concept data access layer in category .net

This is an excerpt from Manning's book Entity Framework 4 in Action. Login to get full access to this book.

Data access layer—Interacts with the database and shields the rest of the application from its specific logic. Concepts like connections, commands, and tables only make sense within this layer and should never be exposed to the upper layers. This is also where Entity Framework fits in; in most cases, it can be considered the entire data access layer on its own.

Business layer—Holds all the business logic and provides services that implement the real-world processes that the application is built to take care of. Although it doesn’t care where its inputs come from, it knows whether a fund transfer can take place between two bank accounts and how to handle it correctly, invoking the data access layer when it needs to query the database or store something there.

When we talk about unit-testing the data access layer, we don’t mean verifying whether a customer is correctly stored in its table; we mean checking whether our infrastructure interacts with Entity Framework in the way we expect.

This is an excerpt from Manning's book LINQ in Action. Login to get full access to this book.

Figure 13.5. The traditional three-tier application architecture, with its presentation, business logic, and data access layers, as well as the optional object models that may be used with it

The impact of the use of LINQ to SQL may be so profound that we may have to reconsider the very nature of a data access layer.