In Access and other database applications (such as GIS), data entry often requires some form of validation. Some validation can be done just by setting the correct type of data for a field. For example, in a sales order, the “quantity” column should use a type of “number” instead of “text”. This guarantees some minimal validation that non-numbers cannot be used for data of this field.
However, not all validation can be done with the type of a field. For example, the Canadian postal code has a format of AOA OAO. This means that it has six characters, with letters and digits interleaved. For example, “K1A 0B1” and “X5G 2M9” are both valid postal codes.
Validating such a pattern is not easy. While it can be done with conventional string (text) functions that exist in all implementations of BASIC, the logic requires a bit of coding.