Loop-Back SOAP Calls and Direct Linking
Published: May 2010
If you are writing code within Microsoft SharePoint Foundation, for example, a custom Web Part, custom aspx page, and so on, you should make direct calls to Microsoft.Office.Excel.Server.WebServices.dll. You do this by linking directly to Microsoft.Office.Excel.Server.WebServices.dll.
Using Simple Object Access Protocol (SOAP) from a Web server to communicate with the same Web server is also known as using loop-back SOAP calls. It is strongly recommended that you do not attempt to use loop-back SOAP calls. If you are writing code within SharePoint Foundation, you should not use SOAP to call the Excel Web Services. You should instead link to Microsoft.Office.Excel.Server.WebServices.dll locally and make calls to it as you would any local assembly.
To link directly to Microsoft.Office.Excel.Server.WebServices.dll in your project and call it from your code, you add a reference to it. On the computer where you have installed Microsoft SharePoint Server 2010, using the Add Reference dialog box in Microsoft Visual Studio, you can do one of the following:
Select Excel Web Services from the Component Name list in the .NET tab.
Browse to Microsoft.Office.Excel.Server.WebServices.dll located in:
[drive:]\Program Files\Common Files\Microsoft Shared\web server extensions\14\ISAPI