Re: Latest version of glossary

dawn schrieb:
> I tried to find the latest draft of the cdt glossary, but wasn't sure
> if I found the most recent one, so mAsterdam or anyone -- could you
> repost the glossary so we can perhaps add in some terms to help with
> some of these discussions? We could maybe add dimension, entity, flat,
> and a few others.
>
> For example (just off the top of my head -- these should be improved
> upon):
>
> entity: a thing of interest

Although it is an official definition it has the following problems:

- it is too general and hence useless
- it is equivalent to the term "thing", which is used to refer to anything
- entity != dimension, entity != attribute, entity != reference

So entity is much more concrete term than simply a thing of interest. I would define it as follows:

entity is a thing of interest which has properties, that is, can be characterized by one or more other (primitive or non-primitive) entities, and has an associated identifier.

In other words, without an identifier a thing is NOT an entity. Without properties it is also NOT an entity.

I do not insist on this definition of course but I simply think that having too general definitions is not very useful. It will be simply misleading in discussions.

> Note: this term is often used when doing conceptual data modeling.
> When it is used with a particular product, technique, or technology,
> such as XML, refer to the use of the term within that "namespace" using
> an adjective, such as "XML entity" to distinquish it from the more
> generic use of the term.
>
> (we could possibly add in strong and weak entity)
>
> dimension:
> 1) A relation R is of dimension n if each tuple in R is an n-tuple
> 2) An n-dimensional data structure, S, is one where each element of S
> can be uniquely addressed as S[i1][i2]...[in]

The second requirement is not necessary in general and to define dimension in particular. How tuples are accessed is a separate issue that has nothing to do with the dimensionality. Uniqueness is a property of the representation mechanism - it is not a dimensionality issue. In other words, I find it very important to separate these two concerns: how dimensions are defined and how tuples are represented/accessed.

Another note. You defined the term "dimensionality" rather than "dimension". What is one separate dimension has to be defined separately.

> Note: Because a table in a SQL-DBMS can be modeled as a mathematical
> relation where the dimension is as in 1) above, and can also be
> manipulated using a general purpose programming language with the
> dimension using 2) above being equal to 2, there can be confusion when
> using this term. In this forum, use definition 1) freely and try to
> either avoid 2) or be very clear, such as "2D array," when employing
> def 2).
>
> flat: an object which by any definition could be considered as 2
> dimensional might informally be called flat.

I would give the following short definition:

flat = the absence of hierarchy (multiple levels of details)

> Note: any use of the term flat tends to be seen as inflammatory by
> someone, so take care to use it only when intending to inflame ;-)
>
> Cheers! --dawn

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