EntityTypes are those concepts defined in an InfoGrid Model whose instances can stand by themselves and do not depend on other instances. Contrast with RelationshipTypes, which are those concepts defined in an InfoGrid Model whose instances depend on other instances (the source and destination MeshObject).
EntityType is similar to the concept of a class in UML, or the notion of an entity in entity-relationship or information modeling. However, as all concepts in an InfoGrid Model, EntityTypes are a conceptual-level concept and do not reflect their implementation in a particular programming language or storage technology. For example, instances of EntityTypes may be stored in relational databases, in XML files, in object databases, encrypted or in memory without any impact on the definition of the EntityType.
For example, in an ordering system, Customer, Order, and LineItem each are an EntityType. Customer_Places_Order, and Order_Contains_LineItem each are a RelationshipType. Customer_FirstName, Order_PlacedOn etc. each is a PropertyType.