XSD to XML and vice versa

I was looking for a quick and free tool that could convert XSD schema files to sample XML files and also generate a XSD file from a sample XML file. Commerical tools such as XML Spy and OxygenXML were powerful tools that provided these features, but I was looking for a free one.
First I checkout the open source Java IDEs.

• Netbeans had a beautiful editor to visualize and edit a XSD schema in a graphical tree structure. But unfortunately it did not have the ability to generate sample XML file or vice versa.
• Eclipse too had a visual editor and allowed visual editing of schema elements. It could generate a sample XML file from a XSD file, but had no option for the reverse; i.e. generating a schema file from a sample XML.
• VS 2008 SP1 had both the options - coversion between XML and XSD. For schema files, right click on a node in XSD Explorer view and select "Generate XML". For XML files, select "Tools -> Generate schema" to create the XSD file. Both these operations are very quick in Visual Studio.
• VS 2010 has extensive support for XML tooling. You have 3 different views for schema designing that should suffice for most complex schema definition.

Besides these free tools, there are other command line tools that can be used. For e.g.

XSD.exe tool can be schema to XML and vice versa transformation.

There was another .NET tool that I found on MSDN for generating XML documents from XSD.

Another cool Java desktop tool that supported these features was XMLSpear.

Ruminating over XML Schema concepts

In a recent discussion with my team members, I sensed a lot of confusion over basic concepts on XML Schemas and namespaces - especially over targetNamespace, DefaultNamespace, elements vs types, etc. Well first, lets get the fundamentals right.

A XML schema defines and declares types (complex and simple) and elements. All elements have a type. If the type has not been specified, it defaults to xsd:anyType. It's easy to understand this by drawing an anology between a class and an object. New elements can be created by referencing existing elements.

In a WSDL message description, a WSDL part may reference an element or a type. If the SOAP binding specifies style="document", then the WSDL part must reference an element. If the SOAP binding specifies style="rpc", then the WSDL part must reference a type.
Now coming to namespaces, users typically get confused over the difference between a targetNamespace and defaultNamespace. The 'targetNamespace' attribute is typically used in schema files to identify and select the namespace into which new elements that are defined are created in. It is the namespace an instance is going to use to access the types it declares. For e.g. An XML document may use this schema as the default schema. Default schema is defined simply by using 'xmlns=' without a prefix.
It is important to remember that XML schema is itself an XML document. Hence a schema can contain a namespace attribute and also a targetNamespace attribute. Typically they are the same.

Jotting down links where more explanation is given:
http://www.coderanch.com/
http://www.oracle.com/technology/