(wahoo, my first attempt at blogging!)

mini “dictionary” for blog:
attribute - word used to describe a measurement for the Ecological Metadata Language. ex. temperature and chlorophyll-a are attributes (disclaimer: future naming conventions may change the way ‘temperature’ and ‘chlorophyll-a’ are written/displayed)
unit - a measurement standard used by EML to describe attribute. ex. the attribute ‘depth’ might have units of ‘meters’

________ - word used to represent the attribute-unit pair

________ - word used to describe the type of measurement (SI page uses ‘quanitity’)

The SI standard (as maintained by the international BIPM) defines a limited number of units and the types of measurements they describe. In EML, these measurement quantities are called ‘unitType’s. The unitTypes are the links between the units and the attributes.

Example: Temperature is a unitType as well as an EML attribute, the three units that describe this quanitity are Celsius, Kelvin and Fahrenheit. Length is a unitType with many describing units, including meter, foot, fathom, etc. Many attributes are quantities of length, including swell height, depth, and distance. All length attributes will be measured with one of the units under the unitType length.

The parentSI is the organization-prescribed main unit for each unitType. All units of each unitType must be mathematically related to the parentSI unit, and thus indirectly related to all other units of the same type.

Example: The three units under unitType temperature are Celsius, Kelvin and Fahrenheit, the parentSI unit is Kelvin, so the other two are defined by their mathematical relation to Kelvin. The parentSI unit of length is the meter, all other units of unitType length are defined by their relationship to the meter.

The reason for the parentSI units is a fundamental one: With physical standards behind each parentSI unit, thus measurements are able to be definitively reproduced, and that reproducability is the key to the scientific method. There is a physical object that defines a meter and that single object is what is used to create instruments of measurement. Similarly, there is a weight kept in a secure place that is THE kilogram. Since these physical standards are confined to the limited set of units, all other units must inherently relate back to the physically defined, hence using the parentSI as a means of conversion rather than another more indirect method.

SO, to define a unit, we need: unitName, unitType, and a multiplier or constant to SI. Abbereviations and descriptions also come in handy on a user level though are not necessary to the definition/conversion process.