.. (לתיקייה המכילה) | ||
In question 4 - can we provide the empty relation as an answer? (both sections of the question) | |
No, there exists a non-empty content for the relations that satisfies the question's demands. |
In question 4 section ב - how is a semijoin defined between two relations that don't have any common attributes (their schema is completely disjoint)? | |
If R and S don't have any common attributes (for example: R(A,B), S(C,D) ) and S is NOT empty then - R semijoin S = R Otherwise, if S is empty - R semijoin S = empty |
In question 4 - what are we supposed to do? How is our answer supposed to look? | |
You should show the "content" of each of the relations, actual examples for values that the relations contain, such that the requirements of the question are satisfied. For example: R1 A | B -------- 1 | 2 3 | 4 5 | 6 |
In Q3 section 3, do we need to have any primary key on the Edge table? | |
You need to enforce only the specified constraints, so since we didn't mention any primary keys on the Edge table you don't need to declare any. We will accept also answers that contain a primary key, but you are required only for the specified requirements. |