SIGIR Workshop Report
The SIGIR Heterogeneous and Distributed
Information Retrieval Workshop
Ranieri Baraglia

Domenico Laforenza

HPC-Lab
ISTI-CNR, Italy
ranieri.baraglia@isti.cnr.it

HPC-Lab
ISTI-CNR, Italy
domenico.laforenza@isti.cnr.it

Fabrizio Silvestri
HPC-Lab
ISTI-CNR, Italy
fabrizio.silvestri@isti.cnr.it

1Introduction

In the last few years there have been the explosion in the use of heterogeneous distributed systems. Ranging from simple Network of Workstations to the more modern and complex Gridsystems, the adoption of distributed systems instead of massively parallel supercomputers
has been preferred due to their reduced cost of ownership. These kinds of systems pose many
challenges in terms of information access, storage and retrieval. Usually, in fact, instead of
having collections stored at a single site they are collected, and sometimes managed, at different sites (possibly owned by different institutions). Particular interest has been expressedon architectures and specifications for information retrieval in the context of heterogeneous
distributed computing systems.
The workshop have been focused on new methods and algorithms to efficiently and effectively access data distributed over large heterogeneous distributed systems. The workshop
particularly encouraged papers addressing the creation and the search in distributed, dynamic information systems as well as papers presenting novel architectural solution for thesesystems. However, more broadly, papers were solicited on any topic related to information
retrieval in distributed architectures, including the topics listed below.
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• Meta-IR: coping with heterogeneous distributed data;• Algorithms for distributed IR;• Grid IR;• Peer-to-Peer (P2P) IR;• Complex queries specification and resolution;• Collection selection;• Query routing (especially in Grid and P2P systems);• Data fusion;• Query execution scheduling;• Index structures;• Specific architectures;• Scalability;• Fault tolerance;• Privacy;• Applications.

The workshop was held in Salvador, Bahia, Brazil following the SIGIR 2005 conference.
Even if the venue of the conference might have teased people to go outside having a swim ortaking sun in one of the many beautiful beaches around Salvador, about 20 people attendedthe workshop. The group was really interested and active throughout the entire workshop.
The papers submitted were all of high quality and the people that actually presented themdid that in a very clear and precise way. We have only one remarkable point. Despite thefact that in the Call for Paper Grid Computing was mentioned as an interesting topic, noneof the major player of this field was neither attracted to submit any paper nor interested
in being included into the Program Committee. Even though we took care to contact them
directly.

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2Presentations

Here we are going to provide a very brief description of the papers that have been presented
during the workshop. The workshop was divided into four sessions. The complete proceedings are available in electronic form at
http://hdir2005.isti.cnr.it/cameraready/cameraready.pdf.
The first session hosted an invited presentation given by Prof. Ricardo Baeza-Yates entitled“Recent Advances on Distributed Information Retrieval”. He started with a brief introduction to the attendant on the topic of what modern Information Retrieval is especially in lightof the enormous quantity of highly dynamic data available in the Web. Then, he depicted
some current trends in distributed (i.e. parallel) information retrieval systems showing someongoing works on this field. In particular, one interesting thing is a work that has been
done in collaboration with Moffat, Webber, and Zobel showing that a pipelined and termpartitioned architecture for a parallel search-engine is superior to the more traditional farmand document-partioned one. At the end of the talk he cited a list of open problems:• New retrieval models.
• More on Indexing & Searching.
• Quality evaluation (Web, XML).
• Real distributed architecture.
• More on P2P.
• New ranking sources.
• Spamming detection.
• Multimedia.
• Grid computing.
Each of them needs attention especially if thought in light of the current new directions
the Web is going to move toward.
On the second session three papers about “Peer-to-Peer” were presented. The first paper
entitled “p2pDating: Real Life Inspired Semantic Overlay Networks for Web Search” waspresented by Josiane Xavier Parreira. The paper was about a novel method for building
an overlay network on the basis of the novel notion of peer-to-peer “dating” - p2pdating.
The authors used and tested p2pDating into JXP and MINERVA. JXP is an algorithm for
dynamically computing global authority scores, whereas MINERVA is a distributed search
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engine implemented by authors in previous works. Both benefit by the use of SemanticOverlay Networks built through p2pdating. Experiments have shown the superiority of thecombination of JXP and p2pDating over just JXP. Moreover, p2pDating is also used tocompute in a distributed manner the PageRank score of the pages managed by each node.
Experiments have shown that this approach is useful too and the real PageRank score may
be approximated in a good way.
The second paper entitled “An integrated approach for searching and browsing in heterogeneous peer-to-peer networks” was presented by Henrik Nottelmann. In their paper they
proposed a service oriented architecture (SOA) for supporting searching and browsing in ahierarchical network. Their approach is characterized by an high extensibility and reusability. More than proposing new algorithms, their paper proposes a very good architecture
exploiting in a highly optimized fashion state-of-the-art technology in both P2P and IR.
The last paper of the session entitled “A Scalable Semantic Indexing Framework for peerto-peer Information Retrieval” was presented by ChengXiang Zhai. The paper proposes aninformation retrieval framework that clusters documents similar in semantics into the samegroup, and stores them on nearby nodes using a two-phase DHT-based indexing method.
The proposed system seems to show attractive properties, in particular: (a) tunable tradeoff
between search accuracy and efficiency; (b) support for advanced retrieval methods (such as
feedback and personalized search). (c) adaptation to the dynamic nature of P2P networks
with incremental incorporation of new concepts.
On the third session there were scheduled two papers on “Distributed Systems”. Unfortunately the second speaker Mikhail Sogrin was not able to flew in Brazil and withdrew histalk. The only presented paper in this session is the one entitled “Distributed Processingof Conjunctive Queries” presented by Claudine Badue. This paper carefully and extensively
discusses several experiments results regarding a parallel Search Engine that exploits a usual
inverted file index distributed according to a document partition scheme. The authors assessed a experimental setup for analyzing in detail performance issues of a small distributed
WSE processing real queries on a real index. Load imbalance, broker behavior, CPU and I/O
costs of local index servers, overall throughput were studied in depth. The figures obtained
cannot probably be obtained in a different setup or in a large-scale WSE, but trends and thegeneral behavior should be.
On the last session two presentation were given on “Heterogeneous Systems”. The first
speaker Jens Graupmann presented a work on “The Light-Weight Semantic Web: Integrating Information Extraction and Information Retrieval for Heterogeneous Environments”. In
the paper they show a light-weight version of the Semantic Web. By advocating the useof available off-the-shelf Information Extraction tools, they are able to automatically detectand annotate important classes of information that are frequently used in queries, like locations and dates. They eventually propose a query language that is able to exploit the extra
annotations and allows novel range and join conditions.
The last speaker of the workshop has been Pierangelo Veltri who presented a quite orthogonal paper entitled “An Architecture for Managing Mass Spectrometry Data for a Distributed
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Proteomics Laboratory”. Aim of this work has been to present an architecture that may
be used to efficiently organize Mass Spectrometer (MS) samples. The presented a systemfor loading, preprocessing, storing and managing mass spectra data. In the paper they alsopresent a possible distributed architecture for the management of such a kind of data.

3Conclusions

At the end of the workshop day there have been a discussion about the possible interesting
topics in the near future.
All the participants agreed on the fact that due to the very high dynamic nature of the Web
in the (not so far) future maybe traditional Search Engines might not be able to fulfill users’
need as they were able so far.
One of the major problem, as indicated also in the invited talk of Amit Singhal from Google,is Spam. But not only spam is an issue. There also is the enormous quantity of dynamical
data being produce every instant through the Web: blogs, multimedia archives, mailing lists,and so on and so forth, are only examples of what we are talking about. It seems clear thattraditional crawling techniques will become soon inadequate. There are some possible interesting solutions to this problem. One might be to let Web server crawl their local collection
and to send the indexed local collection to a centralized index. Several problem will arise
from this organization. How to trust each sent index? How can we efficiently merge each index? Another possible solution is represented by distributed IR. May be not intended in thetraditional sense but also in a hybrid manner. For instance, one could maintain a centralized
database for static (or quasi-static) contents, whereas a decentralized index maintained byservers authoritative for certain topics might be designed to index dynamic contents.
Peer-to-Peer may represent another solution to the problem of content freshness. Typical applications of P2P to IR are represented by discovering information dislocated at various sites.
Many of the works presented at this workshop considered this problem but seem to not keep
into account the problem of the high churn rate characterizing typical P2P networks. Simulations are rarely done in environments where nodes are continuously entering and exiting
the network. As noted in previous workshops on P2P and IR, this research area still lacks
a good method for modeling large dynamic networks with reasonable hardware resources.
Another problem that is felt really important by the P2P IR community is the lacking of
good datasets (including relevance judgments) coming from real networks having large query
streams. Another issue came up during the discussion. Traditional distributed (or P2P) IR
models try to represent a collection by modeling the amount of potential relevant information
contained within the collection itself. On the other hand traditional (i.e. centralized) SearchEngines developers pose a lot of attention to efficiency. A possible improvement in P2P IR
systems usability might be represented by the inclusion within effectiveness-based models ofACM SIGIR Forum

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metrics that would keep into account the efficiency of each collection manager. In this way
we could also have systems aware of response times and throughput.
Another interesting question that have been raised during the discussion is the usefulness of amodel to predict performance of parallel IR systems. The work presented by Claudine Badueet al. goes precisely toward this goal. There have been, though, many people that raisedinteresting questions. How to model the presence of a cache in front of the system? How tomodel the behavior of operating system mechanisms (i.e. buffer cache, disk cache, processscheduling, network subsystem, etc.)? How to consider the collection distributed (random ornot)?

4Acknowledgments

We thank all the PC members for their great and precise support in reviewing the papers wereceived, their comments have certainly been of help for authors in improving their works. We
would like to thank also the organizers of the SIGIR conference for giving us the opportunity
to set up this workshop and for their continuous support during the months before theworkshop took place. Last but not least, we also thanks all the participants at the workshop
for their comments, questions and doubts, this workshop has been possible, obviously, becauseof their work. Thank you all!

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