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Author Question: What is a relational database model? How do relations differ from nonrelation tables? What will ... (Read 119 times)

HCHenry

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on: Jul 7, 2018
What is a relational database model? How do relations differ from nonrelation tables?
 
  What will be an ideal response?

Question 2

The ________ defines the number of instances of entity B that can (or must) be associated with each instance of entity A.
 
  A) Cardinality
  B) Relationship
  C) Identifier
  D) Association
Modern Systems Analysis and Design ¦ Valacich, George ¦ 8th Edition
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ebonylittles

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Reply #1 on: Jul 7, 2018
Answer to Question 1

The relational database model represents data in the form of related tables, or relations. A relation is a named, two-dimensional table of data. Each relation (or table) consists of a set of named columns and an arbitrary number of unnamed rows. Each column in a relation corresponds to an attribute of that relation. Each row of a relation corresponds to a record that contains data values for an entity. Relations have several properties that distinguish them from nonrelational tables: 1. Entries in cells are simple. An entry at the intersection of each row and column has a single value. 2. Entries in a given column are from the same set of values. 3. Each row is unique. Uniqueness is guaranteed because the relation has a nonempty primary key value. 4. The sequence of columns can be interchanged without changing the meaning or use of the relation. 5. The rows may be interchanged or stored in any sequences.

Answer to Question 2

A


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