Database Reference
In-Depth Information
Entity relationship modeling is the process of visually representing entities, attributes, and
relationships, producing a diagram called an entity relationship diagram (ERD). Non-tech-
nical people can easily understand it. It provides great value to technical persons. ERDs are
platform independent and can even be used for non relational databases if desired. It was
developed by Peter Chen in 1976. Many variations in ERD have been developed by various
vendors, computer scientists, and academician. The elements common to all ERD formats
are shown below:
Entities are represented as rectangles or boxes.
Relationships are represented as lines.
Line ends indicate the maximum cardinality of the relationship . Symbols near the line
ends indicate the minimum cardinality of the relationship. Attributes may be optionally
included.
3.6.1 One-to-One ( 1: 1) Relationships
A one-to-one relationship is an association where an instance of one entity can be associ-
ated with at most one instance of the other entity, and vice versa. The one-toone relation-
ship is simplest type of relationship. A pair of tables have a one-to-one relationship when
a one record in the first table is related to only one record in the second table, and a single
record in the second table is related to only one record in the first table. In one-to-one rela-
tionship, one table serves as a "parent" table and the other
