*Equivalent Representations of a Relation*

On May 02, 2013, In The Relational Data Model by Admin

Views (1918)

Relations are sets of tuples, not lists of tuples. Therefore the order in which the tuples of a relation are presented is unimportant. For instance, we can list the three tuples of the following figure, in any of their six possible orders, and the relation is "the same" as shown in figure.

Furthermore, we can reorder the attributes of the relation as we choose, without changing the relation. Nevertheless, when we reorder the relation schema, we must be careful to remember that the attributes are column headers. Therefore, when we change the order of the attributes, we also change the order of their columns. When the columns move, the components of tuples change their order as well. The result is that each tuple has its components arranged in the same way as the attributes are arranged.

For example, the following figure shows one of the many relations that could be obtained from above figure by arranging rows and columns. These two relations are considered "the same". More exactly, these two tables are different presentations of the same relation.

### Tags

- tuples
- attributes
- schema
- Scrolling Cursors
- Protecting Against Concurrent Updates
- Modifications by Cursor
- Cursors
- Instead-Of Triggers
- Triggers in SQL
- Schema-Level Constraints and Triggers
- Tuple-Based CHECK Constraints
- Constraints on Attributes and Tuples
- Declaring Foreign-Key Constraints
- Keys Declared With UNIQUE
- Constraints and Triggers
- Modifying Views
- View Definitions
- Introduction to Selection of Indexes
- Default Values / Indexes
- Simple Table Declarations
- Defining a Relation Schema in SQL
- Deletion / Updates
- Database Modifications
- Grouping / HAVING Clauses
- Full-Relation Operations
- Natural Joins / Outerjoins
- Subqueries in FROM Clauses
- Conditions Involving Tuples
- Subqueries
- Union, Intersection, and Difference of Queries
- Interpreting Multirelation Queries
- Tuple Variables
- Disambiguating Attributes
- Queries Involving More Than One Relation
- Null Values and Comparisons Involving NULL
- Selection in SQL
- Projection in SQL
- The Database Language SQL
- Additional Constraint Examples
- Extending the Projection Operator
- Grouping
- Extended Operators of Relational Algebra
- Selection on Bags / Product of Bags / Joins of Bags
- Union, Intersection, and Difference of Bags
- Relational Operations on Bags
- A Linear Notation for Algebraic Expressions
- Dependent and Independent Operations
- Renaming
- Combining Operations to Form Queries
- Natural Joins / Theta-Joins
- Selection / Cartesian Product
- Set Operations on Relations
- An Algebra of Relational Operations
- Relational Algebra
- Attribute Lists
- Document Type Definitions
- XML and Its Data Model
- Information Integration Via Semistructured Data
- Semistructured Data Representation
- Object-Oriented Versus Object-Relational
- References
- Nested Relations
- The Object-Relational Model
- What If There Is No Key
- Representing ODL Relationships
- Representing Other Type Constructors
- Representing Set-Valued Attributes
- Nonatomic Attributes in Classes
- Declaring Keys in ODL
- Subclasses in ODL / Multiple Inheritance in ODL
- Types in ODL
- Methods in ODL
- Multiplicity of Relationships
- Relationships in ODL / Inverse Relationships
- Attributes in ODL
- Introduction to ODL
- The Type System
- Relationships Among Normal Forms
- Decomposition into Fourth Normal Form
- Reasoning About Multivalued Dependencies
- Definition of Multivalued Dependencies
- Multivalued Dependencies
- Third Normal Form
- Boyce-Codd Normal Form
- Decomposing Relations
- Projecting Functional Dependencies
- Closing Sets of Functional Dependencies
- The Transitive Rule
- Why the Closure Algorithm Works
- Computing the Closure of Attributes
- Trivial Functional Dependencies
- The Splitting/Combining Rule
- Rules About Functional Dependencies
- Keys of Relations
- Using Null Values to Combine Relations - Comparison of Approaches
- An Object-Oriented Approach
- Converting Subclass Structures to Relations
- Handling Weak Entity Sets
- Combining Relations
- From E/R Relationships to Relations
- From Entity Sets to Relations
- From E/R Diagrams to Relational Designs
- Relation Instances
- Tuples / Domains
- Attributes / Schemas
- The Relational Data Model
- Summary of The Entity-Relationship Data Model
- Weak Entity Set Notation
- Requirements for Weak Entity Sets
- Representing Keys in the E/R Model
- Keys in the E/R Model
- The Modeling of Constraints
- Picking the Right Kind of Element
- Design Principles
- Subclasses in the E/R Model
- Converting Multiway Relationships to Binary
- Attributes on Relationships
- Multiway Relationships
- Elements of the E/R Model
- The Entity-Relationship Data Model
- Database System Implementation
- Database Design
- Multimedia Data
- Relational Database Systems