# Glossary¶

## Dimension of a Physical Quantity Type¶

A physical quantity type such as *mass*, *length* or *area* is characterized by its dimension (for example, see https://en.wikipedia.org/wiki/Physical_quantity). It is possible to express the dimension of any physical quantity type using the dimensions of some base quantity types. The choice of the base quantity types is arbitrary to a certain extent. The base quantity types that underly the International System of Units are listed below.

Base Quantity Type |
Dimension Symbol |
---|---|

amount of substance |
N |

electric current |
I |

length |
L |

luminous intensity |
J |

mass |
M |

thermodynamic temperature |
Θ (Greek capital letter Theta) |

time |
T |

Using the symbols given in the table, the dimension of *length* is L, and the dimension of *area* is L∙L, or L^{2}.

## Unified Modeling Language¶

The Unified Modeling Language (UML) is a general-purpose modeling language for the *analysis, design, and implementation of software-based systems* [UML:1]. Within this specification, we use the notation [UML:x] to refer to section x of *OMG*^{®} *Unified Modeling Language*^{®} *(OMG UML*^{®}*), Version 2.5.1* (see https://www.omg.org/spec/UML/2.5.1).