[snip]
Jean-Sebastien Delfino wrote:
comments inline
Venkata Krishnan wrote:
Hi,
I am trying to bring the SPI model and the Loaders in sync with the
current
level of the specs as available on OSOA site. I am currently looking at
'references' - as and how they are defined in ComponentType,
ComponentDefinition and Composite and have the following questions: -
With respect to references defined in ComponentDefitions and the
'target'
attribute therein
- the specs says that whatever is mentioned in the target overrides that
which is mentioned in the implementation. Now, my understanding is
that a
target is used to wire a reference to another Component's service.
Given
this, I thought defining a target makes sense only within a
composite. So
what does it mean by an implementation specifying a target for a
reference?
The idea is to allow a component implementation developed with a
particular composition in mind to specify a target right in the
implementation. This makes the SCA programming model more compact as
you may not even have to write SCDL then. SCA for PHP for example
leverages this capability, here's a sample from
http://us2.php.net/manual/en/ref.SCA.php:
<?php
/**
* The currency exchange rate service to use.
*
* @reference
* @binding.php ../ExchangeRate/ExchangeRate.php
*/
public $exchange_rate;
?>
The componentType/reference/target attribute allows you to express the
same thing in a .componentType SCDL file.
Then later if you want to reuse your component implementation in other
compositions you can rewire the reference using a
component/reference/target attribute in the particular component
declaration, without changing your implementation.
More generally, I've started to look more closely at the model spi as
well as I'm trying to see how to reuse it as an individual module, and
I'm not sure that the current ReferenceDefinition and ReferenceTarget
classes correctly represent references as defined in the SCA assembly
spec.
The assembly spec defines the following:
- abstract reference definitions in constraining types
- reference definitions in component types
- component references
- composite references
I'll try to come up with some ideas for an accurate representation of
references at these 4 levels.
Venkat,
I've checked in a few interfaces representing the 4 kinds of References
above at
http://svn.apache.org/repos/asf/incubator/tuscany/branches/sca-java-integration/sca/assembly/src/main/java/org/apache/tuscany/assembly/model/
(plus a few base interfaces to represent SCA interfaces, multiplicity,
basically what I found in the SCA assembly spec for references).
I think that we're going to need interfaces for the model SPI to achieve
good modularization of the Kernel, so I thought I'd try to have these
few interfaces actually in sync with the SCA 1.0 assembly spec.
It's probably premature to try to use this assembly module as I just got
it barely building today and it's not used by the rest of the runtime,
but I hope that the few interfaces can help give some ideas or at least
help initiate a discussion on how best to represent SCA assembly references.
Let me know what you think.
--
Jean-Sebastien
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