Question

I read my notes and I am now unsure about the keys.

My logical diagram

alt text http://files.getdropbox.com/u/175564/db/db-11.png

This table should be in line with the following physical ERD

alt text http://files.getdropbox.com/u/175564/db/db-22.png

I have only one foreign key in the table Question.

I would like to know

• should the question-id and question-tag in the table Question-tag-xref, AND question-id and answer in the table Answers be also foreign keys?

Answer 1

Masi – Logical models don’t usually contain data type (string, int, etc) information, but do indicate if the attribute (becomes a column in the Physical model) is optional (able to be null or not).

That said, yes – the QUESTION-ID and QUESTION-TAG columns would be foreign keys in the QUESTION-TAG-XREF table. Here’s a physical view of QUESTION-TAG-XREF:

QUESTION-TAGS-XREF

• QUESTION-ID (pk, fk relationship with QUESTIONS table)
• QUESTION-TAG-CODE (pk, fk relationship with QUESTION-TAG table)

Both columns are the pk to ensure you can’t have duplicate tags for a given question.

You are correct that QUESTION-ID would be a foreign key in the ANSWERS table, in reference to the QUESTION table.