I'm attempting to answer the question, "Does any XML document described by A.xsd satisfy the constraints of B.xsd?" ...

Ouch! Well that told me :)

I have to say that the thought that crosses my mind is an old joke about the guy that answered the question:

How can I get to X^*, from here?

^*Avoiding racial sterotypes here!

And got the reply.

If I were you, I wouldn't be starting from here!

I happen to think that the benefits of XML have been way oversold, and I'm not even certain that I know what an .xsd is.

In any case, I wish you the very best of luck in your endevour.

For example, this is a fragment I found:

  <xsd:complexType name="Items">
    <xsd:sequence>
      <xsd:element name="item" minOccurs="0" maxOccurs="unbounded">
        <xsd:complexType>
          <xsd:sequence>
            <xsd:element name="productName" type="xsd:string"/>
            <xsd:element name="quantity">
              <xsd:simpleType>
                <xsd:restriction base="xsd:positiveInteger">
                  <xsd:maxExclusive value="100"/>
                </xsd:restriction>
              </xsd:simpleType>
            </xsd:element>
            <xsd:element name="USPrice"  type="xsd:decimal"/>
            <xsd:element ref="comment"   minOccurs="0"/>
            <xsd:element name="shipDate" type="xsd:date" minOccurs="0"
+/>
          </xsd:sequence>
          <xsd:attribute name="partNum" type="SKU" use="required"/>
        </xsd:complexType>
      </xsd:element>
    </xsd:sequence>
  </xsd:complexType>

  <!-- Stock Keeping Unit, a code for identifying products -->
  <xsd:simpleType name="SKU">
    <xsd:restriction base="xsd:string">
      <xsd:pattern value="\d{3}-[A-Z]{2}"/>
    </xsd:restriction>
  </xsd:simpleType>
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It does embed regular expressions here and there to define new data types (the definition of "SKU" for example). If those are all you are trying to validate, our suggestions should work. Otherwise, this is a much more difficult problem.

Update: I'm also having trouble seeing the utility of this proposed checker. Suppose I have two arbitrary web applications A and B, and both were kind enough to supply xsd schemas. Can I determine if they can interact meaniningfully? Not really. It's a matter of semantics, not just matching schemas. Say both define a "Price" field. How do I know one is not in dollars and the other in euros? I think that's why the usual practice is "pre-negotiated" schemas.

Update: I'm also having trouble seeing the utility of this proposed checker. Suppose I have two arbitrary web applications A and B, and both were kind enough to supply xsd schemas. Can I determine if they can interact meaniningfully? Not really. It's a matter of semantics, not just matching schemas.

I hope the OP answers this, because its been interesting so far. But for the calendaring application mentioned, why not create a simple schema and require conformance? It would need to be done per client with xslt (the glue language of xml!) or whatever. But without explicit agreement you are just guessing that elements from different schemas with similar names describe the same real-world objects. Sounds dangerous.

Um, stupid question time: Since it sounds like you are already using XML (or could), and already have an XSD (or two), why aren't you either:

• Changing the input and output programs to use the SAME .XSD. Then either end can validate the document against the XSD and assume that if it is valid it will work. Or,
• Using an XSLT to get from one format to the other. If you have XSD for both, then you should only have to build the XSL transform once, and just run it on the data as it goes through.

It just really sounds like you're making this too hard. Or I completely don't get it.

Footnote: For those wondering what XSLT is, it is an XML application that defines transformations that can be applied to XML documents. It can convert XML to XML, HTML, or just about anything else.