DBMS ER to relational model

Question

Comments

should be cid

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it should be ssn ...because Professors are in full participation ..and relation is 1 to 1 ...

correct me if  i am wrong ...??

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take the sample example and realize

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course dont have total participation ...so what will you put in front of CID in tuple ??please help @ Shaik Masthan

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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

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what is causing the problem if we take ssn as the key ? all in one table

@Shaik+Masthan

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@daksirp,

Then how could you find the courses which are not participating in the relation?

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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

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You want to put null in ssn?

Note that ssn is key, it cannot have null or duplicate values

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noo, we will put NULL in courses, if courses is not participating, then we will put NULL in courses.

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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

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yaa, now understood, with this my other doubts are also cleared :)

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That's why I commented that " take examples you can realise"

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yaa :)

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What is the relationship type (and which side has many , is its 1:m)?

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@smsubham, it is 1:1 relationship, having full participation on Professor entity side.