63 votes 63 votes Relation $R$ with an associated set of functional dependencies, $F$, is decomposed into $\text{BCNF}$. The redundancy (arising out of functional dependencies) in the resulting set of relations is Zero More than zero but less than that of an equivalent $3NF$ decomposition Proportional to the size of F+ Indeterminate Databases gatecse-2002 databases database-normalization normal + – Kathleen asked Sep 15, 2014 • edited Feb 16, 2018 by dj_1 Kathleen 20.3k views answer comment Share Follow See all 9 Comments See all 9 9 Comments reply Show 6 previous comments Aanshi Dua commented Dec 21, 2016 reply Follow Share Any good references to study MVDs? 0 votes 0 votes set2018 commented Oct 9, 2017 reply Follow Share based on functional dependency BCNF has 0 percent redundancy ,but is there any chance for other type redundancy m not getting other type ?explain pls 0 votes 0 votes Venky8 commented May 4, 2021 i edited by Venky8 May 4, 2021 reply Follow Share @set2018 A table is in 4NF if it is in BCNF and it should not have any multivalued dependencies. Databases with multivalued dependencies exhibit redundancy. So redundancy arising out of functional dependencies is 0 in BCNF but if the table has any multivalued dependencies then it has redundancy due to the multivalued dependencies. See Ref: 1. https://en.wikipedia.org/wiki/Multivalued_dependency#Example 2. https://www.studytonight.com/dbms/fourth-normal-form.php 1 votes 1 votes Please log in or register to add a comment.
Best answer 71 votes 71 votes Answer is A. If a relation schema is in BCNF then all redundancy based on functional dependency has been removed, although other types of redundancy may still exist. A relational schema R is in Boyce–Codd normal form if and only if for every one of its dependencies X → Y, at least one of the following conditions hold: X → Y is a trivial functional dependency (Y ⊆ X) X is a super key for schema R http://en.wikipedia.org/wiki/Boyce%E2%80%93Codd_normal_form Priya_das answered Jan 27, 2015 • edited Jun 22, 2018 by Milicevic3306 Priya_das comment Share Follow See all 13 Comments See all 13 13 Comments reply Show 10 previous comments prithatiti commented Apr 5, 2020 i edited by prithatiti Apr 5, 2020 reply Follow Share (C) Proportional to the size of F+ I really didn't understand this option. What does it mean by the size of the F closure? 0 votes 0 votes aditya_cracks2021 commented Nov 18, 2020 reply Follow Share Yes, it's the size of closure. 0 votes 0 votes KartikGawande commented Nov 25, 2022 reply Follow Share Jean no Multivalued Dependencies doesnt follow armstrong axioms like decomposition etc so they r NOT a type of FD 0 votes 0 votes Please log in or register to add a comment.
42 votes 42 votes should be zero.. BCNF can have Multi valued dependency but no redundancy due to FDs.. Digvijay Pandey answered May 15, 2015 • edited May 15, 2015 by Digvijay Pandey Digvijay Pandey comment Share Follow See all 9 Comments See all 9 9 Comments reply Hemant Parihar commented Oct 9, 2017 reply Follow Share @digvijay pandey can you please explain what is multi valued dependency? And how it can be present in BCNF? 1 votes 1 votes Rupendra Choudhary commented Jan 14, 2018 reply Follow Share Hello hemant A relation would be BCNF when functional dependencies are like $x->y$ ; where x is super key and in that way when attributes are dependent on super key , redundancy can't exist. But what will happen when we have such a relation that doesn't contain any non-trivial functional dependency?Hope you can guess that in such case super key will be the whole set of attributes.So eventually we can say such a relation will be BCNF relation. Can we say that this kind of relation will be free of redundancies ? There comes the term call 'Multivalued dependency', whose presence make the relation redundant. like R(course_id,professor_name,Books_name) Course_id Professor_name Books_name C1 P1/P2 B1/B2/B3 C2 P2/P3 B4/B5 C3 P4 B4 You can see , this relation is in BCNF as no functional dependencies exist there. But here exists multivalued dependencies (basically multivalued dependency means multiple values of some attributes are dependent on some attribute value ) 18 votes 18 votes srestha commented Jul 11, 2018 reply Follow Share https://stackoverflow.com/questions/46273778/bcnf-and-4nf-property 0 votes 0 votes ayushsomani commented Sep 4, 2019 reply Follow Share @Rupendra Choudhary @srestha @Priya_das Answer should be Zero coz in BCNF we cannot have redundancies due to Functional dependencies but can have other redundancies like Multi-valued Dependency. Correct me, if i am wrong. One more thing, basic definition of a Relation says that a Table should have atomic attributes i.e. neither Multi-valued nor composite. Then, how can we relate in BCNF as a Relation in BCNF qualifies to be in 1NF. 1 votes 1 votes srestha commented Sep 4, 2019 reply Follow Share BCNF has "Multi-valued Dependency.". No , it is not correct. MVD is for4NF 1 votes 1 votes ayushsomani commented Sep 5, 2019 reply Follow Share Thanks @srestha for Replying. Can you share the Resource where it is mentioned? Coz, What i have learnt is that, by definition, a Relation is always in 1NF and in 1NF, we cannot have either Composite or Multi-valued Attributes. Please, Confirm. 1 votes 1 votes srestha commented Sep 5, 2019 reply Follow Share 1NF is atomic relation. I donot think attribute depends on it. Multivalued dependency is not in 1NF. 0 votes 0 votes ayushsomani commented Sep 6, 2019 reply Follow Share @srestha Thanks. I got it now. In 1NF we make attributes atomic, either by removing Composite attributes (by breaking them into simpler attributes), or, Multi-valued attributes (by making a new tuple for each 'value' in Multi-valued attribute) Multi-valued Dependency is removed in 4NF. 0 votes 0 votes prithatiti commented Apr 5, 2020 i edited by prithatiti Apr 5, 2020 reply Follow Share @srestha In 4NF we remove the multivalued dependency. That means in BCNF multi-valued dependencies might be present. Because in 4NF, the table must be present in the form of BCNF. Correct me if I am wrong. 0 votes 0 votes Please log in or register to add a comment.
6 votes 6 votes Yes , the answer should be zero. There should not be any redundancy due to FD in BCNF. worst_engineer answered May 15, 2015 • edited May 15, 2015 by worst_engineer worst_engineer comment Share Follow See all 2 Comments See all 2 2 Comments reply Digvijay Pandey commented May 15, 2015 reply Follow Share **redundancy. There should not be any //dependency due to FD in BCNF. 0 votes 0 votes worst_engineer commented May 15, 2015 reply Follow Share ohh yaa.. typos there.. correcting it..thanks :) 0 votes 0 votes Please log in or register to add a comment.
1 votes 1 votes Explain please BCNF can have Multi valued dependency but no redundancy due to FDs flash12 answered Dec 16, 2018 flash12 comment Share Follow See all 0 reply Please log in or register to add a comment.