It is common for Thing Characteristics to be simply entered and stored. Sometimes, however, it is useful to be able to describe a characteristic that is derived from others. The mechanism for doing this is the Thing Derivation Element, shown in Figure 9-8. Here, each Thing Derivation Element is the fact that a particular Thing Characteristic is calculated from either another Thing Characteristic, a System Variable (typically system date), or a Constant.

Figure 9-8: Thing Characteristic Derivations

Where appropriate, as described in each of the detailed chapters, the Formula for the derivation is shown as an attribute ...

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