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From Peter Royal <pro...@apache.org>
Subject Re: Constraints on dependencies
Date Mon, 10 Jun 2002 14:44:02 GMT
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.

peter royal -> proyal@apache.org

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