The identifier has a hierarchical structure as follows:
where NSS is the Namespace Specific String composed as follows:
- <jurisdiction> is the part providing the identification of the jurisdiction, generally corresponding to the country where the source of law is issued.
- <local-name> is the uniform name of the source of law in the country or jurisdiction where it is issued; its internal structure is common to the already adopted schemas.
Illustrative examples of sources of law identifyed by lex URNs:
urn:lex:it:stato:legge:2003-09-21;456 (Italian act) urn:lex:fr:etat:lois:2004-12-06;321 (French act) urn:lex:es:estado:ley:2002-07-12;123 (Spanish act) urn:lex:ch;glarus:regiere:erlass:2007-10-15;963 (Glarus Swiss Canton decree) urn:lex:eu:council:directive:2010-03-09;2010-19-UE (EU Council Directive) urn:lex:us:federal.supreme.court:decision:1963-03-18;372.us.335 (US FSC decision)
- urn:lex:br:federal:lei:2008-06-19;11705: Law nº 11.705, of June 19, 2008, known also as "Brazilian Prohibition".
URNs are used as unique identifiers (unique IDs), like in, for example, to identify a book by its ISBN – so, the URN is also nominated as "public (unique) ID". In that kind of public utilization, the need for a central authority (the International ISBN Agency in the example) as unique and necessary URN-resolver, is a problem. In that context, the identifier's user must to query the authority about the correct ID, from some object's metadata, like year or title. IDs like ISBN, that need a central authority are also named "opaque IDs".
A common use of Lex URNs, by other hand, is to express transparent identifiers, that can be built up by simple rules or inferences from basic metadata. Example: the Brazilian Lex URN is used for both, legislative and case law unique and universal identifier, using rules of formatting and abbreviation of the authority's name, the publication date, and the local identifier (present in the title of the document).
- NOTE about terminology. In computer science a identifier is a data type, and an opaque data type is a data type whose concrete data structure is not defined in an interface. In opposition, a data type whose representation is visible is called transparent.
URN schemes where each URN is also a transparent identifier, can be used in distributed (non-central) URN-resolution systems; and the URNs can be created in absence of these systems, even before to the recording in these systems.