Schema for obix contracts

Hi,

    

    regarding the previous discussion on specifying a schema for the
    oBIX contracts I just want to double check if I understood the
    problem. 

    We have now the standard library with the standard obix contract
    definitions, expressed by example objects and here we want to have a
    machine-interpretable definition that can be checked by standard XML
    tools, right?

    

    I think with XML schema this is not possible since it describes the
    generic oBIX object model and the contracts are the same as any
    other oBIX object. Any constraints on them can be just represented
    by having an according definition for human readers in the standard.

    

    It would be desirable to have a formal description that can be used
    to verify automatically if an oBIX object adheres to a certain
    contract. 

    

    I think we have two options:

    -) Schematron or something similar or

    -) describing the oBIX meta model using MOF, which allows to define
    constraints on models (e.g. contracts) based on OCL

    

    Schematron is a rule-based validation language for making assertions
    about the presence or absence of patterns in XML trees. It is a
    structural schema language expressed in XML using a small number of
    elements and XPath. (http://en.wikipedia.org/wiki/Schematron)

    

    Using MOF to define the oBIX meta-model (the object model) which is
    currently expressed using the core schema would be a nice step
    towards a model-driven engineering approach. The different models
    could then be serialized using XMI, which would mean that contracts
    can be expressed based on XMI instead of plain XML example objects
    and then OCL could be used to express contraints. 

    (http://en.wikipedia.org/wiki/Meta-Object_Facility)

    

    However, I am not really aware of how much industry support such
    technologies have and how mature they are.

    

    Personally, I would prefer the MOF option since it seams to be more
    mature and opens the door to a variety of features such model driven
    engineering and code generation and maybe a standardized way to
    exchange oBIX contracts automatically using XMI.

    

    Just my thoughts on the topic. But keep in mind, the complexity of
    such technologies and standards should not be underestimated, since
    I think one of the strengths of oBIX is its simplicity.

    

    Best regards,

    Markus