I have this schema:
create table hall( building-id int, hall-id int, capacity int, primary key(building-id, hall-id) ); create table semester( sem-id char(5), start-date date, eend-date date, primary key(sem-id) ); create table weekly-event( weid int, course-id numeric(7,0), sem-id char(5), weekday varchar(10), start-time time, duration interval, registered int, primary key(weid), foreign key(sem-id) references semester ); create table one-time-event( oeid int, event-name varchar(50), end-date date, start-time time, duration interval, registered int, primary key(oeid) ); create table timetable( start-date date, start-time time, hall-id int, building-id int, event-id int, duration interval, primary key(start-date, start-time, hall-id, building-id, event-id), foreign key(hall-id, building-id) references hall );
where either events that occur on a weekly basis or one-time events are scheduled on some campus. I want to draw entity-relationship diagram (ERD) for this schema and first of all I don't have much experience in drawing ERDs.
Also, I'm wondering if I should use some kind of "IS A" relationship for the weekly and one-time events and unite some attribute under event table which would have children which would contain only the attributes specific to them.
This is the ERD I have so far:
As far as I see it, timetable is dependent on other tables that's why I chose rhombuses with double lines. I also think that the relationship between timetable and hall and weekly-events is one-to-many while the relationship between timetable and one-time-event is one-to-one.
semester it has total participation.
timetable cannot exist without at least one
weekly-event that's why it also has total participation in those.