Normalization A337

Structure What is a database? Types Tables of information Rows are referred to as records Columns are referred to as fields or attributes Record identifier is referred to as a record key Types Relational - Most common, Object-Oriented Hierarchical, Network (much older types) A337 - Reed Smith

Database structure Two approaches to the structure issue: Conceptual (you start with the question of “what information should I have?”) ERD from “scratch” Empirical (you already know what data there will be - you just want to organize it into tables) – NORMALIZATION A337 - Reed Smith

Database Tables and Normalization Normalization - Process for evaluating and correcting table structures to minimize data redundancies Works through a series of stages called normal forms: Normal form (1NF) Second normal form (2NF) Third normal form (3NF) There are higher forms but are rarely necessary

Normalization Why? How? Data structures need to: Minimize redundancy Avoid insertion, update, and deletion anomalies How? Restructure information such that: Only flat (rectangular) files exist (1st normal form) – No Nulls All items in each record depend upon) the primary record key (2nd normal form) – No Partial Dependencies If a field depends upon another then the “other” must be a primary key (3rd normal form) – No Transitive Dependencies A337 - Reed Smith

Normalize the following table: A337 - Reed Smith

What is wrong with this solution? A337 - Reed Smith

First Normal Form Eliminate Nulls/Repeating Groups – Eliminate repeating groups by eliminating nulls, filling in cells with implied values with actual values Select a primary key may be a composite key

1NF: A337 - Reed Smith

What is wrong with this solution? Partial Dependencies For example, the sales order number is not relevant in the determination of the item name Similarly, the customer code and customer name do not depend upon the Item ID, they only depend upon the sales order number. A337 - Reed Smith

Second Normal Form Eliminate Partial Dependencies Write each key component on separate line, and then write the original (composite) key on the last line Each component will become the key in a new table Identify the Dependent Attributes Determine which attributes are dependent on which other attributes

Creating 3 Tables SO_Number, Item_Number SO_Number, Item_Number

2NF: A337 - Reed Smith

What is wrong with this solution? Transitive Dependencies Notice that the third column of the Sales Orders file has the Customer name and that depends upon the customer number. But the customer number is not the primary key A337 - Reed Smith

Third Normal Form For every transitive dependency, write its determinant as a PK for a new table Identify the attributes dependent on each determinant identified in Step 1 and identify the dependency Remove the dependent attributes in transitive relationship(s) from each table that has such a transitive relationship Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

3NF: A337 - Reed Smith

Denormalization Creation of normalized relations is important database design goal Processing requirements should also be a goal If tables decomposed to conform to normalization requirements Number of database tables expands

Denormalization (continued) Joining larger number of tables takes additional disk input/output (I/O) operations and processing logic Reduces system speed Conflicts among design efficiency, information requirements, and processing speed are often resolved through compromises that may include denormalization A337 Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel