An Information Model defines a contract between OPC UA Applications. OPC UA Clients can rely on the mandatory parts defined in such an Information Model and OPC UA Servers are not required to provide more than the specified mandatory information.

Elements defined in an Information Model are qualified by their Namespace, which is a unique URI. When a new version of such an Information Model is defined, some rules need to be considered to re-use the existing Namespace. If those rules cannot be followed, the existing NamespaceUri should not be used. However, a new NamespaceUri implies that all information is new, that is, even using the same name and NodeId (without NamespaceIndex) for a type, OPC UA Applications will consider it to be a completely different Node with no relation to the one qualified by the old Namespace.

The next clauses describe the rules that must be followed to re-use the existing Namespace when versioning an Information Model.