Domain, Entity, Attribute, and Association Role node names can contain only alphanumeric characters (letters and numbers), and underscores. However:

Domain, Entity, Attribute, and Association Role node names can not begin with a number.

Spaces are not allowed in Domain, Entity, Attribute or Association node names. If the preferred name is a combination of multiple words, then the underscore characters can be used to combine them into a single-word name.

Domain, Entity, Attribute, and Association Role node names can begin with an underscore.

Domain, Entity, Attribute, and Association Role node names can begin with either an upper or lower case letter.

No two Entities in the same Domain can have the same node name (case-insensitive).

Names of Operators (such as sum, size, month, now, today) or Extended Operators (if any) can not be used as Entity or Domain node names. They can be used as Attribute or Association Role node names.

Custom Data Type names cannot use the names of any of the base data types (such as string, decimal, boolean). See the Rule Modeling Guide’s chapter Creating the Vocabulary for more information about Custom Data Types.

Names of aliases in the Scope section cannot match (case-sensitive) the node names of Entities in the Vocabulary.

No two Attributes/Association Role nodes in the same Entity can have the same name (case-insensitive).

No two Domains within another Domain can have the same node name (case-insensitive).

No two root-level Domains can have the same node name(case-insensitive).

No association can have the same name as an entity.