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Racoosin 703 849-1997 Database Normalization TJ Racoosin 2 Dec 1998 CPCUG Access SIG.

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Presentation on theme: "Racoosin 703 849-1997 Database Normalization TJ Racoosin 2 Dec 1998 CPCUG Access SIG."— Presentation transcript:

1 Racoosin Database Normalization TJ Racoosin 2 Dec 1998 CPCUG Access SIG

2 Overview Introductions The Normal Forms Primary Key Relationships and Referential Integrity When NOT to Normalize Real World Exercise Resources Racoosin Solutions

3 Introductions TJ Racoosin You –Are you familiar with normalization? –Used the relationship window ? Enforce referential integrity? Cascade Delete? –Any issues with normalizing data? Racoosin Solutions

4 Why Normalize? Flexibility –Structure supports many ways to look at the data Data Integrity –“Modification Anomalies” Deletion Insertion Update Efficiency –Eliminate redundant data and save space Racoosin Solutions

5 Normalization Defined “ In relational database design, the process of organizing data to minimize duplication. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective 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.” - Webopedia, Racoosin Solutions

6 Another Definition "Normalization" refers to the process of creating an efficient, reliable, flexible, and appropriate "relational" structure for storing information. Normalized data must be in a "relational" data structure. - Reid Software Development, Racoosin Solutions

7 The Normal Forms A series of logical steps to take to normalize data tables First Normal Form Second Third Boyce Codd There’s more, but beyond scope of this Racoosin Solutions

8 First Normal Form (1NF) All columns (fields) must be atomic –Means : no repeating items in columns Racoosin Solutions Solution: make a separate table for each set of attributes with a primary key (parser, append query) Customers CustomerID Name Orders OrderID Item CustomerID OrderDate

9 Second Normal Form (2NF) In 1NF and every non-key column is fully dependent on the (entire) primary key –Means : Do(es) the key field(s) imply the rest of the fields? Do we need to know both OrderID and Item to know the Customer and Date? Clue: repeating fields Racoosin Solutions Solution: Remove to a separate table (Make Table) OrderDetails OrderID Item Orders OrderID CustomerID OrderDate

10 Third Normal Form (3NF) In 2NF and every non-key column is mutually independent –means : Calculations Racoosin Solutions Solution: Put calculations in queries and forms OrderDetails OrderID Item Quantity Price Put expression in text control or in query: =Quantity * Price

11 2/16/9810 MGS 404 2/16/9810 Boyce-Codd Form (3NF) - Examples A more restricted version of 3NF (known as Boyce-Codd Normal Form) requires that the determinant of every functional dependency in a relation be a key - for every FD: X => Y, X is a key Consider the following relation: STU-MAJ-ADV (Student-Id, Major, Advisor) Advisor => Major, but Advisor is not a key Boyce-Codd Normal Form for above: STU-ADV (Student-Id, Advisor) ADV-MAJ (Advisor, Major) Kumar Madurai:

12 Primary Key Unique Identifier for every row in the table –Integers vice Text to save memory, increase speed –Can be “composite” –Surrogate is best bet! Meaningless, numeric column acting as primary key in lieu of something like SSN or phone number - (both can be reissued!) Racoosin Solutions

13 Relationships Racoosin Solutions One to many to enforce “Referential Integrity” Two “foreign” keys make a composite primary key and “relate” many to many tables A look up table - it doesn’t reference any others

14 Table Prefixes Aid Development –First, we’ll get replace text PK with number –The Items table is a “look up” with tlkp prefix –tlkp “lookup” table (no “foreign keys”) –OrderDetails is renamed “trelOrderItem” a “relational” table trel “relational” (or junction or linking) –two foreign keys make a primary Racoosin Solutions tblOrders OrderID CustomerID OrderDate OrderDetails OrderID Item trelOrderItem OrderID ItemID tlkpItems ItemID ItemName

15 Referential Integrity Every piece of “foreign” key data has a primary key on the one site of the relationship –No “orphan” records. Every child has a parent –Can ’t delete records from primary table if in related table Benefits - Data Integrity and Propagation –If update fields in main table, reflected in all queries –Can’t add a record in related table without adding it to main –Cascade Delete: If delete record from primary table, all children deleted - use with care! Better idea to “archive” –Cascade Update: If change the primary key field, will change foreign key Racoosin Solutions

16 When Not to Normalize Want to keep tables simple so user can make their own queries –Avoid processing multiple tables Archiving Records –If No need to perform complex queries or “resurrect” –Flatten and store in one or more tables Testing shows Normalization has poorer performance –“Sounds Like” field example –Can also try temp tables produced from Make Table queries Racoosin Solutions

17 Real World - School Data Racoosin Solutions StudentStudent Previous Current Last First Parent 1Parent 2 Teacher Teacher SmithReneeAnn JonesTheodore SmithHamilBurke Mills LucyBarbara MillsSteve Mills Hamil Burke JonesBrendanJennifer Jones Stephen Jones Hamil Burke …. Street AddressCityStatePostal CodeHome Phone 5551 Private HillAnnandaleVirginia (703) Acme CtAnnandaleVirginia (703) Gains StreetFairfaxVirginia (703) …. First Year Last Year Age ProgramEnrolledAttended BirthdayinSeptMap CoordNotes PF / 0 0 6/25/93522 A-3 PF96/97 08/14/93521 F-3 PH96/97 0 6/13/94421 A-4

18 One Possible Design Racoosin Solutions

19 Books Access97 Developers Handbook Litwin,Getz & Gilbert –Chapter 4 Access and SQL Server Developers Handbook Viescas, Gunderloy and Chipman –Chapter 2 Access97 Expert Solutions Lezynski –Chapter 10 Racoosin Solutions

20 Internet Papers Slides Racoosin Solutions


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