referencing a schema fails

I'm embarrassed to be asking anything so basic.  New to schemas, I am
failing at the very first step:  validators don't seem to be aware that I
even HAVE a schema.  I must be declaring it incorrectly or in the wrong
element.  

I have two files, in the same directory on my hard drive.  My test file
begins this way:  

<?xml version="1.0" encoding="ISO-8859-1"?>
<reviews xmlns="http://www.w3schools.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="http://www.w3schools.com artml.xsd">
  <review author="John Haber" completed="2003-07-30">

and my artml.xsd file begins this way:  

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com" xmlns="http://www.w3schools.com"
elementFormDefault="qualified">
<xsd:element name="reviews">
  <xsd:complexType>
    <xsd:sequence maxOccurs="unbounded">
	  <xsd:element ref="review" />
	</xsd:sequence>
  </xsd:complexType>
</xsd:element>
<xsd:element name="review">

I'll spare you what comes next in each file, but I figured I better show
what I think defines a root element.  I'd be grateful for the help getting
me started, so I can really mess up in more serious ways.  

Thank you,
John Haber
jhaber@haberarts.com