Ubiquitous annotation systems allow users to annotate physical places, objects, and persons with digital information. Especially in the field of location based information systems much work has been done to implement adaptive and context-aware systems, but few efforts have focused on the general requirements for linking information to objects in both physical and digital space. This paper surveys annotation techniques from open hypermedia systems, Web based annotation systems, and mobile and augmented reality systems to illustrate different approaches to four central challenges ubiquitous annotation systems have to deal with: anchoring, structuring, presentation, and authoring. Through a number of examples each challenge is discussed and HyCon, a context-aware hypermedia framework developed at the University of Aarhus, Denmark, is used to illustrate an integrated approach to ubiquitous annotations. Finally, a taxonomy of annotation systems is presented. The taxonomy can be used both to categorize system based on the way they present annotations and to choose the right technology for interfacing with annotations when implementing new systems.
['Frank Allan Hansen']
Ubiquitous annotation systems: technologies and challenges