TESI DOCTORAL - La Salle

Chapter 1. Framework of the thesis
Figure 1.1: Evolution of the total number of websites across all Internet
domains, from November 1995 to February 2009 (extracted from
http://news.netcraft.com/archives/2009/02/index.html).
Resorting to the WWW example again, we have all witnessed, through the last decade, how
web pages have evolved from static plain text to dynamic multimedia contents. That is,
the information available on the Web is, to a large extent, no longer restricted to a single
modality (e.g. news in text format). Rather the contrary, data is increasingly becoming
multimodal, i.e. a combination of several modalities (e.g. text news accompanied with
photos, graphics, audio or video).
This shift towards data multimodality can be regarded as a change of paradigm which
is also found in many other domains (Klosgen, Zytkow, and Zyt, 2002). For instance,
meteorological information often combines satellite and radar imagery with meteorological
data in numerical form (e.g. temperature, humidity, wind speed, rainfall, etc.). In medical
contexts, repositories often contain data obtained from several diagnostic tests (e.g.
blood analysis, radiography, electrocardiophy, electroencephalography, functional magnetic
resonance) whose results are represented under distinct modalities (nominal and numerical
data, images, etc.).
To sum up, despite providing enormous quantities of information on a silver plate, the
development and expansion of the ICT pose a serious challenge to human analytic and
understanding capabilities, not only by the large volumes of data available, but also by its
growing complexity. Therefore, it seems logical to highlight the importance of developing
automatic tools that allow knowledge extraction from large multimodal data repositories,
regardless of their domain (Witten and Frank, 2005). The techniques supporting these tools
belong to the fields of knowledge discovery and data mining (Klosgen, Zytkow, and Zyt,
2002), which constitute, in a broad sense, the frame of reference of this thesis.
When it comes to extracting knowledge from a given data collection, one of the primary
tasks one thinks of is organization: clearly, arranging the contents of a data repository
according to some meaningful structure helps to gain some perspective on it –in fact, orga-
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