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Explain the concepts of relational data model?
Relational Data Model - The relational model was first introduced through Prof. E.F. Codd of the IBM Research in the year 1970 and attracted immediate attention because of its simplicity and mathematical foundation. The model uses the concept of a mathematical relation (such as a table of values) as its primary building block, and has its theoretical basis within set theory and first-order predicate logic. The relational model represents the database as a collection of relations. The relational model such as all other models consists of three basic elements:
What subschema expresses ? A subschema expresses the external view. (External schemas are called also called as subschemas)
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
Explain the term- Periodic recomputation Periodic recomputation: Base values are often updated in bunches. Sometimes, it is possible to just recompute all derived attributes p
construct a b-tree for the following set of key values 2,3,5,7,11,17,19,23,29,31.assume that the tree is initial empty and the values are added in ascending order
Explain Domain calculus Domain calculus is one of the types of the relational calculus. The formal specification of the domain calculus was planned after the development of the
Set Difference If R1 and R2 are two union compatible relations or relations then result of R3 =R1- R2 is the relation that have only those tuples that are in R1 but not in R2.
what is the importance of back up files
How can i turn a conceptual entity relationship diagram into a logical entity relationship diagram? what do i have to do with "mandetory or" and "optional or" relationships?
Database Manager It is the interface among low-level data, queries and application programs. Databases typically need a large amount of storage space. It is kept on disks, as
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