IEC 81346-1:2009, published jointly by IEC and ISO, establishes general principles for the structuring of systems including structuring of the information about systems. Based on these principles, rules and guidance are given for the formulation of unambiguous reference designations for objects in any system. The reference designation identifies objects for the purpose of creation and retrieval of information about an object, and where realized about its corresponding component. This edition includes the following substantial changes with respect to the previous one: - a new introductory clause providing a description and explanation to the concepts used elsewhere in the publication; - a more comprehensive description of the structuring principles and rules for structuring are provided; - "other aspects" are introduced, and the prefix sign # is assigned to these aspects; - the concept of reference designation group has been deleted; - the specific term "transition" has been avoided and been replaced by an improved textual description of this phenomenon in annex D; - a new clause about labelling is introduced; - the old annexes have been removed with the exception of the annex showing an example of the application of reference designations within a system; - a new annex explaining the manipulation of objects is introduced; - 4 new annexes are introduced as rearrangement of detailed examples or explanatory information. It has the status of a horizontal standard in accordance with IEC Guide 108.