What does mutually and non mutually mean?
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Hi, I'm reading a book on data models, there is a piece of text that reads as follows: The subtypes within an entity should represent a complete set of classifications (meaning that the sum of the subtypes covers the supertype in its entirety) and at the same time be mutually exclusive of each other. What does this mean? Examples will be much appreciated. Thanks Brendan
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Hi, I'm reading a book on data models, there is a piece of text that reads as follows: The subtypes within an entity should represent a complete set of classifications (meaning that the sum of the subtypes covers the supertype in its entirety) and at the same time be mutually exclusive of each other. What does this mean? Examples will be much appreciated. Thanks Brendan
Simple minded example. Suppose an order processing system has a payment method field. This would be the supertype - every order has to be paid. Now suppose we break it down by the method used to make the payment. We could have e.g. cash, cheque, debit card, credit card, money order, etc. We need to ensure that all the possible methods are covered (i.e. the set is complete). We also need to make sure that a payment can only fall in one method. So, e.g. electronic payment (EFT) would not be allowed because it could be debit or credit card. I.e. debit and credit are mutually exclusive it's either one or the other but it cannot be both. This assumes the system must distinguish between debit and credit card payments. If it does not need to do so it might be EFT is good enough.
Regards David R --------------------------------------------------------------- "Every program eventually becomes rococo, and then rubble." - Alan Perlis The only valid measurement of code quality: WTFs/minute.
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Simple minded example. Suppose an order processing system has a payment method field. This would be the supertype - every order has to be paid. Now suppose we break it down by the method used to make the payment. We could have e.g. cash, cheque, debit card, credit card, money order, etc. We need to ensure that all the possible methods are covered (i.e. the set is complete). We also need to make sure that a payment can only fall in one method. So, e.g. electronic payment (EFT) would not be allowed because it could be debit or credit card. I.e. debit and credit are mutually exclusive it's either one or the other but it cannot be both. This assumes the system must distinguish between debit and credit card payments. If it does not need to do so it might be EFT is good enough.
Regards David R --------------------------------------------------------------- "Every program eventually becomes rococo, and then rubble." - Alan Perlis The only valid measurement of code quality: WTFs/minute.
Thank you :)