Hello,

I have something like:

TABLE A
a PK

TABLE B
b PK

TABLE AB (many-to-many table)
a, b PK

TABLE AB-1 (AB subtype)
a, b PK

TABLE AB-2 (AB subtype)
a, b PK

Can I use the attribute "a" (part of PK) as subtype discriminator?

Thanks,
philip

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff

On Aug 31, 9:51 am, philiptaylo... (AT) yahoo (DOT) com wrote:
Hi, Philip.

I think that's a bad idea. I know this may sound a bit shop-worn, but
all subtypes should be mutually exclusive and exhaustive. Further,
they should each describe a semantically unique "kind of" the
supertype, with each subtype described by attributes unique to it.

Taking these two guidelines together, this suggests (to me, anyway)
that if all subtypes are known, then all instances of the domain of
any category discriminator of these subtypes are also to be known.

Inspecting the value of the PK to decide which subtype to navigate to
also smacks of "smart" keys, which gets us to the whole natural key
vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
a 4-byte unsigned integer, are you saying you'd have (in order to
satisfy the "exhaustive" property) 4,294,967,296 subtypes?

Now, if you wanted to add a category discriminator to your AB
supertype and make it part of a three part composite key, that's
possible, assuming you're enforcing a business rule that mandates that
you may only have one instance of each subtype.

Perhaps you can elaborate a bit more on what you're after, and we can
humbly suggest better approaches?

Regards,

--Jeff