Normalization. Normal Forms. Normal Forms

Transcription

1 Normalization A technique that organizes data attributes (or fields) such that they are grouped to form stable, flexible and adaptive entities. 5- Normal Forms First Normal Form (NF) There are no attributes (fields) that have more than one value for a single instance (record) of the entity. There are no repeating fields Second Normal Form (2NF) NF The value of all non-primary key fields are dependent on the full primary key - not just part of it 5-2 Normal Forms Third Normal Form (3NF) 2NF The values of its non-primary key fields are not dependent on any other non-primary key field 5-3

2 Keys Primary A field whose values identify one and only one record in a table Every ACCESS table must have EXACTLY one primary key Foreign A primary key of one table that is included in another table Links the records in one database table to another table 5-4 Steps Of Normalization. Remove repeating groups of data fields. 2. Remove partial dependencies: If any data fields are dependent upon only part of the primary key defined for your core business transaction, split those fields out into a separate table, using the field(s) upon which they are dependent as the primary key. 5-5 Steps Of Normalization 3. Remove transitive dependencies: If any fields are dependent upon a non-key field, split those fields out into a separate table, using the non-key field as the primary key. 4. Remove any field which can be easily derived from other field(s): If any fields can be derived from others, remove from database. 5. Check by drawing/comparing to E-R diagram: is this model correct/logical? 5-6 2

3 Non-normalized table In this example, we want to design an order database. Identify all fields needed in this database Which attribute above uniquely identifies each order? Order Number is the starting primary key 5-7 Non-normalized table Original An order can have many parts. This is a repeating field. What fields above are more closely related to a part than an order? Part Number, Number of Parts [quantity ordered], Part Description, Unit Cost, Supplier Number [for the part], supplier name, supplier address. Remove these fields and put them into a separate table. Which one of these fields uniquely identifies the part information? [Part Number] The Primary Key to the new table will be the original primary key combined with the new unique identifier (Part Number) When a primary key has two or more parts, it is called a composite primary key. 5-8 First Normal Form Composite plus Part Number 5-9 3

4 Checking Second Normal Form Composite plus Part Number Look at the second table If you know a part of the primary key, could you derive any of the non-keyed fields? For example: If you know the part number [part of the primary key], could you derive the part description, the unit cost and the supplier information for that part? Violation of second normal form 5-0 Checking Second Normal Form Composite plus Part Number Remove the non-keyed fields from the second table that are dependent on only part of the primary key and put them in a new table [Part Description. Unit Cost, Supplier Information] Copy the part of the primary key from which these fields can be determined into the new table. This field will become the primary key of the new table. 5- Second Normal Form Composite plus Part Number Notice: I moved the PART table name to the table that had the most information about the part. The ordered part table name came from the rules for the ERD. One order can have many parts on it and one part [product line] can be on many orders

5 Checking Third Normal Form Composite plus Part Number Look at the third table: If you know the Supplier Number [a non-keyed field], you can determine the supplier name and address [non-keyed fields] Violation of third normal form 5-3 Checking Third Normal Form Composite plus Part Number Remove the fields that can be determined from the other field from this table. Put them [supplier name and address] in a new table. Copy the field that determines them from the original table into the new table [supplier number]. This field will be the primary key of the new table. 5-4 Part of Third Normal Form Composite plus Part Number 5-5 5

6 Checking Third Normal Form Composite plus Part Number The top table has the same violation as before but with the customer information. Customer name and address can be determined from the customer number Violation of 3 rd Normal Form 5-6 CheckingThird Normal Form Composite plus Part Number Remove the fields that can be determined from the other field from this table. Put them [cust name, address] in a new table. Copy the field that determines them from the original table into the new table [customer number]. This field will be the primary key of the new table. 5-7 Third Normal Form Primary Key: Customer Number Composite plus Part Number 5-8 6

7 Draw the ERD for Validation Customers Cust No Cust Name Cust Address Locate M Parts [Inventory] Part Number Part Description Unit Cost Supplier No Place Supplier Supplier No Supplier Name Supplier Address Locate M m Orders Order No Order Date Delivery Date Order Total Customer No Contain M Ordered Part Order No Part Number Number of Parts 5-9 Normalized Relation