  Ontologies provide a formal description of concepts and their relationships
in a knowledge domain. The goal of ontology alignment is to identify
semantically matching concepts and relationships across independently developed
ontologies that purport to describe the same knowledge. In order to handle the
widest possible class of ontologies, many alignment algorithms rely on
terminological and structural meth- ods, but the often fuzzy nature of concepts
complicates the matching process. However, one area that should provide clear
matching solutions due to its mathematical nature, is units of measurement.
Several on- tologies for units of measurement are available, but there has been
no attempt to align them, notwithstanding the obvious importance for tech-
nical interoperability. We propose a general strategy to map these (and
similar) ontologies by introducing MathML to accurately capture the semantic
description of concepts specified therein. We provide mapping results for three
ontologies, and show that our approach improves on lexical comparisons.
