Re: Using Service / Component Selector in Phoenix

[Stephen McConnell]

The document 
http://jakarta.apache.org/avalon/phoenix/guide-example-configuration.html 
contains a description of how to handle this inside Phoinix.

Cheers, Steve.
Andrei Ivanov wrote:
Hi,
I came across with simple problem (I think it is simple for experienced
Avalon developers) with my Phoenix-based application.
The problem is as follows:
I have phoenix service which contract is defined in interface
A. ServiceInterface
I have two different block which offer service A (in other words different
implementation for the same service):
Blocks
B. offers A
C. offers A
B and C should be configured and initialized differently as well as they
will depend on different services.
I would like to be able to specify which block will be used (B or C) to
provide service A changing only configuration (config.xml) file.
Can anyone give me example how to achieve that and what is the standard
practice for Phoenix-based application for this?
Regards,
Andrei

----- Original Message -----
From: "Peter Royal" <[EMAIL PROTECTED]>
To: "Avalon-Phoenix Developers List" <avalon-phoenix-dev@jakarta.apache.org>
Sent: Monday, June 10, 2002 5:44 PM
Subject: Re: Constraints on dependencies
 

On Thursday 06 June 2002 07:43 pm, Peter Donald wrote:
   

1. Are constraints container specific or not?
2. Is there a subset of constraints that are container agnostic?
3. How do we represent constraints in the system? An opaque string? A
Configuration tree? An XPath expression?
4. Do the providers or the Kernel validate the constraints?
5. Do the providers get informed that they must conform to certain
constraints?
6. Does validation occur at initialization time or assembly time?
My answers would be;
     

1. Sometimes. I haven't seen any container-specific examples yet though ;)
2. Yes. Mainly anything that involves lookup( ROLE ), ie. component
   

assembly
 

3. XPath or other evaluated expression :)
4. Kernel
5. No, but there may be cases where they need to be queried by the kernel
   

for
 

constraint resolution (like the ORB example. the kernel will most likely
   

be
 

unaware that its ORB component hosts others)
6. Both. As much as possible should be done at assembly, but I'm sure some
must be defered to init time.
   

The problem is basically that in some cases it is going to be
     

practically
 

impossible for kernel to validate the constraint unless the provider
conforms to very specific contracts or is self validating.
     

I agree. I'd opt more for the "specific contracts" option, which could be
   

as
 

easy as exposing MetaInfo classes.
-pete
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Stephen J. McConnell
OSM SARL
digital products for a global economy
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