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> So the color of one's hair is more of an attribute, but the hair itself, or any organ, such as heart, liver or lung, is an "element"
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> Any objections to this?
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I'm afraid so. Philosophers have devoted their lives to these questions, and even in the more mundane world of data modelling, many books have been written.
Since you've chosen the human body as your subject area, consider disease. Is a disease a thing, or an attribute of a thing? Is there an absolute answer to this question, or is it an engineering choice in how we model it?
It's an attribute of a thing because we are only concerned about a diseases behavior with respect to the infected entity.
