MOTIVATION AND OBJECTIVES
People generally need more and more advanced tools that go beyond those implementing the canonical search paradigm for seeking relevant information. A new search paradigm is emerging, where the user perspective is completely reversed: from finding to being found. Recommender systems may help to support this new perspective, because they have the effect of pushing relevant objects, selected from a large space of possible options, to potentially interested users. To achieve this result, recommendation techniques generally rely on data referring to three kinds of objects: users, items and their relations.
Recent developments in the Semantic Web community offer novel strategies to represent data about users, items and their relations that might improve the current state of the art of recommender systems, in order to move towards a new generation of recommender systems that fully understand the items they deal with.
More and more semantic data are published following the Linked Data principles, that enable to set up links between objects in different data sources, by connecting information in a single global data space: the Web of Data. Today, the Web of Data includes different types of knowledge represented in a homogeneous form: sedimentary one (encyclopedic, cultural, linguistic, common-sense) and real-time one (news, data streams, ...). These data might be useful to interlink diverse information about users, items, and their relations and implement reasoning mechanisms that can support and improve the recommendation process.
The primary goal of this challenge is twofold. On the one hand, we want to create a link between the Semantic Web and the Recommender Systems communities. On the other hand, we aim to show how Linked Open Data (LOD) and semantic technologies can boost the creation of a new breed of knowledge-enabled and content-based recommender systems.

TARGET AUDIENCE
The target audience is all of the Semantic Web and the Recommender Systems communities, both academic and industrial, which are interested in personalized information access with a particular emphasis on Linked Open Data.
During the last ACM RecSys conference more than 60% of participants were from industry. This is for sure a witness of the actual interest of recommender systems for industrial applications ready to be released in the market.

TASKS

* Task 1: Rating prediction in cold-start situations
This task deals with the rating prediction problem, in which a system is requested to estimate the value of unknown numeric scores (a.k.a. ratings) that a target user would assign to available items, indicating whether she likes or dislikes them.
In order to favor the proposal of content-based, LOD-enabled recommendation approaches, and limit the use of collaborative filtering approaches, this task aims at predicting ratings in cold-start situations, that is, predicting ratings for users who have a few past ratings, and predicting ratings of items that have been rated by a few users.
The dataset to use in the task - DBbook - relates to the book domain. It contains explicit numeric ratings assigned by users to books. For each book we provide the corresponding DBpedia URI.
Participants will have to exploit the provided ratings as training sets, and will have to estimate unknown ratings in a non-provided evaluation set.
Recommendation approaches will be evaluated on the evaluation set by means of metrics that measure the differences between real and estimated ratings, namely the Root Mean Square Error (RMSE).

* Task 2: Top-N recommendation from binary user feedback
This task deals with the top-N recommendation problem, in which a system is requested to find and recommend a limited set of N items that best match a user profile, instead of correctly predict the ratings for all available items.
Similarly to Task 1, in order to favor the proposal of content-based, LOD-enabled recommendation approaches, and limit the use of collaborative filtering approaches, this task aims to generate ranked lists of items for which no graded ratings are available, but only binary ones. Also in this case, the DBbook dataset is used.
In this task, the accuracy of recommendation approaches will be evaluated on an evaluation set using the F-measure.

* Task 3: Diversity
A very interesting aspect of content-based recommender systems, and then of LOD-enabled ones, is giving the possibility to evaluate the diversity of recommended items in a straight way. This is a very popular topic in content-based recommender systems, which usually suffer from over-specialization.
In this task, the evaluation will be made by considering a combination of both accuracy (F-measure) of the recommendation list and the diversity (Intra-List Diversity) of items belonging to it. Also for this task, the DBbook dataset is used.
Given the domain of books, diversity with respect to the two properties http://dbpedia.org/ontology/author and http://purl.org/dc/terms/subject will be considered.

JUDGING AND PRIZES
After a first round of reviews, the Program Committee and the chairs will select a number of submissions that will have to satisfy the challenge requirements, and will have to be presented at the conference. Submissions accepted for presentation will receive constructive reviews from the Program Committee, and will be included in post-proceedings. All accepted submissions will have a slot in a poster session dedicated to the challenge. In addition, the winners will present their work in a special slot of the main program of ESWC’14, and will be invited to submit a paper to a dedicated Semantic Web Journal special issue.

For each task we will select:
* the best performing tool, given to the paper which will get the highest score in the evaluation
* the most original approach, selected by the Challenge Program Committee with the reviewing process

An amount of 700 Euro has already been secured for the final prize. We are currently working on securing further funding.

A task with less than 3 participants will be cancelled. Nonetheless, in any case, participants will be provided with reviews from members of the programme committee, and the possibility of publishing their results in the post-proceedings volume of the conference.

If a task is cancelled, its prize will be re-distributed among the remaining tasks.

IMPORTANT DATES
* March 7, 2014, 23:59 CET: Result submission due
* March 14, 2014, 23:59 CET: Paper submission due
* April 9, 2014, 23:59 CET: Notification of acceptance
* May 27-29, 2014: The Challenge takes place at ESWC’14

CHALLENGE CHAIRS
* Tommaso Di Noia (Polytechnic University of Bari, IT)
* Iván Cantador (Universidad Autónoma de Madrid, ES)

EVALUATION COORDINATOR
* Vito Claudio Ostuni (Polytechnic University of Bari, IT)

PROGRAM COMMITTEE (to be completed)
* Pablo Castells, Universidad Autonoma de Madrid, Spain
* Oscar Corcho, Universidad Politécnica de Madrid, Spain
* Marco de Gemmis, University of Bari Aldo Moro, Italy
* Frank Hopfgartner, Technische Universität Berlin, Germany
* Andreas Hotho, Universität Würzburg, Germany
* Dietmar Jannach, TU Dortmund University, Germany
* Pasquale Lops, University of Bari Aldo Moro, Italy
* Valentina Maccatrozzo, VU University Amsterdam, The Netherlands
* Roberto Mirizzi, Polytechnic University of Bari, Italy
* Alexandre Passant, seevl.fm, Ireland
* Francesco Ricci, Free University of Bozen-Bolzano, Italy
* Giovanni Semeraro, University of Bari Aldo Moro, Italy
* David Vallet, NICTA, Australia
* Manolis Wallace, University of Peloponnese, Greece
* Markus Zanker, Alpen-Adria-Universitaet Klagenfurt, Austria
* Tao Ye, Pandora Internet Radio, USA

ESWC CHALLENGE COORDINATOR
* Milan Stankovic (Sépage & Université Paris-Sorbonne, FR)