Re: [sca-assembly] ISSUE 6 - alternate proposal - Version 2 updated

I've updated the proposal to put in
more text dealing with the error cases for multiplicity in

section 3.0.1.1, to answer points raised
in the discussion on the list.

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

3.0.1 Specifying the Target Service(s) for a Reference

A reference may define one or more target services which satisfy the

reference.  The target service(s) may 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 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). 

Some combinations of these different methods are not allowed:

If @autowire="true" applies to the reference, the autowire procedure
is 

only used to find a target service if no target is identified by any of
the 

other ways listed above.  It is not an error if autowire="true"
applies to 

a reference and a target is also defined through some other means.

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 are available for
use 

on each wire created implied by the @target attribute.

3.0.1.1 Multiplicity and the Valid Number of Target Services for a

Reference

For references with multiplicity 0..1 or 0..n, it is valid for the

reference to have no target service defined.

For references with multiplicity 0..1 or 1..1, it is an error for the

reference to have more than 1 target service defined.

For references with multiplicity 1..1 or 1..n, it is an error for the

reference to have no target service defined.

For references with multiplicity 0..n or 1..n, it is valid for the

reference to have 1 or more target services defined.

The assembler of a composite MUST ensure that references are properly

configured according to these rules. 

For the error cases identified above, an error MUST
be generated by the SCA

runtime 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 defines
the 

programming model for interacting with an untargetted
reference. 

Where a component reference is promoted by a composite reference, the

promotion is 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 may identify 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 may identify 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 can 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.

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