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The Data We Want

How to Obtain It

Relational data

System.Data.dll, System.Data.SqlClient.dll, etc.

XML document data

System.Xml.dll

Metadata tables

The System.Reflection namespace

Collections of objects

System.Array and the System.Collections/System.Collections.

Generic namespaces

Of course, nothing is wrong with these approaches to data manipulation. In fact, when pro-

gramming with .NET 3.5/C# 2008, you can (and will) certainly make direct use of ADO.NET, the

XML namespaces, reflection services, and the various collection types. However, the basic problem

is that each of these APIs is an island unto itself, which offers very little in the way of integration.

True, it is possible (for example) to save an ADO.NET DataSet as XML, and then manipulate it via

the System.Xml namespaces, but nonetheless, data manipulation remains rather asymmetrical.

The LINQ API is an attempt to provide a consistent, symmetrical manner in which program-

mers can obtain and manipulate “data” in the broad sense of the term. Using LINQ, we are able to

create directly within the C# programming language entities called 

query expressions. These query

expressions are based on numerous 

query operators that have been intentionally designed to look

and feel very similar (but not quite identical) to a SQL expression.

The twist, however, is that a query expression can be used to interact with numerous types of

data—even data that has nothing to do with a relational database. Specifically, LINQ allows query

expressions to manipulate any object that implements the IEnumerable interface (directly or

indirectly via extension methods), relational databases, DataSets, or XML documents in a consistent

manner.