What is meant by the attribute preservation condition on a decomposition?

Database normalization is a systematic approach of organizing the fields and tables of a relational database to reduce redundancy and improve data integrity. The ultimate goal of normalization is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.

Normalization involves dividing large tables into smaller, more manageable pieces according to a set of normalization rules, known as normal forms. These forms, ranging from the first normal form (1NF) through the fifth normal form (5NF), each tackle different types of anomalies and issues to ensure that the data within the databases is clean, well-structured, and efficient.

For students tackling database design, understanding normalization is crucial as it underpins many decisions in structuring data effectively. It ensures that the database supports the needs of the users while minimizing duplication, thus streamlining the data update processes.

Relation decomposition is a strategy used in database normalization to divide a relation with potential problems, like redundancy or update anomalies, into two or more well-structured relations that collectively satisfy a desirable normal form. Decomposition must achieve two main objectives: The resulting relations should have less redundancy, and they should preserve all information as well as the integrity of the database.

Lossless-Join Decomposition

Essentially, for a decomposition to be lossless, you should be able to join the decomposed relations back to retrieve the original relation without losing any information or adding spurious tuples.

To refine database designs through decomposition, practitioners often apply a set of algorithms that automatically split problematic relations into several well-defined ones. It is a balance between enhancing structure without losing sight of inter-relationships between the data items in the process.

Data integrity refers to the accuracy, consistency, and reliability of data throughout its lifecycle. It is a critical aspect of database management as it ensures that the information stored is correct and can be trusted for various operations, from business decisions to application functions. Data integrity encompasses a range of measures and constraints, including:

• Entity Integrity: Ensuring that each record (or row) in a table is unique and identifiable.
• Referential Integrity: Verifying that relationships between tables remain consistent, meaning that foreign keys match primary keys in related tables.
• Domain Integrity: Enforcing valid entries for a given column by restricting the type, format, or range of possible values.
• User-Defined Integrity: Applying specific business rules to the data as required.

By maintaining high data integrity, databases not only preserve the quality of the data but also defend against unintended data corruption, thereby ensuring that users can depend on the information for their various needs.