Normalization

Database Normalization TJ Racoosin 2 Dec 1998 CPCUG Access SIG Racoosin Solutions rSolutions@erols.com 703 849-1997

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

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

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

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, http://webopedia.internet.com/TERM/n/normalization.html Racoosin Solutions

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, http://www.accessdatabase.com/normalize.html Racoosin Solutions

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

First Normal Form (1NF) All columns (fields) must be atomic Means : no repeating items in columns 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 Racoosin Solutions

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 Solution: Remove to a separate table (Make Table) OrderDetails OrderID Item Orders OrderID CustomerID OrderDate Racoosin Solutions

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

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) 2/16/98 10 MGS 404 2/16/98 10 Kumar Madurai: http://www.mgt.buffalo.edu/courses/mgs/404/mfc/lecture4.ppt

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

Relationships 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 Racoosin Solutions

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 tblOrders OrderID CustomerID OrderDate OrderDetails OrderID Item trelOrderItem OrderID ItemID tlkpItems ItemID ItemName Racoosin Solutions

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

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

Real World - School Data Student Student Previous Current Last First Parent 1 Parent 2 Teacher Teacher Smith Renee Ann Jones Theodore Smith Hamil Burke Mills Lucy Barbara Mills Steve Mills Hamil Burke Jones Brendan Jennifer Jones Stephen Jones Hamil Burke …. Street Address City State Postal Code Home Phone 5551 Private Hill Annandale Virginia 22003- (703) 323-0893 4902 Acme Ct Annandale Virginia 22003- (703) 764-5829 5304 Gains Street Fairfax Virginia 22032- (703) 978-1083 …. First Year Last Year Age Program Enrolled Attended Birthday inSept Map Coord Notes PF / 0 0 6/25/93 5 22 A-3 PF 96/97 0 8/14/93 5 21 F-3 PH 96/97 0 6/13/94 4 21 A-4 Racoosin Solutions

One Possible Design Racoosin Solutions

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

Internet Papers http://www.mtjeff.com/~calvin/devhbook/databasedesign.html http://www.swin.edu.au/infotech/subjects/bt220/bt220s1.html http://www.bus.okstate.edu/lhammer/AISweb/Normaliz.htm http://www.inetspace.com/database.html Slides http://www.mgt.buffalo.edu/courses/mgs/404/mfc/lecture4.ppt http://www.state.sd.us/people/colink/datanorm.htm http://www.cba.nau.edu/morgan-j/class/subtop2_3/sld001.htm Racoosin Solutions

Normalization

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