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Normalisation FIRST NORMAL FORM 1NF 2NF 3NF BCNF DEFINITION: A table is in its first normal form if it contains no repeating attributes or groups of attributes. NON-KEY KEY NON-KEY KEY KEY NON-KEY NON-KEY KEY STUDENT(Number, Name, Classes) | V STUDENT(Number, Name, Classes) SECOND NORMAL FORM CODD’S TWELVE RULES FOR RELATIONAL DATABASES 1. Data should be presented to the user in table form. 2. Every data element should be accessible without ambiguity. 3. A field should be allowed to remain empty for future use. 4. The description of a database should be accessible to the user. 5. A database must support a clearly defined language to define the database, view the definition, manipulate the data, and restrict some data values to maintain integrity. 6. Data should be able to be changed through any view available to the user. 7. All records in a file must be able to be added, deleted, or changed with a single command. 8. Changes in how data is stored or retrieved should not affect how the user accesses the data. 9. The user's view of the data should be unaffected by its actual form in files. DEFINITION: A table is in the second normal form if it is in the first normal form AND no column that is not part of the primary key is dependant only a portion of the primary key. Remove any partial dependencies in a relation THIRD NORMAL FORM DEFINITION: A table is in the third normal form if it is in the second normal form and there are no nonkey columns dependant on other non-key columns that could not act as the primary key. Ignore the key fields and check for any dependencies between the other fields BOYCE-CODD NORMAL FORM DEFINITION: All attributes in a relation should be dependant upon the key, the whole key and nothing but the key Within each of the candidate keys check for dependencies Only need to check for BCNF is when there is more than one candidate key for a relation and at least one of is composite 10. Constraints on user input should exist to maintain data integrity. 11. A database design should allow for distribution of data over several computer sites. 12. Data fields that affect the organization of the database cannot be changed. BIOGRAPHIES DEPENDENCY If ‘X’ is a set of attributes within a relation, then we say ‘A’ (an attribute or set of attributes), is functionally dependant on X, if and only if, for every combination of X, there is only one corresponding value of A We write this as : X -> A 2NF, 3NF and BCNF are concerned with dependencies 2NF is concerned with partial dependencies Raymond ‘Ray’ Boyce Ray Boyce grew up in New York, he went to college in Providence, Rhode Island and got his PhD in Purdue. Together with Don Chamberlin he developed SEQUEL. He died in 1974. PUBLICATION - Donald D. Chamberlin, Raymond F. Boyce: SEQUEL: A Structured English Query Language. SIGMOD Workshop, 1, 1974 Edgar ‘Ted’ Codd Ted Codd is the father of the relational database. Born in 1923 in Portland, UK, he got his PhD at the University of Michigan. He received the 1981 Turing award for "his fundamental and continuing contributions to the theory and practice of database management systems." He died in 2003. PUBLICATION - E. F. Codd: A Relational Model of Data for Large Shared Data Banks. CACM 13 (6), 1970