What does the delete operation exception in relational normalization mean?

The deletion operation anomaly in relational normalization refers to the deletion of data that should not be deleted, and normalization is a set of rules to solve problems such as abnormal insertion, deletion, and modification of data in the database; relational normalization theory provides Theoretical standards for judging the quality of relational logic patterns, helping to predict possible problems in patterns, and serving as algorithmic tools for generating various patterns.

The deletion operation exception in relational normalization means that data that should not be deleted is deleted.

Normalization is a set of rules to solve problems such as insertion, deletion, and modification exceptions of data in the database.

Normalization theory is a guide and tool for database logical design. The specific steps are as follows:

(1) Examine the functional dependencies of the relational model and determine the paradigm level. Analyze each relationship pattern one by one, examine whether there are partial functional dependencies, transitive functional dependencies, etc., and determine which paradigm they belong to.

(2) Merge or decompose relationship patterns. According to the application requirements, examine whether these relationship patterns meet the requirements to determine whether these patterns need to be merged or decomposed. For example, relationship patterns with the same primary key can generally be merged; for non-BCNF relationship patterns, "abnormal disadvantages" should be examined "Will it have an impact in actual applications? For those that are just queries and do not perform update operations, there is no need to normalize (decompose) the schema. In actual applications, the higher the degree of normalization, the better. Sometimes decomposition can eliminate update anomalies. The benefits are outweighed by the inefficiency of frequent natural joins required for frequent queries. For those relationship patterns that need to be decomposed, standardized methods and theories can be used to decompose the pattern. Finally, each generated relationship model is evaluated and adjusted to determine a more appropriate set of relationship models.

Relationship normalization theory provides theoretical standards for judging the pros and cons of relational logic models, helps predict possible problems in the model, and is an algorithmic tool for generating various patterns, so it is a powerful tool for designers.

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