Re: Merlin Roles

[Stephen McConnell]

Riven, Rodney wrote:

In article <[EMAIL PROTECTED]>, [EMAIL PROTECTED] says...
 

Rodney:

Riven, Rodney wrote:

   

From what I saw, this would probably impact dependency and service. A
solution could be as follows:
	<service
		type="blah.foo:1.0:role_hint" />
then on dependency 
	<dependency
		role="blah.foo/my_role"
		type="blah.foo:1.0:role_hint" />

     

A couple of problems here - structurally speaking we should not be 
holding any information in the type descriptor concerning assembly 
information, and secondly, this introduces semantics into the type key 
that can/should be handled at the level of attributes.

   

This would allow a service to be dependent on a particular 
implementation of a given service without a lot of impact to 
the entire meta-data structure.

     

What I have been thinking about is something like the following:

Assembly of a component dependency using a named component.

 <component name="sally" class="PersonImp"/>

 <component name="fred" class="PersonImp">
   <assembly>
     <assemble key="girlfriend" use="sally"/>
   </assembly>
 </component>
Assembly of a component dependency using a selection constraint:

 <component name="sally" class="PersonImp"/>

 <component name="fred" class="PersonImp">
   <assembly>
     <assemble key="girlfriend">
       <select feature="hair" constraint="red"/>
       <select feature="age" value="gt(21)"/>
     </assemble>
   </assembly>
 </component>
In the second case a constraint could be a regular expression of some 
sort.  In the above example a feature would simply correspond to an 
attribute in a candidate <service> definition, or an attribute in the 
<info> block of the source component (in that order - i.e. attributes in 
the service definition override attributes in the info definition).  
This information would then be used to parameterize a profile/appliance 
selector internally within Merlin.

   

In this case would the key used to assemble the component match the key/role
of the dependency?
Yes.

The <assemble key="girlfriend"> statement in the above example would be 
interprited by the container as a directive when dealing with a 
dependency declared by the component type PersonImp.  If "girlfriend" 
what was not declared as the key of a dependency, a validation error 
would occur.

 

Additionally, I also have a question about embedding Merlin in a servlet.
Is there a way to embed it that does not require url's for service
resolution? 

A very guarded yes.

We have some non-avalon objects that use the services and i was 
wondering if there was an easier way to get them to talk
   

This is something I have been playing with as part of remote service 
management - for example - using block urls to map to corbaloc urls 
which establish non-Avalon components.  I'm currently using a custom 
appliance to do this but I don't want to encorage this as it locks you 
into the API more deaply than needed.

What is the object/component model that we are talking about here?  
Specifically, how are you establishing the component and its services?

Cheers, Steve.

   

What we have is an enhanced struts based web-app.  We wrappered 
struts to have it run on a services based framework.  So the regular 
code will be the struts actions, etc. Then when they need services 
provided (ie. caching, lookups, etc.) they currently call a service
manager and lookup the service. 

When you make a call on the service manager is it correct to assume that 
you are using the interface classname as the key?

We are moving to avalon in order to 
have a better lifecycle and are looking at merlin to provide the 
proper dependencies between the many services that are currently
in our application. The issue for us is that the customer will not 
allow the url method of your current servlet example. So, I was 
wondering if there was another way to embed merlin that would work 
a little more like our current way.

Is it safe to assume that your client would be ok with a JNDI based 
access mechanisms (that's the direction that I want to take the servlet 
example - i.e. the example should be totally independent of the Merlin 
APIs).

Cheers, Steve.

--

Stephen J. McConnell
mailto:[EMAIL PROTECTED]
http://www.osm.net
Sent via James running under Merlin as an NT service.
http://avalon.apache.org/sandbox/merlin
   

 

--

Stephen J. McConnell
mailto:[EMAIL PROTECTED]
http://www.osm.net
Sent via James running under Merlin as an NT service.
http://avalon.apache.org/sandbox/merlin


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