Relationship Cardinality

You can set the cardinality for the relationships in your model. Relationship cardinality represents the fact that each parent entity or table within a relationship is connected to a particular number of instances of the child entity or table. In IDEF1X, IE, and DM notations, the cardinality of a relationship can be represented in one of the following ways:

• Zero, one, or more - Signified by a blank space. Each parent in the relationship is connected to zero, one, or more instances of the child entity or table.
• One or more - Signified by the letter P. Each parent in the relationship is connected to one or more instances of the child entity or table.
• Zero or one - Signified by the letter Z. Each parent in the relationship is connected to zero or one instance of the child entity or table.
• Exactly - Each parent in the relationship is connected to an exact number of instances of the child entity or table. You specify the number of instances.
• Range - Specify a range using the double dot notation.

You can optionally display the cardinality symbols for a relationship at the child end of a relationship line.

When you create a non-identifying relationship you can choose whether a parent is required for each child by setting the null option for the relationship.

More information:

Relationship Null Options