如何在类和应用程序层之间传递数据?

For example, if I am creating a 3 layer application (data / business / UI) and the data layer is grabbing single or multiple records. Do I convert everything from data layer into generic list/collections before sending to the business layer? Is it ok to send data tables? What about sending info back to the data layer? For example, if I am creating a 3 layer applica