The cardinality is the number of times that an Entity can appear in a Relationship. Between Entities and Relationships there can be a
one-to-one correspondence. To enter a cardinality of '1', click next to 1. This value is not displayed in the diagram unless you click in the visible box.
fixed cardinality, shown by a number. To enter a fixed cardinality, click next to n, click on the line n=, type a number then click on OK.
variable cardinality, shown by a letter. Typically, the letters 'n' and 'm' are used. To enter a fixed cardinality, click next to n (or m) and then click on OK. Alternatively, you can click next to n (m), click on the line n= (m=) and type a letter of your choice.
range of cardinality, shown by two values within brackets, representing upper and lower bounds.
To enter a range with a lower bound of 1 and a variable upper bound, click next to (1,n) then click on OK.
To enter a range with variable lower and upper bounds, click next to (n,m) then click on OK. To enter a range with fixed values, click next to (n,m), click on the line n= and type a number, click on the line m= and type a number, then click next to OK.