The earlier database management systems where hierarchical and network models. There are many disadvantages of using them when compared to the relational database management systems that are available now-a-days. In the earlier models a child segment could not have more than one parent segment. In relational database management systems this is possible. The relational database management systems developed by Codd is superior to the earlier systems.

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The features of the relational database systems are worthy to note. They have atomic values as their column values. All the columns in a particular table have unique names and the column values belong to one group for a particular column. It is not important that the order of the columns and rows to be in a particular order. The sequence of the columns and the rows is not at all important.

The tables and their relationships are defined for a particular table. You should know that a table has a set of records and the same columns in each row. It is not necessary that all the columns in a particular row should have values. Null values are also allowed which means that it is not compulsory to store a value in it. These are all defined in the table.

A table can have a key. Mostly they have a key in them. This key is important for linking it to other tables. Based on this key only you will be retrieving values from other tables that have the same key value. Having a key in the table enables you to retrieve values faster than in a table that does not have one. Indexing is another factor that you should consider in a table that is used to search for values. For example if you are going to search for a term in a text field, then it is wise to create an index on that column so that the search is performed faster.