This paper introduces a new structural causal model tailored for representing threshold-based IT systems and presents a new algorithm designed to rapidly detect root causes of anomalies in such systems. When root causes are not causally related, the method is proven to be correct; while an extension is proposed based on the intervention of an agent to relax this assumption. Our algorithm and its agent-based extension leverage causal discovery from offline data and engage in subgraph traversal when encountering new anomalies in online data. Our extensive experiments demonstrate the superior performance of our methods, even when applied to data generated from alternative structural causal models or real IT monitoring data.

On a wide range of natural language processing and information retrieval tasks, transformer-based models, particularly pre-trained language models like BERT, have demonstrated tremendous effectiveness. Due to the quadratic complexity of the self-attention mechanism, however, such models have difficulties processing long documents. Recent works dealing with this issue include truncating long documents, in which case one loses potential relevant information, segmenting them into several passages, which may lead to miss some information and high computational complexity when the number of passages is large, or modifying the self-attention mechanism to make it sparser as in sparse-attention models, at the risk again of missing some information. We follow here a slightly different approach in which one first selects key blocks of a long document by local query-block pre-ranking, and then few blocks are aggregated to form a short document that can be processed by a model such as BERT. Experiments conducted on standard Information Retrieval datasets demonstrate the effectiveness of the proposed approach.

Combining query tokens and document tokens and inputting them to pre-trained transformer models like BERT, an approach known as interaction-based, has shown state-of-the-art effectiveness for information retrieval. However, the computational complexity of this approach is high due to the online self-attention computation. In contrast, dense retrieval methods in representation-based approaches are known to be efficient, however less effective. A tradeoff between the two is reached with late interaction methods like ColBERT, which attempt to benefit from both approaches: contextualized token embeddings can be pre-calculated over BERT for fine-grained effective interaction while preserving efficiency. However, despite its success in passage retrieval, it's not straightforward to use this approach for long document retrieval. In this paper, we propose a cascaded late interaction approach using a single model for long document retrieval. Fast intra-ranking by dot product is used to select relevant passages, then fine-grained interaction of pre-stored token embeddings is used to generate passage scores which are aggregated to the final document score. Multi-task learning is used to train a BERT model to optimize both a dot product and a fine-grained interaction loss functions. Our experiments reveal that the proposed approach obtains near state-of-the-art level effectiveness while being efficient on such collections as TREC 2019.

Transformer-based models, and especially pre-trained language models like BERT, have shown great success on a variety of Natural Language Processing and Information Retrieval tasks. However, such models have difficulties to process long documents due to the quadratic complexity of the self-attention mechanism. Recent works either truncate long documents or segment them into passages that can be treated by a standard BERT model. A hierarchical architecture, such as a transformer, can be further adopted to build a document-level representation on top of the representations of each passage. However, these approaches either lose information or have high computational complexity (and are both time and energy consuming in this latter case). We follow here a slightly different approach in which one first selects key blocks of a long document by local query-block pre-ranking, and then aggregates few blocks to form a short document that can be processed by a model such as BERT. Experiments conducted on standard Information Retrieval datasets demonstrate the effectiveness of the proposed approach.

We study task composition in crowdsourcing and the effect of personalization and diversity on performance. A central process in crowdsourcing is task assignment, the mechanism through which workers find tasks. On popular platforms such as Amazon Mechanical Turk, task assignment is facilitated by the ability to sort tasks by dimensions such as creation date or reward amount. Task composition improves task assignment by producing for each worker, a personalized summary of tasks, referred to as a Composite Task (CT). We propose different ways of producing CTs and formulate an optimization problem that finds for a worker, the most relevant and diverse CTs. We show empirically that workers' experience is greatly improved due to personalization that enforces an adequation of CTs with workers' skills and preferences. We also study and formalize various ways of diversifying tasks in each CT. Task diversity is grounded in organization studies that have shown its impact on worker motivation [33]. Our experiments show that diverse CTs contribute to improving outcome quality. More specifically, we show that while task throughput and worker retention are best with ranked lists, crowdwork quality reaches its best with CTs diversified by requesters, thereby confirming that workers look to expose their “good” work to many requesters.

We assess here whether standard stochastic mixed membership models are adapted for link prediction in social networks by studying how they handle homophily and preferential attachment. According to the homophily hypothesis, two vertices are more likely to be connected if they share common characteristics whereas preferential attachment states that a vertex prefers to join the more connected nodes existing in the network. To study these properties, we first introduce formal definitions of these phenomena; we then study how stochastic mixed membership models relate to these definitions. Our theoretical analysis reveals that standard stochastic mixed membership models comply with homophily with the similarity that underlies them. For preferential attachment, the situation is more contrasted: if these models do not comply with global preferential attachment, their compliance to local preferential attachment depends on whether the memberships to latent factors are hard or soft, and in the latter case on whether the underlying latent factor distribution is bursty or not. We illustrate these elements on synthetic and real networks by using the generative properties of Bayesian model.

Crowdsourcing has gained popularity in a variety of domains as an increasing number of jobs are "taskified" and completed independently by a set of workers. A central process in crowdsourcing is the mechanism through which workers find tasks. On popular platforms such as Amazon Mechanical Turk, tasks can be sorted by dimensions such as creation date or reward amount. Research efforts on task assignment have focused on adopting a requester-centric approach whereby tasks are proposed to workers in order to maximize overall task throughput, result quality and cost. In this paper, we advocate the need to complement that with a worker-centric approach to task assignment, and examine the problem of producing, for each worker, a personalized summary of tasks that preserves overall task throughput. We formalize task composition for workers as an optimization problem that finds a representative set of k valid and relevant Composite Tasks (CTs). Validity enforces that a composite task complies with the task arrival rate and satisfies the worker's expected wage. Relevance imposes that tasks match the worker's qualifications. We show empirically that workers' experience is greatly improved due to task homogeneity in each CT and to the adequation of CTs with workers' skills. As a result task throughput is improved.

We propose in this paper two new models for modeling topic and word-topic dependencies between consecutive documents in document streams. The first model is a direct extension of Latent Dirichlet Allocation model (LDA) and makes use of a Dirichlet distribution to balance the influence of the LDA prior parameters wrt to topic and word-topic distribution of the previous document. The second extension makes use of copulas, which constitute a generic tools to model dependencies between random variables. We rely here on Archimedean copulas, and more precisely on Franck copulas, as they are symmetric and associative and are thus appropriate for exchangeable random variables. Our experiments, conducted on three standard collections that have been used in several studies on topic modeling, show that our proposals outperform previous ones (as dynamic topic models and temporal \LDA), both in terms of perplexity and for tracking similar topics in a document stream.

The problem of summarizing a large collection of homogeneous items has been addressed extensively in particular in the case of geo-tagged datasets (e.g. Flickr photos and tags). In our work, we study the problem of summarizing large collections of heterogeneous items. For example, a user planning to spend extended periods of time in a given city would be interested in seeing a map of that city with item summaries in different geographic areas, each containing a theater, a gym, a bakery, a few restaurants and a subway station. We propose to solve that problem by building representative Composite Items (CIs).

We address in this paper the problem of efficiently finding a few number of representative frequent itemsets in transaction matrices. To do so, we propose to rely on matrix decomposition techniques, and more precisely on Constrained Binary Matrix Factorization (CBMF) which decomposes a given binary matrix into the product of two lower dimensional binary matrices, called factors. We first show, under binary constraints, that one can interpret the first factor as a transaction matrix operating on packets of items, whereas the second factor indicates which item belongs to which packet. We then formally prove that one can directly mine the CBMF factors in order to find (approximate) itemsets of a given size and support in the original transaction matrix. Then through a detailed experimental study, we show that the frequent itemsets produced by our method represent a significant portion of the set of all frequent itemsets according to existing metrics, while being up to several orders of magnitude less numerous.

For large-scale category systems, such as Directory Mozilla, which consist of tens of thousand categories, it has been empirically verified in earlier studies that the distribution of documents among categories can be modeled as a power-law distribution. It implies that a significant fraction of categories, referred to as rare categories, have very few documents assigned to them. This characteristic of the data makes it harder for learning algorithms to learn effective decision boundaries which can correctly detect such categories in the test set. In this work, we exploit the distribution of documents among categories to (i) derive an upper bound on the accuracy of any classifier, and (ii) propose a ranking-based algorithm which aims to maximize this upper bound. The empirical evaluation on publicly available large-scale datasets demonstrate that the proposed method not only achieves higher accuracy but also much higher coverage of rare categories as compared to state-of-the-art methods.

This paper provides an overview of the workshop Web-Scale Classification: Web Classification in the Big Data Era which was held in New York City, on February 28th as a workshop of the seventh International Conference on Web Search and Data Mining. The goal of the workshop was to discuss and assess recent research focusing on classification and mining in Web-scale category systems. The workshop brought together members of several communities such web mining, machine learning, text classification and social media mining.

We investigate the problem of learning an IR function on a collection without relevance judgements (called target collection) by transferring knowledge from a selected source collection with relevance judgements. To do so, we first construct, for each query in the target collection, relative relevance judgment pairs using information from the source collection closest to the query (selection and transfer steps), and then learn an IR function from the obtained pairs in the target collection (self-learning step). For the transfer step, the relevance information in the source collection is summarized as a grid that provides, for each term frequency and document frequency values of a word in a document, an empirical estimate of the relevance of the document. The self-learning step iteratively assigns pairwise preferences to documents in the target collection using the scores of the former learned function. We show the effectiveness of our approach through a series of extensive experiments on CLEF and several collections from TREC used either as target or source datasets. Our experiments show the importance of selecting the source collection prior to transfer information to the target collection, and demonstrate that the proposed approach yields results consistently and significantly above state-of-the-art IR functions.

While multi-class categorization of documents has been of research interest for over a decade, relatively fewer approaches have been proposed for large scale taxonomies in which the number of classes range from hundreds of thousand as in Directory Mozilla to over a million in Wikipedia. As a result of ever increasing number of text documents and images from various sources, there is an immense need for automatic classification of documents in such large hierarchies. In this paper, we analyze the tradeoffs between the important characteristics of different classifiers employed in the top down fashion. The properties for relative comparison of these classifiers include, (i) accuracy on test instance, (ii) training time (iii) size of the model and (iv) test time required for prediction. Our analysis is motivated by the well known error bounds from learning theory, which is also further reinforced by the empirical observations on the publicly available data from the Large Scale Hierarchical Text Classification Challenge. We show that by exploiting the data heterogenity across the large scale hierarchies, one can build an overall classification system which is approximately 4 times faster for prediction, 3 times faster to train, while sacrificing only 1% point in accuracy.

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We first present in this paper an analytical view of heuristic retrieval constraints which yields simple tests to determine whether a retrieval function satisfies the constraints or not. We then review empirical findings on word frequency distributions and the central role played by burstiness in this context. This leads us to propose a formal definition of burstiness which can be used to characterize probability distributions wrt this phenomenon. We then introduce the family of information-based IR models which naturally captures heuristic retrieval constraints when the underlying probability distribution is bursty and propose a new IR model within this family, based on the log-logistic distribution. The experiments we conduct on three different collections illustrate the good behavior of the log-logistic IR model: it significantly outperforms the Jelinek-Mercer and Dirichlet prior language models on all three collections, with both short and long queries and for both the MAP and the precision at 10 documents. It also outperforms the InL2 DFR model for the MAP, and yields results on a par with it for the precision at 10.

In this paper, we define an online algorithm to learn the generalized cosine similarity measures fork-NN classification and hence a similarity matrix A corresponding to a bilinear form. In contrary to the standard cosine measure, the normalization is itself dependent on the similarity matrix which makes it impossible to use directly the algorithms developed for learning Mahanalobis distances, based on positive, semi-definite (PSD) matrices. We follow the approach where we first find an appropriate matrix and then project it onto the cone of PSD matrices, which we have adapted to the particular form of generalized cosine similarities, and more particularly to the fact that such measures are normalized. The resulting online algorithm as well as its batch version is fast and has got better accuracy as compared with state-of-the-art methods on standard data sets.

In this paper, we propose an algorithm for learning a general class of similarity measures for kNN classification. This class encompasses, among others, the standard cosine measure, as well as the Dice and Jaccard coefficients. The algorithm we propose is an extension of the voted perceptron algorithm and allows one to learn different types of similarity functions (either based on diagonal, symmetric or asymmetric similarity matrices). The results we obtained show that learning similarity measures yields significant improvements on several collections, for two prediction rules: the standard kNN rule, which was our primary goal, and a symmetric version of it.

In this paper, we revisit the dependence language modelfor information retrieval proposed in [1], and show that thismodel is deficient from a theoretical point of view. We thenpropose a new model, well founded theoretically, for integratingdependencies between terms in the language model.This new model is simpler, yet more general, than the oneproposed in [1], and yields similar results in our experiments,on both syntactic and semantic dependencies.

Non-negative Matrix Factorization (NMF, [5]) and Probabilistic Latent Semantic Analysis (PLSA, [4]) have been successfully applied to a number of text analysis tasks such as document clustering. Despite their different inspirations, both methods are instances of multinomial PCA [1]. We further explore this relationship and first show that PLSA solves the problem of NMF with KL divergence, and then explore the implications of this relationship.