[Frunkie]

This ERD is what we were working on yesterday and I have pretty much completed the basics. One thing that I forgot to include in my example yesterday was an "account" table. I see that account should also be a superclass.

The account table will store the company information. A company will have a phone and email which I also have on the "person" side.

Should I superclass the phone and email tables also or just create an account_phone and account_email table?

I can see that the address is repeated in the person and account tables and was wondering if that should also be superclassed.

Thanks,

Frank

[r937]

frank, step back from the detail, you cannot see the forest for the trees

you cannot "superclass" the phone and email tables

regarding the supertype/subtype structure, the way to think about it is that each subtype is a particular kind of a supertype

so in the person-employee-complainant situation, an employee is a type of person, and a complainant is a type of person

to avoid three more days of back and forth trying to hammer this idea home, i'm going to jump ahead and suggest that your supertype should be called "party" and that it should have two subtypes: companies and people

[r937]

regarding your city_state and zip tables, just remove them, okay?

[Frunkie]

Originally Posted by r937

regarding the supertype/subtype structure, the way to think about it is that each subtype is a particular kind of a supertype

Ok, I understand that when I think about it in those terms and you were right, I could not see the forest for the trees. I kind of got into a mode where I was just looking to have 1 theme per table I guess.

Originally Posted by r937

i'm going to jump ahead and suggest that your supertype should be called "party" and that it should have two subtypes: companies and people

Ok. Thanks Rudy. I really appriciate the help and I will remove the city_state and zip tables.

**scratches head and whispers** were they modeled wrong?

[r937]

Originally Posted by fjm1967

... and I will remove the city_state and zip tables.

**scratches head and whispers** were they modeled wrong?

if i had to answer yes or no, i would have to say yes, they were modelled wrong

you do not care about them as entities, they are just attributes of an address

remember the surname table -- you don't automatically create a surname table just because it's possible for two Smiths to show up in your database!!

[Frunkie]

Originally Posted by r937

remember the surname table -- you don't automatically create a surname table just because it's possible for two Smiths to show up in your database!!

Now that statement really hits home with me. I understand. I also understand why my idea of superclassing the email and phone tables wouldn't work.

Example: Lifeform would be a superclass to person, mammal, etc. A vehicle is superclass to color, engine, wheels, etc. See? I got it...



Thanks Rudy.

[r937]

Originally Posted by fjm1967

Example: Lifeform would be a superclass to person, mammal, etc. A vehicle is superclass to color, engine, wheels, etc. See? I got it...

yes you do, more or less

you keep using the word superclass, which might have some meaning i'm not familiar with

(the only thing i know about OO is that it's pronounced "uh oh")

but as for supertype/subtype, remember, the trick is whether you can construct a meaningful sentence using the verb is

so a person is a mammal, and a mammal is a lifeform

but a colour is not a vehicle, an engine is not a vehicle

those relationships are typically called a bill of materials or parts explosion (both of which terms you could google)

and interestingly enough, they are implemented in the same table structures

but they are not supertype/subtype

[Frunkie]

Originally Posted by r937

you keep using the word superclass, which might have some meaning i'm not familiar with

Its possible that I am talking about something different than Supertype and Subtype.

I have a book with all of 3 total pages that describes an "EER" diagram referencing Superclass and Subclass with disjoint and nondisjoint type constraints. I will have to do a little research to understand the differences.

Originally Posted by r937

but as for supertype/subtype, remember, the trick is whether you can construct a meaningful sentence using the verb isso a person is a mammal, and a mammal is a lifeform

The verb is the key then. I can see that it "flows" when you read it. That seems easy enough.

[r937]

Originally Posted by fjm1967

That seems easy enough.

it is easy, and not just when you read it

[r937]

Originally Posted by fjm1967

... referencing Superclass and Subclass with disjoint and nondisjoint type constraints. I will have to do a little research to understand the differences.

disjoint: a person can only be an employee or a complainant, not both

non-disjoint: a person can be both

see how easy this is?

[Frunkie]

Yes... I see. It really is easy. Here look..

Supertype Car
Subtype Convertable
Subtype Wagon
Subtype Compact
Subtype Sedan

Then we could have shared subclasses for each of the subtypes.

Thanks for the clarification on the disjoint and nondisjoint. I was still reading and trying to understand from this book. Why can't people just put things in easy terms when trying to describe complex things? Its like they have to impress themselves or something and it only confuses the reader trying to gain the understanding.

By the way Rudy, you were, once again correct. The terms are Supertype and Subtype and not superclass/subclass.

Are you ever wrong about anything???

[Pat Phelan]

Color choices and styles for lederhosen!

-PatP