Second Edition of the "XML and Information Retrieval" Workshop
Held at SIGIR’2002, Tampere, Finland, Aug 15th , 2002
Ricardo Baeza-Yates, University of Chile, Chile
Norbert Fuhr, University of Dortmund, Germany
Yoelle S. Maarek, IBM Research Lab in Haifa, Israel

Introduction
The previous workshop on “XML and Information Retrieval” was held in the context of
SIGIR'2000 (Athens, Greece) and showed that there is a serious interest in managing
semi-structured data from an IR (i.e., unstructured) perspective rather than from thedominating database (i.e., structured) perspective. As a direct outcome of the workshop, a
special JASIS issue on XML and IR was edited and published in March 2002. The topic
is still in its prime both in the Academia, as evidenced by XML related papers presented
at SIGIR'2001, and in the business world with more search engines adding "XMLsupport" as a requirement.
The purpose of this workshop was to continue the effort of applying an "IR approach" to
XML search and retrieval. We believe that this approach is crucial to extending the roleof XML from pure data exchange in business-to-business applications to actual
information exchange in end-users facing and Knowledge Management applications. Asa side issue, we also intended to ask the IR community how it should relate, if at all, tothe XQuery initiative at W3C. The workshop included 3 presentation sessions, for a totalof 8 reviewed papers, an invited talk and a panel. The workshop attracted an audience ofmore than 30 people, who were encouraged to interact with the speakers as well as theaudience.

XML Query and Retrieval
The first session of the workshop included 3 papers. Torsten Grabs, from ETH in Zurich,
opened the morning with his work co-authored with Hans-Jörg Schek on “Generating
Vector Spaces on the Fly for Flexible XML Retrieval”. Torsten first discussed theshortcomings of conventional IR for XML collections, which are mostly due to the factthat IR assumes flat document structures and that indexing granularity is restricted tocomplete documents or predefined fields, thus term statistics on which ranking is basedrefer to a very precise scope. Since XML has a heterogeneous form, queries might havevery different scopes and term statistics should reflect the scope of the query. This scope
will typically be a DOM subtree, or in the case of a multi-category query, the statistics forthe term weights should be derived on the fly from the new universe, or vector space, ofthe query. Törsten presented the flexible IR model for single-category, multi-category
and nested retrieval where the basic index and statistics data are integrated on the fly at
retrieval time depending on the scope of the query. Preliminary results for different
categories of flat documents showed that the dynamic integration required less than 30%
overhead with up to 16 different categories. The authors have good hope that they willobtain also reasonable results on arbitrary XML collections.

The second paper entitled “An Extension of the Vector Space Model for Querying XML
Documents via XML Fragments” also discussed a variation of the vector space, which
concentrated on a new way of expressing queries rather than on their scope. This work
was presented by Yoelle Maarek, and was co-authored with, David Carmel and Yosi
Mass, from the IBM Research Lab in Haifa, and Nadav Efraty and Gad Landau from
Haifa University. Yoelle argued that, when the basic user’s need in querying an XML
collection is an information or discovery need rather than a management need, thesimplest approach is to follow an IR model and express this “fuzzy” need as an XML
fragment that can easily compare to XML documents. This approach of expressing
queries of the same form of the objects being searched thus imitates the full- text search
approach where queries are expressed as free-text rather than formal Boolean queries.
Yoelle then presented a novel measure of similarity between XML fragments and XML
documents that is an augmentation of the classical cosine measure of similarity, where
not only the textual part of the XML structure is compared but also the context of its
occurrence (which can be expressed as a path in the DOM tree). She also introduced ameasure of similarity between such paths, which allowed users to be approximate in
specifying not only the free-text part but also the various contexts. She finally showedsome examples of querying an XML collection of car reviews via XML fragments, andranked results associated with these examples.
The last presentation of this sessio n was given by Kai Großjohann from the University ofDortmund, and co-authored with Norbert Fuhr, Daniel Effing and Sascha Kriewel. Theirwork entitled “Query Formulation and Result Visualization for XML Retrieval” is afollow-up of the XIRQL work presented at the previous edition of this workshop at
SIGIR’2000. Kai reminded the key principles of XIRQ. Queries consist of a set of
atomic query conditions, which are combined either via Boolean or structural
combination. Kai argued that the primitives needed for dealing with XML need to bereflected both in the query formulation and the results visualization. He introduced anovel interface for expressing queries in an XPath- like form. The query by example
interface lets users pick a term (or value) in an XML document, and obtain all thepreferred path expressions for that term location, with the possibility to filter, or expose
the commonality between paths so as to allow for structural combinations. The second
contribution of this work is a method for visualizing results that shows in a unified form
fragments possibly originating from different documents and yet keep the tree structureof the XML documents. Kai used a variation of the well-known treemap method, called“partial treemap” that omits nodes that are not a retrieved node or an ancestor of a
retrieved node. He concluded by discussing experiments that compared text, tilebars andpartial treemaps.

XML Stores
The second session dealt with XML stores and was opened by a paper on “Knowledge
Discovery from Mixed-model XML documents” by Junji Tomita, Tetsuo Ikeda, Tamio
Kihara and Tetsuji Satoh from NTT Cyberspace Laboratories. Tomita-san, who presented
this work, proposed a comprehensive analysis method for analyzing both text and metadata encoded in mixed- model XML documents. He proposed to store the textual part inan IR system (or text database as referred to by the authors) and the meta-data in a
relational database so as to provide rich text and metadata handling operation. The
suggested analysis method involves 3 steps: specifying entity that should be analyzed(via XPath), specifying the “viewpoint” (how it should be analyzed), and classifying the
viewpoint into one of two classes text or metadata, according to the operations to be
conducted on it (which include searching, clustering, summarizing, visualizing, etc.).
A preliminary evaluation was conducted on a collection of Japanese patents, and a live
demo of the system was given to the workshop audience.
The second 1 paper of this session was “Index Infrastructure for an XML repository” by
Alain Azagury, Michael Factor, Naama Kraus, Irit Loy and Benjamin (Benny) Mandler
from the IBM Research Lab in Haifa . Benny presented this work, which was a follow-up
of a previous work on the XMLFS introduced at the previous edition of this workshop at
SIGIR’2000. Benny described a generic infrastructure for XML repositories that coded
both textual and structural information into a single repository rather than in 2 distinct
ones like in the previous paper of this session. Support for XML is achieved via a simple
extension of the classical trie-based lexicon, and associated inverted index, used by many
IR systems. The extension consists of decorating each word appearing in the full- text partof XML documents (e.g., “Paul”) with its context, where the context is a unique id (e.g.,“4”) that represents the XPath (e.g., “/name/first”) of a word in question. Thus in our
example instead of storing simply “Paul” in the lexicon, the new entity “Paul#4” is stored
and points to the postings of the documents that contain Paul under “name/first” rather
than anywhere in the document. Benny then explained how this store is generic enough to
support a variety of operations from regular free-text, to context sensitive, relationa l,partial and composite operations to cite just a few.

Modeling Semi-Structured Data
The third session of the workshop included 2 papers. The first one entitled “Processing
Queries with Metrical Constraints in XML Based IR Systems” by Shmuel Tomi Klein
from Bar-Ilan University. Tomi explained how he revisited, in the context of XML, aprevious work of his on the computation of word proximity across annotations on fulltext. XML documents are more complex than annotated text for 2 reasons: annotations
have by definition an inferior status than text, which cannot be assumed in XML, andannotations represent only a second layer of metadata while the metadata encoded in
XML is a full tree. Tomi then offered a formal definition for expression metrical1

Due to laptop problems, this presentation was actually given right after the lunch break in place of Tomi
Klein’s presentation, and Tomi kindly accepted to replace Benny on the fly. Yet for the sake of thestructure (no XML pun intended:-), we keep ,in this report , the original order of presentations.

constraints on queries. He explained the need to define the coordinates of tokens in the
DOM tree, to label the DOM tree nodes and within nodes, define a flat representation.
Word proximity constraints are then allowed exclusively across elements that are either
siblings (left to right and right to left), or are descendants (in top down order only). Tomithen discussed implementation issues and concluded by insisting that the presented work
was theoretical in nature and needed to be validated by experimentations in order to be ofpractical value.
The final paper of this session presented “A Bayesian Network Model for Document
Retrieval in a Hierarchically Structured Collection”. It was co-authored by Benjamin
Piwowarski and Patrick Gallinari, from University Paris 6. Benjamin started his
presentation by stating the goal of this work, which is to support content only and content
and structure queries. He proposed a model to compute and combine the scores of
document parts, which is based on Bayesian networks and makes use of a learning
machine method for learning the model parameters when faced to incomplete data. Moreprecisely, the Bayesian Network learns its conditional probability tables via the
Estimation Maximization method. While this work was first targeted at the specific taskof retrieving Web pages from a hierarchically structured Web site, it could easily be
extended to the retrieval of documents from an XML corpus by mapping the document
structure into a Bayesian network, the same way a Web collection can be mapped into a
structure. Benjamin concluded by describing the experiments they conducted as well as
mentioning the few current limitations of the model, which include the fact that only aspecial case of structure was considered and the fact that textual information was notincluded in the network.

Invited talk: INEX
The invited talk of the workshop dealt with the INEX evaluation initiative, to which
many of the workshop attendees participated. An abstract of this talk entitled “INEX:
Initiative for the Evaluation of XML Retrieval” by Norbert Fuhr, Norbert Gövert from the
University of Dortmund, and Gabriella Kazai and Mounia Lalmas, from the Queen Mary
University of London is included in the Workshop Notes.
Gabriella started by stating the aim of INEX, which is to support research within the
XML retrieval community by providing a large XML test collection, evaluation measuresand, most of all a forum to compare results. One key point of the initiative is that it has adocument centric view of XML for relevance-oriented retrieval. The test collection
consists of 3 parts: a set of XML documents, a set of queries and the associated relevanceassessments. The XML documents were donated by the IEEE Computer Society andconsist of more than 12000 article s representing about 500MB. The query set consists of
60 queries, half of them were “content-and-structure” (CAS) queries, and half of themwere “content-only” (CO) queries. Queries were selected from a larger set provided by
the INEX participants. At the time of the workshop, relevance assessments, which werealso to be provided by the INEX participants, had not been conducted yet. The audiencestrongly supported the initiative, and all agreed that it is a “must” for promoting researchin the field. Two concerns were expressed though with respect to the form of theevaluation: Djoerd Hiemstra regretted that guidelines on how assessments would be
conducted had not been published ahead of time, and David Carmel requested thatparticipants be at least educated on the guidelines before the assessment starts. The INEX
workshop will be held in Dagstuhl, Germany in Dec (9-11), 2002.

Panel
The workshop ended with a panel to which participated, Ross Wilkinson, from CSIRO,
Ian Soboroff, from NIST, David Hawking from CSIRO and Djoerd Hiemstra from the
University of Twente. Yoelle Maarek, from IBM Research Lab in Haifa acted asmoderator and initiated the debate by asking the panel whether XML retrieval (and thisvery workshop) make sense at all, and if they do, how would the conjecture that it would
provide better results than full- text search would be proven. Ross Wilkinson proposed thefollowing answer: “Does XML retrieval make sense? The answer is not ‘yes or no’, butrather absolutely some time!” which provoked a huge laugh in the audience. Moreseriously, Ross believes that XML search will work when it captures this reduction andwhen there is an agreement on what it means. He does not believe on a general technique,and is pretty skeptical on the semantic Web simply because we will never agree on acommon structure. He added that the only way to prove the conjecture is to go back to thepeople to verify whether in the end, they can perform the task at hand more effectively.
Ian Soboroff agreed with Ross, as he believes that XML retrieval will work in the proper
settings. David Hawking offered that IR should stand for “Inexact Retrieval”, and heclaimed that there is nothing really special about XML, “it's only annotation”. Yet in thecase of multi-source collections, retrieval starts to be really complicated unless we all
agree on DTDs. David then mentioned Andrei Broder's classification of Web users’
needs into informational, navigational and transactional. The users’ needs, in the context
of XML, have also to be identified, in order to answer the first question of what toretrieve. He concluded by a rhetorical question of whether XML document retrieval
systems should pay a certain price to support DB operations? David answered his own
question with a categorical “N o!” and concluded by provocatively telling the audience“XQuery who cares?” which earned him enthusiastic applauses from the audience. In
trying to address the conjecture question, Djoerd stated that he did not know what thekiller application would be (which would prove conjecture), yet XML retrieval is crucial
and those who argue are probably the same who said, 20 years ago, “who cares aboutranked retrieval!” He agreed that it will be very hard to prove it but that should notdiscourage us. The debate then became more interactive with the audience. Examples ofniches or domains (such as the full Finish health records) and suggestions on how to findthe killer application were offered.

Conclusion
The workshop ended with the panel on a very positive tone, where most felt encouraged
to continue their research. The informal atmosphere triggered many debates, and part of
the audience even stayed after the conclusion of the workshop for more discussions. The
workshop was considered a success, and indeed obtained the best evaluation by
SIGIR’2002 participants.