The Schema Registration and Schema Location Hint Thread

Question

The purpose of this thread is to two fold. The first is to address issues related to the process of registering an XML Schema with Oracle XML DB. The second is to explain how Oracle XML DB determines whether or not a particular XML document is associated with a particular XML Schema.
An XML Schema decribes a class of XML. An XML document that is associated with a particular XML Schema is considered to be an instance of that class, and is often referred to as an instance document.

Answer 1

The methodolgy used by XML DB to match instance documents to XML schemas is based on a mechansim defined by the W3C XML schema standard. The W3C standard uses the XMLSchema-instance namespace to add schema specific information to instance documents.
The XMLSchema-instance namespace defines two attibutes that can be used to identify which XML Schema a document is associated with. These attributes are the noNamespaceSchemaLocation attribute and the schemaLocation attribute.
The noNamespaceSchemaLocation attribute is used in conjunction with XML Schemas that do not include a targetNamespace declaration. The schemaLocation attribute is used in conjunction with XML Schemas that declare a targetNamespace
The noNamspaceSchemaLocation attribute is used to supply the Schema Location Hint of the XML schema the document is associated with. For XML DB to recognize that the document is a member of the class defined the XML schema the Schema Location Hint must be an exact for the schemaURL that was used tor register the XML schema with XML DB.
The schemaLocation attribute is used to supply a Schema Location Hint for each namespace used by the instance document. The attribute consists of a set of namespace location mappings. A namespace location mapping consists of a namespace and the Schema Location Hint for the XML Schema that declares that namespace.
An XML Document is considered to be instance of the XML schema if the Schema Location Hint matches the URL of a registered XML Schema that declares the namespace associated with the Schema Location Hint as it's targetNamespace.
For example
First, the instance document must declare the XMLSchema-instance namespace
eg
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"The XMLSchema-instance namespace is used to associated the XML document with an XML schema. It does by supplying a "Schema Location Hint" for the target XML schema. The Schema Location Hint is typically the authoritive location for the XML Schema. When using XML DB the Schema Location Hint must match the URL used to register the XML schema with XML DB when working with XML DB.
The manner is which the schema location hint is supplied depends on hether or not the xml schema contains a targetNamespace declaration
If a targetNamespace is defined then it the instance must include the schemaLocation attribute. The schemaLocation attribute must contain a mapping between the targetNamespace and the Schema Location Hint in the form "namespace schemaLocationHint".
If the XML schema declares a target namespace such as targetNamespace="http://www.opengis.net/examples/packet" and the Schema Location Hint is "gmlpacket.xsd" then you use the schemaLocation attribute. It will look like this.
xsi:schemaLocation="http://www.opengis.net/examples/packet gmlpacket.xsd"If the XML schema does not declare a target namespace then you the noNamespaceSchemaLocation attribute. It will look like this..
xsi:noNamespaceSchemaLocation="gmlpacket.xsd"