Publications

Journals:

• L. M. Aiello, A. Barrat, R. Schifanella, C. Cattuto, B. Markines, F. Menczer
  Friendship prediction and homophily in social media
  In ACM Transaction on the Web (TWEB). To appear.
  [abstract]

  Web 2.0 applications have attracted a considerable amount of attention because their open-ended nature allows users to create lightweight semantic scaffolding to organize and share content. To date, the interplay of the social and semantic components of social media has been only partially explored. Here we explore the presence of homophily in three systems that comine tagging of social media with online social network. We find a substantial level of local semantic similarity among users who lie close to each other in the social network. We introduce a null model that preserves user activity while removing local correlations, allowing us to disentangle the actual local similarity between users from statistical effects due to the assortative mixing of user activity and centrality in the social network. This analysis suggests that users with similar interests are more likely to be friends, and therefore semantic similarity measures among users based solely on their annotation metadata should be predictive of social links. We test this hypothesis on several data sets, confirming that social networks constructed from semantic similarity capture actual friendship accurately.

• M. I. Mandel, R. Pascanu, D. Eck, Y. Bengio, L. M. Aiello, R. Schifanella, F. Menczer
  Contextual Tag Inference
  In ACM Transactions on Multimedia Computing, Communications and Applications (TOMCCAP), Special Issue on Social Media. Volume 7S Issue 1, October 2011, ACM New York, NY, USA.
  [abstract | link]

  This paper examines the use of two kinds of context to improve the results of content-based music taggers. Context in this case means the relationships between tags and the relationships between the clips of songs that are tagged. We show that users agree more on the tags that should be applied to clips that are temporally "closer" to one another; that conditional restricted Boltzmann machine models of tags that take this context into account can more accurately predict related tags; and that when context is used to "smooth" training data, support vector machines can better rank these clips according to the original, unsmoothed tags.

• A. Panisson, A. Barrat, C. Cattuto, W. Van den Broeck, G. Ruffo, R. Schifanella
  On the Dynamics of Human Proximity for Data Diffusion in Ad-Hoc Networks
  In Ad Hoc Networks, Elsevier. Available online 21 June 2011.
  [abstract | link]

  We report on a data-driven investigation aimed at understanding the dynamics of message spreading in a real-world dynamical network of human proximity. We use data collected by means of a proximity-sensing network of wearable sensors that we deployed at three different social gatherings, simultaneously involving several hundred individuals. We simulate a message spreading process over the recorded proximity network, focusing on both the topological and the temporal properties. We show that by using an appropriate technique to deal with the temporal hetero- geneity of proximity events, a universal statistical pattern emerges for the deliv- ery times of messages, robust across all the data sets. Our results are useful to set constraints for generic processes of data dissemination, as well as to validate established models of human mobility and proximity that are frequently used to simulate realistic behaviors.

• L. M. Aiello, M. Milanesio, G. Ruffo, R. Schifanella
  An identity-based approach to secure P2P applications with Likir
  Peer-to-Peer Networking and Applications, Springer, August, 2011
  [abstract | pdf | bibtex | link]

  Structured overlay networks are highly susceptible to attacks aimed at subverting their structure or functionalities. Although many secure architectural design proposals have been presented in the past, a widely accepted and comprehensive solution is lacking. Likir (Layered Identity-based Kademlia-like InfRastructure) is our proposed solution for implementing a secure Peer-to-Peer (P2P) network based on a Distributed Hash Table (DHT). Our purpose is to focus on three main goals: (1) providing security services and a secure overlay infrastructure against the vast majority of security threats on P2P systems, (2) dynamically creating a bridge between randomly generated peer identifiers and user identities, and (3) supplying the developer with a middleware API that can easily deal with peers' identities. Placing the emphasis on user identity results in a highly secure distributed framework which is very fitting for privacy-aware and efficient implementation of identity-based applications like social networking applications. Detailed security analysis and performance evaluation are provided. Moreover, an implementation of Likir is introduced and a case study is presented in order to show its practical use in a real-life example.

  @article {aiello11p2p,
  author = {Aiello, Luca Maria and Milanesio, Marco and Ruffo, Giancarlo and Schifanella, Rossano},
  affiliation = {Computer Science Department, Universit\`a degli Studi, di Torino, corso Svizzera, 185, 10149 Torino, Italy},
  title = {An identity-based approach to secure P2P applications with Likir},
  journal = {Peer-to-Peer Networking and Applications},
  publisher = {Springer New York},
  issn = {1936-6442},
  keyword = {Engineering},
  pages = {420-438},
  volume = {4},
  issue = {4},
  url = {http://dx.doi.org/10.1007/s12083-010-0099-6},
  note = {10.1007/s12083-010-0099-6},
  year = {2011}
  }

• G.Ruffo, R.Schifanella
  A Peer-to-Peer Recommender System Based on Spontaneous Affinities
  In ACM Transactions on Internet Technology (TOIT), Vol. 9, No. 1, Feb. 2009, pp.1-34, ACM Press, New York, NY, USA.
  [abstract | pdf | bibtex | link]

  Network analysis has proved to be very useful in many social and natural sciences, and in particular Small World topologies have been exploited in many application fields. In this paper, we focus on P2P file sharing applications, where spontaneous communities of users are studied and analyzed. We define a family of structures that we call "Affinity Network" (or even Graphs) that show self organized interest-based clusters. Empirical evidence proves that affinity networks are small worlds and shows scale-free features. The relevance of this finding is augmented with the introduction of a proactive recommendation scheme, namely DeHinter, that exploits this natural feature. The intuition behind this scheme is that a user would trust her network of "elective affinities" more than anonymous and generic suggestions made by impersonal entities. The accuracy of the recommendation is evaluated by way of a 10-fold cross validation, and a prototype has been implemented for further feedbacks from the users.

  @article{Ruffo:2009:PRS:1462159.1462163,
  author = {Ruffo, Giancarlo and Schifanella, Rossano},
  title = {A peer-to-peer recommender system based on spontaneous affinities},
  journal = {ACM Trans. Internet Technol.},
  volume = {9},
  issue = {1},
  month = {February},
  year = {2009},
  issn = {1533-5399},
  pages = {4:1--4:34},
  articleno = {4},
  numpages = {34},
  url = {http://doi.acm.org/10.1145/1462159.1462163},
  doi = {http://doi.acm.org/10.1145/1462159.1462163},
  acmid = {1462163},
  publisher = {ACM},
  address = {New York, NY, USA},
  keywords = {Peer-to-Peer, complex networks, file sharing systems, recommender system, social networks},
  }

• W. Allasia, F. Gallo, M. Milanesio and R. Schifanella
  Indexing and Retrieval of Multimedia Metadata on a Secure DHT
  In Informatica - Special Issue on Multimedia Information System Security, Vol. 33, No. 1, March 2009, pp. 85-100.
  [abstract | pdf | bibtex]

  This paper proposes a decentralized, distributed and secure communication infrastructure for indexing and retrieving multimedia contents with associated digital rights. The lack of structured metadata describing the enormous amount of multimedia contents distributed on the the web leads to simple search mechanisms that usually are limited to queries by title or by author. Our approach is based on structured peer-topeer networks and allows complex queries using standard MPEG-7 and MPEG-21 multimedia metadata. Moreover, security aspects limit the development of general purpose real applications using a peer-topeer routing infrastructure for sharing digital items with an associated license. Accordingly, we propose a framework made up of a secure Distributed Hash Table layer based on Kademlia, including an identity based scheme and a secure communication protocol, providing an effective defense against well known attacks.

  @article{DBLP:journals/informaticaSI/AllasiaGMS09,
  author = {Walter Allasia and Francesco Gallo and Marco Milanesio and Rossano Schifanella},
  title = {Indexing and Retrieval of Multimedia Metadata on a Secure DHT},
  journal = {Informatica (Slovenia)},
  volume = {33},
  number = {1},
  year = {2009},
  pages = {85-100},
  bibsource = {DBLP, http://dblp.uni-trier.de}
  }

• G.Ruffo, R.Schifanella
  FairPeers: Efficient Profit Sharing in Fair Peer-to-Peer Market Places
  In Aiko Pras, Jürgen Schönwälder, Burkhard Stiller Guest Editors, Journal of Network and Systems Management (JNSM), special issue on Peer-to-Peer Technologies Service Management, September 2007, Springer Press
  [abstract | pdf | bibtex | link ]

  The technical impact of the Peer-to-Peer paradigm on content distribution applications has been proved successful and efficient, when participants cooperation is achieved. Conversely, the business model is not clear: given a copy-protected object, its owner must be paid back for each transaction taking place from a provider to a receiver. The P2P paradigm assumes that a receiver turns into a provider, but it is questionable why she/he should provide properly the content, if the owner wants to be reimbursed. Actual systems introduce fairness, giving incentives (e.g., a differential service, like in BitTorrent) to altruistic peers, with the consequence that the owner of an object is economically damaged everyday. Hence, music and film industry sees P2P techniques as a hostile framework for distributing copy protected content for free: today's answer of the industry is investing in DRM-based solutions, that are not interoperable between different devices and players.
  In this paper, we present FairPeers, a peer-to-peer market framework, that joins a straightforward intellectual property protection and a fair economic model. Quite importantly, this is performed by maintaining features that make P2P file sharing systems efficient, as multi-source downloading, that is implemented via a lottery scheme, thus avoiding the execution of many redundant micro-payment operations.
  The study is completed with an exhaustive security analysis, and the description of a prototype implementation that shows that the Peer-to-Peer paradigm is mature enough to present to the broadest community new revenue models, simply using available tools and state-of-the-art techniques.

  @article {springerlink:10.1007/s10922-007-9066-9,
  author = {Ruffo, Giancarlo and Schifanella, Rossano},
  affiliation = {University of Turin Computer Science Department Corso Svizzera 185 10149 Turin Italy},
  title = {FairPeers: Efficient Profit Sharing in Fair Peer-to-Peer Market Places},
  journal = {Journal of Network and Systems Management},
  publisher = {Springer New York},
  issn = {1064-7570},
  keyword = {Computer Science},
  pages = {355-382},
  volume = {15},
  issue = {3},
  url = {http://dx.doi.org/10.1007/s10922-007-9066-9},
  note = {10.1007/s10922-007-9066-9},
  year = {2007}
  }

International conferences and workshops:

• R. Schifanella, L. M. Aiello, G. Ruffo
  Tagging relations to achieve complex search goals
  In NWeSP'11: Proceedings of the 7th International Conference on Next Generation Web Services Practices, October 19-21, Salamanca, Spain, 2011
  [abstract | pdf | bibtex | link ]

  Social search is having a flourishing success for its effectiveness in retrieving high quality information useful to achieve complex search goals. Surprisingly, the potential of the social paradigm at the basis of collaborative tagging in satisfying complex search intents has been unexplored so far. We propose an extended model of folksonomies that allows to compose and tag complex user-defined relations between items, users, and tags. We show that this model offers several means to fulfill complex search tasks that are hard to be achieved by other existing services. Furthermore, we support the validity of our approach through a data-driven analysis on Flickr photosets and we present an online portal that provides this new user experience.

  @inproceedings{schifanella11nwesp,
  author = {Schifanella, Rossano and Aiello, Luca Maria and Ruffo, Giancarlo},
  title = {{Tagging relations to achieve complex search goals}},
  booktitle = {NWeSP'11: Proceedings of the 7th IEEE International Conference on Next Generation Web Services Practices},
  year = {2011},
  isbn = {978-1-4577-1126-8},
  location = {Salamanca, Spain},
  pages = {308-313},
  numpages = {6},
  publisher = {IEEE Press},
  }

• L. Weng, R. Schifanella, F. Menczer
  Design of Social Games for Collecting Reliable Semantic Annotations
  In the Proc. of the 16th International Conference on Computer Games: AI, Animation, Mobile, Interactive Multimedia, Educational & Serious Games (CGAMES 2011), 27th-30th July, Louisville, Kentucky, USA.
• L. Weng, R. Schifanella, F. Menczer
  The Chain Model for Social Tagging Game Design
  In the Proc. of the 6th International Conference on the Foundations of Digital Games, Bordeaux, France, June 28-July 1, 2011
  [abstract]

  We introduce the Chain Model for the object association games, and describe two social tagging games based on this model. GiveALink Slider and Great Minds Think Alike harness human power to generate large streams of high-quality social tagging data. Such social annotations are utilized to help people organize Web resources and infer semantic relationship, which in turn can enhance Web applications such as search, recommendation, navigation, and categorization. The two games leverage several design features as well as external social media resources to create entertaining incentives for the players to generate reliable annotation data.

• L. M. Aiello, A. Barrat, C. Cattuto, G. Ruffo, R. Schifanella
  Link creation and profile alignment in the aNobii social network
  In SocialCom'10: Proceedings of the 2nd IEEE International Conference on Social Computing, Minneapolis, MN, USA, 2010
  [abstract | pdf | bibtex]

  The present work investigates the structural and dynamical properties of aNobii, a social bookmarking system designed for readers and book lovers. Users of aNobii provide information about their library, reading interests and geographical location, and they can establish typed social links to other users. Here, we perform an in-depth analysis of the system’s social network and its interplay with users’ profiles. We describe the relation of geographic and interest-based factors to social linking. Furthermore, we perform a longitudinal analysis to investigate the interplay of profile similarity and link creation in the social network, with a focus on triangle closure. We report a reciprocal causal connection: profile similarity of users drives the subsequent closure in the social network and, reciprocally, closure in the social network induces subsequent profile alignment. Access to the dynamics of the social network also allows us to measure quantitative indicators of preferential linking.

  @inproceedings{aiello10socialcom,
  author = {Aiello, Luca Maria and Barrat, Alain and Cattuto, Ciro and Ruffo, Giancarlo and Schifanella, Rossano},
  title = {{Link creation and profile alignment in the aNobii social network}},
  booktitle = {SocialCom '10: Proceedings of the Second IEEE International Conference on Social Computing},
  location = {Minneapolis, Minnesota, USA},
  year = {2010}
  }

• R. Schifanella, A. Barrat, C. Cattuto, B. Markines, and F. Menczer
  Folks in Folksonomies: Social Link Prediction from Shared Metadata
  In the 3rd ACM International Conference on Web Search and Data Mining (WSDM 2010), February 3-6, 2010, New York, USA.
  [abstract | pdf | bibtex | link]

  Web 2.0 applications have attracted a considerable amount of attention because their open-ended nature allows users to create lightweight semantic scaffolding to organize and share content. To date, the interplay of the social and semantic components of social media has been only partially explored. Here we focus on Flickr and Last.fm, two social media systems in which we can relate the tag- ging activity of the users with an explicit representation of their social network. We show that a substantial level of local lexical and topical alignment is observable among users who lie close to each other in the social network. We introduce a null model that preserves user activity while removing local correlations, allowing us to disentangle the actual local alignment between users from statistical effects due to the assortative mixing of user activity and centrality in the social network. This analysis suggests that users with similar topical interests are more likely to be friends, and therefore semantic similarity measures among users based solely on their annotation metadata should be predictive of social links. We test this hypothesis on the Last.fm data set, confirming that the social net- work constructed from semantic similarity captures actual friend- ship more accurately than Last.fm's suggestions based on listening patterns.

  @inproceedings{Schifanella:2010:FFS:1718487.1718521,
  author = {Schifanella, Rossano and Barrat, Alain and Cattuto, Ciro and Markines, Benjamin and Menczer, Filippo},
  title = {Folks in Folksonomies: social link prediction from shared metadata},
  booktitle = {Proceedings of the third ACM international conference on Web search and data mining},
  series = {WSDM '10},
  year = {2010},
  isbn = {978-1-60558-889-6},
  location = {New York, New York, USA},
  pages = {271--280},
  numpages = {10},
  url = {http://doi.acm.org/10.1145/1718487.1718521},
  doi = {http://doi.acm.org/10.1145/1718487.1718521},
  acmid = {1718521},
  publisher = {ACM},
  address = {New York, NY, USA},
  keywords = {collaborative tagging, folksonomies, lexical and topical alignment, link prediction, maximum information path, social media, social network, social semantic similarity, web 2.0},
  }

• L. M. Aiello, M. Milanesio, G. Ruffo, R. Schifanella
  "Tagging with DHARMA, a DHT-based Approach for Resource Mapping through Approximation"
  In HOTP2P '10 : 7th International Workshop on Hot Topics in Peer-to-Peer Systems, Atlanta, Georgia, 2010
  [abstract | pdf | bibtex]

  We introduce collaborative tagging and faceted search on structured P2P systems. Since a trivial and brute force mapping of an entire folksonomy over a DHT-based system may reduce scalability, we propose an approximated graph maintenance approach. Evaluations on real data coming from Last.fm prove that such strategies reduce vocabulary noise (i.e., representation's overfitting phenomena) and hotspots issues

  @inproceedings{aiello10hotp2p,
  author = {Aiello, Luca Maria and Milanesio, Marco and Ruffo, Giancarlo and Schifanella, Rossano},
  title = {{Tagging with DHARMA, a DHT-based Approach for Resource Mapping through Approximation}},
  year = {2010},
  booktitle = {HOT-P2P '10 : 7th International Workshop on Hot Topics in Peer-to-Peer Systems},
  location = {Atlanta, USA},
  publisher = {IEEE press}
  }

• R. Schifanella, A. Panisson, C. Gena and G. Ruffo
  MobHinter: Epidemic Collaborative Filtering and Self-Organization in Mobile Ad-Hoc Networks
  In the 2nd ACM International Conference on Recommender Systems 2008 (RecSys 2008), October 23-25, 2008, Lausanne, Switzerland. ACM Press.
  [abstract | pdf | bibtex | link]

  We focus on collaborative filtering dealing with self-organizing communities, host mobility, wireless access, and Ad-Hoc communications. In such a domain, knowledge representation and users profiling can be hard; remote servers can be often unreachable due to client mobility; and feedback ratings collected during random connections to other users' ad-hoc devices can be useless, because of natural differences between human beings. Our approach is based on so called Affinity Networks, and on a novel system, called MobHinter, that epidemically spreads recommendations through spontaneous similarities between users. Main results of our study are two fold: firstly we show how to reach comparable recommendation accuracies in the mobile domain as well as in the centralized scenario; secondly, we propose epidemic collaborative strategies that can reduce rapidly and realistically the cold start problem.

  @inproceedings{Schifanella:2008:MEC:1454008.1454014,
  author = {Schifanella, Rossano and Panisson, Andr\'{e} and Gena, Cristina and Ruffo, Giancarlo},
  title = {MobHinter: epidemic collaborative filtering and self-organization in mobile ad-hoc networks},
  booktitle = {Proceedings of the 2008 ACM conference on Recommender systems},
  series = {RecSys '08},
  year = {2008},
  isbn = {978-1-60558-093-7},
  location = {Lausanne, Switzerland},
  pages = {27--34},
  numpages = {8},
  url = {http://doi.acm.org/10.1145/1454008.1454014},
  doi = {http://doi.acm.org/10.1145/1454008.1454014},
  acmid = {1454014},
  publisher = {ACM},
  address = {New York, NY, USA},
  keywords = {ad-hoc networks, recommender systems, social collaborative filtering},
  }

• L. M. Aiello, M. Milanesio, G. Ruffo, R. Schifanella
  Tempering Kademlia with a Robust Identity Based System
  In P2P '08 : Proceedings of the 8th International Conference on Peer-to-Peer Computing, Aachen, Germany, 2008
  [abstract | pdf | bibtex]

  The lack of a trusted authority, responsible for peers' identity verification or for authentication purposes, makes actual P2P systems extremely vulnerable to a large spectrum of attacks. The main purpose of this paper is to present Likir (Layered Identity-based Kademlia-like InfRastructure), a framework that includes an identity based scheme and a secure communication protocol, built on top of Kademlia, that may provide an effective defense against well known attacks. This will be accomplished with the adoption of a certification service, with the use of an authentication protocol between nodes and with the introduction of credentials to make non-repudiable the ownership of the contents and messages inserted in the DHT. For sake of interoperability with other social networking services, Likir enables identity management under the Identity 2.0 framework. Under this perspective, the IBS (Identity-Based Signature) scheme is taken into consideration and analyzed as well.

  @inproceedings{aiello08p2p,
  author = {Aiello, Luca Maria and Milanesio, Marco and Ruffo, Giancarlo and Schifanella, Rossano},
  title = {{Tempering Kademlia with a robust identity based system}},
  booktitle = {P2P '08: Proceedings of the 2008 Eighth International Conference on Peer-to-Peer Computing},
  year = {2008},
  isbn = {978-0-7695-3318-6},
  pages = {30--39},
  location = {Aachen, Germany},
  doi = {http://dx.doi.org/10.1109/P2P.2008.40},
  publisher = {IEEE Computer Society},
  address = {Washington, DC, USA}
  }

• W. Allasia, F. Gallo, M. Milanesio, R.Schifanella
  Governed Content Distribution on DHT Based Networks
  In the Third International Conference on Internet and Web Applications and Services (ICIW08) - Track P2P Systems and Applications (P2PSA), June 8-13, 2008, Athens, Greece. IEEE Press.
  [abstract | pdf | bibtex | link]

  Peer-to-Peer (P2P) systems are widely used for sharing digital items without structured metadata and in absence of any kind of digital rights management applied to the distributed contents. In this paper we propose the implementation of a prototype application that makes use of a structured P2P system enabling the indexing of complex metadata, used to express digital rights. In this way the media contents are exchanged and played according to the expressed grants. The creation and the consumption of the shared contents can be performed through any MPEG-21 REL compliant software and the application allows indexing and search for both governed and ungoverned contents. The information about the license can be included in the queries and the P2P network can be used to share governed contents (both free and with fee) in a legitimate way. In particular the proposed approach represents a suitable solution for indexing and querying rights complex structures on DHT based networks.

  @article{10.1109/ICIW.2008.40,
  author = {Walter Allasia and Francesco Gallo and Marco Milanesio and Rossano Schifanella},
  title = {Governed Content Distribution on DHT Based Networks},
  journal ={Internet and Web Applications and Services, International Conference on},
  volume = {0},
  isbn = {978-0-7695-3163-2},
  year = {2008},
  pages = {391-396},
  doi = {http://doi.ieeecomputersociety.org/10.1109/ICIW.2008.40},
  publisher = {IEEE Computer Society},
  address = {Los Alamitos, CA, USA},
  }

• A. Panisson, G. Ruffo and R. Schifanella
  X-Hinter: a Framework for Implementing Social Oriented Recommender Systems
  In the Proceedings of the 21th ACM Conference on Hypertext and Hypermedia (Hypertext 2008), June 19-21, 2008, Pittsburgh, Pennsylvania, USA. ACM Press.
  [abstract | pdf | bibtex | link]

  Accordingly to the nature of data-driven applications that produce information overload, users need a support to make choices, even without sufficient personal experience of the alternatives. In this context, social networking techniques could be useful applied for finding affinities between users and filter information in a personalized way. After proposing a generalized model for social recommender systems, called X-Hinter, we describe a Java API that provides a set of libraries and tools to build social filtering systems in a wide range of domains. A prototype implementation, named DeHinter,shows the feasibility of the proposed approach in a P2P file sharing application.

  @inproceedings{Panisson:2008:XFI:1379092.1379142,
  author = {Panisson, Andr\'{e} and Ruffo, Giancarlo and Schifanella, Rossano},
  title = {X-hinter: a framework for implementing social oriented recommender systems},
  booktitle = {Proceedings of the nineteenth ACM conference on Hypertext and hypermedia},
  series = {HT '08},
  year = {2008},
  isbn = {978-1-59593-985-2},
  location = {Pittsburgh, PA, USA},
  pages = {235--236},
  numpages = {2},
  url = {http://doi.acm.org/10.1145/1379092.1379142},
  doi = {http://doi.acm.org/10.1145/1379092.1379142},
  acmid = {1379142},
  publisher = {ACM},
  address = {New York, NY, USA},
  keywords = {peer-to-peer, recommender systems, social networks},
  }

• W. Allasia, F. Gallo, F. Chiariglione, A. Difino, M. Milanesio, R. Schifanella
  Digital Rights Metadata Management and Retrieval on Structured Overlay Networks
  In the Proceedings of the 9th International Workshop on Image Analysis for Multimedia Interactive Services - Special Session: Multimedia Metadata Management and Retrieval (WIAMIS 2008), May 7-9, 2008, Klagenfurt, Austria. IEEE Press.
  [abstract | pdf | link]

  This paper introduces a suitable way for indexing multimedia metadata on a structured peer-to-peer overlay network, with special attention to the rights metadata management expressed by MPEG-21 REL. We have indexed them in two steps: few metadata are indexed on a DHT and the others are stored into exchanged DCF files. We have chosen a subset of MPEG-21 elements to be indexed in order to map governed contents into a flat indexing space, and an insertion/retrieval method for such contents. Furthermore, we present a distributed application built on a structured overlay network, that enables users to search multimedia items through rights related information. Our solution is completely decentralized and can be exploited in any MPEG-21 REL compliant metadata representation.

• M. Milanesio, G.Ruffo, R.Schifanella
  A Totally Distributed Iterative Scheme for Web Services Addressing and Discovery
  In the 19th IASTED International Conference on Parallel and Distributed Computing and Systems (PDCS 2007) November 19-21, 2007, Cambridge, Massachusetts, USA. ACTA Press.
  [abstract | pdf | link]

  Both web services framework and peer-to-peer networks provide a discovery process, but as current P2P systems focus more on the discovery of content in the form of common files (possibly associated with metadata), a centralized UDDI registry serves content in the form of metadata describing web services. Thus, the intersection between P2P and Web services is clear, so that it recently gained lots of interest: there is the need of finding a way to exploit the high potential of web services without paying in terms of scalability or single-point-of-failures. Our aim in this paper is two-fold: on one hand, we want to present a high level protocol for the addressing and the discovery of web services that is totally decentralized and based on a structured P2P topology. On the other hand, we introduce a way to solve the exact match key-based routing problem, that afflicts structured P2P systems. This model guarantees that all addressed web services will be discovered in a logarithmic number of hops, as it is based on a Distributed Hash Table. One of the key innovation is the possibility of customizing the categorization of web services using tags, which are becoming very common in the so calledWeb 2.0.

• G.Ruffo, R.Schifanella
  Evaluating Peer-to-Peer Recommender Systems that Exploit Spontaneous Affinities
  In the 22nd Annual ACM Symposium on Applied Computing (SAC) March 11 - 15, 2007, Seoul, Korea. ACM Press
  [abstract | pdf | bibtex | link]

  The validation of a recommender system is always a quite hazardous task, because of the difficulty of modeling the tastes of a given user. Novel (decentralized) recommender systems are proposed and evaluated by way of well known logs of user profiles and buddy tables, that contain lists of items with feedback ratings assigned by a given set of users. These information are cross linked, and the precision of the recommendation is compared with other well known (centralized) systems. This evaluation approach cannot be applied in the actual peer-to-peer domain: it is difficult, if not impossible, to build and maintain user profiles, and users are not required to give feedbacks to a data collector entity. Moreover, objects are poorly or not structured, and meta-information, when present, cannot be trusted because of fake files and incomplete item descriptions. In this paper, we present an evaluation process based on a 10-fold cross validation task, that we applied to estimate accuracy of the suggestions of a P2P recommender system recently proposed. The complexity of the evaluation of this peculiar recommender is increased because of ``spontaneous affinities'' between users that are used instead of classical knowledge representation based strategies.

  @inproceedings{Ruffo:2007:EPR:1244002.1244338,
  author = {Ruffo, Giancarlo and Schifanella, Rossano},
  title = {Evaluating peer-to-peer recommender systems that exploit spontaneous affinities},
  booktitle = {Proceedings of the 2007 ACM symposium on Applied computing},
  series = {SAC '07},
  year = {2007},
  isbn = {1-59593-480-4},
  location = {Seoul, Korea},
  pages = {1574--1578},
  numpages = {5},
  url = {http://doi.acm.org/10.1145/1244002.1244338},
  doi = {http://doi.acm.org/10.1145/1244002.1244338},
  acmid = {1244338},
  publisher = {ACM},
  address = {New York, NY, USA},
  keywords = {complex and social networks, file sharing systems, peer-to-peer, recommender system},
  }

• G.Ruffo, R.Schifanella, E.Ghiringhello
  A Decentralized Recommendation System based on Self-Organizing Partnerships
  IFIP-Networking 2006, May 2006, Coimbra (Portugal) LNCS 3976, pp. 618-629, Springer-Verlag, 2006.
  [abstract | pdf | bibtex | link]

  Small World patterns have been found in many social and natural networks, and even in Peer-to-Peer topologies. In this paper, we analyze File Sharing applications that aggregate virtual communities of users exchanging data. In these domains, it is possible to define overlaying structures that we call “Preference Networks” that show self organized interest-based clusters. The relevance of this finding is augmented with the introduction of a proactive recommendation scheme that exploits this natural feature. The intuition behind this scheme is that a user would trust her network of “elective affinities” more than anonymous and generic suggestions made by impersonal entities.

  @inproceedings {springerlink:10.1007/11753810_52,
  author = {Ruffo, Giancarlo and Schifanella, Rossano and Ghiringhello, Enrico},
  affiliation = {Dipartimento di Informatica, Università di Torino, Corso Svizzera, 185 - 10149, Torino (Italy)  },
  title = {A Decentralized Recommendation System Based on Self-organizing Partnerships},
  booktitle = {Networking 2006. Networking Technologies, Services, and Protocols; Performance of Computer and Communication Networks; Mobile and Wireless Communications Systems},
  series = {Lecture Notes in Computer Science},
  editor = {Boavida, Fernando and Plagemann, Thomas and Stiller, Burkhard and Westphal, Cedric and Monteiro, Edmundo},
  publisher = {Springer Berlin / Heidelberg},
  pages = {618-629},
  volume = {3976},
  url = {http://dx.doi.org/10.1007/11753810_52},
  note = {10.1007/11753810_52},
  year = {2006}
  }

• D. Catalano, G. Ruffo, and R. Schifanella
  A P2P Market Place Based on Aggregate Signatures
  In the Proceedings of the 3rd International Symposium on Parallel and Distributed Processing and Applications (ISPA 05), 2005 Int. Workshop on Applications and Economics of Peer to Peer Systems, November, Nanjing, P. R. China, in G. Chen et al. (Eds.): ISPA Workshops 2005, LNCS 3759, pp. 54-63, Springer-Verlag, 2005.
  [abstract | pdf | link]

  A peer-to-peer market place is likely to be based on some underlying micro-payment scheme where each user can act both as a customer and as a merchant. Such systems, even when designed for largely distributed domains, may be implemented according to hybrid topologies where trusted third intermediaries (e.g. the broker) are single points of failures. For this reason it is crucial that such central entities scale well w.r.t. the overall number of transactions. In this paper, we focus on PPay as a case study, to show how the broker would greatly benefit in terms of computational cost if aggregate signatures are adopted instead of RSA signatures.

• G. Ruffo and R. Schifanella
  Scalability Evaluation of a Peer-to-Peer Market Place based on Micro-Payments
  In the Proceedings of the 2nd Inter. Workshop on Hot Topics in Peer-to-Peer Systems (HOT-P2P 2005), July 2005. San Diego, CA (USA). IEEE Press.
  [abstract | pdf | link]

  A fair peer-to-peer market place should protect intellectual properties as well as account peers that act as distributors of the source. FairPeers is a scheme in which some central authorities are necessary, with the drawback that when the number of transactions grows, these entities can represent single points of failure. This paper proposes a generic model to analytically evaluate such a market place and estimate its performance in terms of scalability w.r.t. the total number of printed coins and the overall transactions that can occur in the given peer-to-peer system.

• G. Ruffo, R. Schifanella, M. Sereno and R. Politi
  WALTy: A Tool for Evaluating Web Application Performance
  In the Proceedings of the 1st International Conference on Quantitative Evaluation of Systems (QEST) 2004, Enschede, The Netherlands, September 27 - 30, 2004. IEEE Press.
  [abstract | pdf | link]

  In this paper we present WALTy (Web Application Loadbased Testing tool), a set of tools that allows the performance analysis of web applications as they are perceived by the end users. The proposed approach is based on a workload characterization created from informations extracted from log files. The workload is generated by using of Customer Behavior Model Graphs (CBMGs) that allow to describe the behaviors of typical users on a web site.

• G. Ruffo, R. Schifanella, M. Sereno and R. Politi
  WALTy: A User Behavior Tailored Tool for Evaluating Web Application Performance
  In the Proceedings of the 3rd IEEE International Symposium on Network Computing and Applications (IEEE NCA04), August 30 - September 1, 2004, Cambridge, MA, USA. IEEE Press.
  [abstract | pdf | link]

  In this paper we present WALTy (Web Application Loadbased Testing tool), a set of tools that allows the performance analysis of web applications by means of a scalable what-if analysis on the test bed. The proposed approach is based on a workload characterization generated from information extracted from log files. The workload is generated by using of Customer Behavior Model Graphs (CBMG), that are derived by extracting information from the web application log files. In this manner the synthetic workload used to evaluate the web application under test is representative of the real traffic that the web application has to serve. One of the most common critics to this approach is that synthetic workload produced by web stressing tools is far from being realistic. The use of the CBMGs might be useful to overcome this critic.

Book Chapters

• G. Ruffo, R. Schifanella, G. Ballocca, and R. Politi
  Integrated Techniques and Tools for Web Mining, User Profiling and Benchmarking analysis
  In "Web Mining: An Overview", ICFAI University Press, ISBN: 81-314-0420-X

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