[ISSUE 27] Proposal to Resolve Bindings Issue 27 - "Identifying databinding and operation selection"

Folks,

The following is a proposed resolution
of Bindings Issue 27 - "Identifying data binding and operation selection".

Note: This proposal does NOT aim to
solve the question of the form of the data binding in the implementation
code.

That is a problem for the various SCA
language bindings TCs to consider and to solve, since those forms of language

bindings are specific to each language
(eg in Java, XML on the wire might be represented in the code as JAXB objects

or as SDOs).

Note that we in the Bindings TC can
vote on this resolution, but since it involves changing stuff in the Assembly
spec, the

main outcome will be an action item
to raise and progress an issue in the Assembly TC  :-(

I leave out the question of defining
specific databindings like databinding.xml, databining.jms - I think that
we should raise

issues separately for each of these.

Proposal:

In SCA, the form of databindings on
the wire (ie the format of the data as carried by a particular transport
binding) is defined by

means of a <sca:databinding/>
element, which is a child element of the <binding/> element.

There is an abstract <databinding/>
element in the sca schema, which any specific databinding extends by means
of a 

substitution group, to give a particular
<databinding.xxx/> element.  This proposal does not attempt
to define the details of

any of the specific databindings.  Specific
databindings will be defined through separate issues raised against appropriate

Bindings specifications.

A specific databinding may be unique
to one SCA binding or it may apply to multiple SCA bindings.

Detailed proposal material follows -
unfortunately it will require a set of changes to the SCA Assembly specification,
since the

general description of SCA Binding elements
is held there.  The following material deals with the specifications
at these levels:

1) sca-assembly-1.1-spec-cd01-rev1.doc

2) sca-wsbinding-1.1-spec-WD-03.doc

3) sca-jmsbinding-1.1-spec-WD-03.doc

A) Material for the Assembly Specification

a1) replace the <binding/> element,
following each of lines 2646, 2650, 2663, 2667, with the following:

<binding
uri="xs:anyURI"?
name="xs:NCName"?

         
              requires="list
of xs:QName"? policySets="list
of xs:QName"?/>*

       
<databinding
/>?

</binding>

(this makes the assumption that policy
cannot be applied separately to a databinding - policy is inherited from
the containing

binding element)

----------------------------------------

a2) add, following line 2706

A binding element has the following
child elements:

databinding (0..1) - a
databinding to apply to the data flowing using the binding.  See the
databinding section for details.

---------------------------------------------------------

a3) new Subsection, following line 2733

8.6 Databinding

A databinding is the form
that a data structure takes when it is transmitted using some communication
binding.  Another way to 

describe this is "the form that
the data takes on the wire".  A databinding can be specific to
a given communication method, or

it may be general, applying to many
different communication methods.  An example of a general databinding
is XML text format.

Where a particular SCA binding can accommodate
transmitting data in more than one format, the configuration of the binding
MAY

include a definition of the databinding
to use.  This is done using an optional <sca:databinding/> subelement
of the <binding/> element.

Where a binding supports more than one
databinding, the binding defines one of the databindings to be the default
databinding

which applies if no <databinding/>
subelement is present.

The base sca:databinding element is
abstract and it has no attributes and no child elements.  For a particular
databinding, an

extension subtype is defined, using
substitution groups, for example:

<sca:binding.xml/>

A databinding that transmits the data as an XML text datastructure

<sca:binding.jms/>

The "default JMS databinding" as described in the JMS Binding
specification

Specific databindings can have elements
that include either attributes or subelements or both.  

For details about specific databindings,
see the related SCA Binding specifications.

------------------------------------------------------------------------

a4) Changes/additions to the SCA XML
Schemas

Change the definition of the Binding
complex type (line 3820) to:

    <complexType
name="Binding"
abstract="true">

           
<sequence>

           
        <element
name="databinding"
type="sca:Databinding"
minOccurs="0"
maxOccurs="1"
/>

       
        <element
name="operation"
type="sca:Operation"
minOccurs="0"
maxOccurs="unbounded"
/>

           
</sequence>

        <attribute
name="uri"
type="anyURI"
use="optional"/>

        <attribute
name="name"
type="NCName"
use="optional"/>

        <attribute
name="requires"
type="sca:listOfQNames"
use="optional"/>

        <attribute
name="policySets"
type="sca:listOfQNames"
use="optional"/>

    </complexType>

add a Databinding complex type after
line 3843:

    <complexType
name="Databinding"
abstract="true">

           
<sequence>

           
        <any
namespace="##other"
processContents="lax"
minOccurs="0"
maxOccurs="unbounded"
/>

           
</sequence>

      <anyAttribute
namespace="##other"
processContents="lax"/>

    </complexType>

Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.

Co Chair OASIS SCA Assembly TC.

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