The symbols used in the data model diagrams are:
Single-headed arrow -- one end of a 1:1 or 1:M relationship
Double-headed arrow -- one end of a 1:M or M:M relationship
1 -- indicates that there must be one element at this end of the relationship
C -- indicates that there may be zero or one element at this end of the relationship
N -- indicates that there must be one and may be many elements at this end of the relationship
CN -- indicates that there may be zero or many elements at this end of the relationship