Cardinal
of a relationship sets the minimum and maximum participation of each entity.
These are represented by the symbols at each end of the relationship line.
There is no agreement among CASE tools and authors about what terms to use for cardinal, what symbols to use, or even in which direction to read the symbols - whether they belong next to the "from" entity or the "to" entity.
In DataArchitect we read the symbols at the far end of the line - the "to" entity in each point of view.
The symbol on top of the relationship line near each end represent entities' minimum participation, which PowerDesigner calls Existence. An o (think of it as zero or optional) means participation is optional in PowerDesigner's terms. A single line crossing the relationship line represents the numeral 1 and means participation is mandatory.
The symbols which connect the relationship line to the entities represent their maximum participation, which PowerDesigner calls Cardinal (a narrower use of the more general term). A single line means a cardinal or maximum of one; a crow's foot of three lines means a cardinal of more than one.