Physical quantities of real-world systems are described using scientific systems of units and dimensions. SysML1.0 extends the UML Property system to include physical values of quantities measured or stated relative to a chosen Unit, as well as industrial quantities. You can define custom ValueTypes (which may be used to type value properties in SysML).
There are two main uses of ValueTypes (which are illustrated in the following pages of this trail):
- To indicate and assign a specific Unit (with a Dimension) to a value property that represents a named quantity. The value of the quantity is then stated (or measured) relative to that Unit (see the example default value statements). The ValueType is usually named after the symbol of it's fixed Unit. The examples following have been denoted «unit-like» for illustration only.
- To define a "kind of quantity" that is not bound to a specific block. The ValueType is named to indicate the kind of quantity (not the Unit chosen). Changes to the chosen Unit will propagate throughout the system, so special care must be taken with statement of values and defaults ! The examples following have been denoted «quantity kind» for illustration only.
You may also define custom "industrial" Units and Dimensions for use by a custom ValueType.
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