Re: Entity vs. Table

> But everyone just uses the term "entity" to
> mean "entity set", and tuple, row, or instance to mean one instance
> (example) of that entity set.

If everyone (except a single person) uses the term "entity" for something, shouldn't the single person conform to what everyone is using ?

>
> But back to the difference between an entity and a table - Briefly(?):
> An entity is a thing of interest in the real world. A table is a
collection
> of rows and columns that contain data about the entity (set). An entity is
> used on an Entity Relationship Diagram (ERD) to explain the realtionships
> among the data. An EMPLOYEE works_for a DEPARTMENT (works_for is the
> relationship). A CUSTOMER purchases ITEMS. ITEMS make_up an ORDER.

What about things which are not real but get a 'real' meaning in the modelling world (sometimes only after a long time or several versions). (Things like groupings, relationships etc. which only evolved to 'real' things
because the computer forced the users into this 'kind' of model.).

Or what about things which are less real, but are percieved real by most people, for example a 'relationship', is this an object, an entity, or a relation.

The entity I have borrowed this book from that library. Or is it the registration
off that fact. Is a fact an entity ? Or an attribute and from who ?

What I am actually saying that in the actual world (even the one without computers)
it is difficult to define what is an entity and what is not. In a world with computers
this is even more difficult, because working methods adapt to the computers and
concepts which were first only part of an artificial world become part of the
real world.
(Things like internal unique numbers become external clientnumbers in the next version
and therefore an entity for the next generation of modelers)

just my 2 cents

ben brugman Received on Tue Jun 08 2004 - 17:11:10 CEST