Referential integrity is a relational database concept, which states that table relationships must always be consistent. In other words, any foreign key field must agree with the primary key that is referenced by the foreign key. Thus, any primary key field changes must be applied to all foreign keys, or not at all. The same restriction also...
First normal form (1NF) sets the fundamental rules for database normalization and relates to a single table within a relational database system. Normalization follows three basic steps, each building on the last. The first of these is the first normal form.
The first normal form states that:
The first step in confirming 1NF is modifying multivalued columns to make sure that each column in a table does not take more than one entry.
Searching records with duplicate entries is complex. To overcome this situation, all records involved in a relational database table have to be identified by a unique value which will have a seperate column (or attribute). This unique key is called an index key and is used to locate data for retrieval or other manipulation.
Having a unique key does not resolve the requirements of 1NF. According to the rules, there can be no multiple entries into a single field. For example, in a data table of customer information, a single field could be allowed to store multiple entries, such as where a customer has mulutiple telephone numbers. This is a violation of the 1NF rules. This particular problem in our example can be resolved by creating a customer ID index in the main table and then adding a separate table that has a column for the telephone numbers and another column for the customer ID.
This allows proper use of relational queries to extract data from a relational database. Null, or multiple entry fields both cause issues with data manipulation and extraction so the normalizing process removes ambiguity.
Removing repeating values from a table is the next step toward first normalized form. Repeating values can be moved to a new table.
The final step in implementing first normal form is maintaining atomicity of data. Each individual field should hold the smallest data element possible to facilitate easy sorting and searching. For instance, the date column can be separated into day, month and year.
Tables satisfying first normal form can also contain functionally dependent fields. Functional dependency exists between two fields when the value in field 1 determines the value in field 2 and there is only one value in field 2. In such a case, field 2 is functionally dependent on field 1.
Tables satisfying the higher normal forms (second, third and fourth) necessarily follow first normal form but the reverse is not true. All tables complying with first normal form may not follow the higher normal forms, as the higher normal forms include even more stringent rules.
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