RE: [sca-assembly] ISSUE 16: Component URI is not well described

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

Dave,

Good comments - replies inline plus
an updated proposal document.



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

David Booz <booz@us.ibm.com>

22/02/2008 15:30

To	sca-assembly@lists.oasis-open.org
cc
Subject	RE: [sca-assembly] ISSUE 16: Component URI is not well described

Unfortunately I'm being called away on other business
next week, so I'll
drop my comments here for the record.

1) implementation dependent Domain URI - YES, it should be implementation
dependent, but don't feel strongly.  I'll note that one must create
a
Domain before one can install or deploy anything into it, so installing
the
first contribution with the definitions file containing the Domain URI
definition in it will be awkward at best.  I would prefer that it
was up to
the runtime to create Domains and manage them however they want.  I'd
like
it to be possible for SCA runtime to  create relationships between
the
Domain and other scoping mechanisms, so the more room we have in the spec,
the better.

<mje>OK, glad to
see opinions being expressed on that point</mje>

2) I would like to see examples with promotion.  I found the promotion
text
confusing.

<mje>OK, I wondered
about that myself, so I've produced some examples</mje>

3) I have no idea why we'd want to support different Domain URIs for two
services that are in the same domain.  What's the point of having
a domain
URI then?  I note that it is currently possible for a binding to provide
an
absolute URI, so perhaps this is the thought behind multiple Domain URIs.
I would be fine with the removal of absolyute URIs for bindings.

<mje>I agree on the
different Domain URIs point - what do other folk think? </mje>

4) I really like the fact that the composites are absent from the URI
construction

<mje>Good</mje>

5) I'm not sure that 9.2.1.1 is really needed.  It's just basic URI
resolution rules.  For example, ./foo is also a valid relative URI
that I
think ends up having no effect on any parent URI segments.  I suspect
there's more of these kinds of things, do we really want to describe them
all?

<mje>You're right
in saying that this does describe basic URI construction rules - but I
defend the presence of
this section in that it points out a particular usage of the rules that
are relevant to particular
SCA usage.  I dislike specs that depend on a lot of other specs
and which don't take the
time to explain the more important parts of those dependencies.
Such specs end up being
very cryptic to the average reader.  I had to go find and read
the URI specs myself in
order to write this section and it wasn't so easy to find and interpret
the material.
</mje>


Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093  or  8-295-6093
e-mail:booz@us.ibm.com
http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome


                    
                     
                     
          
             Mike Edwards      
                     
                     
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ISSUE 16:        
                    
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URI is not well described 
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          





Michael,

I don't know if you noticed the set of comments that I inserted into your
original proposal text - I note that you did
not make any response to those comments.

I've taken your original document, your examples below and I've built a
revised version of the proposal, which
also contains the changes to the Component section of the specification.
All based on the latest WD-03 version
of the Assembly specification:



This contains various tweaks, which are fully change marked.

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

                    
                     
                     
          
 "Michael Rowley"              
                     
                     
 <mrowley@bea.com>              
                     
                    
                    
                     
                     
          
                    
                     
                     
       To 
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From: Mike Edwards [mailto:mike_edwards@uk.ibm.com]
Sent: Wednesday, February 20, 2008 6:46 AM.
To: OASIS Assembly
Subject: Re: [sca-assembly] ISSUE 16: Component URI is not well described


Michael,

Thanks for getting this done.

First, some high level observations.

- this is clearly a proposal that involves more than simply improving the
description of how URIs are constructed.  There are some
significant changes and additions to the capabilities here - all I'm asking
for is that everyone should be clear about this.  I'm not
against the changes, but would like us to be clear about them.

- I note that you are making it explicit that the Base Domain URI is set
in
some implementation dependent way.  Is this something that
everyone is happy with?  Do we instead need a way of capturing this
information, say in a definitions file?

I believe that even before the SCA 1.0 spec was published there was a
general agreement among the authors that this should be left unspecified,
but that fact never made it into the spec.  There may be many factors
into
deciding what host and port to use, whether to use https vs. http, etc.
 We
then should just say how URIs are constructed below that.


- I find the notation concerning cardinality that is being used somewhat
confusing.  While I think I follow that "Component URI"
may turn
up one or more times, I'm not clear which portion of the complete URI is
targeted by the "?" notation at the end - is it just the Binding
URI
or does it also apply to the Service Name?  ie which of these is intended:


Implementation-Dependent Base URI / {Component URI /}+ Service Name {/
Binding URI}?


Implementation-Dependent Base URI / {Component URI /}+ {Service Name /
Binding URI}?


You are right that I meant the first of these, and I agree that your
suggested syntax makes it clearer.



I assume it's the first of these, but the text below does not make this
clear (it would be useful to explicitly state the cardinality in the text
as well).  This implies that I'm answering your question about an
empty
Binding URI in the negative - ie the complete URI should NOT
end with a "/".

- I am keen on examples - I'd like to see examples for various cases not
covered at the moment:


Before adding anything to the spec, I’ll try to answer here.  Assume
that
each of these is for the following deployment composite:

<composite name="forDeployment">
  <component name=”C1”>
     <implementation.composite name=”ns:composite1”/>
   </component>
</composite>


Also assume that the implementation dependent base URI is http://acme.com/.



a) a service exposed by a nested component (no component URIs)


<composite name="composite1">
  <component name=”C2”>
     <implementation.foo/>
     <service name=”S”/>
   </component>
</composite>


The URI of S:  http://acme.com/C1/C2/S



b) a service with a relative binding URI


<composite name="composite1">
  <component name=”C2”>
     <implementation.foo/>
     <service name=”S”>
        <binding.ws uri=”../T”/>
     </service>
   </component>
</composite>


The URI of S:  http://acme.com/C1/C2/T



c) a service with an absolute binding URI


<composite name="composite1">
  <component name=”C2”>
     <implementation.foo/>
     <service name=”S”>
        <binding.ws uri=”http://acme.com/frontDoor”/>
     </service>
   </component>
</composite>


The URI of S:  http://acme.com/frontDoor



d) a service exposed by a component with a component URI attribute
specified


<composite name="composite1">
  <component name=”C2” uri=”foo”>
     <implementation.foo/>
     <service name=”S”/>
   </component>
</composite>


The URI of S:  http://acme.com/C1/foo/S



e) a service exposed with a shortened URI


<composite name="composite1">
  <component name=”C2” uri=”../foo”>
     <implementation.foo/>
     <service name=”S”/>
   </component>
</composite>


The URI of S:  http://acme.com/foo/S



For these examples, appropriate composites should be shown, with relevant
attributes on elements
such as bindings, services, components - and the resulting URI quoted.


Hope that helps.


Michael




I'm happy to help create these examples.


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>


                    
                     
                     
          
 "Michael Rowley"              
                     
                     
 <mrowley@bea.com>              
                     
                    
                    
                     
                     
          
                    
                     
                     
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  Subject 
                    
                     
 [sca-assembly] ISSUE 16:       
                    
                     
 Component URI is not well      
                    
                     
 described                
     
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          










I’ve enclosed a proposed modification to section 9.2 to improve the
description how URIs should be constructed.  The enclosed Word document
has
change tracking to show how it has changed.  I’ve also included it
into the
email, so that people can comment on or question specific sections as part
of this email thread.





Note that this URI construction requires that there be a new optional @uri
attribute on components.  The ability to specify a URI (which is usually
relative) makes it possible to design the URI hierarchy independent from
the structure of the domain, which I believe is valuable.


<mje> This will require changes to the text fo the section dealing
with
components - and this should be included in the eventual proposal text.
</mje>





Michael





9.2 Form of the URI of a Deployed Binding





9.2.1 Constructing Hierarchical URIs


Bindings that use hierarchical URI schemes construct the effective URI
with
a combination of the following pieces (using a pseudo-BNF representation
of
its structure):


Implementation-Dependent Base URI / {Component URI /}+ Service Name /
Binding URI?





Each of these components deserves addition definition:


Implementation-Dependent Base Domain URI .  SCA does not specify the
content of the base URI that should be used for any deployed binding,
except to say that it must be a hierarchical URI.  There is also no
requirement that the base URI be the same for any two uses of it.


<mje> That final sentence is cryptic in the extreme.  I'd appreciate
a good
explanation of what you mean by it </mje>


{Component URI /}+. This is a “/” separated sequence of the relative
URIs
specified by components (or the component name, if a URI is unspecified).
These are the relative URIs of the components, starting from the
domain-level component and following down each of the
<implementation.composite> components until reaching a component
that
exposes the service that the binding is for.  This means that promoted
services get a URI which is computed based on the highest promotion of
that
service, not based on the lowest-level component that offered the service
to be promoted.


Service Name. The service name is the name of the service that the binding
is for, as defined by the component’s component type.
<mje> A component does not have a component type.  An implementation
has a
component type. So at best this should read:


"as defined by the component type of the component's implementation".


</mje>


Binding URI.  The Binding URI is the relative URI specified in the
“uri”
attribute of a binding element of the service.  The default value
of the
attribute is value of the binding’s name attribute treated as a relative
URI.  If the binding has neither a @uri nor a @name attribute, then
the
last path segment of the URI will not be present (i.e. it defaults to the
empty string).


The binding URI may also be absolute, in which case the absolute URI fully
specifies the full URI of the service.  Some deployment environments
may
not support the use of absolute URIs in service bindings.


<mje> OK, here we have (yet) another optional conformance point.
 Do we a)
want to allow this optionality  b) prefer to outlaw the use of absolute
URIs for simplicity </mje>


The name of the containing composite does not contribute to the URI of
any
service, but the name of the higher-level component that uses the
containing composite as an implementation is used instead.


<mje> I suggest removing the word "instead" at the end
of this
sentence</mje>


For example, a service where the Base URI is "http://acme.com",
the
component is named "stocksComponent" and the service name is
"getQuote",
the URI would look like this:


http://acme.com/stocksComponent/getQuote


Allowing a binding’s relative URI to be specified that differs from the
name of the service allows the URI hierarchy of services to be designed
independently of the organization of the domain.


It is good practice to design the URI hierarchy to be independent of the
domain organization, but there may be times when domains are initially
created using the default URI hierarchy.  When this is the case, the
organization of the domain can be changed, while maintaining the form of
the URI hierarchy, by giving appropriate values to the uri attribute of
select bindings.  Here is an example of a change that can be made
to the
organization while maintaining the existing URIs:


To move a subset of the services out of one component (say "foo")
to a new
component (say “bar”), the new component should have bindings for the
moved
services specify a URI “../foo/MovedService”..


The URI attribute may also be used in order to create shorter URIs for
some
endpoints, where the component name may not be present in the URI at all.
For example, if a binding has a uri attribute of "../myService"
the
component name will not be present in the URI.


<mje> I know that this material about binding URIs is not new, but
the
special meaning of "../"  deserves some fuller explanation
- and it also
raises the question of whether this can be used in the component URIs</mje>


9.2.2 Non-hierarchical URIs


Bindings that use non-hierarchical URI schemes (such as jms: or mailto:)
may optionally make use of the “uri” attritibute, which is the complete
representation of the URI for that service   binding. Where the binding
does not use the "uri" attribute, the binding must offer a different
mechanism for specifying the service address.


<mje>An example of a non-hierarchical URI is called for, I think</mje>:)








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