Referencing External Schemas

You can use one of three schema components to reference external schemas:

import. You use an import to add multiple schemas with different target namespaces to your XML schema file. See Adding an import Component to an XML Schema File.
include. You use an include to add multiple schemas with the same target namespace to your XML schema file. See Adding an include Component to an XML Schema File.
redefine. You use a redefine to redefine simple and complex types, groups, and attribute groups from an external schema. See Adding a redefine Component to an XML Schema File.

If you added import or include statements using the Source view, or if you copied files with URL references into your project, the referenced schema may only be accessible through a URL. In this case, your project may not contain the true closure of all the documents. When the schemas are referenced, the IDE will perform the same logic that is used when retrieving XML resources using the External XML Schema Document wizard and transparently fetch the documents and store them in a non-version controlled area. This may cause a delay the first time these documents are accessed on your machine, because the referenced documents are not local. Subsequent accesses will be faster. If the URL points to an Internet resource, you may need to set up the correct proxy information in the IDE to ensure that the retriever process completes successfully (Tools > Options > General > Proxy).

See Also: Retrieving XML Resources; XML Schema Tasks; About XML Schema Tools