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The Relational Model

The Relational Model. Pratt & Adamski, Chapter 2. Project Select Join. Union Intersect Subtract Product Division. Relational Algebra. Relational Database. Based in formal set theory Most common data structure Provable design principles. Relational Definition. Relations Attributes

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The Relational Model

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  1. The Relational Model Pratt & Adamski, Chapter 2

  2. Project Select Join Union Intersect Subtract Product Division Relational Algebra

  3. Relational Database • Based in formal set theory • Most common data structure • Provable design principles

  4. Relational Definition • Relations • Attributes • Relationships • Operations

  5. Relation Attributes Occurrences or Tuples

  6. Relation Requirements • Attributes are single valued, and all entries have the same data type • Each attribute has a distinct name • All values in a column are values of the same attribute • The order of columns is irrelevant • Each row is distinct • The order of rows is irrelevant

  7. Premiere Products Example

  8. Row Operations:Select, Project, Join • SELECT returns desired rows • PROJECT returns desired columns • JOIN creates one table from two by matching specified column values in the two tables

  9. Set Operations:Union, Intersection, Difference Returns the union, intersection, or difference of rows in two tables Note: both tables must be “union compatible.” They must have the same number of columns and the corresponding columns must have the same data types.

  10. Table Operations:Product, Division • PRODUCT (Cartesian product) produces a table with the columns of both tables and rows consisting of all combinations of rows from the two tables. If table A has m rows and table B has n rows, the product will have m*n rows. • DIVISION (A divided by B where the columns in B are also in A) produces a table consisting of columns in A that are not in B and match all the rows in B.

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