This may be a trivially simple question, but for some reason I can't get it to work or find the basic information on how to do it

I have an xml document and an xml schema file and I'd like to add a reference to the schema file in the xml document

In the root element of my xml document, I have the following:

<TXLife Version="2.16.00" xmlns="" schemaLocation="CITS_PendingExtractSchema.xsd">

The namespace is correct and the schema file is in the same directory as the xml file, but the file isn't being validated against the schema.

What is it that I'm doing wrong here?