A Digital Object Identifier (DOI) is a globally unique and unchanging address that can be used to access electronic resources, such as websites. Accessibility is guaranteed even if, for example, the so-called "Uniform Resource Locator" (URL) of a resource changes. The main benefit of the DOI system is therefore the sustainable citability of electronic resources. This is achieved through simple mapping: The DOI-foundation maintains a register in which the current URL of a resource is assigned to each DOI. When a URL is changed, the change must be made accordingly in the register of the DOI-foundation. URL changes must be reported to the DOI-foundation by the DOI-registration agency that registered the DOI in question. The registration of VerbaAlpina's web resource in the DOI-register is carried out by the "Associated Electronic Publishing Divisions" of the LMU University Library, which in turn does not register directly with the DOI-foundation, but with the DataCite consortium, a member of the DOI-foundation. The prerequisite for registering a DOI with DataCite is the creation and submission of an XML file whose structure and content conform to the DataCite metadata standard. The XML code used for the registration of the VerbaAlpina-URL can be viewed and retrieved here. For the creation of DataCite-compliant XML files, two useful tools have been developed by the university library and digital humanities of the LMU: the DataCite Metadata Generator and the DataCite Best Practice Guide.

A prerequisite for the reliable functioning of the DOI-concept is not only responsible conduct by the domain operator, but also trustworthiness on the part of the institution entrusted with the maintenance of the corresponding allocation tables, i.e., the responsible DOI-registration agency. It should aim for unlimited existence, as is the case with university, state and national libraries, for example. In any case, the domain operator should report any changes made to the address of a digital object to the registration agency so that the corresponding entries in the DOI register can be adjusted. Conversely, regular checks on the part of the DOI-registration agency(ies), roughly comparable to the traditional "revisions" in libraries, are also conceivable.

The DOI of VerbaAlpina is doi:10.5282/verba-alpina. The number before the slash (10.5282) is called the prefix, the string following it is the suffix. The prefix is assigned to the responsible DOI-registration agency – the LMU University Library, in this case. For a citation, e.g., in a scientific paper, to lead directly to the VerbaAlpina portal, the DOI must be preceded by the URL of the DOI-foundation: http://dx.doi.org/10.5282/verba-alpina.

The so-called Uniform Resource Name (URN) serves almost the same purpose as the DOI and its mode of operation is also more or less the same. In contrast to the DOI, however, it is possible to register several URLs for a resource with the URN. This may, for example, be of interest when resources are stored on different servers with different URLs for the purpose of fail-safety or sustainability. Unlike the DOI, the URN-registry is not operated by a single institution, but by various decentralised national organisations. A web resource can only be found via the registration server ("resolver") of the institution where the URN was registered. In Germany, this task is performed by the German National Library (DNB). The URN of VerbaAlpina is urn:nbn:de:bvb:19-verba-alpina-8. The VerbaAlpina-portal can be accessed via the DNB resolver under the URL http://nbn-resolving.de/urn:nbn:de:bvb:19-verba-alpina-8.

In principle, it is even possible to register DOIs and URNs for partial resources of a domain (e.g., individual web pages or media files). Alternatively, partial resources can also be referenced by including the URL parameters in the DOI. For this, a special syntax must be used, which is illustrated in the following example: The DOI referring to the URL of the entry Research Data Management looks like this:

http://dx.doi.org/10.5282/verba-alpina?urlappend=/%3fpage_id=493%26db=xxx%26letter=F#112

The example shows that the question mark as well as the so-called "ampersands" (&) must be replaced by the respective hexadecimal value of the character in the Unicode table (? = 3f, & = 26).

Literature: Dreyer 2012