If possible, you may want to breakup the database file into smaller components so that each survey participant only has access to their own database component. Data that has been entered onto a web server through a server application can be accessed directly from the server. The time the data will be retrieved by you is an important consideration in the server application model. You do not want to retrieve the data before a user has completed their data entry. If you are using the same server application for data entry as for reporting the survey results, you may want to consider incorporating some features for turning off the data entry part of the server application at some point in time after the survey deadline date.
Data validation is a little tricky with a server based application.
In essence the user will complete the questionnaire and submit it back to the server. The server application will check the responses and look for data entry errors. This error message may prompt the user for a correction or may simply notify the user that an error was made and the data will be saved with the error. A useful way of dealing with data validation is that if a fatal error has been entered by the user, then the server application should send to the client's browser a message detailing the error and possible correction. No action should be taken at this time by the server with respect to the error.