MTConnect中 DataItem的子类描述

类（全部继承自DataItem）	描述
Event	an alias for DataItem
Sample	a data item with a floating point value
Message	an event with an additional native code. The text of the message is the value.
Condition	A condition handles the fact that a single condition can have multiple activations and needs to check when the are present and are cleared.
Active	The Activation is itself a data item. This is so it can be cleared and treated like other data items when generating text.
TimeSeries