Regex SPARQL filter

Ontop supports the regex SPARQL filter by translating into similar filter expressions in sql. As regular expression filtering is not part of standard SQL, the use of the regex filter in SPARQL expressions therefore depends on the underlying database. (Note that the LIKE filter, which is standard in SQL, only supports a limited form of pattern mathing, where % and _ are wildcards.). Most notably, for DB2 and MS SQLServer we have not found a proper translation, and the regex filter will not work, except for matching single words.