Subset, superset and INIT section issues

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berg
Posts: 2
Joined: Mon Mar 15, 2010 2:23 pm

Subset, superset and INIT section issues

Post by berg »

Hello,

I was wondering if anyone could tell me, if I have understood some things correctly and these issues, I am having, really are bugs.

For defining "foreign keys" in Tutorial D one can use subsets - defining that an attribute is a subset of a key attribute in another table?

Is it correct that if I use attribute names in a INIT section of a base variable, which also has a header definition, the attribute names are ignored and the values are added according to the attribute names of the header?

Example:

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VAR Department
 BASE RELATION {company_name CHAR, department_name CHAR}
 INIT (RELATION {
TUPLE{department_name "Research and Development", company_name "General Electronics"
},
TUPLE{department_name "Management", company_name "Ads are Us"
},
TUPLE{department_name "Management", company_name "General Electronics"
}
})
 KEY {department_name, company_name};
The command

Code: Select all

Department
clearly shows that the values were added ignoring the INIT section attribute names.

Now if I add another variable

Code: Select all

VAR Company
 BASE RELATION {company_name CHAR}
 INIT (RELATION {
TUPLE{company_name "General Electronics"
},
TUPLE{company_name "Ads are Us"
},
TUPLE{company_name "Sushi and Pizza place"
}
})
 KEY {company_name};
and a "foreign key"

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CONSTRAINT department_company_name_fk Department {company_name} <= Company {company_name};
it will fail. Which is correct, since the attributes contain wrong values.

But if I reverse the subset sign it will succeed, even though there are no common values.

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CONSTRAINT department_company_name_fk2 Department{company_name} >= Company {company_name};
...

While writing this post I found that

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CONSTRAINT department_company_name_fk3 Company {company_name} >= Department {company_name};
also succeeds even though it should be equivalent to the first constraint.
Dave
Site Admin
Posts: 368
Joined: Sun Nov 27, 2005 7:19 pm

Re: Subset, superset and INIT section issues

Post by Dave »

berg wrote: Is it correct that if I use attribute names in a INIT section of a base variable, which also has a header definition, the attribute names are ignored and the values are added according to the attribute names of the header?
They're not supposed to be ignored. The header definition and the INIT section must match, and the tuples in the INIT section should be mapped to match the defined header. It appears you've found a bug! :roll: This will be fixed in the next update. I suspect this bug is affecting how the <= and >= operators work, but will do some testing to make sure they behave correctly once the bug is fixed.
Dave
Site Admin
Posts: 368
Joined: Sun Nov 27, 2005 7:19 pm

Re: Subset, superset and INIT section issues

Post by Dave »

This bug has been fixed in the version 1.0.0 beta update.
berg
Posts: 2
Joined: Mon Mar 15, 2010 2:23 pm

Re: Subset, superset and INIT section issues

Post by berg »

Thanks, Dave!
Keep up the good work!
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