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Chapter 6: Normalization

Chapter 6: Normalization. Database Modeling and Design . Paul Chen. www.cs522.com (Please reference white papers on Data Modeling at Seattle U teaching materials website). Chapter 6 - Objectives. Purpose of normalization. Problems associated with redundant data.

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Chapter 6: Normalization

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  1. Chapter 6: Normalization Database Modeling and Design Paul Chen www.cs522.com (Please reference white papers on Data Modeling at Seattle U teaching materials website)

  2. Chapter 6 - Objectives • Purpose of normalization. • Problems associated with redundant data. • Identification of various types of update anomalies such as insertion, deletion, and modification anomalies. • How to recognize appropriateness or quality of the design of relations.

  3. Chapter 6 - Objectives • How functional dependencies can be used to group attributes into relations that are in a known normal form. • How to undertake process of normalization. • How to identify most commonly used normal forms, namely 1NF, 2NF, 3NF, and Boyce–Codd normal form (BCNF). • How to identify fourth (4NF) and fifth (5NF) normal forms.

  4. Normalization A technique to make sure the data in a logical data models is defined once and only once. Normalization helps minimum data redundancy, and minimize update abnormalities. They are: • First Normal Form • Second Normal Form • Third Normal Form • Boyce–Codd normal form (BCNF)

  5. Normalization • First Normal Form: Relationships between primary key and each attribute must be one-to-one; ie., remove repeating group. • Second Normal Form: All non-key elements are dependent upon the entire primary key rather than any part thereof. • Third Normal Form: Elimination of the dependence of non-key field upon any other field excepts the primary keys.

  6. Data Redundancy • Major aim of relational database design is to group attributes into relations to minimize data redundancy and reduce file storage space required by base relations. • Problems associated with data redundancy are illustrated by comparing the following Staff and Branch relations with the StaffBranch relation.

  7. Data Redundancy

  8. Data Redundancy • StaffBranch relation has redundant data: details of a branch are repeated for every member of staff. • In contrast, branch information appears only once for each branch in Branch relation and only branchNo is repeated in Staff relation, to represent where each member of staff works.

  9. Update Anomalies • Relations that contain redundant information may potentially suffer from update anomalies. • Types of update anomalies include: • Insertion • Deletion • Modification.

  10. Functional Dependency • Main concept associated with normalization. • Functional Dependency • Describes relationship between attributes in a relation. • If A and B are attributes of relation R, B is functionally dependent on A (denoted A  B), if each value of A in R is associated with exactly one value of B in R.

  11. Functional Dependency • Property of the meaning (or semantics) of the attributes in a relation. • Diagrammatic representation: • Determinant of a functional dependency refers to attribute or group of attributes on left-hand side of the arrow.

  12. Functional Dependency

  13. The Process of Normalization • Formal technique for analyzing a relation based on its primary key and functional dependencies between its attributes. • Often executed as a series of steps. Each step corresponds to a specific normal form, which has known properties. • As normalization proceeds, relations become progressively more restricted (stronger) in format and also less vulnerable to update anomalies.

  14. OrderNo (PK) part-no Qty part-name PK + PK NN ND FK FK 1 1 123 Nut 3 5 123 Bolt PK: Primary KeyFK: Foreign KeyNN: No NullND: No duplicate Order Part Relationship Order/Part

  15. Unnormalized Form (UNF) • A table that contains one or more repeating groups. • To create an unnormalized table: • transform data from information source (e.g. form) into table format with columns and rows.

  16. First Normal Form (1NF) • A relation in which intersection of each row and column contains one and only one value.

  17. UNF to 1NF • Nominate an attribute or group of attributes to act as the key for the unnormalized table. • Identify repeating group(s) in unnormalized table which repeats for the key attribute(s).

  18. UNF to 1NF • Remove repeating group by: • entering appropriate data into the empty columns of rows containing repeating data (‘flattening’ the table). Or by • placing repeating data along with copy of the original key attribute(s) into a separate relation.

  19. First Normal Form Item Table Qty-Store-2 Qty-Store-3 Qty-Store-1 Item No PK 3000 4000 5000 101 The above is an violation of first normal form because there exists a repeated group.

  20. Rule Number 1 • For each occurrence of an entity, there is only one and only one value for each its attributes. Attributes with repeating values form at least one new entity. • N other words, relationship between primary key and each attribute must be one-to-one.

  21. Possible Solution Store Store/Item Store ID Store ID Item- No Qty Sold + PK PK FK FK S1 S1 3000 101 S2 S2 102 4000

  22. Second Normal Form (2NF) • Based on concept of full functional dependency: • A and B are attributes of a relation, • B is fully dependent on A if B is functionally dependent on A but not on any proper subset of A. • 2NF - A relation that is in 1NF and every non-primary-key attribute is fully functionally dependent on the primary key.

  23. 1NF to 2NF • Identify primary key for the 1NF relation. • Identify functional dependencies in the relation. • If partial dependencies exist on the primary key remove them by placing them in a new relation along with copy of their determinant.

  24. Second Normal Form Student/Course Course Name Course No Student No Teacher code Grade PK + FK FK FK 3.0 Math ST01 100 T2 Lee ST02 4.0 T1 CS Doe 200 Both course name and student name should be removed because They are not related to the entire student/course primary key.

  25. Possible Solution Student No Course Name Student Name Student Course No Student/Course

  26. Rule Number 2 • Each attribute must be related to the entire primary key.

  27. Second Normal Process Order Part Part Name Order No Pt-price PartNo Order-Dt PK PK 1/2/01 Nut 1 1 1.5 1/3/01 5 Bolts 2.0 3 Order/Part Order No Partno QTY How about Putting PartName In Order/part Table? PK + 1 123 1 1 5 3 123

  28. Third Normal Form (3NF) • Based on concept of transitive dependency: • A, B and C are attributes of a relation such that if A  B and B  C, • then C is transitively dependent on A through B. (Provided that A is not functionally dependent on B or C). • 3NF - A relation that is in 1NF and 2NF and in which no non-primary-key attribute is transitively dependent on the primary key.

  29. 2NF to 3NF • Identify the primary key in the 2NF relation. • Identify functional dependencies in the relation. • If transitive dependencies exist on the primary key remove them by placing them in a new relation along with copy of their determinant.

  30. Third Normal Form COURSE Course Id Teacher Code Course Name Dept Name Teacher Name Dept -Id PK T1 DOE MH400 Math Math A1 CS DB CS401 T2 CS Lee The relationship between any two non-primary key components must not be one-to-one. What’s wrong with the above?

  31. Rule Number 3 • The relationship between any two non-primary key components must not be one-t-one; ie., remove tables within tables.

  32. The Normal Process Order Customer Cust-Name Order ID Order DT Cust-Id Cust-Id PK PK FK 1 Lee 1 1/2/ 01 1 Sato 1/5/21 3 3 5 It would be a violation of third normal form to place cust-name in the order table.

  33. Why Reasons: • One-to-one relationship between two non-primary key columns (Cus-Id and Cust-name). • Redundancy • An update anomaly (when a customer name was changed) • Worse yet when a new name was added (the name could not be stored until the customer placed at least one order)

  34. Normalization (such as TV, Bed) Item Qty_ Hotel _no -2 Qty_ Hotel _no -3 Qty_Hotel _no-1 Item No PK 6 9 14 101 The above is an violation of first normal form because there exists a repeated group. Relationships between primary key and each attribute must be one-to-one.

  35. Possible Solution Hotel Hotel/Item Hotel name Hotel ID Hotel ID Item- No Qty + PK PK Min-nan FK FK H1 H1 6 101(TV) H2 Xiamen H2 102 5

  36. Second Normal Form Room/Hotel Hotel No Price Room No Hotel name Type 100 101 Xiamen 4 double Hotel Name should be removed because it is not related to the entire room/hotel primary key. What happens if one of the hotel names is being changed?

  37. Third Normal Form • The relationship between any two non-primary key components must not be one-t-one; ie., remove tables within tables.

  38. Third Normal Form City Hotel/City City ID City name Hotel ID Hotel - name City Id PK PK Las Vegas H0 C1 Circus C1 H1 C1 Flemingo C2 Seattle H2 Holiday C2 What happens if a new City name is added to the Hotel/City Table?

  39. Boyce–Codd Normal Form (BCNF) • Based on functional dependencies that take into account all candidate keys in a relation, however BCNF also has additional constraints compared with general definition of 3NF. • BCNF - A relation is in BCNF if and only if every determinant is a candidate key.

  40. Boyce–Codd Normal Form (BCNF) • Difference between 3NF and BCNF is that for a functional dependency A  B, 3NF allows this dependency in a relation if B is a primary-key attribute and A is not a candidate key. • Whereas, BCNF insists that for this dependency to remain in a relation, A must be a candidate key. • Every relation in BCNF is also in 3NF. However, relation in 3NF may not be in BCNF.

  41. Boyce–Codd Normal Form (BCNF) • Violation of BCNF is quite rare. • Potential to violate BCNF may occur in a relation that: • contains two (or more) composite candidate keys; • the candidate keys overlap (ie. have at least one attribute in common).

  42. Review of Normalization (UNF to BCNF)

  43. Review of Normalization (UNF to BCNF)

  44. Review of Normalization (UNF to BCNF)

  45. Review of Normalization (UNF to BCNF)

  46. Fourth Normal Form (4NF) • Although BCNF removes anomalies due to functional dependencies, another type of dependency called a multi-valued dependency (MVD) can also cause data redundancy. • Possible existence of MVDs in a relation is due to 1NF and can result in data redundancy.

  47. Fourth Normal Form (4NF) - MVD • Dependency between attributes (for example, A, B, and C) in a relation, such that for each value of A there is a set of values for B and a set of values for C. However, set of values for B and C are independent of each other.

  48. Fourth Normal Form (4NF) • MVD between attributes A, B, and C in a relation using the following notation: A ¾¾ØØ B A ¾¾ØØ C

  49. Fourth Normal Form (4NF) • MVD can be further defined as being trivial or nontrivial. • MVD A ¾¾ØØ B in relation R is defined as being trivial if (a) B is a subset of A or (b) A  B = R. • MVD is defined as being nontrivial if neither (a) nor (b) are satisfied. • Trivial MVD does not specify a constraint on a relation, while a nontrivial MVD does specify a constraint.

  50. Fourth Normal Form (4NF) • Defined as a relation that is in BCNF and contains no nontrivial MVDs.

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