Addressing on the Internet and limitations of location-dependent references

Addressing on the Internet

The primary addressing mechanism on the internet is based on the application of a special type of cross-references for navigation in the World Wide Web (WWW), the hyperlinks. They are substantial elements of markup languages which describe the logical and physical structure of documents. Examples include the Hypertext Markup Language (HTML) and eXtensible Markup Language (XML) of the World Wide Web Consortium (W3C) describing and defining content, structure and semantic of documents.

The HTML-specification-4.0.1, for example, defines hyperlink as link between two resources with a starting point and a target. The target description of a hyperlink must include the indication of a worldwide unequivocal address. At present, Uniform Resource Locators (URLs), determining the document location, are predominantly used for this purpose.

However, hypertexts lose consistency and navigation functionality if their links are unstable. The reason for this is the link dependency on the storage location of digital objects.

Alternative approaches providing location-independent addressing through separating link targets from direct reference to the storage location, have already been developed. One example for this is the ISO-Standard HyTime - Hypermedia/Time-based Structuring Language. Yet, these alternatives had no wide-spread impact.

Associated XML-standards for resource linking as e.g. XML Linking Language (XLink) or HLink - Link recognition for the XHTML Family W3C increase semantic referencing and the functions of HTML-links. These standards, also, include approaches for location-independent addressing, yet, they are application-related and have no mechanism for (totally) location-independent addressing.

Time stability of location-dependent links: applied methods and their limitations

Methods

To compensate the disadvantages of location-dependent links, two different methods are applicable, providing time stability of links through e.g.

Limitations

The methods described offer only medium term solutions for specific situations.

Reliable, persistent referencing of digital contents through location-independent identification and addressing mechanisms must be applied. Persistent referencing requires, in the long-term, institutional support embedded in an international infrastructure.


02.01.2008