Re: Latest version of glossary

dawn wrote:
> entity: a thing of interest
>
> 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)

I agree with Alexandr that this is currently far too general. This is an incredibly tough term to define (I'm not even completely convinced that the entity/relationship split is actually a useful one, and it is not preferable to model everything as relationships). However if forced I would probably refer to however the term "entity" is defined in E-R modelling.

> 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]

Another incredibly tough term as it has so many different uses - multidimensional databases/OLAP for instance.

> 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

This first line of this requires iteration imo - a table in an SQL-DBMS is not modelled as a mathematical relation (only information is modelled). Rather tables are a conventional visualization (I think you convinced me that representation is an incorrect word) for those underlying relations.

> 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).

When one talks about 2-dimensions and arrays in respect to RM, one is talking about the visualization, not the underlying model. I believe that this could be a useful distinction, and probably the root of most miscommunication on the matter.

all best, Jim Received on Fri Feb 24 2006 - 16:59:26 CET