Errata/E18

At present it is unclear whether the mentioned constraining facets can be added to OWL 2 DL without jeopardising decidability. To understand why this is so, note that OWL 2 DL allows for existential quantification over datatype values, which essentially means that, unlike a conventional XML Schema processor, an OWL 2 DL reasoner may need to solve constraints over an infinite domain. The computational properties of such tasks fir XML literals are currently not sufficiently understood, which is why constraining facets for XML literals were not included into the OWL 2 specification.