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Database Normalization

March 9, 2012 Leave a comment

What is Normalization?

Normalization is the process of efficiently organizing data in your database. There are two goals of the normalization process: reducing redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (all fields in a tale can be uniquely determined from the primary key). Both of these are the main goals as they reduce the amount of space a database consumes and ensure that data is logically stored.
The Normal Forms

The database community has developed a series of guidelines for ensuring that databases are normalized. These are referred to as normal forms and are numbered from one (the lowest form of normalization, referred to as first normal form or 1NF) through five (fifth normal form or 5NF). In practical applications, you’ll often see 1NF, 2NF, and 3NF. Fourth and Fifth normal forms won’t be discussed in this article since they are not much seen.

Before we begin our discussion of the normal forms, it’s important to point out that they are guidelines and guidelines only. Occasionally, it becomes necessary to stray from them to meet practical business requirements. However, when variations take place, it’s extremely important to evaluate any possible ramifications they could have on your system and account for possible inconsistencies. That said, let’s explore the normal forms.
First Normal Form (1NF)

First normal form (1NF) sets the very basic rules for an organized database:
• Eliminate duplicative columns from the same table (For example, to track an inventory item that may come from two possible sources, an inventory record may contain fields for Vendor Code 1 and Vendor Code 2.
What happens when you add a third vendor? Adding a field is not the answer; it requires program and table modifications and does not smoothly accommodate a dynamic number of vendors. Instead, place all vendor information in a separate table called Vendors, then link inventory to vendors with an item number key, or vendors to inventory with a vendor code key.)
• Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
Second Normal Form (2NF)

Second normal form (2NF) further addresses the concept of removing duplicative data:
• Meet all the requirements of the first normal form.
• Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
• Create relationships between these new tables and their predecessors through the use of foreign keys.
Third Normal Form (3NF)

Third normal form (3NF) goes one large step further:
• Meet all the requirements of the second normal form.
• Remove columns that are not dependent upon the primary key.

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Cannot access a closed file

October 14, 2011 Leave a comment

This Error occured usually when trying to upload a file which is more than a 100 kb.

The solution of this error is:
Add this line in the web.config after <custom errors> [<httpRuntime executionTimeout=”90″ maxRequestLength=”20000″ useFullyQualifiedRedirectUrl=”false” requestLengthDiskThreshold=”8192″/>]

P.S. Please note that 20000 are in KB.