To update a sharepoint list very first requirement is to reach upto that list. This can be possible with the help of sharepoint webservices. Share point webservice cannot called without authorization. If a user has full permission for sharepoint server access then by using his/her credentials we can call the share point webservices. First we need to add the required web service in our asp.net application. After adding webservices we get classes access of that webservice. Then call authentication webservice. This webservice is used for authentication of the user. Call to sharepoint webservices also depend upon the subsite process or subfolder process. So be careful during the call to subsites.
After successful authentication of the user a ticket will be generated by the sharepoint service for future operations. By using this ticket a user can call another webserice of sharepoint server. To update a list user need to call the lists.asmx webservce. By using authentication ticket of authentication.asmx websevice one can get list of all lists under root or subdomain. With the help of user defined xml one can update the required list of sharepoint server by using Update method of lists.asmx webservice.
