The add alias option is used to create an alias representing a database name.
sp_webservices 'addalias' alias_name , database_name
alias_name
The alias for the specified database. This parameter is required.
database_name
The name of the database for which the alias is specified. This parameter is required.
An alias provides greater control in specifying the portion of the URL representing the database name. Used with the userpath option of the create service command, an alias provides complete control over the URL used to access a user-defined Web service.