The iServer platform developed in the Global Information Systems (GlobIS)
research group at ETH Zurich enables cross-media linking based on a general Resource-Selector-Link
(RSL) model. iServer not only supports links between different kinds of digital media, but also
allows for the integration of physical and digital content. Links managed by the iServer platform
are always directed. Every link is bound to at least one source anchor and points to one or more
target components (multi-headed links). Furthermore, iServer does not distinguish between components
which can be used as link sources and those applicable as target objects. This is achieved by
introducing a general concept of entities as link anchors and targets within the underlying RSL hypermedia metamodel.
The simplest type of an entity is a resource, always representing an entire information unit. Using
the resource concept we can, for example, link from an HTML document to a movie clip. To control the
granularity of link anchors and targets we introduce selector as a subtype of entity enabling us to address
parts of a resource. Further, each selector is located on a specific layer which allows for overlapping links
with well-defined semantics (multi-layered links). Access control and link sharing is supported by the user
management unit.
The iServer architecture is designed as a platform which can be extended based on a plug-in mechanism. By
implementing media-specific instances of the selector and resource components, any new type of media can be
integrated. The framework has been used within the European projects Paper++ and PaperWorks for integrating
physical paper and digital content and is the main component of the interactive paper infrastructure.
Further, we are developing plug-ins for XHTML documents, movie clips and sound files. The sharing of link
knowledge is supported by the distributed iServer version based on peer-to-peer concepts.
More recently active components have been added to the iServer platform. An active component is a configurable
piece of program code which gets executed on link activation. By using active components, we can not only
link to static content but design very interactive information environments.
Resource Plug-ins
A resource plug-in mechanism based on the resource and selector concepts enables the integration of new
resource types by providing a resource-specific Java implementation of a resource and its corresponding selector.
Fig. 2: Resource plug-ins
The Selectors representing elements within a resource in combination with the Resources which represent
entire resources are the central components for the resource plug-in mechanism. For a particular media type,
we can extend the iServer platform by introducing a component that defines selectors and resources for that media
type. Figure 2 shows a component for movies (iMovie) where a resource is a movie and a selector may
be a time span. Another plug-in is responsible for dealing with web pages (iWeb) where a resource is an XHTML
document and a selector is an XPointer expression.
A major advantage of the chosen plug-in mechanism is the tight integration over all types of media based on a
common core link model rather than isolated applications for specific kinds of media. As soon as a plug-in for
a new resource type has been implemented, entities of that medium can be cross-linked with instances of any
existing media type. With each resource plug-in introduced, the iServer platform becomes more powerful and
provides a richer cross-media information space. In The following table provides a list of existing iServer
resource plug-ins represented by the corresponding resource and selector types for each type of media. Note
that the list of plug-ins is far from being complete since arbitrary digital or physical resources could be added.
Medium
Resource
Selector
paper
document page
shape
web page
XHTML document
XPointer
movie
mpeg file, avi file etc.
time span
movie
mpeg file, avi file etc.
shape
sound
mp3 file, wav file etc.
time span
image
gif file, jpeg file etc.
shape
database
database workspace
query
physical object
RFID space
RFID tag
For a given resource type there may be varying types of selectors based on the requirements
of specific applications. In the table, we suggest time spans to be used as a candidate for movie
selectors. However, a specific application might need to link movies based on spatial information within
the movie whereas another application might need to define links based on a combination of temporal
and spatial information. The iServer architecture therefore supports the definition of different
selectors for a single resource type.
A first iServer plug-in was implemented for interactive paper to integrate paper and digital content.
More recently we developed three additional iServer plug-ins to fully integrate XHTML content, movies and
arbitrary RFID-tagged physical objects. Of course, XHTML documents and movies already have some basic support
in the core iServer implementation as it is possible to link for example from a web page to a movie. However,
to fully support these resource types, it should be possible to link to/from elements within a resource
and not just associate entire resources. This implies that we have to implement a resource plug-in with
the corresponding selector for addressing parts of a resource.
A Dynamically Extensible Open Cross-Document Link Service,
Ahmed A.O. Tayeh and Beat Signer,
Proceedings of WISE 2015, 16th International Conference on Web Information Systems Engineering,
Miami, USA, November, 2015 (acceptance rate: 31%)
An Architecture for Open Cross-Media Annotation Services,
Beat Signer and Moira C. Norrie,
Proceedings of WISE 2009, 10th International Conference on Web Information Systems Engineering,
Poznan, Poland, October 2009 (acceptance rate: 23%)
A Framework for Cross-Media Information Management,
Beat Signer and Moira C. Norrie,
Proceedings of EuroIMSA 2005, International Conference on Internet and Multimedia Systems and Applications,
Grindelwald, Switzerland, February 2005
