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Subject: NEW ISSUE (v1.2): Remotable interface compatibility should not berestricted to a WSDL 1.1 mapping

Target: sca-assembly-1.2-spec-wd01.doc

Title: Remotable interface compatibility should not be restricted to a WSDL 1.1 mapping


The latest version of the Assembly specification (sca-assembly-1.1-spec-cd05), in section 6.2, defines interface compatibility in section 6.2.1, item #6 "for checking the compatibility of 2 remotable interfaces which are in different interface languages, both are mapped to WSDL 1.1 (if not already WSDL 1.1) and compatibility checking is done between the WSDL 1.1 mapped interfaces."

There are various reasons why this will fall over and not behave as expected.

False positives:
  • Some other interface kind may impose data type semantic restrictions which are not apparent in a WSDL 1.1 representation.  WSDL 1.1 uses XML Schema 1.0 types for its representation of data.  Unfortunately, there are limitations here, where XML Schema largely focuses on the syntactic representation, and not as much on the semantic values.  Some random examples:
    • all odd numbers/all even numbers
    • string validation via regular expressions, where some semantic is required on a portion of the string.  Example - credit card numbers
    • string contents - XML Schema "string" type allows for a subset of all possible characters.  This means that certain characters cannot be represented in XML Schema representations, and must be somehow mapped.
  • Object networks - representing a network of objects serialized to XML, certain objects should be serialized at most once, and then referenced.  Creating and enforcing the linking of representations is at best an imperfect alignment, as there are numerous ways that this can be accomplished, depending on the type of the object network.  Unfortunately, something conforming to the XML Schema requirements could easily not align on the semantic requirements, either in generating a request, or receiving a response.
False negatives:
  • Intrinsic to mapping to WSDL are choices about how that mapping might be done.  For example, implementations might map JMX to WSDL in myriad ways.  Forcing the consumer and provider to do so in a way that offers up a WSDL 1.1 mapping as part of the component type could lead to a declaration of "incompatible" even where the JMX interfaces are, in fact compatible (albeit, at runtime, the implementation of the JMX conduit must be shared)
  • Bad compromises - certain existing bindings (binding.jms) allow for possibility of sending Java Objects via JMS.  To not be able to call these bindings remotable is a mockery of the notion of "remote", however, forcing a mapping of a generic Java Object to some XML representation will have "binding" trade-offs.  Implementers will then have to invest time to "maximize compatibility", whereas if they simply used existing interfaces compatiblity would simply be there.
(Partial) Proposal:

Remoting compatibility should not be restricted to WSDL 1.1 mappings.  Interface type definitions ought to be allowed to at least define a compatible relationship with themselves.


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