Subhash,
Flex is not a web alternative for ArcObjects, so there is none. What are you attempting to do? If you are attempting to create a new featureclass than that is not possible using flex. You may want to look at writing a Geoprocessing Procedure or model and publishing that to ArcGIS server. If you have questions about that thought you would be best to post to a forum more specific to GPs and models.
