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Tim Ferguson wrote:
I just cannot imagine the business need that requires doctors and their patients to be considered the same entities snip Thanks Tim, You post neatly puts forward the case point I was trying to make but you put it much better than I ever could. Jamie. -- |
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Mike Sherrill wrote: If you can't understand "Every doctor is a person, and every person has zero or more mailing addresses", the odds you'll understand DDL are slim. Try me. Jamie. -- |
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On Wed, 16 Feb 2005 09:55:58 -0800, Tim Ferguson
wrote: Mike Sherrill wrote in news At the conceptual level (that is, in the real world), a doctor and a patient are both persons; they both have zero or more mailing addresses; their mailing address are drawn from the same domain; and their mailing addresses have the same semantics (that is, they mean the same thing). The thing that has bothered me about this thread is that it seems to lack any basis in the real world. That's funny. I'm pretty sure that I've been talking *only* about the real world, and not about tables and databases and DDL. I just cannot imagine the business need that requires doctors and their patients to be considered the same entities. In general, I find it pretty easy to imagine things. In this specific case, it was easy for me, because I already knew that doctors and patients were people. And this particular paragraph sums up why it's wrong: A doctor has a clinic slots and qualifications and hire dates and CPD requirements and appraisal needs; A patient has diagnoses and treatment plans and heights and weights dietary preferences and religions; What they have in common is trivial. I think the problem is that, while you're quite good at identifying how doctors and patients are different, you're ignoring how they're alike. Doctors and patients have, literally, hundreds of things in common. Doctors have names; patients have names. Doctors have mailing addresses, patients have mailing addresses. Doctors have phone numbers; patients have phone numbers. And doctors can be patients; patients can be doctors. Doctors and patients have these things in common because doctors are people, and patients are people. People have names; people have mailing addresses; people have phone numbers. Some people are doctors by profession. Some people see a doctor for treatment. The names are different -- my mum, in common with many women, continued to use her maiden name at work, and used her married name for everything else, including when she was receiving care as a patient. Please don't tell me you are suggesting a one-to-many relationship for last names too! Every doctor has a name. Every patient has a name. (And every patient has a doctor, too, but not every doctor sees patients.) I'm not sure what you mean when you say "the names are different". If a person uses more than one name, and that's important to you, then model it. In the US, we usually call them either aliases or akas (for "also know as"). How you implement them depends on the conceptual model. I've worked on legal systems that used two different conceptual models. But I don't think they're relevant to this topic. The mailing addresses are not drawn from the same domain: A simple test is to try to mail something to a mailing address. Does the post office try to deliver it? If they do, the mailing address is in the domain of mailing addresses. cough professional addresses have DepartmentName and JobTitle and ExtensionNumber and PagerNumber, while home addresses have streets and cities. Can I send mail to professional addresses and to home addresses? I'm pretty sure I can. I agree that DB design is about semantics -- but frankly ProfessionalAddresses and HomeAddresses are completely different things, in any sensible kind of business need analysis. Yes, but that has nothing to do with mailing addresses, which are yet another thing. And while we're here, "professional addresses" and "home addresses" are *not* completely different things. I'm pretty sure I can send mail through the USPS to either a home address or a professional address, and I don't have to know which is a home address and which is a professional address to do that. It's childish over- enthusiasm to force them into a complex supertype-subtype arrangement when it's unlikely to bring any benefit to the system except showing what big cojones the designer has. KISS! Who said anything about supertypes? -- Mike Sherrill Information Management Systems |
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