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  • The Inria's Research Teams produce an annual Activity Report presenting their activities and their results of the year. These reports include the team members, the scientific program, the software developed by the team and the new results of the year. The report also describes the grants, contracts and the activities of dissemination and teaching. Finally, the report gives the list of publications of the year.

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Section: New Results

Mining of Complex Data

Participants : Nacira Abbas, Guilherme Alves Da Silva, Alexandre Blansché, Lydia Boudjeloud-Assala, Quentin Brabant, Brieuc Conan-Guez, Miguel Couceiro, Adrien Coulet, Alain Gély, Laurine Huber, Nyoman Juniarta, Florence Le Ber, Joël Legrand, Pierre Monnin, Tatiana Makhalova, Amedeo Napoli, Abdelkader Ouali, François Pirot, Frédéric Pennerath, Justine Reynaud, Chedy Raïssi, Sébastien Da Silva, Yannick Toussaint.

Keywords:

formal concept analysis, relational concept analysis, pattern structures, pattern mining, association rule, redescription mining, graph mining, sequence mining, biclustering, hybrid mining, meta-mining

FCA and Variations: RCA, Pattern Structures and Biclustering

Advances in data and knowledge engineering have emphasized the needs for pattern mining tools working on complex data. In particular, FCA, which usually applies to binary data-tables, can be adapted to work on more complex data. In this way, we have contributed to two main extensions of FCA, namely Pattern Structures and Relational Concept Analysis. Pattern Structures (PS [73]) allow building a concept lattice from complex data, e.g. numbers, sequences, trees and graphs. Relational Concept Analysis (RCA) is able to analyze objects described both by binary and relational attributes [84] and can play an important role in text classification and text mining. Many developments were carried out in pattern mining and FCA for improving data mining algorithms and their applicability, and for solving some specific problems such as information retrieval, discovery of functional dependencies and biclustering.

We got several results in the discovery of approximate functional dependencies [8], the mining of RDF data and the and visualization of the discovered patterns [1], and redescription mining (detailed later). Moreover, we have also investigated the use of the MDL principle (“Minimum Description Length”) for the selection of interesting and diverse patterns [37], [39].

In the framework of the CrossCult European Project about cultural heritage, we worked on the mining of visitor trajectories in a museum or a touristic site. We presented a theoretical and practical research work about the characterization of visitor trajectories and the mining of these trajectories as sequences [32], [33]. The mining process is based on two approaches in the framework of Formal Concept Analysis (FCA). We focused on different types of sequences and more precisely on subsequences without any constraint and frequent contiguous subsequences. In parallel, we introduced a similarity measure allowing us to build a hierarchical classification which is used for interpretation and characterization of the trajectories. In addition, for completing the research work on the characterization of trajectories, we also studied how biclustering may be applied to trajectory recommendation [31], [52].

Redescription Mining

Among the mining methods developed in the team is redescription mining. Redescription mining aims to find distinct common characterizations of the same objects and, vice versa, to identify sets of objects that admit multiple shared descriptions [82]. It is motivated by the idea that in scientific investigations data oftentimes have different nature. For instance, they might originate from distinct sources or be cast over separate terminologies. In order to gain insight into the phenomenon of interest, a natural task is to identify the correspondences that exist between these different aspects.

A practical example in biology consists in finding geographical areas that admit two characterizations, one in terms of their climatic profile and one in terms of the occupying species. Discovering such redescriptions can contribute to better our understanding of the influence of climate over species distribution. Besides biology, applications of redescription mining can be envisaged in medicine or sociology, among other fields.

This year, we used redescription mining for analyzing and mining RDF data with the objective of discovering definitions of concepts and as well disjunctions (incompatibilities) of concepts, for completing knowledge bases in a semi-automated way [49], [44].

Text Mining

In the context of the PractikPharma ANR Project, we study how cross-corpus training may guide the task of relationship extraction from texts, and especially, how large annotated corpora developed for alternative tasks may improve the performance of biomedical tasks, for which only a few annotated resources are available [34].

Transfer learning proposes to enhance machine learning performance on a problem, by reusing labeled data originally designed for a related problem. This is particularly relevant to the applications of deep learning in Natural Language Processing, because those usually require large annotated corpora that may not exist for the targeted domain, but exist for side domains. In a recent work, we experimented the extraction of relationships from biomedical texts with two deep learning models. The first model combines locally extracted features using a Multi Channel Convolutional Neural Network (MCCNN) model, while the second model exploits the syntactic structure of sentences using a Tree-LSTM (Long Short-Term Memory) architecture. The experiments show that the Tree-LSTM model benefits from a cross-corpus learning strategy, i.e. performances are improved when training data are enriched with off-target corpora, whereas it is not the case with MCCNN.

Indeed our approach leads to state of the art performances in four biomedical tasks for which only a few annotated resources are available (less than 400 manually annotated sentences) and even surpass state of the art performances in two of these four tasks. We particularly investigated how the syntactic structure of a sentence, which is domain independent, participates in the increase of performance when adding additional training data. This may have a particular impact in specialized domains in which training resources are scarce, because it means that these resources may be efficiently enriched with data from other domains for which large annotated corpora exist.

Mining subgroups as a single-player game

Discovering patterns that strongly distinguish one class label from another is a challenging data-mining task. The unsupervised discovery of such patterns would enable the construction of intelligible classifiers and to elicit interesting hypotheses from the data. Subgroup Discovery (SD) is one framework that formally defines this pattern mining task. However, SD still faces two major issues: (i) how to define appropriate quality measures to characterize the uniqueness of a pattern; (ii) how to select an accurate heuristic search technique when exhaustive enumeration of the pattern space is unfeasible. The first issue has been tackled by the Exceptional Model Mining (EMM) framework. This general framework aims to find patterns that cover tuples that locally induce a model that substantially differs from the model of the whole dataset. The second issue has been studied in SD and EMM mainly with the use of beam-search strategies and genetic algorithms for discovering a pattern set that is non-redundant, diverse and of high quality. Consequently,

In our current work [9], we proposed to formally define pattern mining as a single-player game, as in a puzzle, and to solve it with a Monte Carlo Tree Search (MCTS), a technique mainly used for artificial intelligence and planning problems. The exploitation/exploration trade-off and the power of random search of MCTS lead to an any-time mining approach, in which a solution is always available, and which tends towards an exhaustive search if given enough time and memory. Given a reasonable time and memory budget, MCTS quickly drives the search towards a diverse pattern set of high quality. MCTS does not need any knowledge of the pattern quality measure, and we show to what extent it is agnostic to the pattern language.

Consensus and Aggregation Functions

Aggregation and consensus theory study processes dealing with the problem of merging or fusing several objects, e.g., numerical or qualitative data, preferences or other relational structures, into a single or several objects of similar type and that best represents them in some way. Such processes are modeled by so-called aggregation or consensus functions [76], [78]. The need to aggregate objects in a meaningful way appeared naturally in classical topics such as mathematics, statistics, physics and computer science, but it became increasingly emergent in applied areas such as social and decision sciences, artificial intelligence and machine learning, biology and medicine.

We are working on a theoretical basis of a unified theory of consensus and to set up a general machinery for the choice and use of aggregation functions. This choice depends on properties specified by users or decision makers, the nature of the objects to aggregate as well as computational limitations due to prohibitive algorithmic complexity. This problem demands an exhaustive study of aggregation functions that requires an axiomatic treatment and classification of aggregation procedures as well as a deep understanding of their structural behavior. It also requires a representation formalism for knowledge, in our case decision rules and methods for discovering them. Typical approaches include rough-set and FCA approaches, that we aim to extend in order to increase expressivity, applicability and readability of results. Applications of these efforts already appeared and further are expected in the context of three multidisciplinary projects, namely the “Fight Heart Failure” (research project with the Faculty of Medicine in Nancy), the European H2020 “CrossCult” project, and the “ISIPA” (Interpolation, Sugeno Integral, Proportional Analogy) project.

In the context of the project RHU “Fighting Heart Failure” (that aims to identify and describe relevant bio-profiles of patients suffering from heart failure) we are dealing with biomedical data, highly complex and heterogeneous, that include, among other, sociodemographical aspects, biological and clinical features, drugs taken by the patients, etc. One of our main challenges is to define relevant aggregation operators on this heterogeneous patient data that lead to a clustering of the patients. Each cluster should correspond to a bio-profile, i.e. a subgroup of patients sharing the same form of the disease and thus the same diagnosis and medical care strategy. We are working on ways for comparing and clustering patients, namely, by defining multidimensional similarity measures on this complex and heterogeneous biomedical data. To this end, we recently proposed a novel approach, that we named “unsupervised extremely randomized trees” (UET) [27], that is inspired by the frameworks of unsupervised random forests (URF) [85] and of extremely randomized trees (ET) [75]. The empirical study of UET showed that it outperforms existing methods (such as URF) in running time, while giving better clustering. However, UET was implemented for numerical data only, and this is a drawback when dealing with biomedical data. We are now working on the adaptation of UET for heterogeneous data (both numerical and symbolic), possibly, with missing values.

In the context of the project ISIPA, we mainly focused on the utility-based preference model in which preferences are represented as an aggregation of preferences over different attributes, structured or not, both in the numerical and qualitative settings. In the latter case, the Sugeno integral is widely used in multiple criteria decision making and decision under uncertainty, for computing global evaluations of items based on local evaluations (utilities). The combination of a Sugeno integral with local utilities is called a Sugeno utility functional (SUF). A noteworthy property of SUFs is that they represent multi-threshold decision rules. However, not all sets of multi-threshold rules can be represented by a single SUF. We showed how to represent any set of multi-threshold rules as a combination of SUFs and studied their potential advantages as a compact representation of large sets of rules, as well as an intermediary step for extracting rules from empirical datasets [51]. For further results in the qualitative approach to decision making see, e.g., [10] [3]; and see also [24] for a survey chapter on new perspectives in ordinal evaluation.