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CategoryObservation

 
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I have a question regarding the conceptual domain model at page 147 of "UML Distilled". I don't understand what the purpose of boolean attribute isPresent of class CategoryObservation is. I wonder if anybody could clarify.
Thanks,
Panagiotis.
 
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I'm not sure, but here's my best stab at it. There are two type of Observations: Measurements and Category Observations. Since Category Observations are not measured, it is simply noted whether is present or not. It is easy to think you just wouldn't observe it if it wasn't present, but this isn't always the case. Example: diagnosing a runner after a marathon. If had a Category Observation of sweating: isPresent = false then you might diagnose dehydration. This observation is notable for its *absence*.
It's a little hacked-up, but I hope this helps
Paul R
 
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I understand it as how the state of CategoryObservation is changed.Depending of its state, we decide, if the isPresent attribute is true or false.
Hope this helps,
Sandeep
 
Desai Sandeep
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Hi,
I am not convinced with the reasoning in my previous post.Am trying once again.Let me know your views on this.
The Figure 11-1 suggests CategoryObservation being associated with a Phenomenon.The Phenomenon specifies the valid Range for each Phenomenon.
In the example that Fowler mentions, the possible phenomenons are Blood Group O and Blood Group A.If the Nurse or the Doctor happens to makes a observation of say Blood Group Z then the CategoryObservation is not present or is incorrect,i.e., isPresent attribute is false.
Since the Phenomenons are being monitored by CategoryObservation, the isPresent attribute would best fit in the Category Observation concept.
Hope this makes sense.
Thanks,
Sandeep
[This message has been edited by Desai Sandeep (edited June 03, 2001).]
 
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