2003), MPEG-7 and several ad hoc syntaxes.
• A profile containing demographical data of the
viewer (age, gender, job, ...), together with point-
ers to contents/products that he/she has evaluated
in the past (each one labeled with a degree of in-
terest, DOI) and products that he/she owns (la-
beled with a degree of satisfaction, DOS).
The filtering is triggered by context information
indicating what the viewer is watching. The person-
alization servers proceed over complete ontologies
and viewer profiles, whereas the local instances of
AVATAR handle partial versions due to the limited
resources. In the latter case, the quality of the rea-
soning can be enhanced using ontological information
and stereotypical profiles received through the broad-
cast networks. This supporting material, inserted in
the IDTV head-end, can be tailored to the programs
and the advertisements which are broadcast at any
moment.
2.3 The I-Spot Composer
The product selections made by AVATAR are the en-
try for the i-spot composer to assemble interactive ser-
vices that let the viewers navigate for detailed infor-
mation about the products, search for the closest es-
tablishment where they can be bought, purchase on-
line, subscribe to the notification of novelties, etc.
It is foreseeable that many i-spots will provide es-
sentially the same functionality. In our system, there-
fore, they are assembled from template classes, and
it is up to the i-spot composer to decide which tem-
plates to use (considering hardware requirements, re-
turn channel availability, ...) and which contents to
lay over them (received through broadcast or down-
loaded from the Internet). The outcome of those de-
cisions is later used in the receivers to start the ser-
vices, retrieving the corresponding templates from the
broadcast stream and setting them up using the Java
reflection mechanisms. This approach enables good
use of bandwidth while not increasing the computa-
tional cost for the receivers, as it is not necessary to
modify or recompile any source code.
Remarkably, the selection of contents in the i-spot
composer can be driven by the same semantic reason-
ing algorithms of AVATAR, to increase the odds that
the viewer will appreciate the information included in
the i-spots.
2.4 The Feedback Agent
Just because the interests, preferences and needs of
the viewers may vary with time, the model of spon-
taneous and personalized advertising requires mech-
anisms to update their profiles by capturing new data
and discarding obsolete knowledge. In literature, one
can find proposals to do this implicitly, by inferring
information from the viewers’ interaction with a sys-
tem, or explicitly, by asking the viewers to enter some
information from time to time.
Our prototype system supports both forms of feed-
back to recompute the DOI values stored in the
profiles, for which it applies the same functions of
gradual forgetting and relevance feedback defined
in (Montaner et al., 2002). The implicit form gath-
ers information by monitoring how long the viewer
takes to learn about the different products, whether
he/she decides to buy, hire or subscribe, and how
much money he/she spends. On the other hand, the
explicit form relies on interactive questionnaires, con-
structed just the same way as the i-spots. We also
provide the viewers with questionnaires to enter DOS
values for the products they own, and to update their
demographical data.
3 A SAMPLE SCENARIO
For a brief example, consider the case of a TV viewer
whose profile indicates, among other facts, that she
has two children and a middle-income economy (de-
mographical data), that she is a loyal viewer of pro-
grams devoted to travel (viewing history), and that she
is subscribed to an oenology magazine (consumption
data). The viewer is watching a documentary about
Switzerland on her PDA, with the current scene de-
scribing a town in the Geneva canton. As shown in
Figure 2, the metadata linked to this part of the audio-
visual contents identify four things on screen, namely
the village, the sky, the lake and the vineyard. These
entities are related to some concepts in the system on-
tologies, represented by the gray and dashed elements
of the figure.
If the viewer clicked over the village, our sys-
tem would be able to locally assemble one i-spot de-
scribing affordable trips and tourist attractions around
Geneva, getting the contents from broadcast. Alter-
natively, if bi-directional communication were avail-
able, another i-spot could be designed that described
rural tourism houses in the viewer’s area, emphasiz-
ing those which offer facilities for children, and giv-
ing the viewer the possibility to book a room for her
holidays (see Figure 3).
On the other hand, clicking on the vineyard, the
viewer’s expertise in wine would take our system to
display a list of remarkable vintages (with i-spots al-
lowing her to purchase some bottles), trips to famous
wineries, etc. Other viewers would be offered wines
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