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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:
List some instances of collection types? a) sets b) arrays c) multisets
What is the difference between link and reference? The fundamental difference between links and references is that links are symmetrical on the other hand references refer only
explain external view
What are the various forms of data transparency? a) fragmentation transparency b) replication transparency c) location transparency
Differance between Unordered and ordered file ? Unordered file do no has any sequence although ordered file has arranged in a few sequence and data are assigned in ordered form
What are the different approaches for database design? There are two basic approaches for database design which are as follows: Attribute driven: It compiles a list of att
List the set operations of SQL? 1) Union 2) Intersect operation 3) The except operation
Having Clause with sub queries: First we have to recollect the GROUP BYclause. The following query searches the minimum salary in every department. SELECT DEPTNO, MIN (SAL)
Define Hash files organization a. Hashing includes computing the address of a data item by calculating a function on the search key value. b. A hash function h is a functi
read-set(T) : Each data items that are read by a transaction T Timestamps : for all transaction T, the start-time and the end time are reserved for all the three phases.
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