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   Loosely Typed Extensible Schemas

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  • To: <xml-dev@lists.xml.org>
  • Subject: Loosely Typed Extensible Schemas
  • From: "Brian Frank" <bfrank@tridium.com>
  • Date: Mon, 2 May 2005 09:50:34 -0400
  • Thread-index: AcVPHen46tkTaxrtS7yIgvpjPI8mkA==
  • Thread-topic: Loosely Typed Extensible Schemas

Data Model
We have a abstract data model defined as a tree of objects. 
  - there are fixed number of primitive object types such as bool, int, or str
  - any object can contain any other objects
  - sometimes this tree structure is predefined
  - other times this tree structure is highly dynamic
Problem Statement
Ideally we would like to create a simple XML syntax for this data model where:
  - a small simple XML Schema can describe any tree of objects
  - larger XML Schemas which could be used to describe predefined trees of objects
    so that standard tools could be used to generate code stubs, etc
  - but either of the above the Schemas would provide a unified XML syntax
  - this XML will be used for REST and in SOAP/WSDL web services
Current Syntax
Our current schema produces XML which looks like this:
<obj name="WeatherReport">
   <real name="temperature" val="75.0" units="fahrenheit"/>
   <real name="humidity" val="53" units="percent"/>
   <bool name="sundown" val="true"/>
This is a nice simple schema where the content is completely self defining.  However it doesn't play
real nice with XML Schema tools since if you want a "getTemperature()" method, "temperature"
really needs to be the element name. 
Ideal Syntax
That leads to us to syntax which looks something like this:
<obj name="WeatherReport">
   <temperature real="75.0" units="fahrenheit"/>
   <humidity real="53" units="percent"/>
   <sundown bool="true"/>
But we have have great trouble arriving at a XML Schema design that would let us solve our problem
statement - we know ahead of time that WeatherReport has a temperature, but we don't know about
humidity and sundown (however we do know they all conform to a limited number of object types).
Is this possible?  What is the preferred design which plays well with XML Schema tools?


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