Figure 2-1 Entities and Associations
Shown below is Figure 2-1 from the Cadastral Data Content Standard. This figure illustrates the associations of entities. The "crows foot" symbol indicates "many" and the single line indicates "one".
Figure 2-1 Entities and Associations
In the above figure, a one to one relationship is shown at the top: one person has one social security number. The vertical line in the diagram means a "one" relationship.
Shown in the middle above is a one to many association,
where a single geodetic control mark may have many names or mark identifiers.
The geodetic mark has a one-to-many association with its names and identifiers.
The "one" is represented by the vertical line and the "many" is represented
by the crows foot type indicator: 
Finally, shown at the bottom of Figure 2-1 is a many-to-many relationship, in which one parcel can be located in many administrative districts such as fire, police, school, and emergency response, while one administrative district is composed of many parcels. Click the green forward arrow below for information about cardinality.
Learning the Cadastral Data Content Standard
Presented by the United States Department of the Interior Bureau of Land Management, and
the Federal Geographic Data Committee Cadastral Subcommittee