1.2 KiB
lec21
Strong & Weak Entity sets
Strong: has a primary key in the set
Weak: opposite of strong
Diagram things
pretty formatting on diagrams means stuff
-
Arrows
-
solid lines
- many
- Contributer [solid] contribution [solid] candidate
-
dotted lines
- only one
Let's say we have solid/arrow
student{id/name} --- [advisor] --> instructor{id/name}
Students can have at most 1 advisor
Instructor's can advise multiple students
If we want to have some kind of advisor table we can identify each relationship with just the student-id. We can do this because each student will only every 0,1 instructor's in an adivsory relationship
Composite Structures
Logically compositing makes sense but SQL does not like much aside from primitives so we can't really do that
Say then we have:
contributor:
id
name
address <-- f to pay respects
city
state
zip
We just drop the address part if we wanted to convert this to something in sql. Reasoning here is case by case likewise need-to-know basis: ergo stick to da plan.
Normalization
Process used to imporve schemas
Basically a method of setting up rules to stop random bs from happennig. Also we typically remove redundancy from our schemas through this process