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Вы можете ознакомиться и скачать презентацию на тему Normalization Theory. Доклад-сообщение содержит 46 слайдов. Презентации для любого класса можно скачать бесплатно. Если материал и наш сайт презентаций Mypresentation Вам понравились – поделитесь им с друзьями с помощью социальных кнопок и добавьте в закладки в своем браузере.

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Lecture 8. Normalization theory of the relational model National Aviation University Computer Science Faculty Department of Software Engineering

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CONTENTS What is the purpose of the normalization theory of RM Bad DB projects Functional dependencies Multivalued dependencies Join dependencies Normal forms Design of relational model schema

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What is the purpose of the normalization theory The theory of relational model normalization establish : how initial relational schema may be transformed into other relational schema, which equivalent initial one in some sense and Is better it in any sense. Thus this theory should answer to the following questions: What criteria of equivalence of relational schemas exist?; What criteria of estimation of relational schemas quality exist? What techniques of equivalent transformations of relational schemas exist?

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Bad DB design (1)

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Bad DB design (2)

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Normalization

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Compound domains and the First Normal Form (1NF)

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Functional dependencies (FD)

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Keys

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Properties of functional dependencies

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Logical inference of functional dependencies

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Closure, completeness, equivalence and minimal cover of FD

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FD и сущности предметной области Thesis. If application domain contains functional dependence А  В there exists class of the entities that consist of attributes (A, B). More over in this class set of attributes A is an unique identifier of entities of this class (key) and B are properties of these entities . If А  В1, А  В2, …, А  Вn, the exists class of entities with attributes(А, В1,…,Вn), where А – unique identifier and В1,…, Вn – are ordinary attributes.

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Not full (partial) functional dependencies and second normal form (2NF)

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Anomalies of insertion, deleting and updating when not full FD exist

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The second normal form (2NF)

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Example of reduction to the 2NF

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Example of reduction to the 2NF - Summary Source relation contains information from 2 entities, every resulting relations contain information about one entity each. Resulting relations do not contain anomalies of deletion, inserting and updating. Source relation can be restored from resulting relations with the help of natural join. Such decomposition do not lose functional dependencies. They may be restored from decomposed relations.

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Transitive dependencies and the Third Normal Form (3NF)

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Anomalies of insertion, deleting and updating when transitive FD exist

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The Third Normal Form (3NF)

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Example of reduction to the 3NF

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Example of reduction to the 3NF - Summary Results the same as in reduction to the 2NF: Source relation contains information from 2 entities, every resulting relations contain information about one entity each. Resulting relations do not contain anomalies of deletion, inserting and updating. Source relation can be restored from resulting relations with the help of natural join. Such decomposition do not lose functional dependencies. They may be restored from decomposed relations.

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Strong 3NF (S3NF)

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Reduction to the S3NF

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Boyce-Codd normal form (BCNF)

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Multivalued dependencies and the Fourth Normal Form (4NF)

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Definition of the multivalued dependency (MVD)

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MVD axioms

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Axioms that relates FD и MVD 1) Replication axiom

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Some additional properties of MVD 1) Union

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The fourth nornal form (4NF)

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Reduction to the 4NF and embedded MVD Algorithm reduction to the 4NF. Lets given relation R with attributes (set of attributes) А, В, С, and given multivalued dependence R.A  R.B. Relation R decomposed into the following two relations: R[A, B] и R[B, С]. If resulting relations are not in 4NF the algorithm is applied once more to these relations .

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Join dependency (JD) and the Fifth Normal Form (5NF)

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Relationships between JD and MVD Every JD of the form *(A, B) in relation with schema R(A,B), where А and В - set of attributes, is equivalent to the MVDs А ∩ В →→ А and А ∩ В →→ В. (Any MVD is JD, but not wise versa!!!) But there exist JD that are not equivalent any MVD. An example of such JD in relation R(A, B, C) is the dependency *((A,B), (B, C), (A,C)). It is not equivalent to any MVD. Example:

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The Fifth Normal Form - 5NF Classic example to motivate 5NF involves a join n-way decomposition that cannot be derived by a sequence of 2-way decompositions

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Example of the relation in the 5NF

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Example of the relation that violates 5NF, and reduction it to the 5NF

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Example of the relation that violates 4NF, and reduction it to the 4NF

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Design of relational model schema Formal description of the relational schema design task Decomposition of the relational schema Equivalence of relations Loosless decomposition with data preservation Loosless decomposition with dependencies preservation Equivalence of the normal forms Criteria of a relation qualities

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Formal definition of the relational schema design task In this definition it is necessary to clarify the following items: what procedure must be used to convert one set of relations into another; what does equivalence of the two schemas mean ; how can we estimate that one relational schema is better than another .

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Decomposition of the relational schema

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Equivalence of relational schemas by dependencies

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Equivalence of relational schemas by data

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Equivalence of the normal forms

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Criteria of the relational schema quality Let us consider how can we estimate the schema quality: that is criteria that one schema is better than other. One schema is better that other if it does not have data manipulation anomalies . Actually quality of the schema may be estimated by normal forms. The higher form is used the more qualified schema is received .

Теги Normalization Theory

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