This paper describes the Update Protocol Model (UPM), a formal language for the expression of database update semantics. UPM has been used primarily to capture and communicate in a precise and uniform notation the plethora of database semantics described by a variety of "fourth generation" models, many of which are imprecise when it comes to update semantics. Several computing trends?knowledge-based expert systems, distributed database management systems, and new applications based on higher order semantic models?point to the need for modeling techniques beyond that which current data models such as the relational and entity-relationship models provide.