Identifiers have been extremely important standardization tools among publishers, booksellers, and libraries for many years. There are a number of unique identifier services that have been developed for electronic resources. The PURL System, which stands for Persistent URL, was designed to be a short-term, partial solution to the naming problem. For example, it is not fully location-independent. Information providers registering resources on a particular PURL Resolver must rely on OCLC services for support.
Resolution is the mechanism by which a computer on the Internet can discover what a name refers to.
Resolution is necessary because today's standard browsers do not understand how to convert identifiers to URLs and vice versa. In CNRI parlance, URNs are called handles. It is a distributed system designed to support global interoperability. The DOI System of unique identifiers is based on Handle System technology and allows the allocation of a unique digital identifier to commercial digital publications. CrossRef, a newly formed organization comprised of leading scientific, technical, and medical publishers, uses DOIs to link more than 2 million article records for over 3,000 journals.