Review of WS-CDL by the WS-Addressing WG

I am sending this on behalf of the WS-Addressing Working Group.

 

Yin Leng

 

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The WS-Addressing Working Group has reviewed the WS-Choreography
Description Language Version 1.0
(http://www.w3.org/TR/2004/WD-ws-cdl-10-20041217/) from the point of
checking for potential impacts between the two specifications.

 

Here are the review comments:

1.  Review conclusion -  As the WS-Choreography Description Language is
aimed at a relatively higher abstract level than WS-Addressing
specification which is closer to the implementation level, there is no
direct impact on the WS-Addressing specification or vice-versa.

    This is seen from two aspects.

i)  The 'Choreography Description Language is not an "executable
business process description language" or an implementation language.'
It is at an abstract level, providing 'a contract containing a "global"
definition of the common ordering conditions and constraints under which
messages are exchanged.'  On the other hand, WS-Addressing 'provides
transport-neutral mechanisms to address Web services and messages'.

ii) WS-CDL intentionally uses abstractions to avoid being coupled
tightly to specifics.  For example, it uses Information Types to
'describe the type of information used within a Choreography. By
introducing this abstraction, a Choreography definition avoids
referencing directly the data types, as defined within a WSDL document
or an XML Schema document.'

    Similarly, it uses a Token to 'reference a document fragment within
a Choreography definition', and Token Locator to 'provide a query
mechanism to select them. By introducing these abstractions, a
Choreography definition avoids depending on specific message types, as
described by WSDL, or a specific query string, as specified by XPATH.
Instead the document part and the query string can change without
affecting the Choreography definition.'

 

2.  Having said the above, there remains the issue of mapping (or
binding) from (the higher abstract level of) some WS-CDL model entities
to related WS-Addressing model entities.

    For example, the WS-CDL model consists of various entities, two of
which, roughly speaking, correspond to WS-Addressing's information
models for Endpoint References and for Message Addressing Properties.

    The two are Channels and Interactions respectively.

    It is recommended that the WS-CDL Working Group define the bindings
between related concepts in WS-CDL and WS-Addressing.

 

3.  In "Section 7 Relationship with the Addressing framework" of WS-CDL,
an old version of WS-Addressing specification Abstract is quoted.  It
should be updated to the most current.

    The old version is:

    The WS-Addressing specification [WSAD] provides transport-neutral
mechanisms to address Web services and messages, specifically, XML
[XML], [XMLNS] elements to identify Web service endpoints and to secure
end-to-end endpoint identification in messages. WS-Addressing enables
messaging systems to support message transmission through networks that
include processing nodes such as endpoint managers, firewalls, and
gateways in a transport-neutral manner.

    The current version is:

    Web Services Addressing provides transport-neutral mechanisms to
address Web services and messages. Web Services Addressing 1.0 - Core
defines a set of abstract properties and an XML Infoset [XML Information
Set] representation thereof to identify Web service endpoints and to
facilitate end-to-end identification of endpoints in messages. The
specification enables messaging systems to support message transmission
through networks that include processing nodes such as endpoint
managers, firewalls, and gateways in a transport-neutral manner.

 

4.  "Section 7 Relationship with the Addressing framework" of WS-CDL
says:

    "WS-Addressing can be used to convey the reference and correlation
information for normalizing expanded Channel Variable information into
an uniform format that can be processed independently of transport or
application." 

 

    There is agreement with this statement.  Further, this statement is
consistent with the conclusion stated in point 1.

 

5.  "Section 7 Relationship with the Addressing framework" of WS-CDL
further says:

    "The WS-Addressing specification is in progress and the
WS-Choreography Working Group will review and comment on developments in
this effort on an ongoing basis."

We look forward to reviews and comments from the WS-CDL Working Group.

 

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