Yup.. the nskf: represents a namespace alias. You should find more info as to what it actually is in the header of the schema file.

<xs:schema xmlns:nskf="http://SomeUri.com">

<xs:import namespace="http://SomeUri.com" schemalocation="some XSD filename.xsd"/>

etc....

</xs:schema>

This is telling you that a bunch of types are defined in a separate XSD file ("some XSD filename.xsd"). Anywhere in this local schame that uses that nskf: alias is essentially pointing you to go find the definition in the OTHER file.

note: it's an alias so the actual nskf is purely arbitrary (probably means something to whoever put the file together).