A webarchive link: Entity-Relationship Diagram Symbols and Notation
The whole can also be briefly summed up by the following image:
More at Wikipedia: Entity–relationship model
The Asterisk PjSip documentation refers to
'Entity-Relationship Diagram Symbols and Notation'. This is also known as
'Crow's foot notation'. Unfortunately, this page doesn't exist anymore.
A webarchive link:
Entity-Relationship
Diagram Symbols and Notation
The whole can also be briefly summed up by the following image:
More at Wikipedia:
Entity–relationship
model