What Are Normal Forms in Database
This means that this table must also be decomposed to satisfy the fourth normal form: If you want to learn more about database design concepts. I would recommend the following articles: Database normalization or database normalization (see spelling differences) is the process of structuring a relational database into a series of so-called normal forms to reduce data redundancy and improve data integrity. It was first proposed by British computer scientist Edgar F. Codd as part of his relational model. There are some basic skills you need to know as a master to become a DBA. The most important of these are the convenient backup and restoration of databases. EXCEPTION: Adherence to the third normal form is theoretically desirable, but not always feasible. If you have a Customers table and want to eliminate all possible dependencies between fields, you must create separate tables for cities, postal codes, sales reps, customer classes, and any other factors that can be duplicated in multiple records. Theoretically, standardization is worth it. However, many small tables can affect performance or exceed the capacity of open files and memory.
Speaking of design with Customer1, Customer2, Customer3 attributes: www.orafaq.com/usenet/comp.databases.theory/2001/05/17/0244.htm A large database defined as a single relationship can lead to data duplication. This iteration of data can lead to the following: Before we go too far, let`s look at the sample table we`ll use to demonstrate database normalization. As for normalization, I did this before exploring joins because I thought it would be good to give my readers an idea of why their data is spread across so many tables and why they need to go to the trouble of learning how to gather it. Because this table structure consists of a composite primary key, it contains no non-key attributes and is already in BCNF (and therefore satisfies all previous normal forms). Assuming that all available books are offered in each region, the title is not only tied to a specific location and, therefore, the table does not satisfy 4NF. It is clear that we cannot create our simple database in the 2nd form of normalization unless we partition the table above. That has been very helpful. I`ve read blogs and articles on the subject, but I have a hard time understanding why standardization rules are really important and how they affect the database in the long run, so I can make my own informed decision – thanks for that! There are certain rules for database normalization. Each rule is called the “normal form.” If the first rule is followed, the database is called the “first normal form.” If the first three rules are followed, the database is considered to be in “third normal form”. Although other levels of standardization are possible, the third normal form is considered the highest level required for most applications. Codd introduced the concept of normalization and what is now known as the first normal form (1NF) in 1970. [5] Codd defined the second normal form (2NF) and the third normal form (3NF) in 1971,[6] and Codd and Raymond F.
Boyce defined the Boyce-Codd normal form (BCNF) in 1974. [7] Thus, not transitively dependent means that all columns depend on the primary key (a criterion for the 2nd normal form) and not on the other columns in the table. It is obvious that you only need to know the CustomerID. For this reason, the Customer table is not in the 2nd normal form, because there are columns that do not depend on the full primary key. We should move them to another table. Does the 3rd normal form correct modification anomalies? If a relationship contains a compound or multivalued attribute, it violates the first normal form, or a relationship has the first normal form if it does not contain a compound or multivalued attribute. A relationship has the first normal form if each attribute of that relationship is a single-valued attribute. Hi Chris, your guess is correct. It would be preferable to have a table of people to accommodate customers, employees and advertisers. In this case, normalization does not speak directly about duplicate data in different tables. I think you might consider the standardized table, but of course, that`s not the design we`re looking for. We can rely on concepts of generalization and specialization to guide our design.
In particular, common attributes can be placed in a generalized entity, which in our case is a person. The specialized attributes are then placed in their own entities: customer, employee, and referrer. The shapes are progressive, which means that to qualify for the 3rd normal form, a table must first meet the rules of the 2nd normal form, and the 2nd normal form must match those of the 1st normal form. Before discussing the different shapes and rules in detail, let`s summarize the different forms: To satisfy the first normal form, each column in a table must have only one value. Columns that contain nested value sets or records are not allowed. Now it`s time to look at the second normal form. I like to think that the reason why we put tables in 2. The normal form is to reduce it to a single purpose.
This clarifies the design of the database, facilitates the description and use of a table, and tends to remove change anomalies. Can database standardization go too far? Certainly! There are times when it`s not worth completely standardizing a database. In our example, you could argue to keep the database in the second normal form, that CustomerCity`s dependence on CustomerPostalCode is not a breaker. A fully standardized database allows you to expand its structure to accommodate new types of data without making too much changes to the existing structure. This minimizes the impact on applications that interact with the database. These situations are modification anomalies. Normalizing the database corrects them. Three modification anomalies can occur: this means that for data in non-standardized form (the least normalized) and the goal of achieving the highest degree of normalization, the first step is to ensure compliance with the first normal form, the second step is to ensure that the second normal form is met, and so on in the order above.
until the data correspond to the sixth normal form. These steps illustrate the process of normalizing a fictitious student table. Database normalization is a process used to organize a database into tables and columns. There are three main forms: the first normal form, the second normal form, and the third normal form. The main idea is that each table should deal with a specific topic and that only support topics should be included.
