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# Ajutor:How can i relate my type to the correct SI unit?

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Question
Question:=How can i relate my type to the correct SI unit?
Description:=Use the "corresponds to SI" property.

Units of measurement can be specified for data types. For instance, the `Type:Velocity` can be could have the unit km/h. SMW provides a special attribute for this task. The article for `Type:Velocity` should contain the following line: [[corresponds to:=1 km/h]] For now, "km/h" is only an arbitrary string without a meaning. A reasoning system like Aura has to understand these units, so the unit has to be specified as SI unit:

[[corresponds to SI := 0.27777778 m/s]]

Such a definition must appear at most once on a page.

An SI definition consists of a conversion factor (with respect to the primary unit - the one with `corresponds to = 1...`) and the unit expression.

The unit expression is a division of products of SI base units with an optional exponent. There must be at least the enumerator and an optional denominator. Products are written with * or blank. Exponents are introduced by ^, followed by a positive or negative integer.

The SI base units are:

• `m` - Meter
• `kg` - kilograms
• `s` - Second
• `A` - Ampere
• `K` - Kelvin
• `mol` - Mole
• `cd` - Candela

Examples:

• `m` - Meter
• `m^2 = m*m = m m` - Square meter
• `m/s` - meters per second
• `m/s^2 = m*s^-2 = m s^-2` - Acceleration
• `kg*m/s^2 = kg m /s^2 = kg m s^-2` - Newton
• `1/s = s^-1` - Hertz

To test the parser, create a page for a new type e.g. <code>Type:Velocity</code>. The following text is semantical nonsense but contains several test cases for the parser:

```

[[corresponds to:=1 m/s]]

[[corresponds to:=3.6 km/h]]

[[corresponds to SI:=1 m]]
[[corresponds to SI:=1 m/s]]
[[corresponds to SI:=1 1/s]]
[[corresponds to SI:=1 m*m*m/s*s*s]]
[[corresponds to SI:=1 m*m*m^-1/s*s*s^-1]]
[[corresponds to SI:=1 s^-1]]
[[corresponds to SI:=1 s^-1/m^-1]]
[[corresponds to SI:=1 m^2/s^2]]
[[corresponds to SI:=1 m*kg/s^2]]
[[corresponds to SI:=1 m kg/s^2 A]]
[[corresponds to SI:=1 m*kg/s^2*A*cd]]

[[corresponds to SI:=1 m^0]]
[[corresponds to SI:=1 s/1]]
[[corresponds to SI:=1]]
[[corresponds to SI:=1meter/sec]]
[[corresponds to SI:= m/s]]
[[corresponds to SI:=1 M/S]]
[[corresponds to SI:=1 m//s]]
[[corresponds to SI:=1 m/m/s]]
[[corresponds to SI:=1 m**m/s**s]]
[[corresponds to SI:=1 m*m*m/m*m*m]]

```