2003N 2 1ϊ | "CLASS" VS. "SET" | BACK >> Ϊ |

CLASS VS. SET @We have two kinds of description (words) for denoting a data-cluster: a "class" and a "set." @A "class" is a "category" to group any set of persons or things together: let a class of "customer" be expressed as a data-cluster (stored) in a clothing (apparel) store, and the store has trinomial data of customers such as "man", "woman" and "corporate body"--they are the pairwise disjoint union of "customer"--, then an "individual" customer is a "class" to put together the set of "man" and the set of "woman", and likewise a "customer" is a higher class for both an "individual" and "institutional" customers. @A decomposition of "customer" into classes--"man", "woman" and "corporate body"--is called "partition" of "customer." Note: 1. Trinomial (three kinds of) data in sets:
(1) "man"@oMasami S., Wittgenstein L.,...p 2. Then we have a hierarchical data structure as noted below:
@customer
@individual customer
@A set is mathematically a data-cluster of objects, and the objects in a set are called its "members" or "elements." If "a" is an element of the set A, we say "'a' belongs to A" and denote it as noted below: @A set is, from the view point of "entity-relationship" model, equivalent to an entity.
@If every element of a set A is an element of a set B, that is if a Έ A then a Έ B, A is called a "subset" of B. A is contained in B, or B contains A, we write A Ό B or B ½ A. @As we can see, a "class" and a "set" is the two sides of the same coin--to be exact, they make a difference in the mathematical definition, but I should not worry about it here because it may be noninformation for the topic that we are talking about today. @ |

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