Entity Relationship modeling from an ORM perspective: Part 3
This article is the third in a series of articles dealing with Entity Relationship (ER) modeling from the
perspective of Object Role Modeling (ORM). Part 1 provided a brief overview of the ER approach, and
then covered the basics of the Barker ER notation. Part 2 completed the examination of the Barker ER
notation by discussing verbalization, exclusion constraints, frequency constraints, subtyping and non-
transferable relationships. Both parts compared the Barker notations with the corresponding ORM notations
This article discusses the Information Engineering notation for ER, relating it to relevant ORM constructs.
(IE) approach began with the work of Clive Finkelstein in Australia, and
CACI in the UK, and was later adapted by James Martin. Different versions of IE exist, with no single
standard. In one form or other, IE is supported by many data modeling tools, and is one of the most popular
notations for database design.
Entity types, attributes
In the IE approach,
are shown as named rectangles, as in Figure 1(a). A
displayed in a compartment below the entity type name, as in Figure 1(b), but are sometimes displayed
(e.g. bubble charts). Some versions support basic constraints on attributes (e.g. Ma/Op/Unique).
Typical IE notation for (a) entity type and (b) entity type with attributes
are typically restricted to binary associations only, which are shown as named lines
connecting the entity types. As with the Barker notation, a half-line or line end corresponds to a role in
ORM. Optionality and cardinality settings are indicated by annotating the line ends. To indicate that a role
, a circle “
” is placed at the other end of the line, signifying a minimum participation frequency
of 0. To indicate that a role is
, a stroke “|” is placed at the other end of the line, signifying a
minimum participation frequency of 1. After experimenting with some different notations for a cardinality
”, Finkelstein settled on the intuitive crow’s foot symbol suggested by Dr. Gordon Everest.
In conjunction with a minimum frequency of 0 or 1, a stroke “|” is often used to indicate a maximum