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Re: Bolt-in Type Systems (RE: Relax NG and WebServic

• To: Dare Obasanjo <dareo@m...>
• Subject: Re: Bolt-in Type Systems (RE: Relax NG and WebServices (formerly Joining the church))
• From: James Clark <jjc@j...>
• Date: Sat, 12 Jul 2003 09:35:21 +0700
• Cc: "Bullard, Claude L \(Len\)" <clbullar@i...>, xml-dev@l...
• In-reply-to: <830178CE7378FC40BC6F1DDADCFDD1D1173AD4@R...>
• References: <830178CE7378FC40BC6F1DDADCFDD1D1173AD4@R...>
• User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2.1) Gecko/20030225

> 2.) A RELAX NG can dynamically learn how to validate a type library by
> dereferencing the namespace URI. I've heard there are Java interfaces
 > type library authors can implement so arbitrary RELAX NG validators can
 > support them. In this case there should be no problem as long as the 
dataype
 > library is discoverable and implements the correct interfaces.

It doesn't actually dereference the namespace URI in the sense of 
retrieving it. The way it works is:

- There's an (unofficial) standard API that provides an interface 
org.relaxng.datatype.DatatypeLibraryFactory; this has a method 
createDatatypeLibrary(x) that says "give me an implementation of the 
datatypeLibrary with URI x", which may succeed or fail.

- An implementation must provide a class that implements this interface. 
Let's suppose it's com.example.MyDatatypeLibraryFactory. The class files 
must be collected into a jar file and the jar file must also contain a 
text file META-INF/services/org.relaxng.datatype.DatatypeLibraryFactory 
which contains a single line "com.example.MyDatatypeLibraryFactory".

- Users must put the jar files for the datatype libraries they want to 
use on their classpath.

- When a validator encounters a schema that uses datatype library with 
URI X, it reads the files on its classpath called 
META-INF/services/org.relaxng.datatype.DatatypeLibraryFactory to 
discover the names of the implementing classes. It then instantiates 
each in turn calling its createDatatypeLibrary method until it finds one 
that can provide an implementation of the required datatype library.

This is a pretty standard pattern in the Java world. How would you do 
this sort of thing in .NET?

It doesn't support automatic downloading of datatype library 
implementations. I guess you do this by allowing the namespace URI to 
point to an RDDL document that somehow identifies the JAR file providing 
the implementation, download that and then run it in a sandbox. As far 
as I know, no implementations yet support this sort of thing.

James

• References:
  • RE: Bolt-in Type Systems (RE: Relax NG and Web Services (formerly Joining the church))
    • From: "Dare Obasanjo" <dareo@m...>

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