Uses MINUS to remove matches from a result based on the evaluation of two patterns.
Simple SPARQL Tutorial: Using FILTER, NOT EXISTS, MINUS Keywords
Tutorial showing how to modify a query to return instances of data where a specific property does not exist- the FILTER, NOT EXISTS, and MINUS [...]
SPARQL by Example
This is a very in-depth resource that covers nearly every aspect of SPARQL (both 1.0 and 1.1). Includes example queries (over many datasets), links to [...]