[ASSEMBLY 6] Proposal with RFC 2119 & "wiredByImpl" changes

[Mike Edwards <mike_edwards@uk.ibm.com>]

Issue 6 Proposal incorporating Martin Chapman's RFC2119
rewording and 
Mike Edwards' "wiredByImpl" additions
********************

Introduce a new subsection into the specification,
to follow line 330:

3.0.1 Specifying the Target Service(s) for a Reference

A reference defines zero or more target services which
satisfy the
reference.  The target service(s) can be defined in the following
ways:


1) Through a value specified in the @target attribute
of the reference
element

2) Through a target URI specified in the @uri attribute
of a binding
element which is a child of the reference element

3) Through the setting of one or more values for binding-specific
attributes and/or child elements of a binding element which is a child
of the reference element

4) Through the specification of @autowire="true"
for the reference (or
through inheritance of that value from the component or composite
containing the reference)

5) Through the specification of @wiredByImpl="true"
for the reference

6) Through the promotion of a component reference
by a composite reference
of the composite containing the component (the target service is then
identified by the configuration of the composite reference).

Combinations of these different methods are allowed,
and the following 
rules MUST be observed:

If @wiredByImpl="true", other methods of
specifying the target service
MUST NOT be used.

If @autowire="true", the autowire procedure
MUST only be used
if no target is identified by any of the other ways listed above.  
It is not an error if @autowire="true" and
a target is also defined 
through some other means, however in this case the
autowire procedure 
MUST NOT be used.

If a reference has a value specified for one or more
target services in its
@target attribute, the child binding elements of that reference MUST NOT
identify target services using the @uri attribute or using binding specific
attributes or elements.

If a binding element has a value specified for a target
service using its
@uri attribute, the binding element MUST NOT identify target services using
binding specific attributes or elements.

It is possible that a particular binding type MAY
require that the address
of a target service uses more than a simple URI.  In such cases, the
@uri
attribute MUST NOT be used to identify the target service - instead, binding
specific attributes and/or child elements must be used.

Where the reference has a value specified in its @target
attribute, all the
binding types identified by the child binding elements MAY be used
on each wire created by the @target attribute.


3.0.1.1 Multiplicity and the Valid Number of Target
Services for a
Reference

A reference with multiplicity 0..1 or 0..n MAY have
no target service defined.

A reference with multiplicity 0..1 or 1..1 MUST NOT
have more that one target service defined.

A reference with multiplicity 1..1 or 1..n MUST have
at least one target service defined.

A reference with multiplicity 0..n or 1..n MAY have
one or more target services defined.

Where it is detected the the above rules have been
violated, either at deployment 
or at execution time, an SCA Runtime MUST generate
an error before the reference 
is invoked by the component implementation.

Some errors can be detected at deployment time.  For
example, where a
composite is used as a component implementation, wires and target services
cannot be added to the composite after deployment.  As a result, for
components which are part of the composite, both missing
wires and wires with a non-existent target can be detected at deployment
time through a scan of the contents of the composite.  In these cases,
an
error SHOULD be generated by the SCA runtime at deployment time.

Other errors can only be checked at runtime.  Examples
include cases of
components deployed to the SCA Domain.  At the Domain level, the target
of
a wire, or even the wire itself, may form part of a separate deployed
contribution and as a result these may be deployed after the original
component is deployed.  In these cases, the SCA runtime MUST generate
an
error before the reference is invoked by the component implementation.

For the cases where it is valid for the reference
to have no target service
specified, the component implementation language specification MUST define
the
programming model for interacting with an untargetted reference.

Where a component reference is promoted by a composite
reference, the
promotion MUST be treated from a multiplicity perspective as providing
0 or more
target services for the component reference, depending upon the further
configuration of the composite reference.  These target services are
in
addition to any target services identified on the component reference itself,
subject to the rules relating to multiplicity described in this section.


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

Replace lines 274 - 280 with the following:

"A reference identifies one or more target services
which satisfy the
reference.  This can be done in a number of ways, which are fully
described
in section "3.0.1 Specifying the Target Service(s) for a Reference".

Replace lines 1424 - 1430 with the following:

"A reference identifies one or more target services
which satisfy the
reference.  This can be done in a number of ways, which are fully
described
in section "3.0.1 Specifying the Target Service(s) for a Reference".

Replace lines 2372 - 2383 with the following:

uri  - has the following semantic

The uri attribute can be omitted.

For the binding of a reference, the uri attribute
defines the target URI
of the reference.  This MAY be either the componentName/serviceName
for
a wire to an endpoint within the SCA domain, or the accessible address
of some service endpoint either inside or outside the SCA domain (where
the addressing scheme is defined by the type of the binding).

The circumstances under which the uri attribute can
be used are
defined in section 3.0.1 Specifying the Target Service(s) for a
Reference.



Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431  
Email:  mike_edwards@uk.ibm.com

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