| 17 | 15 | Abstract: The Unified Code for Units of Measure (UCUM) provides human-friendly codes for all units of measures with precise semantics to facilitate unambiguous and computable communication between computer systems used in science, engineering and business world wide. UCUM is inspired by earlier standards (ISO2955-1983, ANSI X3.50-1986) which it expands and corrects (resolving various ambiguities). The semantics of units is based on the intuition applied by most physicists when computing with quantities and units (but chemists and medical people may have to enhance their intuition first). It represents the meaning of equivalence, commensurability, conversion, base and derived units, including special units which require arbitrary conversion functions (e.g., logarithm). UCUM’s formal semantics is defined algebraically, which leads to a very compact representation and efficient (constant time) reasoning. However, it is quite different from symbolic knowledge representation methods that many ontologistsare familiar with. While symbolic models in UML are useful for discussing the design of the UCUM implementation, they do not replace the elegance and efficiency of the algebraic definition. This supports the conclusion that units of measure are essentially quantitative phenomena that require a focus on quantitative methods for their definition. UCUM does not, however, attempt to define base units in any formal way but uses those as primitives and refers to appropriate standards bodies (ISO, BIPM) for their definitions. UCUM has been adopted by many standards organization world wide in and outside of the medical domain. While the actual maintenance of the core code system is minimal, defining organization and governance are becoming more important. The key challenge in content is to deal with procedure defined (arbitrary) units that are common in biomedical sciences. |
