ASP.NET Application DAL

When working with data one option is to embed the data-specific logic directly into the presentation layer (in a web application, the ASP.NET pages make up the presentation layer). This may take the form of writing ADO.NET code in the ASP.NET page's code portion or using the SqlDataSource control from the markup portion. In either case, this approach tightly couples the data access logic with the presentation layer.

The recommended approach, however, is to separate the data access logic from the presentation layer. This separate layer is referred to as the Data Access Layer, DAL for short, and is typically implemented as a separate Class Library project.