2 new Relationship types in ERD diagrams (without the "minimal zero/one" symbol o the "optional/mandatory" symbol)

[obonilla66]

Is it posible to add 2 new Relationship types in ERD diagrams?

Currently there are 4 Relationship types:

1. Zero or one (one optional)
2. Exactly one (one mandatory)
3. Zero or more (many optional)
4. One or more (many mandatory)

This new 2 Relationship types are then sames of above but whitout the second symbol that indicates the minimal cardinality, I mean, the zero or one minimal Cardinality, or is the same, the type optional or mandatory of the relationship, they are, just One or Many:

1. Just One (without "minimal zero" or "minimal one" cardinality)
2. Just More (without "minimal zero" or "minimal one" cardinality)

I think the easiest way to include them in the syntax is to replace the "o" symbol with "x", which would indicate not drawing this second symbol. Another alternative is not to put anything in place of the "o" symbol, but the first way seems more explicit to me. See next image:

The reason for this suggestion is that with the current 4 types of relationships you can theoretically generate 16 different relationships (the reality is that, at least in the physical implementation of relational databases, only 4 different relationships can be used, but that is material from another discussion).
Of those 16 different relationships there is 1 that remains graphically ambiguous: 1 optional to 1 optional. Graphically there is no way to express which is the strong table and which is the weak table, because both ends of the relationship are equal. The proposal would allow us to explicitly express which is the strong table and which is the weak one just by looking at the graph.

In the physical implementation of relational databases, the weak tables always will be optional, then, there is no reason to indicate this situation in the graphic. The new proporsal types would be used in on the weak tables and it would mean:

• maximal cardinality one or many of the releationship
• minimal cardinality zero (optional condition) of the releationship (the weak table never could be mandatory, it always will be optional)
• this is the weak table

Strong tables will continue to use traditional relationship types and it means:

• maximal cardinality one of the releationship (the strong table never could be many, it always will be one)
• minimal cardinality zero (optional condition) or one (mandatory condition) of the releationship
• this is the stronge table

And the ERD diagram will be graphically complete.

Regards.