Permitting updates through views of data bases

摘要

Providing different views (logical images of the structure of a data base) to various users creates the problem of determining how update operations expressed in terms of the views should affect the stored form of the data base. For data bases with a relational organization, we indicate the effects of a wide range of update operations on views. We conclude that some operations must be prohibited in order to assure harmonious interactions among data base users, but that many other operations can be allowed even though the structure of the view may differ substantially from the actual structure of the data base. We consider views not only as “windows” through which to see a data base in a particular way, but also as “shades” to conceal and protect information, and as “screens” to intercept any update operations that could leave the stored form of the data base in an unacceptable state.