This document is intended for SEEK and Kepler developers.
It is a DRAFT DOCUMENT and does not reflect functionality as it
currently exists in Kepler or SEEK, or any other beliefs. Comments and feedback are appreciated.
This document serves as some notes on the ontology of measurement. The notion of measurement is very important (even fundamental) in ecology, as in other life sciences.
- Wikipedia on "Metrology". Some interesting sentences: "Measurement is the determination of the size or magnitue of something. Measuremnt is not limitted to physical quantities, but can extend to quantifying almost anything imaginable. Examples of measurement range from degrees of uncertainty to consumer confidence to the rate of increase in the fall in the price of a good or service. ... Established standard objects and events are used as units ... For example, the unit for length might be a well-known person's foot, and the length of a boat can be given as the number of times that person's foot would fit the length of the boat. ... A measurement is a comparison to a standard. -- William Shockley ... Metrology is the study of measurement. A metric is a standard for measurement. The quantification of phenomena through the process of measurement relies on the existence of an explicit or implicit metric, which is the standard to which the measure is referenced. If I say I am 5, I am indicating a measurement without supplying an applicable standard. I may mean I am 5 years old or I am 5 feet high, however the implicit metric is that I mean I am 5 years old."
- Wikipedia on "Physical Units". Some interesting sentences: "Units as Dimensions: Any value of a physical quantity is expressed as a comparison to a unit of that quantity. For example, the value of a physical quantity Q is written as the product of a unit [Q] and a numerical factor: Q = n * [Q] = n[Q]. The multiplication sign is usually left out, just as it is left out between variables in scientific notation of formulas. In formulas the unit [Q] can be treated as if it was a kind of physical dimension: see dimensional analysis for more on this treatment. A distinction should be made between units and standards. A unit is fixed by its definition, and is independent of physical conditions such as temperature. By contrast, a standard is a physical realization of a unit, and realizes that unit only under certain physical conditions. For example, the metre is a unit, while a metal bar is a standard. One metre is the same length regardless of temperature, but a metal bar will be one metre long only at a certain temperature. For most quantities a unit is absolutely necessary to communicate values of that physical quantity. For example, conveying to someone a particular length without using some sort of unit is impossible, because a length cannot be described without a reference used to make sense of the value given."
- Wikipedia on "Dimensionless Numbers". "In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters one's system of units of measurement, for example from English units to metric units. Such a number is typically defined as a product or ratio of quantities which do have units, in such a way that all units cancel. There are infinitely many dimensionless numbers. Some of those that are used most often have been given names, as in the following list of examples (in alphabetical order, indicating their field of use): Dispersion, Archimedes number, Biot number, Bodenstein number, Capillary number, ..."
- Wikipedia on "Quantity". "Quantity is a generic term used when referring to the measurement (count, amount) of a scalar, vector, number of items or to some other way of denominating the value of a collection or group of items. It is usually represented as a number (numeric value) of units together with the type of those units (if required) and a referent defining the nature of the collection. Both parts are required. Examples are: one apple, two apples, three apples, where the number is an integer so does not require a type; 1.76 litres (liters) of milk; 500 people"
Some important concepts we may want to capture and describe:
- Physical Quantity