Hey! how is the microsoft way of 3-tier architecture? see this link: http://sdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/BOAGag.asp how is this article? and what's the best way to map Relational Data to Business Entities? i think you need to create entities that represent the data.. but each entity is one object or one 'datarow', what to do if you want to get a complete list of (selected) rows from the database? create a ilist of the entities? and is better to make an entity for each table? or to merge related data in one class? Thanx, Tarek PS: it still diffecult to chose the way for passing data: - Passing Scalar Values As Inputs and Outputs - Passing XML Strings As Inputs and Outputs - Passing DataSets As Inputs and Outputs - Passing Custom Business Entity Components As Inputs and Outputs - Returning Data Readers As Outputs does someone have a GOOD example of a 3-tier application ? (a complete one, on microsoft site you see each time a part or only one layer:S) that i can use as a refference?