Errors block the transition to the restructuring and translation phases, whereas warnings highlight incomplete parts without halting the process.
Rule violations
| Message | How to fix it |
|---|
| The entity has no internal or external identifier | Mark at least one attribute as Identifier, or identify the entity externally with Ext. Id. |
| A child entity must not have any internal or external identifier | Remove it; the child uses the parent’s identifier. |
| The ‘subset’ generalization must have the properties (p,e) | Set the generalization with a single child to Part.Excl. |
| Maximum cardinality for composite attribute must be 1 | Set the composite attribute to (0,1) or (1,1). |
| For an externally-identified entity, the cardinality of the participation must be (1,1) | Set the identifying participation to (1,1). |
| The relationship must have at least two participations | Use Connect to link a second entity. |
| A recursive relationship requires participation roles | Set a Role on both participations. |
| A ternary relationship requires all participation cardinalities to have maximum value N | Set every participation to (0,N) or (1,N). |
| A relationship involved in external identification cannot have any attributes | Move the attributes to the weak entity. |
| A relationship involved in external identification cannot be recursive | Identify the entity through a different relationship. |
Naming conflicts
| Message | How to fix it |
|---|
| There is a name conflict | Two entities or relationships share a name. Rename one. |
| Multiple attributes with the same name | Rename the duplicate attribute or subattribute. |
Warnings
| Message | What to check |
|---|
| The entity has no attributes (apart from identifiers) | Whether something is missing. |