<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> An entity--relationship model (ER model for short) describes interrelated things of interest in a specific domain of knowledge . A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between instances of those entity types . </P> <P> In software engineering, an ER model is commonly formed to represent things that a business needs to remember in order to perform business processes . Consequently, the ER model becomes an abstract data model, that defines a data or information structure which can be implemented in a database, typically a relational database . </P>

A diagramming tool used to express the relationships between entities in a database is called a