The ADO.NET Entity Framework Overview

Every business application has, explicitly or implicitly, a conceptual data model that describes the various elements of the problem domain, as well as each element's structure, the relationships between each element, their constraints, and so on.

Since currently most applications are written on top of relational databases, sooner or later they'll have to deal with the data represented in a relational form. Even if there was a higher-level conceptual model used during the design, that model is typically not directly "executable", so it needs to be translated into a relational form and applied to a logical database schema and to the application code.

While the relational model has been extremely effective in the last few decades, it's a model that targets a level of abstraction that is often not appropriate for modeling most business applications created using modern development environments.

Let's use an example to illustrate this point. Here is a fragment of a variation of the AdventureWorks sample database that's included in Microsoft SQL Server 2005:


Figure 1
If we were building a human-resources application on top of this database and at some point wanted to find all of the full-time employees that were hired during 2006 and list their names and titles, we'd have to write the following SQL query:
SELECT c.FirstName, e.Title
FROM Employee e
INNER JOIN Contact c ON e.EmployeeID = c.ContactID
WHERE e.SalariedFlag = 1 AND e.HireDate >= '2006-01-01'

Let's say that another application, this time the sales system, is also built on top of the same database. Using the same logical schema we used in the previous example, we would have to use the following query to obtain all of the sales persons that have sales orders for more than $200,000:
SELECT SalesPersonID, FirstName, LastName, HireDate
FROM SalesPerson sp
INNER JOIN Employee e ON sp.SalesPersonID = e.EmployeeID
INNER JOIN Contact c ON e.EmployeeID = c.ContactID
INNER JOIN SalesOrder o ON sp.SalesPersonID = o.SalesPersonID
WHERE e.SalariedFlag = 1 AND o.TotalDue > 200000...