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Hi Folks,
Michael Kay wrote:
Obviously if two things are completely unrelated
then it's wise to choose different names. But usually
the question arises when they're a bit different,
but not completely different. Discovering useful
abstractions, and giving the abstractions names,
is a vital part of data modelling.
Let's take a real use case.
I am working on an XML model of aircraft flights. When planning a flight, a navigator draws a series of legs that the aircraft is to fly. For each leg, the navigator specifies constraints on the aircraft's altitude: the aircraft must be at a certain altitude, at-or-above a certain altitude, or at-or-below a certain altitude. Here is an XML representation of a leg:
<leg>
<altitude>
<at-or-above>
<altitude>29000</altitude>
</at-or-above>
</altitude>
</leg>
Read as: on this leg of the flight, the aircraft should be at-or-above 29,000 feet.
Notice that the XML has two <altitude> elements with different types -- one has a complexType, the other has a simpleType.
Recalling what Michael Kay said:
... if two things are completely unrelated ...
In this case I don't think the two <altitude> elements are completely unrelated.
... usually the question arises when they're a bit different, but not completely different ...
I think this is the case. The two <altitude> elements are different but not completely different.
The outer <altitude> element says,
The aircraft's altitude must satisfy
the constraint specified (in the
element's content).
The inner <altitude> element says,
Here is an altitude.
Do you agree that the two <altitude> elements are different but not completely different?
Again, recalling what Michael Kay said:
... Discovering useful abstractions, and giving the abstractions names, is a vital part of data modelling.
I think there are two abstractions: (1) Constraints on an altitude, and (2) a specific altitude.
Does this mean an element that implements one abstraction should have a different name than an element that implements another abstraction?
Question: Are you okay with the two <altitude> elements? Or should they have different names?
/Roger
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