RE: [sca-assembly] ISSUE 5: Component type allows to specify wire targetson references: PROPOSAL

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

Folks,

I'm finding it very hard to understand
the logic behind the proposals below.  They seem to complicate the
SCA model for no reason.

The proposal that I favour I think is
a very simple one, that fits in well with the current structure of SCA
and requires no new or special
constructs.  Basically, the model
I see is one where an implementation has a componentType.   The componentType
represents
the configurable aspects of the implementation
- services, references, properties and the implementation itself (in the
sense that
intents and policies can be configured
on the implementation).

I see it as being a very simple idea
that the configurable aspects of an implementation may have default values
for any of those
aspects.  

- That value can apply to a Property
by the property having some value defined by the implementation.
- For a service, the default value may
be a specific binding and a relative URI
- For a reference, the default value
may include a specific binding and/or a specific target for the reference,
(some URI)

When an implementation is used within
a component, then the component can decide to configure any or all of the
configurable
aspects of the implementation.  This
is true whether or not there are default values for those aspects.  The
component can get
exactly what it wants, for properties,
for references and for services (other than any intents, of course, which
cannot be overridden).

The neat thing about defaults, is that
if the component writer is OK with the defaults present in the implementation,
then it cuts down
the work required to configure the component
- the component can simply use the default values.

I see the "completely configured
implementation" as only an extreme case of these ideas - ie an implementation
where all the
configurable aspects have default values
supplied, so that, in effect *no* configuration is required from the using
component
in order for the component to work.

This has the happy side effect of allowing
a particular use case to work very neatly.  This is the "zero
effort deployment" scenario,
where an implementation artifact such
as a Java class or a PHP script can be given to a (suitable) runtime and
that runtime can
instantiate the implementation as a
domain-level component without the need for any further effort (ie no need
to separately
supply deployment metadata), since everything
necessary is defined in the implementation artifact.  The runtime
would still
in SCA terms be creating a deployment
time composite for that new component, but its contents are "trivial"
in the sense that
all that is required is a component
element with a name, using the supplied implementation.

I note that no-one is required to build
a runtime that works this way.  A runtime can insist on the deployment
of contributions 
that do contain composites.  On
the other hand, I'd prefer to see it possible to create a runtime that
does not require such
metadata.

Doing this in no way runs against the
principles of SCA - and requires no changes to the model either.  If
a using component
wants to use the same "fully configured
implementation" in a new way, it is free to do so by configuring the
implementation in
whatever way it chooses.  Simply
supply a composite with a component containing the necessary configuration
data.


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

"Patil, Sanjay" <sanjay.patil@sap.com>

11/03/2008 18:50

To	Mike Edwards/UK/IBM@IBMGB, "OASIS Assembly" <sca-assembly@lists.oasis-open.org>
cc
Subject	RE: [sca-assembly] ISSUE 5: Component type allows to specify wire targets on references: PROPOSAL

I am guessing that the rationale
behind the following proposal to close the Issue 5 with no-action is -
to allow for direct deployment of implementation artifacts without requiring
creation of any SCDL files, etc. Assuming that as the target use case ....
 
I would like to note that supporting
the above use case does not depend upon inclusion of deployment specific
configuration (e.g. wire targets on references) in the ComponentType, since
a simple solution to meet the use case would be to embed the deployment
specific configuration directly in the implementation artifacts. Now an
interesting question to answer would be - Is there a language-neutral SCA
construct to represent the deployment specific configuration embedded in
the implementation artifacts? Here are some of the possible answers IMO
-
 
a> None - there is no need
to separately represent the embedded configuration data as an SCA construct,
since the goal of the use case is to avoid creation of any SCDL files,
etc. 
b> Composite  - Since
the SCA model expects that it is a Composite that gets deployed to an SCA
domain, it logical follows that the SCA construct to represent the deployment
specific configuration embedded in an implementation artifact would also
be a Composite (and not ComponentType)
 
So if at all we wanted to have
an SCA construct that reflects the deployment specific configuration in
a directly deployable implementation, we should focus on defining a mapping
between a Composite and the implementation. Mapping of deployment specific
configuration embedded in implementation artifacts to ComponentType is
not necessary, and if allowed for whatever reasons, there are potential
downsides as documented in the issue text [1].
 
In essence, I propose that we
resolve Issue-5 by adopting the proposal specified in the issue text, which
says: Change the schema so that
wire targets cannot be specified. 
 
Thanks,
Sanjay
 
 
[1] http://osoa.org/jira/browse/ASSEMBLY-5

---

From: Mike Edwards [mailto:mike_edwards@uk.ibm.com]
Sent: Tuesday, Feb 12, 2008 4:12 AM
To: OASIS Assembly
Subject: [sca-assembly] ISSUE 5: Component type allows to specify wire
targets on references: PROPOSAL


Folks, 

PROPOSAL:  Close Issue 5 with no action. 

This permits the component type of a component to contain wire targets
on references. 


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

---

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

---

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU