Re: Latest version of glossary

JOG wrote:

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.

I sortof do too, but can't see how to further restrict it. I have used
this one before:

entity: a person, place, thing, or event

Since person, place, and event are all things, this doesn't mean more
than "thing of interest" but gives some possible ideas to those
participating in conceptual modeling.

The "of interest" is only there because it has been defined that way
for long enough, so I figured it was worth keeping it for tradition, at
least. It doesn't add much and surely we can have somone pipe up with
an entity that is of interest to no one else and perhaps not of much
interest to person stating it -- just something that piped to mind.
So, it is an entity for a second on some ERD, perhaps, but isn't really
of interest at all, even if it spent some time as an entity.

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.

What would that definition be?

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.

Yes, I thought of adding a third specifically for that, but it seemed
to me that the reason it is called multidimensional is related to 2)
above, so I didn't add more. It would be fine to do so if it clarifies
something.

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).

Everything is modeled. I'm using the meaning of the term "model."
Whenever mathematics is applied to anything, it is as a model.

Rather tables are a conventional visualization (I think
you convinced me that representation is an incorrect word) for those
underlying relations.

I'm good with saying that tables are a conventional visualization, but
they are also used in an implementation of the RM. Relations are in
the mathematical model of this implementation, but we define tables to
a dbms. I would definitely say that we represent relations as tables.
"Tables" is a very overloaded term, however.

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.

Not just the visualization, but the representation in some data
structure, for example. So, it is a bit more confusing than that
because one person might be thinking about the underlying model of the
data structure they are using.

If you are using a language where you can represent a relation in an
associative array (while trying to do something in JavaScript, I found
that it has no such thing as a multidimensional associative array,
bummer), then you could write something like MyArray['12345','Name'] to
access the value for the Name of a person whose ID is 12345. This did
not require the ordering required of some other structures (such as XML
or Arrays). The relation represented by MyArray might have a dimension
of 15, and be handled by this 2D data structure (as confusing as it
might sound).

I believe
that this could be a useful distinction, and probably the root of most
miscommunication on the matter.

all best, Jim

I'm not sure this nails the distinction. I think it has more to do
with whether you are doing mathematics or writing code. Cheers! --dawn

.

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