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Define multivalued dependency and 4NF.
Ans: Multivalued Dependency - Assume R be a relation schema and let α ⊆ R and β ⊆ R. The multivalued dependency
α →→β
holds on R if, in any type of legal relation r(R), for all pairs of tuples t1 and t2 in r like that
t1[α] = t2[α], there exist tuples t3 and t4 in r like
t1[α] = t2[α] = t3[α] = t4[α]
t3[β] = t1[β]
t3[R - β] = t2[R - β]
t4[β] = t2[β]
t4[R - β] = t1[R - β]
Fourth Normal Form (4 NF) - A relation schema R is in 4NF regarding to a set D of functional and multivalued dependencies if, for all multivalued dependencies in D+ of the
form α →→β, in which α ⊆ R and β ⊆ R, at least one of the subsequent holds:
Can we delete data element, which is being used by table fields. No we cant delete data element.
Example -GRANT CREATE SESSION TO MCA12; (This command gives system level permission on creating a session - not portable) GRANT SELECT ON EMP TO MCA12; (Object level permi
Mappings between Levels and Data Independence The 3 levels of abstraction in the database do not exist separately of each other. There must be some correspondence, or mapping
how design database from begining
By using the delete operation some consisting records can be deleted from a relation. To delete some definite records from the database a condition is also specified based on which
Provide Examples of different types of Time and Date formats. It's most common store dates using a dash (-) as a colon (:)and the delimiter as the time delimiter. The given fo
1. Staff(staffID, firstName, lastName, availabilityID, experience, phone, mobile, email); 2. Availability(availabilityID, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday,
Increased overheads on update : On the drawbacks side, it will need the system to ensure that all replicas of a relation are consistent. This shows that all the replicas of the rel
Concatenation operator Example : Printing name and job as one string as column name employees: SELECT ENAME||JOB "EMPLOYEES" FROM EMP;
What does the extract statement do in extract datasets? The data is written to virtual memory by extract commands.
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