问题
This question is based on my plan at the thread.
My entity-relationship diagram is
alt text http://files.getdropbox.com/u/175564/sequence-diagram.png
I would like to know the following.
Does my sequence diagram match the following relation diagram?
alt text http://files.getdropbox.com/u/175564/table-problem-3.png
回答1:
Reviewing the first diagram as the Logical model, typically the tables defined in the Logical also exist in the physical - you're missing the QUESTION-TAGS (nee QUESTION-SUBJECTS) table. You have a one-to-one relationship between QUESTION and MONITOR-CHECK, which means there's no value to having MONITOR-CHECK - move the attributes into the QUESTION table.
Viewing the second diagram as the Physical ERD model - there's no benefit to having two tables with a one-to-one relationship. I'm speaking about the QUESTION / QUESTION-BODY, and QUESTION / MODERATOR-CHECK tables.
QUESTION-SUBJECTS is poorly named - if by your note the record represents a "tag", then name the table accordingly. This table would be a code table (having CODE, DESCRIPTION columns) because you want to keep the values consistent for queries to perform well. That said, you need an xref/lookup/corollary table between the QUESTION and QUESTION-TAGS table in order to have a one [question related] to many [question tags].
QUESTION-TAG-XREF
- QUESTION-ID (pk)
- QUESTION-TAG-CODE (pk)
回答2:
This is my reply to rexem's answer.
I understand your answer as follows:
alt text http://files.getdropbox.com/u/175564/db-problem-2.png
and the second diagram as
alt text http://files.getdropbox.com/u/175564/db-problem-1.png
I left the xref table for the question-body because I may need to store the changes to my questions too in the future.
回答3:
The first diagram looks a bit more like a class diagram.
来源：https://stackoverflow.com/questions/1182910/how-to-improve-a-erd