|2002年11月 1日||RULES OF RELATIONSHIP-CREATION||BACK >> 目次|
● Rules of relationship-creation (with T-formed ERD)
There are two methods of relationship-creation:
The "binary" method is strongly recommended with T-formed ERD, and the "N-ary" are never used, because the "N-ary" methods never devise a process of "event-creation", it's just an operation of "join (among two and more tables)", i.e.,
As I mentioned above, 3 entities can create 6 possible combination showed below;
All the combination can give a different event.
If we may "join" the 3 entities, as in F(fabric, size, color), we can get, mathematics-wise, a "relation" but we cannot devise a process of "event-creation" with the result cross to our purpose (of semantic data-analysis).
When we form a combination between two entities, the identifier (of either entity) is replicated into another entity to show explicitly that they are related mutually.
customer: (customer-NO, customer-name,...)
(R) is the abbreviation of "Replicated" or "Re-used".
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