DATABASE MANAGEMENT SYSTEM QUESTIONS

Hello, can anyone help me to debunk likes steps by steps way of thinking to answer this questions (in particular please really explain part b)?

Another thing is what is the arrow symbol called and its function?

Another query is please like do it in steps.. so like for example, step 1: we declare the selection first or like which relation will be involved etc

Sooo here's the question:

Using the university example, write relational-algebra queries to find the

course sections taught by more than one instructor in the following ways:

a. Using an aggregate function.

b.Without using any aggregate functions.

Here is the university schema (they're both same but in different illustration):

Here's the answers (this is what I need a clear explanation and the explanation why each symbols are used) (also in particular what is the arrow symbol in part b) of the answers)?

THANKS!

classroom(building, room_number,capacity) department(dept _name, building, budget) course(course_id , title,dept _name,credits) instructor(ID, name, dept_name, salary) section(course_id, sec_id, semester, year, building room_number, time_slot_id) teaches(ID, course_id , sec_id, semester, year) student(ID, name, dept_name,tot _cred) takes(ID, course_id , sec_id, semester, year, grade) advisor(s _iD, i_iD) time_slot(time_slot_id, day, start_time, end _time) prereq(course_id, prereq_id) 2.5 Relational Query Languages student takes ID course_id sec_id semester year ID name dept_name tot cred grade section advisor course course_id title dept_name credits course_id sec_id semester year building room_no time_slot_id department dept_name building budget s id lid time_slot time_slot_id day start_time end_time instructor classroom building room no capacity prereq course id prereq_id ID name dept_name teaches salary ID course id sec_id semester year Figure 2.8 Schema diagram for the university database. a. The relational algebra query to find the course sections taught by more than one instructor using an aggregate function is, Num_Instr>1 (course_id,sec_id semester, year Scount(*) as Num_Instr (teaches)) The relational algebra query to find the course sections taught by more than one instructor without using an aggregate function is, takes _1- (Ptakesi(1D1,course_id sec_id,semester, year) (takes)) I course_id ,sec_id,semester, year ( OiDojdi (takes Da takes _ 1))