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#1
 
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BCNF -
08-01-2008
, 04:45 AM
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A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these |
dependent on attribute on A
#2
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Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A |
Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his
later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal
form if, and only if, every determinant is a candidate key. Most
entities in 3NF are already in BCNF.
BCNF covers very specific situations where 3NF misses inter-dependencies
between non-key (but candidate key) attributes. Typically, any relation
that is in 3NF is also in BCNF. However, a 3NF relation won't be in BCNF
if (a) there are multiple candidate keys, (b) the keys are composed of
multiple attributes, and (c) there are common attributes between the keys.
--
Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington
damorgan@x.washington.edu (replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org
#3
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Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A |
Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his
later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal
form if, and only if, every determinant is a candidate key. Most
entities in 3NF are already in BCNF.
BCNF covers very specific situations where 3NF misses inter-dependencies
between non-key (but candidate key) attributes. Typically, any relation
that is in 3NF is also in BCNF. However, a 3NF relation won't be in BCNF
if (a) there are multiple candidate keys, (b) the keys are composed of
multiple attributes, and (c) there are common attributes between the keys.
--
Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington
damorgan@x.washington.edu (replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org
#4
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Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A |
Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his
later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal
form if, and only if, every determinant is a candidate key. Most
entities in 3NF are already in BCNF.
BCNF covers very specific situations where 3NF misses inter-dependencies
between non-key (but candidate key) attributes. Typically, any relation
that is in 3NF is also in BCNF. However, a 3NF relation won't be in BCNF
if (a) there are multiple candidate keys, (b) the keys are composed of
multiple attributes, and (c) there are common attributes between the keys.
--
Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington
damorgan@x.washington.edu (replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org
#5
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Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A |
Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his
later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal
form if, and only if, every determinant is a candidate key. Most
entities in 3NF are already in BCNF.
BCNF covers very specific situations where 3NF misses inter-dependencies
between non-key (but candidate key) attributes. Typically, any relation
that is in 3NF is also in BCNF. However, a 3NF relation won't be in BCNF
if (a) there are multiple candidate keys, (b) the keys are composed of
multiple attributes, and (c) there are common attributes between the keys.
--
Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington
damorgan@x.washington.edu (replace x with u to respond)
Puget Sound Oracle Users Group
www.psoug.org
#6
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aarklon (AT) gmail (DOT) com wrote: Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A Personally I prefer the following definition: Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal form if, and only if, every determinant is a candidate key. |
determinant is a SUPER key. Sometimes paraphrased as "arrows out of super
keys".
3NF is arguably a mistake because it is concerned only with dependent
non-prime attributes. BCNF is much more important than 3NF although it
should be understood that BCNF is not dependency-preserving whereas 3NF is.
--
David Portas
#7
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aarklon (AT) gmail (DOT) com wrote: Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A Personally I prefer the following definition: Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal form if, and only if, every determinant is a candidate key. |
determinant is a SUPER key. Sometimes paraphrased as "arrows out of super
keys".
3NF is arguably a mistake because it is concerned only with dependent
non-prime attributes. BCNF is much more important than 3NF although it
should be understood that BCNF is not dependency-preserving whereas 3NF is.
--
David Portas
#8
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aarklon (AT) gmail (DOT) com wrote: Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A Personally I prefer the following definition: Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal form if, and only if, every determinant is a candidate key. |
determinant is a SUPER key. Sometimes paraphrased as "arrows out of super
keys".
3NF is arguably a mistake because it is concerned only with dependent
non-prime attributes. BCNF is much more important than 3NF although it
should be understood that BCNF is not dependency-preserving whereas 3NF is.
--
David Portas
#9
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aarklon (AT) gmail (DOT) com wrote: Hi all, BCNF the following is the definition is the definition of BCNF , which i saw in a schaum series book 1) The relation is 1 N.F 2) for every functional dependency of the form X -> A , we have either A C X or X is a super key of r. in other words, every functional dependency is either a trivial dependency or in the case that the functional dependency is not trivial then X must be a super key. now my questions are as follows 1) we know that 2-ND normal form is all about separating partial dependencies and full dependencies.third normal form is all about removing transitive dependencies, in these lines can any one give simple/ easy to understand method/explanation for converting a relation in 3rd normal form to BCNF 2) how correct is the following definition of transitive dependencies transitive dependencies assume that A,B, and C are the set of attributes of a relation(R). further assume that the following functional dependencies are satisfied simultaneously : A -> B , B -/- A, B -> C , and C -/-> A and A -> C observe that C -> B is neither prohibited nor required. if all these conditions are true, we will say that attribute C is transitively dependent on attribute on A Personally I prefer the following definition: Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal form if, and only if, every determinant is a candidate key. |
determinant is a SUPER key. Sometimes paraphrased as "arrows out of super
keys".
3NF is arguably a mistake because it is concerned only with dependent
non-prime attributes. BCNF is much more important than 3NF although it
should be understood that BCNF is not dependency-preserving whereas 3NF is.
--
David Portas
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