All concepts in used in human thought are represented by what are called "designations" that are expressed phonetically in human languages. Each language may employ one or more writing systems that are expressed electronically as "Character sets". In all languages and writing systems, each concept has a unique representation that is determined by a set of characters which can then be used for classifying and grouping concepts by means of explicit rules. It is important for the viewer to understand that "code", when used either in place of designations (commonly referred to as a "term") or the class name, is not the term or the class but a surrogate for the term of class name and because it stands in for the term may be constructed with several different rules that lead to different "codes" for different purposes (see ISO TR 9789). The term designation for a concept is the most specific representation of the concept. In healthcare there are several different common coding systems for classification of the vocabularies used in the EHR. Particular examples are for identifying Diagnosis classes and Procedure. ASTM Specification E-1633 lists those schemes for assigning value sets to the data elements given in ASTM Guide E-1384 for the Structure and Content of the EHR. The HL7 Standard for Healthcare messaging defines the coding schemes used in healthcare messaging formats and these identified value sets are in the process of being harmonized by the two standards developers.