>Hi,
>I used to read couples of about 3 tier article, and I implement it according to what I understand. I have a class, that contain ADD(), DELETE(), LOAD() , SAVE() and etc which will manipulate my vfp data. It contains Validate() method either. So, is it a data layer / data handler or business layer?
>
>Could ypu please identify it?
>
>Thank you

The data layer is where the data actually resides. This could be in a FoxPro DBC, dbfs, a SQL Server database or any other data container.

The business layer is where classes are developed that know how the business object, what the data represents, is supposted to adhere to any business rules that exist. That could mean a field is not allowed to be blank or excepted values that a field must be populated with. In addition, it is the layer that talks with any other object that wants to find out information about the data it represents. Custom methods and properties exposed for other objects to call.

The data handler layer is a fourth layer that can/cannot exist as a seperate class from the business layer. Its purpose is to know how to extract the data from the data layer. The way data is extracted from VFP is quite defferent from extracting data from SQL Server. By separating this function, you allow yourself to change the backend data without needing to modify your business layer.

Hope this explanation helps.