The relational model for database management is based on concepts derived from the mathematical theory of sets. Basically, set theory defines a table as a relation. The number of rows is the cardinality of the relation, and the number of columns is the degree. Any manipulation of a table in a relational database has a consistent, predictable outcome, because the mathematical operations on relations are well-defined.
By way of comparison, database management products based on hierarchical, network, or object-oriented architectures are not built on rigorous theoretical foundations. Therefore, the behavior of such products is not as predictable or as flexible as that of relational products.
The SQL Optimizer in the database builds the most efficient access path to requested data. The Optimizer can readily adapt to changes in system variables by rebuilding access paths without programmer intervention. This adaptability is necessary because database definitions and data demographics can change.