Re: Latest version of glossary

"dawn" <dawnwolthuis_at_gmail.com> wrote:

>entity: a thing of interest

No one really seems to know. It's commonly claimed that an "entity" corresponds to some object or event. That's the common parlance. And so any number of tables/relations could describe this, entity. But in other contexts, entity could refer to something else. You suggested modelling. In ER a record/row might be called a "specific entity", the PK the "entity identifier", and so on.

>dimension:
>1) A relation R is of dimension n if each tuple in R is an n-tuple

More typically called, degree.

>2) An n-dimensional data structure, S, is one where each element of S
>can be uniquely addressed as S[i1][i2]...[in]

Depends. Is the "data structure" a table which roughly represents a "relation"? Is it a network or tree of tables? Might the dimension also mean the scale of measurement which is applied? Anyway.

If an n-tuple, again, it's generally referred to as, degree. The number of tuples/rows would be its cardinality.

If a named table, then it could trivially be addressed in order, if I understand your use of brackets, but only because the foreign keys create that fixed hierarchy.

>flat: an object which by any definition could be considered as 2
>dimensional might informally be called flat.

I would think so. It poses certain problems, which may not seem so great to those in the flat-land. But they could not be flat, at all, with less than two dimensions.

>Note: any use of the term flat tends to be seen as inflammatory by
>someone

It's a lot for a flatlander to consider redesigning his own scheme and place in it if he is given the option of a third dimension. It's a lot of work, at the least. Received on Fri Feb 24 2006 - 02:56:56 CET