Re: [wsrp] ExtensionDescription

[Subbu Allamaraju <subbu@bea.com>]

I don't see how this approach can be used to a broader range of use 
cases. For any of these descriptions to make sense to the other party, 
there needs to be a corresponding entry with in the protocol (similar to 
   customUserProfileItems). This constraint also leaves out consumer 
side extensions (other than those can be expressed at registration time).

It would be best to limit this discussion to the current use cases.

Subbu


Rich Thompson wrote:
> 
> As part of considering more fully describing those custom user profile 
> items which augment the spec-defined user profile structures, I was 
> asked to develop a broader proposal that enables describing extensions 
> more generally.
> 
> */The proposal:/*
> *_1. Add a type for describing an extension:_*
> 
> *ExtensionDescription Type*
> 
> An extension MAY be described using the following structure. This 
> provides an optional means for the Producer and Consumer to exchange 
> metadata concerning items which could appear within an extensions 
> element of WSRP-defined messages:
> 
>  ExtensionDescription
>         [R] QName                name
>         [R] QName                type
>         [R] LocalizedString <\l_LocalizedString_Type>        description
>         [O] string         <\l_LocalizedString_Type_1>        locations[]
>         [O] Extension <\l_RegistrationContext>                extensions[]
> 
> Members:
> 
> name: Name of the extension being described, MUST have a non-zero 
> length. This name will appear in any runtime instance of the extension 
> as the fully qualified XML element name.
> 
> type: The type of the extension element, using a namespace qualified 
> name. The purpose for this information is to enable the receiving party 
> to prepare an appropriate deserializer.
> 
> description: A localized, human-readable description of the extension. 
> This description should include the semantics of the extension.
> 
> locations: An array of type names from the WSRP protocol where this 
> extension can be expected. If no locations are supplied, the extension 
> could appear on any WSRP defined type.
> 
> extensions: The extensions field MAY be used to extend this structure. 
> Extension elements MUST be from namespaces other than WSRP.
> 
> 
> *_2. Fields of type ExtensionDescription:_*
>  - replace ServiceDescription.customUserProfileItemDescriptions[] with 
> extensionDescriptions[]. Note the broadening of this field in its 
> description.
>  - add  [O] registrationData.extensionDescriptions[] with the field 
> description noting that the Consumer is supplying metadata about 
> extension it supplies on runtime messages.
> 
> 
> *_3. Discussion:_*
> There were questions raised about whether this philosophically broke 
> with either the XML concept of what it means to say the type of an 
> element is <any/> and/or the nature of extensions being outside the 
> protocol. I don't see either of these as an issue since what would be 
> transferred is metadata about elements from outside the protocol that 
> might appear in a runtime message. I could possibly see such metadata 
> being an issue if we required the described extension to always appear 
> (one might argue using XML Schema to extend the data structure would be 
> more appropriate), but the intent is to provide syntax (replicated in 
> the runtime message, but provided at discovery time to enable 
> preparation to handle the actual content, much as is done for 
> properties) *and* semantics of what might appear within the open content 
> of the extensions element. I don't think this violates even the spirit 
> of the XML specs.
> 
> As to the question about extensions being outside the spec; we have 
> several areas where extensibility is enabled (properties, modes, 
> windowStates, etc) and the protocol supports carrying metadata about 
> actual extensions so that the other party can discover and potentially 
> prepare to handle receiving the extension. I think this is just another 
> example of enabling a metadata exchange about items that go beyond what 
> the WSRP spec defines.
> 
> Rich 
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