I have created an xml like below
Logon
23424
Just close your xsd file:
</xsd:schema>
I try it now, and for me this works.
dom specially gives two functions to validate with schema. One is to give file path
$doc = new DOMDocument();
$doc->load('PATH TO XML');
$is_valid_xml = $doc->schemaValidate('PATH TO XSD');
or else you could use
$is_valid_xml = $doc->schemaValidateSource($source)
This source should be a string containing the schema. It seems that you are using schemaValidateSource function other than schemaValidate. (Once I was stuck in the same place) cheers