One-To-One Relationships

#41

David Cressey wrote:

Quote:

If a proposition concerning the real world is stated in plain English,
rather than some formal way, there are going to be some nouns in the plain
English. Those nouns are going to have referents. Those referents can be
called "entities". They can also be called "things" or "objects". Whatever
you call them, there will be objections.

But, as much as I appreciate your leaping in defense of entities:
that is subtly beside the point. This discussion is about whether
entities are useful, or make sense, as *language* constructs.
ER modeling says yes, classical logic and relational modeling say no.

--
Reinier

#42

Bob Badour wrote:

[...]

Quote:

He didn't like the figment argument? I thought it was careful and quite
clear. Perhaps, I should elaborate:

Entities are subjective and products more of applied psychology than
applied mathematics.

I'm sorry, but that is only because you choose to be stuck with a particular
brand of applied mathematics that happen to not include them, and you throw
a tantrum when it is argued that it would make perfect sense to do so.

No doubt you have actual, mathematically formalizable arguments as to
why entities don't fit in with this particular brand of applied mathematics,
and how it offers one or more superior alternatives to dealing with the
issue Chen pointed out. I'm eager to learn what they are.

(Tonight I want to post a detailed reply to your earlier posting
to explain why it didn't actually address Chen's issue, so let's go
from there.)

--
Reinier

#43

rpost wrote:

Quote:

Bob Badour wrote:

[...]

He didn't like the figment argument? I thought it was careful and quite
clear. Perhaps, I should elaborate:

Entities are subjective and products more of applied psychology than
applied mathematics.

I'm sorry, but that is only because you choose to be stuck with a particular
brand of applied mathematics that happen to not include them, and you throw
a tantrum when it is argued that it would make perfect sense to do so.

Tantrum? You are an idiot.

Quote:

No doubt you have actual, mathematically formalizable arguments as to
why entities don't fit in with this particular brand of applied mathematics,
and how it offers one or more superior alternatives to dealing with the
issue Chen pointed out. I'm eager to learn what they are.

Figments of your imagination are neither formal nor mathematics.

Quote:

(Tonight I want to post a detailed reply to your earlier posting
to explain why it didn't actually address Chen's issue, so let's go
from there.)

Sure. Maybe someone else will read it. Plonk.

#44

On Nov 30, 3:22 pm, rp... (AT) pcwin518 (DOT) campus.tue.nl (rpost) wrote:

Quote:

JOG wrote:

[...]

Such muddy thinking

Saying that doesn't help anyone. If my thinking is muddy
I want to know why. Thats why I'm here. Explain, post URLs, anything.

--
Reinier

I'm afraid I'm not here to teach you - there are thousands of posts on
cdt that you can mine to come to stronger conclusions. Feel free to
get stuck into them

I would say however that it is important for
you to note that: a logical model should not be bound to a single
conceptual model.

#45

On 29 nov, 23:16, JOG <j... (AT) cs (DOT) nott.ac.uk> wrote:

Quote:

On Nov 28, 8:43 pm, rp... (AT) pcwin518 (DOT) campus.tue.nl (rpost) wrote:

paul c wrote:

[...]

Regarding ER, here are some quotes from Codd's book (available for free
at acm.org). The sarcasm of the second one made me laugh.

The criticisms you quote may be amusing, and they have merit, but
they ultimately miss the point. The distinction between entities and
relationships: entities have identity (they can be referred to; attributes
can have entity-valued domains), while relationships do not (they are
completely identified by their, possibly entity-valued, attributes).

I realise that others have attempted to point out your mistakes, but I
just wanted to echo their sentiment.

How about providing some real arguments, in stead of just sentiments?
Haven't seen much of those here and I think Reinier deserves them.

Quote:

There is absolutely no difference
between an entity and a relationship. E/R modelling has /itself/
conceded this, translating relationships into "associative entities".

Ah, yes, and as we all know, if two concepts have overlap then they
are actually the same. *sigh* The distinction between entities /
relationships, domain objects / predicates is pretty well-established
in linguistics, philosophy and logic. First-order logic, you may have
heard of it, separates them even strictly. Are you now going to claim
that it is no good for reasoning?

-- Jan Hidders

#46

Do you pay taxes? Then you are an entity.
"Bob Badour" <bbadour (AT) pei (DOT) sympatico.ca> wrote

Quote:

David Cressey wrote:
"Bob Badour" <bbadour (AT) pei (DOT) sympatico.ca> wrote in message
news:474dd64a$0$5285$9a566e8b (AT) news (DOT) aliant.net...

rpost wrote:

paul c wrote:

[...]

Regarding ER, here are some quotes from Codd's book (available for free
at acm.org). The sarcasm of the second one made me laugh.

The criticisms you quote may be amusing, and they have merit, but
they ultimately miss the point. The distinction between entities and
relationships: entities have identity (they can be referred to;

attributes

can have entity-valued domains), while relationships do not (they are
completely identified by their, possibly entity-valued, attributes).

Except that relationships have identities too. The identity of the
relationship between an employer and an employee, for example, is a
contract. The relationship between a mother and a child, for example, is
the event of birth. etc.

[...]

3. Even if this distinction had been precisely defined, it would have

added

complexity without adding power. Whatever is conceived as entities,
and
whatever is conceived as relationships, are perceived and operated
upon in the relational model in just one common way: as relations.

This is the exact problem Chen identified. In the relational model
it is impossible to have entity-valued attributes, which, in practice,
we have a huge amount of.

Entities are figments of our imaginations.

You are an entity.

Am I? Or am I billions of cellular entities? Or am I part of a larger
community entity?

#47

"JOG" <jog (AT) cs (DOT) nott.ac.uk> wrote

Quote:

On Nov 30, 3:33 am, paul c <toledobythe... (AT) ooyah (DOT) ac> wrote:
JOG wrote:

...

Yup.

Okay, I think that makes you a natural-born implementor even though I
have no idea what you spend your other time at (besides enjoying
somebody else's company of course). I don't mean "implementor" as in
"don't tell me the problem as that will only slow me down solving it".

Just what is it that qualifies them to be entities? Free will? (I'd be
okay with that.) Or do they not need to qualify?

Anything that can be described as a noun is an entity in my book,
whether abstract or not. We must be able to describe them by their
attributes, and identify them by one attribute that is consistent over
the lifetime in the universe of discourse. That's my take.

Do you mean anything that can be described as a singular noun, or just any
old noun?

Quote:

I'd be okay with that
as well. Personally, I think a system needs no qualification is needed
but some way is needed to distinguish between them and it shouldn't be
hidden from the programmer nor a user. If it's hidden from one but not
the other, they might not be talking about the same entity and for me
that's not a system.

I agree.

This might sound mystical, but after all, Herman Melville has been
called a mystic, so I'm not bothered about it as I've never seen him
post here.

#48

On Nov 30, 9:17 am, JOG <j... (AT) cs (DOT) nott.ac.uk> wrote:

Quote:

Anything that can be described as a noun is an entity in my book,
whether abstract or not. We must be able to describe them by their
attributes, and identify them by one attribute that is consistent over
the lifetime in the universe of discourse. That's my take.

I would like to say that above text is direct consequence of my
solution which is on www.dbdesign10.com
This consequence is in fact one case in my solution because it is not
true in all cases.
It also isn't precise. For example what it means "stabile" or "the
lifetime in the universe of discourse"?
The most important is missing - what is your definition of the
attribute?

Vladimir Odrljin

#49

On Nov 30, 4:19 pm, Jan Hidders <hidd... (AT) gmail (DOT) com> wrote:

Quote:

On 29 nov, 23:16, JOG <j... (AT) cs (DOT) nott.ac.uk> wrote:

On Nov 28, 8:43 pm, rp... (AT) pcwin518 (DOT) campus.tue.nl (rpost) wrote:

paul c wrote:

[...]

Regarding ER, here are some quotes from Codd's book (available for free
at acm.org). The sarcasm of the second one made me laugh.

The criticisms you quote may be amusing, and they have merit, but
they ultimately miss the point. The distinction between entities and
relationships: entities have identity (they can be referred to; attributes
can have entity-valued domains), while relationships do not (they are
completely identified by their, possibly entity-valued, attributes).

I realise that others have attempted to point out your mistakes, but I
just wanted to echo their sentiment.

How about providing some real arguments, in stead of just sentiments?
Haven't seen much of those here and I think Reinier deserves them.

Feel free to offer some of your own for him instead of simply
complaining.

Quote:

There is absolutely no difference
between an entity and a relationship. E/R modelling has /itself/
conceded this, translating relationships into "associative entities".

Ah, yes, and as we all know, if two concepts have overlap then they
are actually the same. *sigh* The distinction between entities /
relationships

Great, if this distinction is so clear feel free to elucidate the
final word on the matter.

Quote:

domain objects / predicates is pretty well-established
in linguistics, philosophy and logic. First-order logic, you may have
heard of it, separates them even strictly.

Puh-lease Jan, this sort of thing is beneath you. There is no need to
be so condescending. This is a usenet forum not ACM transactions, so
there is always going to be loose debate. And anyhow, the question is
not of the use of entities in FOL, but of a preffered role for
entities in a logical data model.

Quote:

Are you now going to claim that it is no good for reasoning?

Who ever claimed that? Reasoning? Seems to me you are the first to
mention the word. It is very unlike you to start trying to push words
into peoples mouths, and I think we'd all normally expect better of
you.

I am sure you don't believe that we should just accede that Jan has
spoken and everything is already decided. Ought we just forgo all the /
ongoing/ issues in identity research, because FOL has its own
definition? Maybe you should have spoken to Geach before he wasted all
his time on relative identity? After all Liebniz had already defined
identity centuries ago right?

Was very disappointed in your post. If you think someone deserves a
longer response, I am more than receptive to that being politely
stated.

Quote:

-- Jan Hidders

#50

On Nov 30, 8:19 am, Jan Hidders <hidd... (AT) gmail (DOT) com> wrote:
The distinction between entities /

Quote:

relationships, domain objects / predicates is pretty well-established
in linguistics, philosophy and logic.

That certainly means you can define them formally in database terms,
right?
Here is one such attempt:
http://arxiv.org/PS_cache/arxiv/pdf/...710.2083v1.pdf
It defines an entity as a relation (aka table:-) with a single
noncomposite key, and relationship as a table with composite key. Does
this definition pretty much exhausts the entity-relationship theory?

(But then BB remark was that order line is a weak entity).