The Relational Model is the most popular logic data model used in SQL databases. It is based on tables and relations, providing a straightforward and intuitive way to organize and analyze data. Developed in 1969 by Edgar F. Codd, an English computer scientist, the Relational Model has remained a fundamental concept in computer programming for over 50 years.
Tables are the building blocks of the Relational Model. They consist of rows and columns, similar to an Excel spreadsheet. Each entry in a table, known as a tuple, represents a specific row. The different attributes within a tuple, such as Name and Age, organize and categorize the data.
In a Relational Model, no duplicate data is allowed. Every row in a table must be unique in at least one attribute. This uniqueness is ensured by the relation key, which is one attribute that uniquely identifies a tuple. If more than one key is possible, a primary key is designated as the main identifier.
To maintain the integrity and consistency of the data, certain constraints are enforced. The key integrity constraint ensures that the key attribute(s) of a tuple are never null and never repeat. This constraint allows for unambiguous referencing to specific rows. Additionally, the domain constraints define the rules for the values that can be stored in each attribute, ensuring that only valid types of data are used.
Referencing other tables or tuples within the same table is a common practice in the Relational Model. To maintain referential integrity, certain rules must be followed. The referential integrity constraint prevents the deletion or editing of primary keys that are referenced elsewhere, prohibits the insertion of new records with non-existing keys, and requires that any changes to the key values are properly reflected in the related tables.
Overall, the Relational Model provides a solid foundation for organizing and analyzing data in SQL databases. Understanding its core concepts is essential for developers and database administrators alike.
Tags: relational model, SQL databases, tables, relations, tuples, attributes, relation key, primary key, key integrity constraint, domain constraints, referential integrity constraint.