a union is always a join!

#41

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote

Quote:

One of the flaws of the mystic persuasion as far as db's are concerned and
as we see it in your posts, is that it denies, in what usually appears to
me to be in a willful and haphazard way, that mechanical db's, so far in
history, don't actually relect reality, only an abstraction of reality.
This has got to be understood in any mention of 'interpretation'.

Bingo!

#42

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote

Quote:

Brian Selzer wrote:
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:ZXlul.17783$PH1.16918 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:apltl.2309$%u5.1252 (AT) nwrddc01 (DOT) gnilink.net...
"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:eY2tl.9205$%54.7793 (AT) nlpi070 (DOT) nbdc.sbc.com...
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:beZsl.15959$Db2.2243 (AT) edtnps83 (DOT) ..
Walter Mitty wrote:

... I'm also going to suggest that what
Brain S. calls "oversimplification" is almost exactly what others
call
"abstraction". I'm also going to suggest that without abstraction
you don't
get any independence, and without independence, you don't get much
of any
bang for the buck. That may be of zero theoretical importance, but
it's of
interest to me.
...
Walter, I'm with the many people who think phyaical and logical
independence are of high importance, both theoretically and
practically. But I'd say many of the nuances and implications of
those haven't been explored much in print. Brain S as you call him
regularly enters the realm of mysticism. I point this out not to
correct him, but to warn newcomers here that he is not exactly
swimming in the main stream of relational theory (to be fair, not
many are, because the theory is often confused with past practice).
I have a number of mystic acquaintances and I like them all, partly
because they don't involve themselves in db theory and there is much
in life for which mysticism offers the only comfortable clues.

Mysticism. If accepting that the universe of discourse contains
things and that at different times a thing can differ in appearance
yet still be the same thing means that I'm a mystic, then I'm guilty
as charged.
What difference does it make whether it's the same thing or a
different thing?
If an employee worked 50 hours on a project and his labor rate is $20
per hour, then it cost $1000 to have him work on the project, right?
WRONG! The employee's labor rate /is/ $20 per hour, but that doesn't
mean that it /had been/ $20 per hour during the time that he worked on
the project. At that time his labor rate might have been $18 per hour
or may even have changed part way through the project. So the record
of cost must not contain just which project, which employee and how
many hours, but also at which labor rate or rates the work was
performed. But the employee is still the same employee even though his
labor rate changed from $18 to $20. Other cost records may exist for
projects that he worked on after the rate increase, and one should
expect that a query of which projects he worked on would return all of
the projects, regardless of the labor rate.

So something can appear different at different times yet still be the
same thing.

This poses a problem because keys are not necessarily permanent
identifiers. (I'm having trouble articulating my thought here because
there is more than one usage of the term, "key." I'm disinclined from
using "key value" because under an interpretation, a key value is a
mapping to a particular thing in the universe, that thing being the
output of the valuation function for the set of symbols for the
components in a tuple of the set of attributes that is the candidate
key, and it's possible for that same set of symbols to map to different
things at different times, or for different sets of symbols to map to
the same thing at different times. But it's unwieldy to say "sets of
symbols for the components in a tuple of the set of attributes that is
the candidate key" instead of just "keys.") The problem stems from how
things in the universe of discourse are identified, and that the scope
of the definition of a candidate key is any database and not all
databases. While a key may uniquely identify something in the context
of its containing database, that doesn't necessarily mean that that
same key uniquely identifies that same something at all databases in
which it appears.
I wish, at least once, you would give an answer that was shorter than
the question.

Ask me a question that has a simple answer, and I'll simply answer it.

That's a cute riposte in that it grants my wish as far as my last question
is concerned. But how about the simple answer to Walter M's question
(which is "none", ie., the attributes that are chosen for relations
determine the consequences)?

As my voluminous reply indicated, I don't think that it is "none."

Quote:

The example of the employee whose hourly cost changes is bogus because it
confuses employee cost with project hourly costs, obviously the latter
would be an attribute of some project relation in any workable system.

But it is clear that at each interval during which the employee was working
on the project, the employee's hourly cost and the project's hourly cost (at
least as far as the employee was concerned) were identical. That fact
cannot be denied even though the database doesn't maintain an explicit
record of the employee's rate changes.

Quote:

One of the flaws of the mystic persuasion as far as db's are concerned and
as we see it in your posts, is that it denies, in what usually appears to
me to be in a willful and haphazard way, that mechanical db's, so far in
history, don't actually relect reality, only an abstraction of reality.
This has got to be understood in any mention of 'interpretation'. At some
point maybe you will come to see that.

Abstraction is a good thing. I don't deny it. The universe of discourse,
or as Codd put it, "the micro-world that the database is supposed to
represent," for most if not all databases is itself an abstraction of just a
subset of reality. But what you appear to be trying to do is apply
mechanisms that only work for static mathematical objects to things that can
change over time. That's not abstraction: that's just illogical.

There is a huge difference between a relation for an operator defined on a
domain of mathematical objects and a relation defined on a domain of things
that that can change over time. In particular, there can only ever be one
extension of the relation for the operator, whereas there are as many
possible extensions of the other as there are legal combinations of tuples.
The relation for the operator is true at all possible worlds at all times
under all interpretations, so the mechanism of its interpretation is moot
since the outcome is always the same. But for things that can change over
time, the mechanism of interpretation becomes critical because whether or
not a tuple appears in a relation depends solely upon whether the assertion
it represents has been assigned a positive truth value under an
interpretation.

Quote:

I wouldn't criticize if you could describe a formal model that could
embody the very extraneous notions you bring up, but the usual assumption
of any reader here is that the RM is the starting point but your starting
point doesn't which makes it very hard for any reader to guess what the
dickens your context is. Nothing wrong with additional abstractions
beyond Codd's, as long as the perpretators recognize that they need to
explain them to the rest of us.

There really isn't room here for a detailed explanation, but perhaps what
follows will at least clarify what my context is.

The way I see it, the Relational Model is equivalent to a formal logical
system based on a first-order modal tense logic. Modal because the set of
all domain constraints, relation constraints and database constraints
together specifies the set of all possible databases, which is the
equivalent of the set of all possible worlds, and tense because a database
is the equivalent of an assertion that states not just what is the case but
rather what has been the case since the last update, and a transition is the
equivalent of an assertion that states in the context of what has been the
case (or more precisely, what had been the case during the interval from the
last update up to this point) what is different and exactly how.

The simple terms of a formal language of that system include, like any
formal first-order language, a set of individual names, a set of individual
variables, and a set of relation names of various degrees. An atomic
formula is of the form P(x1,...,xn) where P is a relation name and
(x1,...,xn) are a set of zero or more individual variables. Complex
formulae are formed by combining atomic formulae with logical operators,
connectives and quantifiers. Constraints are sentences (closed formulae)
that together specify which models are legal under the intended
interpretation. A model is an extension of each formula in each possible
world, a mapping of each term to something in the universe of discourse, and
a mapping of each formula in each extension to a truth value, which as a
consequence states which member of the set of all possible worlds is the
actual world. Constraints fall into four categories: a set of named
constraints partitions the set of individual names; another set of
constraints specifies the set of all legal extensions for each formula; a
third set specifies the legal combinations of extensions that together
constitute the set of all possible worlds, and a fourth set defines which
possible worlds are accessible from another. Under the Unique Name and
Closed World Assumptions, these sets of constraints are the equivalents of
domain definitions, relation constraints, database constraints and
transition constraints in the Relational Model.

If you're interested in other abstractions beyond Codd's, you might want to
investigate Edward Zalta's theory of abstract objects. In particular, his
paper "The Modal Object Calculus and its Interpretation," published in
/Advances in Intensional Logic/, 1996, describes in detail the mechanism of
interpretation--including the assignment of meaning to terms in the formal
language and the assignment of truth values to formulae.

#43

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote

Quote:

"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:apltl.2309$%u5.1252 (AT) nwrddc01 (DOT) gnilink.net...

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:eY2tl.9205$%54.7793 (AT) nlpi070 (DOT) nbdc.sbc.com...
Mysticism. If accepting that the universe of discourse contains things
and that at different times a thing can differ in appearance yet still
be the same thing means that I'm a mystic, then I'm guilty as charged.

What difference does it make whether it's the same thing or a different
thing?

If an employee worked 50 hours on a project and his labor rate is $20 per
hour, then it cost $1000 to have him work on the project, right? WRONG!
The employee's labor rate /is/ $20 per hour, but that doesn't mean that it
/had been/ $20 per hour during the time that he worked on the project. At
that time his labor rate might have been $18 per hour or may even have
changed part way through the project. So the record of cost must not
contain just which project, which employee and how many hours, but also at
which labor rate or rates the work was performed. But the employee is
still the same employee even though his labor rate changed from $18 to
$20. Other cost records may exist for projects that he worked on after
the rate increase, and one should expect that a query of which projects he
worked on would return all of the projects, regardless of the labor rate.

So something can appear different at different times yet still be the same
thing.

This poses a problem because keys are not necessarily permanent
identifiers. (I'm having trouble articulating my thought here because
there is more than one usage of the term, "key." I'm disinclined from
using "key value" because under an interpretation, a key value is a
mapping to a particular thing in the universe, that thing being the output
of the valuation function for the set of symbols for the components in a
tuple of the set of attributes that is the candidate key, and it's
possible for that same set of symbols to map to different things at
different times, or for different sets of symbols to map to the same thing
at different times. But it's unwieldy to say "sets of symbols for the
components in a tuple of the set of attributes that is the candidate key"
instead of just "keys.") The problem stems from how things in the
universe of discourse are identified, and that the scope of the definition
of a candidate key is any database and not all databases. While a key may
uniquely identify something in the context of its containing database,
that doesn't necessarily mean that that same key uniquely identifies that
same something at all databases in which it appears.

Aren't you just saying that a variable does not record its own history?

#44

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote

Quote:

paul c wrote:
...
Infinity is not a problem because when we implement on a digital machine,
all stored values are finite. ...

Maybe I should have qualified 'values' to be ones that aren't allowed to
be treated in an approximate way by the operators allowed, such as many
floating point value representations.

Actually, the floating point arithmetic treats values as producing an exact
result under all the operators involved. At least, so it seems to me from
looking at the FP operators of several computers. The problem is that the
exact result isn't "exactly right" in terms of what we construe exact
rightness to mean. In most cases, that is because what we give the
arithmetic unit as inputs are only approximations to the real values we
would like to give.

#45

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote

Quote:

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:wJDul.17957$PH1.5324 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:ZXlul.17783$PH1.16918 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:apltl.2309$%u5.1252 (AT) nwrddc01 (DOT) gnilink.net...
"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:eY2tl.9205$%54.7793 (AT) nlpi070 (DOT) nbdc.sbc.com...
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:beZsl.15959$Db2.2243 (AT) edtnps83 (DOT) ..
Walter Mitty wrote:

... I'm also going to suggest that what
Brain S. calls "oversimplification" is almost exactly what others
call
"abstraction". I'm also going to suggest that without abstraction
you don't
get any independence, and without independence, you don't get much
of any
bang for the buck. That may be of zero theoretical importance,
but it's of
interest to me.
...
Walter, I'm with the many people who think phyaical and logical
independence are of high importance, both theoretically and
practically. But I'd say many of the nuances and implications of
those haven't been explored much in print. Brain S as you call him
regularly enters the realm of mysticism. I point this out not to
correct him, but to warn newcomers here that he is not exactly
swimming in the main stream of relational theory (to be fair, not
many are, because the theory is often confused with past practice).
I have a number of mystic acquaintances and I like them all, partly
because they don't involve themselves in db theory and there is
much in life for which mysticism offers the only comfortable clues.

Mysticism. If accepting that the universe of discourse contains
things and that at different times a thing can differ in appearance
yet still be the same thing means that I'm a mystic, then I'm guilty
as charged.
What difference does it make whether it's the same thing or a
different thing?
If an employee worked 50 hours on a project and his labor rate is $20
per hour, then it cost $1000 to have him work on the project, right?
WRONG! The employee's labor rate /is/ $20 per hour, but that doesn't
mean that it /had been/ $20 per hour during the time that he worked on
the project. At that time his labor rate might have been $18 per hour
or may even have changed part way through the project. So the record
of cost must not contain just which project, which employee and how
many hours, but also at which labor rate or rates the work was
performed. But the employee is still the same employee even though
his labor rate changed from $18 to $20. Other cost records may exist
for projects that he worked on after the rate increase, and one should
expect that a query of which projects he worked on would return all of
the projects, regardless of the labor rate.

So something can appear different at different times yet still be the
same thing.

This poses a problem because keys are not necessarily permanent
identifiers. (I'm having trouble articulating my thought here because
there is more than one usage of the term, "key." I'm disinclined from
using "key value" because under an interpretation, a key value is a
mapping to a particular thing in the universe, that thing being the
output of the valuation function for the set of symbols for the
components in a tuple of the set of attributes that is the candidate
key, and it's possible for that same set of symbols to map to
different things at different times, or for different sets of symbols
to map to the same thing at different times. But it's unwieldy to say
"sets of symbols for the components in a tuple of the set of
attributes that is the candidate key" instead of just "keys.") The
problem stems from how things in the universe of discourse are
identified, and that the scope of the definition of a candidate key is
any database and not all databases. While a key may uniquely identify
something in the context of its containing database, that doesn't
necessarily mean that that same key uniquely identifies that same
something at all databases in which it appears.
I wish, at least once, you would give an answer that was shorter than
the question.

Ask me a question that has a simple answer, and I'll simply answer it.

That's a cute riposte in that it grants my wish as far as my last
question is concerned. But how about the simple answer to Walter M's
question (which is "none", ie., the attributes that are chosen for
relations determine the consequences)?

As my voluminous reply indicated, I don't think that it is "none."

The example of the employee whose hourly cost changes is bogus because it
confuses employee cost with project hourly costs, obviously the latter
would be an attribute of some project relation in any workable system.

But it is clear that at each interval during which the employee was
working on the project, the employee's hourly cost and the project's
hourly cost (at least as far as the employee was concerned) were
identical. That fact cannot be denied even though the database doesn't
maintain an explicit record of the employee's rate changes.

One of the flaws of the mystic persuasion as far as db's are concerned
and as we see it in your posts, is that it denies, in what usually
appears to me to be in a willful and haphazard way, that mechanical db's,
so far in history, don't actually relect reality, only an abstraction of
reality. This has got to be understood in any mention of
'interpretation'. At some point maybe you will come to see that.

Abstraction is a good thing. I don't deny it. The universe of discourse,
or as Codd put it, "the micro-world that the database is supposed to
represent," for most if not all databases is itself an abstraction of just
a subset of reality. But what you appear to be trying to do is apply
mechanisms that only work for static mathematical objects to things that
can change over time. That's not abstraction: that's just illogical.

There is a huge difference between a relation for an operator defined on a
domain of mathematical objects and a relation defined on a domain of
things that that can change over time. In particular, there can only ever
be one extension of the relation for the operator, whereas there are as
many possible extensions of the other as there are legal combinations of
tuples. The relation for the operator is true at all possible worlds at
all times under all interpretations, so the mechanism of its
interpretation is moot since the outcome is always the same. But for
things that can change over time, the mechanism of interpretation becomes
critical because whether or not a tuple appears in a relation depends
solely upon whether the assertion it represents has been assigned a
positive truth value under an interpretation.

I wouldn't criticize if you could describe a formal model that could
embody the very extraneous notions you bring up, but the usual assumption
of any reader here is that the RM is the starting point but your starting
point doesn't which makes it very hard for any reader to guess what the
dickens your context is. Nothing wrong with additional abstractions
beyond Codd's, as long as the perpretators recognize that they need to
explain them to the rest of us.

There really isn't room here for a detailed explanation, but perhaps what
follows will at least clarify what my context is.

The way I see it, the Relational Model is equivalent to a formal logical
system based on a first-order modal tense logic. Modal because the set of
all domain constraints, relation constraints and database constraints
together specifies the set of all possible databases, which is the
equivalent of the set of all possible worlds, and tense because a database
is the equivalent of an assertion that states not just what is the case
but rather what has been the case since the last update, and a transition
is the equivalent of an assertion that states in the context of what has
been the case (or more precisely, what had been the case during the
interval from the last update up to this point) what is different and
exactly how.

The simple terms of a formal language of that system include, like any
formal first-order language, a set of individual names, a set of
individual variables, and a set of relation names of various degrees. An
atomic formula is of the form P(x1,...,xn) where P is a relation name and
(x1,...,xn) are a set of zero or more individual variables. Complex
formulae are formed by combining atomic formulae with logical operators,
connectives and quantifiers. Constraints are sentences (closed formulae)
that together specify which models are legal under the intended
interpretation. A model is an extension of each formula in each possible
world, a mapping of each term to something in the universe of discourse,
and a mapping of each formula in each extension to a truth value, which as
a consequence states which member of the set of all possible worlds is the
actual world. Constraints fall into four categories: a set of named
constraints partitions the set of individual names; another set of
constraints specifies the set of all legal extensions for each formula; a
third set specifies the legal combinations of extensions that together
constitute the set of all possible worlds, and a fourth set defines which
possible worlds are accessible from another. Under the Unique Name and
Closed World Assumptions, these sets of constraints are the equivalents of
domain definitions, relation constraints, database constraints and
transition constraints in the Relational Model.

If you're interested in other abstractions beyond Codd's, you might want
to investigate Edward Zalta's theory of abstract objects. In particular,
his paper "The Modal Object Calculus and its Interpretation," published in
/Advances in Intensional Logic/, 1996, describes in detail the mechanism
of interpretation--including the assignment of meaning to terms in the
formal language and the assignment of truth values to formulae.

Don't you think Heraclitus said all of this much more clearly, some 2500
years ago?

http://www.spaceandmotion.com/philos...heraclitus.htm

#46

Walter Mitty wrote:

Quote:

...

Don't you think Heraclitus said all of this much more clearly, some 2500
years ago?

http://www.spaceandmotion.com/philos...heraclitus.htm

Sounds like he was a fine old abstracter (abstractionist?). Seems
Abelson and company were hip too:

M

(Even while it changes, it stands still.)

Heraclitus

(also):

Plus ça change, plus c'est la même chose.

Alphonse Karr

(both from the esteemed sicp book)

I gather the temporal db people, whatever their arguments, at least
agree on choosing their desired abstractions up front, not plopping
multiple interpretations onto the basic Codd model with extraneous
lingo like 'tense' and 'modal' in today's popular but despicable
faux-technocratic way. (The general public has allowed the technocrats
to usurp their own name, just like the once-respectable word
'propaganda' in the 1930's. An honest db technocrat ought never
venture into metaphysics.).

#47

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote

Quote:

Walter Mitty wrote:
...

Don't you think Heraclitus said all of this much more clearly, some 2500
years ago?

http://www.spaceandmotion.com/philos...heraclitus.htm

Sounds like he was a fine old abstracter (abstractionist?). Seems Abelson
and company were hip too:

M

(Even while it changes, it stands still.)

Heraclitus

(also):

Plus ça change, plus c'est la même chose.

Alphonse Karr

(both from the esteemed sicp book)

I gather the temporal db people, whatever their arguments, at least agree
on choosing their desired abstractions up front, not plopping multiple
interpretations onto the basic Codd model with extraneous lingo like
'tense' and 'modal' in today's popular but despicable faux-technocratic
way. (The general public has allowed the technocrats to usurp their own
name, just like the once-respectable word 'propaganda' in the 1930's. An
honest db technocrat ought never venture into metaphysics.).

Is this the new liberalism: express a position that is counter to
consensus--regardless if it or the consensus is correct--and endure not just
scorn and ridicule, but even to being cast as morally reprehensible. I
guess it would be too much to ask for a rational argument, if it were even
possible for you to formulate one, since ad hominem attacks are usually
either petty acknowlegements that there is no counterargument or hide an
inability or an unwillingness to comprehend what is under discussion.

#48

"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote

Quote:

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:65Jtl.9343$%54.435 (AT) nlpi070 (DOT) nbdc.sbc.com...

"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:apltl.2309$%u5.1252 (AT) nwrddc01 (DOT) gnilink.net...

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:eY2tl.9205$%54.7793 (AT) nlpi070 (DOT) nbdc.sbc.com...
Mysticism. If accepting that the universe of discourse contains things
and that at different times a thing can differ in appearance yet still
be the same thing means that I'm a mystic, then I'm guilty as charged.

What difference does it make whether it's the same thing or a different
thing?

If an employee worked 50 hours on a project and his labor rate is $20 per
hour, then it cost $1000 to have him work on the project, right? WRONG!
The employee's labor rate /is/ $20 per hour, but that doesn't mean that
it /had been/ $20 per hour during the time that he worked on the project.
At that time his labor rate might have been $18 per hour or may even have
changed part way through the project. So the record of cost must not
contain just which project, which employee and how many hours, but also
at which labor rate or rates the work was performed. But the employee is
still the same employee even though his labor rate changed from $18 to
$20. Other cost records may exist for projects that he worked on after
the rate increase, and one should expect that a query of which projects
he worked on would return all of the projects, regardless of the labor
rate.

So something can appear different at different times yet still be the
same thing.

This poses a problem because keys are not necessarily permanent
identifiers. (I'm having trouble articulating my thought here because
there is more than one usage of the term, "key." I'm disinclined from
using "key value" because under an interpretation, a key value is a
mapping to a particular thing in the universe, that thing being the
output of the valuation function for the set of symbols for the
components in a tuple of the set of attributes that is the candidate key,
and it's possible for that same set of symbols to map to different things
at different times, or for different sets of symbols to map to the same
thing at different times. But it's unwieldy to say "sets of symbols for
the components in a tuple of the set of attributes that is the candidate
key" instead of just "keys.") The problem stems from how things in the
universe of discourse are identified, and that the scope of the
definition of a candidate key is any database and not all databases.
While a key may uniquely identify something in the context of its
containing database, that doesn't necessarily mean that that same key
uniquely identifies that same something at all databases in which it
appears.

Aren't you just saying that a variable does not record its own history?

No. I'm saying that the tuple in one database that maps to a particular
thing in the universe of discourse can be a different set of components from
the tuple in the succeeding database that maps to that same thing. In fact,
any or even all of the components can be different--including key
components.

#49

"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote

Quote:

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:9uVul.22264$Ws1.16416 (AT) nlpi064 (DOT) nbdc.sbc.com...

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:wJDul.17957$PH1.5324 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:ZXlul.17783$PH1.16918 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:apltl.2309$%u5.1252 (AT) nwrddc01 (DOT) gnilink.net...
"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:eY2tl.9205$%54.7793 (AT) nlpi070 (DOT) nbdc.sbc.com...
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:beZsl.15959$Db2.2243 (AT) edtnps83 (DOT) ..
Walter Mitty wrote:

... I'm also going to suggest that what
Brain S. calls "oversimplification" is almost exactly what others
call
"abstraction". I'm also going to suggest that without
abstraction you don't
get any independence, and without independence, you don't get
much of any
bang for the buck. That may be of zero theoretical importance,
but it's of
interest to me.
...
Walter, I'm with the many people who think phyaical and logical
independence are of high importance, both theoretically and
practically. But I'd say many of the nuances and implications of
those haven't been explored much in print. Brain S as you call
him regularly enters the realm of mysticism. I point this out not
to correct him, but to warn newcomers here that he is not exactly
swimming in the main stream of relational theory (to be fair, not
many are, because the theory is often confused with past
practice). I have a number of mystic acquaintances and I like them
all, partly because they don't involve themselves in db theory and
there is much in life for which mysticism offers the only
comfortable clues.

Mysticism. If accepting that the universe of discourse contains
things and that at different times a thing can differ in appearance
yet still be the same thing means that I'm a mystic, then I'm
guilty as charged.
What difference does it make whether it's the same thing or a
different thing?
If an employee worked 50 hours on a project and his labor rate is $20
per hour, then it cost $1000 to have him work on the project, right?
WRONG! The employee's labor rate /is/ $20 per hour, but that doesn't
mean that it /had been/ $20 per hour during the time that he worked
on the project. At that time his labor rate might have been $18 per
hour or may even have changed part way through the project. So the
record of cost must not contain just which project, which employee
and how many hours, but also at which labor rate or rates the work
was performed. But the employee is still the same employee even
though his labor rate changed from $18 to $20. Other cost records
may exist for projects that he worked on after the rate increase, and
one should expect that a query of which projects he worked on would
return all of the projects, regardless of the labor rate.

So something can appear different at different times yet still be the
same thing.

This poses a problem because keys are not necessarily permanent
identifiers. (I'm having trouble articulating my thought here because
there is more than one usage of the term, "key." I'm disinclined
from using "key value" because under an interpretation, a key value
is a mapping to a particular thing in the universe, that thing being
the output of the valuation function for the set of symbols for the
components in a tuple of the set of attributes that is the candidate
key, and it's possible for that same set of symbols to map to
different things at different times, or for different sets of symbols
to map to the same thing at different times. But it's unwieldy to
say "sets of symbols for the components in a tuple of the set of
attributes that is the candidate key" instead of just "keys.") The
problem stems from how things in the universe of discourse are
identified, and that the scope of the definition of a candidate key
is any database and not all databases. While a key may uniquely
identify something in the context of its containing database, that
doesn't necessarily mean that that same key uniquely identifies that
same something at all databases in which it appears.
I wish, at least once, you would give an answer that was shorter than
the question.

Ask me a question that has a simple answer, and I'll simply answer it.

That's a cute riposte in that it grants my wish as far as my last
question is concerned. But how about the simple answer to Walter M's
question (which is "none", ie., the attributes that are chosen for
relations determine the consequences)?

As my voluminous reply indicated, I don't think that it is "none."

The example of the employee whose hourly cost changes is bogus because
it confuses employee cost with project hourly costs, obviously the
latter would be an attribute of some project relation in any workable
system.

But it is clear that at each interval during which the employee was
working on the project, the employee's hourly cost and the project's
hourly cost (at least as far as the employee was concerned) were
identical. That fact cannot be denied even though the database doesn't
maintain an explicit record of the employee's rate changes.

One of the flaws of the mystic persuasion as far as db's are concerned
and as we see it in your posts, is that it denies, in what usually
appears to me to be in a willful and haphazard way, that mechanical
db's, so far in history, don't actually relect reality, only an
abstraction of reality. This has got to be understood in any mention of
'interpretation'. At some point maybe you will come to see that.

Abstraction is a good thing. I don't deny it. The universe of
discourse, or as Codd put it, "the micro-world that the database is
supposed to represent," for most if not all databases is itself an
abstraction of just a subset of reality. But what you appear to be
trying to do is apply mechanisms that only work for static mathematical
objects to things that can change over time. That's not abstraction:
that's just illogical.

There is a huge difference between a relation for an operator defined on
a domain of mathematical objects and a relation defined on a domain of
things that that can change over time. In particular, there can only
ever be one extension of the relation for the operator, whereas there are
as many possible extensions of the other as there are legal combinations
of tuples. The relation for the operator is true at all possible worlds
at all times under all interpretations, so the mechanism of its
interpretation is moot since the outcome is always the same. But for
things that can change over time, the mechanism of interpretation becomes
critical because whether or not a tuple appears in a relation depends
solely upon whether the assertion it represents has been assigned a
positive truth value under an interpretation.

I wouldn't criticize if you could describe a formal model that could
embody the very extraneous notions you bring up, but the usual
assumption of any reader here is that the RM is the starting point but
your starting point doesn't which makes it very hard for any reader to
guess what the dickens your context is. Nothing wrong with additional
abstractions beyond Codd's, as long as the perpretators recognize that
they need to explain them to the rest of us.

There really isn't room here for a detailed explanation, but perhaps what
follows will at least clarify what my context is.

The way I see it, the Relational Model is equivalent to a formal logical
system based on a first-order modal tense logic. Modal because the set
of all domain constraints, relation constraints and database constraints
together specifies the set of all possible databases, which is the
equivalent of the set of all possible worlds, and tense because a
database is the equivalent of an assertion that states not just what is
the case but rather what has been the case since the last update, and a
transition is the equivalent of an assertion that states in the context
of what has been the case (or more precisely, what had been the case
during the interval from the last update up to this point) what is
different and exactly how.

The simple terms of a formal language of that system include, like any
formal first-order language, a set of individual names, a set of
individual variables, and a set of relation names of various degrees. An
atomic formula is of the form P(x1,...,xn) where P is a relation name and
(x1,...,xn) are a set of zero or more individual variables. Complex
formulae are formed by combining atomic formulae with logical operators,
connectives and quantifiers. Constraints are sentences (closed formulae)
that together specify which models are legal under the intended
interpretation. A model is an extension of each formula in each possible
world, a mapping of each term to something in the universe of discourse,
and a mapping of each formula in each extension to a truth value, which
as a consequence states which member of the set of all possible worlds is
the actual world. Constraints fall into four categories: a set of named
constraints partitions the set of individual names; another set of
constraints specifies the set of all legal extensions for each formula; a
third set specifies the legal combinations of extensions that together
constitute the set of all possible worlds, and a fourth set defines which
possible worlds are accessible from another. Under the Unique Name and
Closed World Assumptions, these sets of constraints are the equivalents
of domain definitions, relation constraints, database constraints and
transition constraints in the Relational Model.

If you're interested in other abstractions beyond Codd's, you might want
to investigate Edward Zalta's theory of abstract objects. In particular,
his paper "The Modal Object Calculus and its Interpretation," published
in /Advances in Intensional Logic/, 1996, describes in detail the
mechanism of interpretation--including the assignment of meaning to terms
in the formal language and the assignment of truth values to formulae.

Don't you think Heraclitus said all of this much more clearly, some 2500
years ago?

http://www.spaceandmotion.com/philos...heraclitus.htm

I'm not sure what you're driving at. I'm not trying to answer philisophical
questions about change, nor do I seek to wax metaphysical. I merely accept
that it is not only the micro-world that a database is supposed to represent
that can vary over time, but also the things in that micro-world.

#50

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote

Quote:

"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:sQ7vl.237$6%.14 (AT) nwrddc01 (DOT) gnilink.net...

"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:9uVul.22264$Ws1.16416 (AT) nlpi064 (DOT) nbdc.sbc.com...

"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:wJDul.17957$PH1.5324 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:ZXlul.17783$PH1.16918 (AT) edtnps82 (DOT) ..
Brian Selzer wrote:
"Walter Mitty" <wamitty (AT) verizon (DOT) net> wrote in message
news:apltl.2309$%u5.1252 (AT) nwrddc01 (DOT) gnilink.net...
"Brian Selzer" <brian (AT) selzer-software (DOT) com> wrote in message
news:eY2tl.9205$%54.7793 (AT) nlpi070 (DOT) nbdc.sbc.com...
"paul c" <toledobythesea (AT) oohay (DOT) ac> wrote in message
news:beZsl.15959$Db2.2243 (AT) edtnps83 (DOT) ..
Walter Mitty wrote:

... I'm also going to suggest that what
Brain S. calls "oversimplification" is almost exactly what
others call
"abstraction". I'm also going to suggest that without
abstraction you don't
get any independence, and without independence, you don't get
much of any
bang for the buck. That may be of zero theoretical importance,
but it's of
interest to me.
...
Walter, I'm with the many people who think phyaical and logical
independence are of high importance, both theoretically and
practically. But I'd say many of the nuances and implications of
those haven't been explored much in print. Brain S as you call
him regularly enters the realm of mysticism. I point this out
not to correct him, but to warn newcomers here that he is not
exactly swimming in the main stream of relational theory (to be
fair, not many are, because the theory is often confused with
past practice). I have a number of mystic acquaintances and I
like them all, partly because they don't involve themselves in db
theory and there is much in life for which mysticism offers the
only comfortable clues.

Mysticism. If accepting that the universe of discourse contains
things and that at different times a thing can differ in
appearance yet still be the same thing means that I'm a mystic,
then I'm guilty as charged.
What difference does it make whether it's the same thing or a
different thing?
If an employee worked 50 hours on a project and his labor rate is
$20 per hour, then it cost $1000 to have him work on the project,
right? WRONG! The employee's labor rate /is/ $20 per hour, but that
doesn't mean that it /had been/ $20 per hour during the time that he
worked on the project. At that time his labor rate might have been
$18 per hour or may even have changed part way through the project.
So the record of cost must not contain just which project, which
employee and how many hours, but also at which labor rate or rates
the work was performed. But the employee is still the same employee
even though his labor rate changed from $18 to $20. Other cost
records may exist for projects that he worked on after the rate
increase, and one should expect that a query of which projects he
worked on would return all of the projects, regardless of the labor
rate.

So something can appear different at different times yet still be
the same thing.

This poses a problem because keys are not necessarily permanent
identifiers. (I'm having trouble articulating my thought here
because there is more than one usage of the term, "key." I'm
disinclined from using "key value" because under an interpretation,
a key value is a mapping to a particular thing in the universe, that
thing being the output of the valuation function for the set of
symbols for the components in a tuple of the set of attributes that
is the candidate key, and it's possible for that same set of symbols
to map to different things at different times, or for different sets
of symbols to map to the same thing at different times. But it's
unwieldy to say "sets of symbols for the components in a tuple of
the set of attributes that is the candidate key" instead of just
"keys.") The problem stems from how things in the universe of
discourse are identified, and that the scope of the definition of a
candidate key is any database and not all databases. While a key may
uniquely identify something in the context of its containing
database, that doesn't necessarily mean that that same key uniquely
identifies that same something at all databases in which it appears.
I wish, at least once, you would give an answer that was shorter than
the question.

Ask me a question that has a simple answer, and I'll simply answer it.

That's a cute riposte in that it grants my wish as far as my last
question is concerned. But how about the simple answer to Walter M's
question (which is "none", ie., the attributes that are chosen for
relations determine the consequences)?

As my voluminous reply indicated, I don't think that it is "none."

The example of the employee whose hourly cost changes is bogus because
it confuses employee cost with project hourly costs, obviously the
latter would be an attribute of some project relation in any workable
system.

But it is clear that at each interval during which the employee was
working on the project, the employee's hourly cost and the project's
hourly cost (at least as far as the employee was concerned) were
identical. That fact cannot be denied even though the database doesn't
maintain an explicit record of the employee's rate changes.

One of the flaws of the mystic persuasion as far as db's are concerned
and as we see it in your posts, is that it denies, in what usually
appears to me to be in a willful and haphazard way, that mechanical
db's, so far in history, don't actually relect reality, only an
abstraction of reality. This has got to be understood in any mention of
'interpretation'. At some point maybe you will come to see that.

Abstraction is a good thing. I don't deny it. The universe of
discourse, or as Codd put it, "the micro-world that the database is
supposed to represent," for most if not all databases is itself an
abstraction of just a subset of reality. But what you appear to be
trying to do is apply mechanisms that only work for static mathematical
objects to things that can change over time. That's not abstraction:
that's just illogical.

There is a huge difference between a relation for an operator defined on
a domain of mathematical objects and a relation defined on a domain of
things that that can change over time. In particular, there can only
ever be one extension of the relation for the operator, whereas there
are as many possible extensions of the other as there are legal
combinations of tuples. The relation for the operator is true at all
possible worlds at all times under all interpretations, so the mechanism
of its interpretation is moot since the outcome is always the same. But
for things that can change over time, the mechanism of interpretation
becomes critical because whether or not a tuple appears in a relation
depends solely upon whether the assertion it represents has been
assigned a positive truth value under an interpretation.

I wouldn't criticize if you could describe a formal model that could
embody the very extraneous notions you bring up, but the usual
assumption of any reader here is that the RM is the starting point but
your starting point doesn't which makes it very hard for any reader to
guess what the dickens your context is. Nothing wrong with additional
abstractions beyond Codd's, as long as the perpretators recognize that
they need to explain them to the rest of us.

There really isn't room here for a detailed explanation, but perhaps
what follows will at least clarify what my context is.

The way I see it, the Relational Model is equivalent to a formal logical
system based on a first-order modal tense logic. Modal because the set
of all domain constraints, relation constraints and database constraints
together specifies the set of all possible databases, which is the
equivalent of the set of all possible worlds, and tense because a
database is the equivalent of an assertion that states not just what is
the case but rather what has been the case since the last update, and a
transition is the equivalent of an assertion that states in the context
of what has been the case (or more precisely, what had been the case
during the interval from the last update up to this point) what is
different and exactly how.

The simple terms of a formal language of that system include, like any
formal first-order language, a set of individual names, a set of
individual variables, and a set of relation names of various degrees.
An atomic formula is of the form P(x1,...,xn) where P is a relation name
and (x1,...,xn) are a set of zero or more individual variables. Complex
formulae are formed by combining atomic formulae with logical operators,
connectives and quantifiers. Constraints are sentences (closed
formulae) that together specify which models are legal under the
intended interpretation. A model is an extension of each formula in
each possible world, a mapping of each term to something in the universe
of discourse, and a mapping of each formula in each extension to a truth
value, which as a consequence states which member of the set of all
possible worlds is the actual world. Constraints fall into four
categories: a set of named constraints partitions the set of individual
names; another set of constraints specifies the set of all legal
extensions for each formula; a third set specifies the legal
combinations of extensions that together constitute the set of all
possible worlds, and a fourth set defines which possible worlds are
accessible from another. Under the Unique Name and Closed World
Assumptions, these sets of constraints are the equivalents of domain
definitions, relation constraints, database constraints and transition
constraints in the Relational Model.

If you're interested in other abstractions beyond Codd's, you might want
to investigate Edward Zalta's theory of abstract objects. In
particular, his paper "The Modal Object Calculus and its
Interpretation," published in /Advances in Intensional Logic/, 1996,
describes in detail the mechanism of interpretation--including the
assignment of meaning to terms in the formal language and the assignment
of truth values to formulae.

Don't you think Heraclitus said all of this much more clearly, some 2500
years ago?

http://www.spaceandmotion.com/philos...heraclitus.htm

I'm not sure what you're driving at.

Now we're even!