Background
Units Markup Language (UnitsML) is being developed for encoding scientific units of measure in XML. This UnitsML language is expected to be the first part of a project that is composed of three components: an XML schema (UnitsML), a database containing detailed information on SI (International System of Units) and non-SI scientific units of measure, and tools to facilitate the incorporation of UnitsML into other markup languages. The development and deployment of a markup language for units will allow for the unambiguous storage, exchange, and processing of numeric data, thus facilitating the collaboration and sharing of information over the Internet. It is anticipated that UnitsML markup will be used by the developers of other markup languages to address the needs of specific communities (e.g. mathematics, chemistry, materials science, etc.). Use of UnitsML in other markup languages will reduce duplication of effort and improve compatibility among specifications that represent numerical data.
The XML schema under development for UnitsML allows for the ability to represent scientific units of measure in XML and will be used for validating XML documents that use UnitsML. Development of this schema has initially taken place at NIST, but completion of the development process should include input from the international scientific and engineering community. This work may be accomplished through the creation of an OASIS Working Group to address any needed changes in the schema and publish a final recommendation.
The UnitsML schema is not intended to be a standalone schema, but rather to be used in combination with other specific schemas through the use of namespaces. SI units can be represented through the use of base units (e.g., meter, second), special derived units (e.g., joule, volt), and any combination of these units with appropriate prefixes and exponential powers (e.g., mm o s-2). In addition, commonly used derived SI units (e.g., square meter, meter per second) and non-SI units (e.g., minute, ångström, and inch) will be explicitly supported for reference within XML documents.
Proponents of UnitsML may develop one or more databases to contain detailed units and dimensionality information for an extensive number of SI units and common, non-SI units available for access by users of UnitsML. A database resource of this type would facilitate wide use of the markup language by including information needed to reference units in an XML document, specifically including unique identifiers, and also could include various unit symbols, language-specific unit names, and representations in terms of other units (including conversion factors). In addition to scientific units, such a database may include information about quantities - the measurable, countable, or comparable properties or aspects of a thing, e.g., length.
