1. Engineering
  2. Computer Science
  3. i have a question on er diagram the following pictures...

Question: i have a question on er diagram the following pictures...

Question details

I have a question on ER diagram, the following pictures' sign meaning:

under line: primary key

@ : Foreign key

Each entity can only has one primary key. However, In the pictures, some of the foreign keys also have under line, but some of them are not. And I can't understand why and also can not find a principle rule for that. Please help me.

(1:M) Relationships (1:1) Relationships Bld Price Title Paperback School Phone Book Code PROFESSOR SCHOOL PUBLISHER BOOK SCHOOL (School Code, School_Address, School _Bldg, School_Phone, ..., Prof Num) PUBLISHER Publisher Code, Publisher Name, Publisher City) Publisher Code) (M:M) Relationships PROFESSOR (Prof Num, Specialty, ...) BOOK (Book Code, Title, Price, Type, Paperback, Multivalued attributes (cont.) Max speed Name Branch Lacalion Title Model CAR COLOR Num Employocs Branch Name 1. BRANCH BOOK ID num Section Name CAR (ID num, Model, Manufacturer, A15211 Trim Silver Black On Hand 15211 Year, Engine, Max_speed) COLOR (ID numa, Section, Name A521 Interior White 15211 Top BOOK (Book Code, Title, Price, Type, Paperback) BRANCH (Branch Num, Branch Name, Branch_Location, B15232 etallic blue etallic blue Num Employees) 95-703, DBMB15232 INVENTORY (Branch Num, Book Code, On_Hand)

Solution by an expert tutor
Blurred Solution
This question has been solved
Subscribe to see this solution