create table student ( \
     snum int not null, \
     sname varchar(20), \
     year int, \
     primary key (snum) \
)
create table professor ( \
     pnum int not null, \
     pname varchar(20), \
     office varchar(6), \
     dept varchar(20), \
     primary key (pnum) \
)
create table course ( \
     cnum varchar(10) not null, \
     cname varchar(50), \
     primary key (cnum) \
)
create table class ( \
     cnum varchar(10) not null, \
     term char(3) not null, \
     section int not null, \
     pnum int, \
     primary key (cnum,term,section), \
     foreign key (cnum) \
        references course, \
     foreign key (pnum) \
        references professor \
)
create table enrollment ( \
     snum int not null, \
     cnum varchar(10) not null, \
     term char(3) not null, \
     section int not null, \
     primary key (snum,cnum,term,section), \
     foreign key (snum) \
        references student, \
     foreign key (cnum,term,section) \
        references class \
)
create table mark ( \
     snum int not null, \
     cnum varchar(10) not null, \
     term char(3) not null, \
     section int not null, \
     grade int not null, \
     primary key (snum,cnum,term,section), \
     foreign key (snum,cnum,term,section) \
        references enrollment \
)
create table schedule ( \
     cnum varchar(10) not null, \
     term char(3) not null, \
     section int not null, \
     day varchar(10) not null, \
     time varchar(7) not null, \
     room varchar(6), \
     primary key (cnum,term,section,day,time), \
     foreign key (cnum,term,section) \
        references class \
)