When you say FROM and TO, I presume that you are drawing relationships. What you ought to be typing in those fields is not the names of the entities (tables), but the names for each end of the relationship. Read the relationship like this:
Each (name of the FROM entity) "may be"/"must be" (FROM name) "one and only one"/"one or more" (name of the TO entity), and
Each (name of the TO entity) "may be"/"must be" (TO name) "one and only one"/"one or more" (name of the FROM entity).
For instance, suppose you have our old friends, EMP and DEPT, which are the tables developed from the entities, Employee and Department. The ER diagram looks something like this:
Department
|
^
Employee
You read the relationship like:
Each Employee must be a worker in one and only one Department and Each Department may be composed of one or more Employees.
"worker in" is what you type in the FROM name, and "composed of" is what you type in the TO name. The "must be" or "may be" indicates whether the relationship is mandatory in that direction, and the "one and only one" or "one or more" indicates the cardinality of the relationship. When you use these words to read the relationship to your client or user, they understand them (where they might not understand the diagram) and can tell you if you got it wrong. For instance, they may say, "No, an Employee can work for more than one Department at the same time." Then you know that you either have to redefine what you mean by "worker in" - maybe it should be "paid by", or re-draw the relationship as a many to many.
