it was.
>
> but that only fixes your example.  here's a more difficult example:
>
> a variable has 2 parts, both required, one of which is repeating and
has
> cardinality > 1.  Think of a purchase order request/response, as a
> common
> example
>
> Variable: PO
> Part: PO
> Schema:
> <PurchaseOrder>
>    <PurchaseOrderID/>
>    <LineItem/>+
> </foo>
>
> Variable: POResponse
> Part: POResponse
> Value: Uninitalized
> Schema:
> <PurchaseOrderResponse>
>    <PurchaseOrderID/>
>    <LineItemResponse/>+
> </foo>
>
> Variable: LineIn
> Part: LineIn
> Schema: <LineItem/>
>
> Variable: LineOut
> Part: LineOut
> Schema: <LineItemResponse/>
>
> Now imagine that the process <receive>s a PO, and loops over each line
> item
> to construct a response.  imagine the following code fragments (an
> analogous
> example inside a <sequence> is trivial to imagine):
>
> <flow>
> ...
> <assign name="AssignID">
>   <copy>
>     <from variable="PO" part="PO"
> query="/PurchaseOrder/PurchaseOrderID"/>
>     <to variable="POResponse" part="POResponse"
> query="/PurchaseOrderResponse/PurchaseOrderID"/>
>   </copy>
> <assign>
> ...
> <while "there are line items, loop over them">
>
>   <assign>
>     <copy>
>       <from variable="PO" part="PO"
> query="/PurchaseOrder/LineItem[loopIndex]" />
>       <to variable="LineIn"/>
>     </copy>
>   </assign>
>
>   <invoke operation="ProcessOrderLine" inputVariable="LineIn"
> outputVariable="LineOut"/>
>
>   <assign name="AssignResponseLine">
>     <copy>
>       <from variable="LineOut"/>
>       <to variable="POResponse" part="POResponse"
> query="/PurchaseOrderResponse/LineItemResponse[loopIndex]"/>
>     </copy>
>   </assign>
>
> </while>
> ...
> </flow>
>
> if the AssignID <assign> is reached first, it would cause an
> invalidVariableContent fault to be raised, since there are no line
> items.
> if, however, the AssignResponseLine <assign> is reached first, it
would
> cause the same, since there is no PurchaseOrderID
>
> i don't really have a nice solution to this problem.  i do have some
> thoughts, though, not that i like any of them.
>
> - create an attribute on some (proper?) subset of activities stating
> that
> some list of variables (/subparts?) is to be exempt from validation
> during
> the execution of the activity.  then, for instance, you can wrap the
> above
> code fragment with an <empty> or <scope> (or whatever) that has the
> attribute novalidation="POResponse/POResponse" (syntax is
> variable/part?).
> validation would occur upon completion of the activity.
>
> - don't be so granular:  validation="no"  simpler to deal with for the
> language, doesn't provide as much benefit to the user of a strongly
> typed
> system.
>
> - implicitly allow what yaron calls "automatic incremental
validation."
> question then is when is full validation enforced.  i'm not sure that
> yaron's proposal of "only when dealing with external services" is good
> enough.
>
> - never validate(!)
>
> - programming convention (as per yaron) with type <any> shamelessly
> overused.
>
> BPEL makes use of a strongly typed system, but current limitations
makes
> it
> unusable.  to paraphrase yaron:
>
> > 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 [one where data is messy to deal
> with]
> isn't
> > one programmers are going to successfully use.
>
> danny
>
> ----- Original Message ----- 
> From: "Yaron Goland" <ygoland@bea.com>
> To: <wsbpel@lists.oasis-open.org>
> Sent: Wednesday, August 06, 2003 11:19 AM
> 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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