Editing Entity–relationship model (section)

===Relationships, roles, and cardinalities===
Chen's original paper gives an example of a relationship and its roles. He describes a relationship "marriage" and its two roles, "husband" and "wife".

A person plays the role of husband in a marriage (relationship) and another person plays the role of wife in the (same) marriage. These words are nouns.

Chen's terminology has also been applied to earlier ideas. The lines, arrows, and crow's feet of some diagrams owes more to the earlier [[Data structure diagram|Bachman diagrams]] than to Chen's relationship diagrams.

Another common extension to Chen's model is to "name" relationships and roles as verbs or phrases.