By default, the data type for a field is the same as the data type of the base object column that the field is associated with. You can define custom data types for business entity fields. For example, a string column in a base object might contain information for an image so you configure a custom Image data type for business entity fields.
You define custom data types in a namespace external to the Provisioning tool. When you associate a custom data type with a field, you must enter the location of the namespace where your custom data types are defined.