You mentioned in the
call today that you are in favor of allowing elementType propertyAliases in
correlation. My preference is to require a messageType propertyAlias because I
read the spec to say that all web
service interactions (<receive>, <invoke> ...etc) use a message
variable for sending/receiving data. In cases where the activity provides
an element variable or no variable at all (i.e. <fromPart>
or <toPart>) there is an anonymous WSDL message variable created to
send/receive the data. When the current spec refers to correlation it talks
about messages, not variables. As such, it seems consistent to require a
messageType propertyAlias.
If you or others feel
strongly that support for elementType attributes is needed then I'd ask that
you (or others) look at adding language to handle the following
cases:
1) element variable
used but elementType propertyAlias not available. Is this an error or does the
engine look for a messageType alias?
2) single part message
variable used but messageType propertyAlias not available. Does the processor
look for a suitable elementType alias?
3) no variable used
(<fromPart>, <toPart>). Do we select an elementType or messageType
first? What if both are found and they have different <query>
expressions? Is that an error?
I discussed this with Chris Keller last week and
he seemed to recall that this was already settled by a previous issue. After
doing a little research I found the following issues which touch on this
area:
Issue 145: Properties on Non-Message
Variables
-- This issue added support for propertyAliases
for elements and types. It does not discuss correlation. Perhaps it was
mentioned during the face to face in Hawthorne?
If the intent was to allow elementType
propertyAliases for correlation then this has not made it into the spec. Does anyone else recall the discussion or can they
point me to another issue that might address this? Lastly, if I missed a part
of the spec that covers this I'd appreciate a pointer to it as well.
Thanks.
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Issue - 297 - Does correlation require a propertyAlias with messageType
attribute?
Status: received
Date added: 10 Jun
2006
Date submitted: 09 June 2006
Submitter: Mark
Ford
Description: I'd like a clarification as to the use of a
propertyAlias for message correlation. My reading is that the spec requires a
propertyAlias with a messageType in order to extract values for correlation.
In cases where an activity like a <receive> uses an elementType variable
for its data the spec explains that an anonymous temporary WSDL message
variable is created for the data and its single part is used to populate the
element variable on the <receive>. The same wording (anonymous temporary
WSDL message variable) is used to explain <fromPart> and <toPart>
behavior.
If the intent is to allow propertyAlias with elementType then we would need
to define which propertyAlias would be used in the case that there was a
messageType and an elementType since they could have different queries.
If the intent is to require a propertyAlias with messageType then some
additional text to Section 9.2 could make this explicit.
Submitter's
proposal:
In Section 9.2, change
--- from ---
Observe that in order to retrieve correlation values from a
message, a processor needs to apply a particular <propertyAlias> to
the message. In the case in which the application of the
<propertyAlias> results in a response that contains anything other
than exactly one information item and/or a collection of Character
Information Items then a bpel:selectionFailure fault MUST be thrown.
--- to ---
Observe that in order to retrieve correlation values from a
message, a processor MUST apply a <propertyAlias> with a messageType
value that matches the QName of the message. In the case in which the
application of the <propertyAlias> results in a response that contains
anything other than exactly one information item and/or a collection of
Character Information Items then a bpel:selectionFailure fault MUST be
thrown.
Changes: 10 Jun 2006 - new issue
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