Reading direction indicators for ER diagrams

[materpillar]

Proposal

Mermaid.js should add an option for Entity Relationship diagrams to indicate reading direction of a relationship.
There might be multiple relationships between entities in both directions that shall appear on a diagram.

For example, I want to express a relationship:
A fop can contain 0 or multiple gop.
A gop can call 0 or 1 different fop.

The current available notation will not be able to express this unambigously, as the diagram will imply: A fop can call 0 or 1 gop

erDiagram
    "FOP" ||--|{ "GOP" : contains
    "GOP" o|--|| "FOP" : calls

To workaround this limiation, but only under the precondition of assuming a reading direction from top-to-bottom, one could rename "calls" to "called by". Yet, this stays ambiguous.

The following paragraph from the documentation is in my opinion technically not 100% correct:

For example:
PROPERTY ||--|{ ROOM : contains
This statement can be read as a property contains one or more rooms, and a room is part of one and only one property.

It should read:
A property contains one or more rooms, and a room is partcontained by one and only one property.

In general, the passive voice should be used to reverse a relationship, as anything different will require additional knowledge of the domain (and vocabulary)

The next statement is correct for many cased, but is based on too simplistic assumptions for technical documenation, as I tried to demonstrate in this issue.

When considered from the perspective of the second entity, the equivalent label is usually very easy to infer. (Some ER diagrams label relationships from both perspectives, but this is not supported here, and is usually superfluous).

Example

%%{init: { 'erDiagram': {'directionIndicators': true}} }%%

Screenshots