Mapping between current UML model and EXPRESS rules is inconsistent

Rules are part of the EXPRESS syntax, and are a very convenient to perform data integrity checking when loading a set of instances from a Part21 Express file. In the current UML model, I understand that rules are represented using a text field that embeds the EXPRESS rule. In the UML, such rules thus appear to be disconnected from the data model whereas they're part of it. Am I right ?

Another approach would be to enrich the current UML model with an UML based rule model that can be serialized to an EXPRESS rule.