1 votes 1 votes Databases databases er-to-relational er-diagram + – bts1jimin asked Aug 30, 2018 bts1jimin 1.4k views answer comment Share Follow See all 16 Comments See all 16 16 Comments reply Shaik Masthan commented Aug 30, 2018 reply Follow Share should be cid 1 votes 1 votes SHUBHAM SHASTRI commented Aug 30, 2018 reply Follow Share it should be ssn ...because Professors are in full participation ..and relation is 1 to 1 ... correct me if i am wrong ...?? 0 votes 0 votes Shaik Masthan commented Aug 30, 2018 reply Follow Share take the sample example and realize 0 votes 0 votes SHUBHAM SHASTRI commented Aug 30, 2018 reply Follow Share course dont have total participation ...so what will you put in front of CID in tuple ??please help @ Shaik Masthan 0 votes 0 votes Shaik Masthan commented Aug 30, 2018 reply Follow Share if you want to take ssn as key then two tables required if you make cid as key then only one table is sufficient.... The one table look like as (cid,Cname,ssn,name) which cid doesn't map to ssn ===> put NULL check this https://gateoverflow.in/218954/what-an-interesting-dbms-question 0 votes 0 votes daksirp commented Aug 30, 2018 reply Follow Share what is causing the problem if we take ssn as the key ? all in one table @Shaik+Masthan 0 votes 0 votes Shaik Masthan commented Aug 30, 2018 reply Follow Share @daksirp, Then how could you find the courses which are not participating in the relation? 0 votes 0 votes daksirp commented Aug 30, 2018 reply Follow Share we will make ssn as the key, <ssn, name, cid, cname> wherever courses is not participating in relation corresponding to ssn, we will put NULL. by seeing NULL, we come to know it is not participating in relation. its my view, correct me if im wrong 0 votes 0 votes Shaik Masthan commented Aug 30, 2018 reply Follow Share You want to put null in ssn? Note that ssn is key, it cannot have null or duplicate values 0 votes 0 votes daksirp commented Aug 30, 2018 reply Follow Share noo, we will put NULL in courses, if courses is not participating, then we will put NULL in courses. 0 votes 0 votes Shaik Masthan commented Aug 30, 2018 reply Follow Share Brother Let assume professor table contains 1 A 2 B Courses table contains 101 java 102 php 103 dbms Now assume 101 map to 1 102 map to 2 Now give your table which contains ssn as key 1 votes 1 votes daksirp commented Aug 30, 2018 reply Follow Share yaa, now understood, with this my other doubts are also cleared :) 0 votes 0 votes Shaik Masthan commented Aug 30, 2018 reply Follow Share That's why I commented that " take examples you can realise" 0 votes 0 votes daksirp commented Aug 30, 2018 reply Follow Share yaa :) 0 votes 0 votes smsubham commented Sep 1, 2018 reply Follow Share What is the relationship type (and which side has many , is its 1:m)? 0 votes 0 votes daksirp commented Sep 2, 2018 reply Follow Share @smsubham, it is 1:1 relationship, having full participation on Professor entity side. 0 votes 0 votes Please log in or register to add a comment.