Therefore, the data to be stored in the database must be determined in cooperation with a person who does have expertise in that domain, and who is aware of what data must be stored within the system. This process is one which is generally considered part of requirements analysisand requires skill on the part of the database designer to elicit the needed information from those with the domain knowledge. This is because those with the necessary domain knowledge frequently cannot express clearly what their system requirements for the database are as they are unaccustomed to thinking in terms of the discrete data elements which must be stored. Data to be stored can be determined by Requirement Specification.
Summary This article explains database normalization terminology for beginners. A basic understanding of this terminology is helpful when discussing the design of a relational database.
More Information Description of Normalization Normalization is the process of organizing data in a database. This includes creating tables and establishing relationships between those tables according to rules designed both to protect the data and to make the database more flexible by eliminating redundancy and inconsistent dependency.
Redundant data wastes disk space and creates maintenance problems. If data that exists in more than one place must be changed, the data must be changed in exactly the same way in all locations. A customer address change is much easier to implement if that data is stored only in the Customers table and nowhere else in the database.
What is an "inconsistent dependency"? While it is intuitive for a user to look in the Customers table for the address of a particular customer, it may not make sense to look there for the salary of the employee who calls on that customer.
The employee's salary is related to, or dependent on, the employee and thus should be moved to the Employees table. Inconsistent dependencies can make data difficult to access because the path to find the data may be missing or broken. There are a few rules for database normalization.
Each rule is called a "normal form. As with many formal rules and specifications, real world scenarios do not always allow for perfect compliance.
In general, normalization requires additional Data normalization rules and some customers find this cumbersome. If you decide to violate one of the first three rules of normalization, make sure that your application anticipates any problems that could occur, such as redundant data and inconsistent dependencies.
The following descriptions include examples. First Normal Form Eliminate repeating groups in individual tables. Create a separate table for each set of related data. Identify each set of related data with a primary key. Do not use multiple fields in a single table to store similar data.
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.
Second Normal Form Create separate tables for sets of values that apply to multiple records.
Relate these tables with a foreign key. Records should not depend on anything other than a table's primary key a compound key, if necessary.
For example, consider a customer's address in an accounting system. Instead of storing the customer's address as a separate entry in each of these tables, store it in one place, either in the Customers table or in a separate Addresses table. Third Normal Form Eliminate fields that do not depend on the key.
Values in a record that are not part of that record's key do not belong in the table. In general, any time the contents of a group of fields may apply to more than a single record in the table, consider placing those fields in a separate table.
For example, in an Employee Recruitment table, a candidate's university name and address may be included. But you need a complete list of universities for group mailings.
If university information is stored in the Candidates table, there is no way to list universities with no current candidates. Create a separate Universities table and link it to the Candidates table with a university code key.
Adhering to the third normal form, while theoretically desirable, is not always practical. If you have a Customers table and you want to eliminate all possible interfield dependencies, you must create separate tables for cities, ZIP codes, sales representatives, customer classes, and any other factor that may be duplicated in multiple records.
In theory, normalization is worth pursing. However, many small tables may degrade performance or exceed open file and memory capacities.
It may be more feasible to apply third normal form only to data that changes frequently. If some dependent fields remain, design your application to require the user to verify all related fields when any one is changed. Disregarding these rules may result in less than perfect database design, but should not affect functionality.
Normalizing an Example Table These steps demonstrate the process of normalizing a fictitious student table.The space required to store a JSON document is roughly the same as for LONGBLOB or LONGTEXT; see Section , “Data Type Storage Requirements”, for more timberdesignmag.com is important to keep in mind that the size of any JSON document stored in a JSON column is limited to the value of the max_allowed_packet system variable.
Normalization is the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table).
Venu Perla, Ph.D. Philadelphia Area SAS Users Group (PhilaSUG) Winter Meeting; March 16, Philadelphia University, Philadelphia, PA, USA. 1 Introduction. Extensible Markup Language, abbreviated XML, describes a class of data objects called XML documents and partially describes the behavior of computer programs which process them.
XML is an application profile or restricted form of SGML, the Standard Generalized Markup timberdesignmag.com construction, XML documents are conforming SGML documents.
Name: Description: First Normal Form: An entity is in First Normal Form (1NF) when all tables are two-dimensional with no repeating groups. A row is in first normal form (1NF) if all underlying domains contain atomic values only.
1NF eliminates repeating groups by putting each into a separate table and connecting them with a one-to-many relationship. This has really been a long debate as to which approach is more performance orientated, normalized databases or denormalized databases.
So this article is a step on my part to figure out the right strategy, because neither one of these approaches can be rejected outright.