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

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

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>

20/02/2008 19:45

To	Mike Edwards/UK/IBM@IBMGB, "OASIS Assembly" <sca-assembly@lists.oasis-open.org>
cc
Subject	RE: [sca-assembly] ISSUE 16: Component URI is not well described

---

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>

19/02/2008 14:36

To	<sca-assembly@lists.oasis-open.org>
cc
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>

 

 

[attachment "URI Construction.doc" deleted by Mike Edwards/UK/IBM]

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Issue_16_URI Construction_Proposal_02.doc