Cacheing Feature of ASP.NET 2

Cahche will be invalid when data of database is changed. Folloiwing code is for SQL Server 2005 and VS 2005


void Page_Load(object sender, System.EventArgs e)
{
DataSet categories;
categories = (DataSet) Cache["Categories"];
if (categories == null)
{
SqlConnection conn = new SqlConnection
(ConfigurationSettings.ConnectionStrings"Northwind"]);
SqlDataAdapter adapter = new SqlDataAdapter ("Select * from Categories", conn);
categories = new DataSet();
adapter.Fill(categories);
SqlCacheDependency dependency = new
SqlCacheDependency("Northwind", "Categories");
Cache.Insert("Categories", categories, dependency);
Response.Write("Categories retrieved from the database");
}
else
Response.Write("Categories retrieved from the Cache");

gridCategories.DataSource = categories;
gridCategories.DataBind();
}