2 votes 2 votes kirtikanwar asked Jan 20, 2017 kirtikanwar 1.1k views answer comment Share Follow See all 16 Comments See all 16 16 Comments reply santhoshdevulapally commented Jan 20, 2017 i edited by santhoshdevulapally Jan 22, 2017 reply Follow Share E1RE2 is one relation containing key (D) // partial participation on E1 side we can combine. R2E3 is one relation and key is(G). two tables are sufficient. 0 votes 0 votes Anmol Verma commented Jan 21, 2017 reply Follow Share @santoshdevulapally......I've a doubt...... when we create a relational table.... i) for each entity ii) for multivalued and composite attributes iii) for weak entity and iv) for m:n relationship...... in this question atleast three tables required for 3 entities.....correct me if i'm wrong..... 0 votes 0 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share In the table there are no multivalued attributes and no m:n relationships all 1:1 relationships. 0 votes 0 votes Anmol Verma commented Jan 22, 2017 reply Follow Share but there are 3 entities...??? 1 votes 1 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share @anmol If there is partial participation we can merge into one table . Key value is 'A' act like alternate key and AD act like primary key. 0 votes 0 votes Anmol Verma commented Jan 22, 2017 reply Follow Share When we have to merge the attributes and when to not in the relation......can you please explain me with an example.....???? 0 votes 0 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share If there is one to one correspandance b/w two entities intermediate relation(R) can be merge with any of the two entites because there is one-one correspandance. 2)if there is (A-entity)1:m(B-entity) R is mapped with B entity because In A one attribute mapped to many attributes. 3) if there is (A)m:1(B) R is mapped with entity A same reason. 4) if any multivalued or weak entity set we cannot combine with any of entity this should be kept separate table. 5)If any total participation we can merge two tables and it satisfy the BCNF relation also. 6) if one side partial participation and one one correspandance b/w them we can merge R to participation entity side. If u have any doubt refer std text book once. 0 votes 0 votes Anmol Verma commented Jan 22, 2017 reply Follow Share Thankyou......:-) 0 votes 0 votes Rahul Jain25 commented Jan 22, 2017 reply Follow Share @santosh, I agrre with you that E1 R E2 will form a single table. But you said AD is key?? Why is that so??? I think A as a key is sufficeient. 0 votes 0 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share @rahul If null values are present in E1 we cannot map to any entity in E2.If A is primary key null values not allowed. we cannot guarantee every entity need not participate with every other entity in E2. So A act like alternate key and AD act like primary key. It depends on table which we consider. 1 votes 1 votes Rahul Jain25 commented Jan 22, 2017 reply Follow Share But null values are not allowed in primary key right?? If E1 has 3 tuples and E2 has 5 tuples. Than E1 will habe null values right, that is what you wanted to say in previous comment if I am getting it right. Byt then can an attribute of compound primary key take a null value??? 0 votes 0 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share primary key not allow null values. kk got it .Here A is primary key so A is sufficient key for table E1RE2. 0 votes 0 votes Rahul Jain25 commented Jan 22, 2017 reply Follow Share @santosh i am not sure here, btw I was asking not concluding. How will such relation be stored when E1 has 3 tuples and E2 has 5 tuples with E1 having total participation. I think D should be the key. And my doubt is that , Is attribute of compound PK allowed to take NULL??? 0 votes 0 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share Even i have some doubt in this,now it is cleared. E1(n attributes) and E2(m entities) [n<=m]and E1-E2 participation on E1 side Then m acts like primary key. In the given diagram D is key. primary key may be simple or compound it is not allowed null values. 1 votes 1 votes Rahul Jain25 commented Jan 22, 2017 reply Follow Share Yeah. That should be the answer. Cheers to discussions and gateoverflow☺ 1 votes 1 votes santhoshdevulapally commented Jan 22, 2017 reply Follow Share Ha ha.... 0 votes 0 votes Please log in or register to add a comment.
0 votes 0 votes 4 table i.E1{a,b,c} ii.E2{d,e,f} iii.E3{g,h} iv.R2{g,d} Abhishek prajapati answered Sep 5, 2017 Abhishek prajapati comment Share Follow See all 0 reply Please log in or register to add a comment.
–1 votes –1 votes in case of 1:1 relationship we can merge the two tables into a single table but here where is 1:1 ..is it b/w E2 and E3?? ?? cse23 answered Jan 22, 2017 cse23 comment Share Follow See all 0 reply Please log in or register to add a comment.