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A data type is a predefined set of characteristics for an attribute or column that specifies field length, acceptable characters, and optional and required parameters. For example, the data type char(18) specifies that the column can store up to 18 alpha and numeric characters.
By default, a data type is applied to every attribute in a logical model and to every column in a physical model. In the logical model, the data type is determined by the domain from which the attribute inherits its properties or from the data type that you assign. In the physical model, the data type is determined by the default value specified by the target server or the data type that you assign. Considering the large quantity of attributes or columns a data model usually has, it can be quite tedious to manually assign and maintain consistency of data types. For this reason, there are several tools that help you with this task.
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