MOSS 2007 API to implement check in & check out

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HI ,

I am using MOSS 2007 API's to implement the version controls like check in
and check out in Visual Studio 2005.
I have a sharepoint 2007 server and i am accessing the MOSS API (on
sharepoint server) from dotnet web application on my local machine using a
custom webservice. I am able to check out the document on the sharepoint
server by calling the API "item.File.Chec kOut();" method via custom
webservice. But once i check out the document i need to open the document
and check it in back to the sharepoint server from my application. When i try
to do this i can open the document using the following code

SPDocumentLibra ry docLib =
(SPDocumentLibr ary)web.Lists[System.Configur ation.Configura tionSettings.Ap pSettings["CarizmaDocumen tLibraryName"].ToString()];SPListItem
item = docLib.GetItemB yId(int.Parse(d ocumentID));
SPFile document = web.GetFile(ite m["URL Path"].ToString());
byte[] documentContent = document.OpenBi nary();
Response.ClearC ontent();
Response.Conten tType =
Carizma.Common. CarizmaConfigur ation.GetAppSet ting("CONTENT_T YPE_" + itemType);
Response.AddHea der("Content-Disposition", "attachment;fil ename=" +
documentName);
Response.Binary Write(documentC ontent );
Response.End();

But i am not able to check in the changes made on the document back to the
sharepoint server from my local application. How will i be able to do this?