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Relational Model
The relational database model represents data to the user in the form of tables. Each table is related to other tables in the database in some way. This relationship enables the end user to search the database for particular pieces of information that may not co-exist in the same table.
The relational database model is currently very popular. This is because of the level of abstraction that it provides from the actual data. End users do not see, nor do they need to know about, the file-level operations that the database engine performs. Instead, an end user deals with a conceptual layer that makes the data appear to have a certain logical organization.
The basic structures of a relational database (as defined by the relational model developed by E.F. Codd) are entities and attributes:
- Entities are the primary objects around which a relational database is organized. They include tables, columns, rows, keys, and indexes. For example, in the sample database provided with Pervasive.SQL, entities include courses, classes, instructors, students, grades, etc. (You can find the sample database in the \pvsw\demodata directory.)
- Attributes are descriptors for a column, table, or index. Attributes are the components of entities that define the uniqueness and usefulness of an entity. In the sample database, the Room table (entity) contains the attributes Type and Capacity. (The sample database is found in pvsw\demodata.)
In the relational model shown below, the end user perceives and manipulates data as tables, consisting of rows and columns. A database usually consists of several tables, with all information in a given table being related in some way. For example, in the sample database, there is a Class table. Each row in the table contains columns of information relevant to each class, such as class ID, name, section, maximum size, and so on.
When searching for information in a relational database, the results are generated as a new table, using information from existing tables. This new table is called a derived table, or view, which in turn can itself be used to generate another, different view.
For more information about Pervasive.SQL and relational databases, refer to Chapter 5, Product Architecture.
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