Hi,
Before going to design 3-tier application, I suggest you to go through few articles related to 3-Tier Application and try to design few samples using that then start to implement in your project, coming to your query, if you want to call BAL, DAL from your UI then you need to know what is DAL and BAL,
DAL: In this layer we should be perform DataSource related operations. For communicate to DataBase in our application we use this layer here we perform all operations like insertion,deletion,updation and selection.
BAL: Most of the logics are return in this layer application all other layers use this layer for providing inputs to it and also to get the outputs from it.
UI: In this layer we perform all presentation related information or Graphical User Interface (GUI). The logic or calculations and other code should be return in this layer.
If you want to call BAL in your UI then add the assembly reference and based on class object you can able to call the BAL methods, in the same manner add DAL assembly reference and based on class object you can able to call the DAL methods in BAL class.
Refer below sample link for your reference, here I explain the same with examples;
http://www.dotnetspider.com/resources/45057-Working-with-3Tier-Application-with-Examples.aspx
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Give respect to your work, Instead of trying to impress your boss.
N@veen
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