In a database, a virtual table created by applying predefined selection and joining criteria to one or more physical tables. A view's contents are computed dynamically from these tables when it is invoked. (In practice DBMSs implement some types of view by maintaining a synchronized copy of the relevant data. Such a view is called a materialized view.) Views can always be used for data selection, but their other capabilities depend both on the view's definition and on the capabilities of the particular database management system. For example, the DMBS may not permit data to be updated through a view; and, if it does, views still cannot be updatable if they present data that is summarized or otherwise manipulated so that there is no one-for-one correspondence with the underlying physical data.