Archive for the 'Machine Learning' Category

Elnaz Pazhouhi graduates on Product Name Recognition

Tuesday, March 27th, 2018, posted by Djoerd Hiemstra

Automatic Product Name Recognition from Short Product Descriptions

by Elnaz Pazhouhi

This thesis studies the problem of product name recognition from short product descriptions. This is an important problem especially with the increasing use of ERP (Enterprise Resource Planning) software at the core of modern business management systems, where the information of business transactions is stored in unstructured data stores. A solution to the problem of product name recognition is especially useful for the intermediate businesses as they are interested in finding potential matches between the items in product catalogs (produced by manufactures or another intermediate business) and items in the product requests (given by the end user or another intermediate business).
In this context the problem of product name recognition in specifically challenging because product descriptions are typically short, ungrammatical, incomplete, abbreviated and multilingual. In this thesis we investigate the application of supervised machine-learning techniques and gazetteer-based techniques to our problem. To approach the problem, we define it as a classification problem where the tokens of product descriptions are classified into I, O and B classes according to the standard IOB tagging scheme. Next we investigate and compare the performance of a set of hybrid solutions that combine machine learning and gazetteer-based approaches. We study a solution space that uses four learning models: linear and non-linear SVC, Random Forest, and AdaBoost. For each solution, we use the same set of features. We divide the features into four categories: token-level features, document-level features, gazetteer-based features and frequency-based features. Moreover, we use automatic feature selection to reduce the dimensionality of data; that consequently improves the training efficiency and avoids over-fitting.
To be able to evaluate the solutions, we develop a machine learning framework that takes as its inputs a list of predefined solutions (i.e. our solution space) and a preprocessed labeled dataset (i.e. a feature vector X, and a corresponding class label vector Y). It automatically selects the optimal number of most relevant features, optimizes the hyper-parameters of the learning models, trains the learning models, and evaluates the solution set. We believe that our automated machine learning framework, can effectively be used as an AutoML framework that automates most of the decisions that have to be made in the design process of a machine learning solution for a particular domain (e.g. for product name recognition).
Moreover, we conduct a set of experiments and based on the results, we answer the research questions of this thesis. In particular, we determine (1) which learning models are more effective for our task, (2) which feature groups contain the most relevant features (3) what is the contribution of different feature groups to the overall performance of the induced model, (4) how gazetteer-based features are incorporated with the machine learning solutions, (5) how effective gazetteer-based features are, (6) what the role of hyper-parameter optimization is and (7) which models are more sensitive to the hyper-parameters optimization.
According to our results, the solutions with maximum and minimum performance are non-linear SVC with an F1 measure of 65% and AdaBoost with an F1 measure of 59% respectively. This reveals that the role of classifiers is not considerable in the final outcome of the learning model, at least according to the studied dataset. Additionally, our results show that the most effective feature group is the document-level features with 14.8% contribution to the overall performance (i.e. F1 measure), in the second position, there is the group of token-level features, with 6.8% contribution. The other two groups, the gazetteer-based features and frequency-based features have small contributions of 1% and 0.5% respectively. However more investigations relate the poor performance of gazetteer-based features to the low coverage of the used gazetteer (i.e. ETIM).
Our experiments also show that all learning models over-fit the training data when a large number of features is used; thus the use of feature selection techniques is essential to the robustness of the proposed solutions. Among the studied learning models, the performance of non-linear SVC and AdaBoost models strongly depends on the used hyper-parameters. Therefore for those models the computational cost of the hyper-parameters tuning is justifiable.

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Ranking Learning-to-Rank Methods

Monday, October 2nd, 2017, posted by Djoerd Hiemstra

Slides of the keynote at the 1st International Workshop on LEARning Next gEneration Rankers, LEARNER 2017 on 1 October 2017 in Amsterdam are now available:

Slides of Learner 2017 keynote

Download the paper: Niek Tax, Sander Bockting, and Djoerd Hiemstra. “A cross-benchmark comparison of 87 learning to rank methods’’, Information Processing and Management 51(6), Elsevier, pages 757–772, 2015 [download pdf]

Cum laude degree for Masrour Zoghi

Friday, February 24th, 2017, posted by Djoerd Hiemstra

Dueling bandits for online ranker evaluation

by Masrour Zoghi

In every domain where a service or a product is provided, an important question is that of evaluation: given a set of possible choices for deployment, what is the best one? An important example, which is considered in this work, is that of ranker evaluation from the field of information retrieval (IR). The goal of IR is to satisfy the information need of a user in response to a query issued by them, where this information need is typically satisfied by a document (or a small set of documents) contained in what is often a much larger collection. This goal is often attained by ranking the documents according to their usefulness to the issued query using an algorithm, called a ranker, a procedure that takes as input a query and a set of documents and specifies how the documents need to be ordered.
This thesis is concerned with ranker evaluation. The goal of ranker evaluation is to determine the quality of the rankers under consideration to allow us to choose the best option: given a finite set of possible rankers, which one of them leads to the highest level of user satisfaction? There are two main methods for carrying this out: absolute metrics and relative comparisons. This thesis is concerned with the second, relative form of ranker evaluation because it is more efficient at distinguishing between rankers of different quality: for instance interleaved comparisons take a fraction of the time required by A/B testing, but they produce the same outcome. More precisely, the problem of online ranker evaluation from relative feedback can be described as follows: given a finite set of rankers, choose the best using only pairwise comparisons between the rankers under consideration, while minimizing the number of comparisons involving sub-optimal rankers. This problem is an instance of what is referred to as the dueling bandit problem in the literature.
The main contribution of this thesis is devising a dueling bandit algorithm, called Copeland Confidence Bounds (CCB), that solves this problem under practically general assumptions and providing theoretical guarantees for its proper functioning. In addition to that, the thesis contains a number of other algorithms that are better suited for dueling bandit problems with particular properties.

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Fieke Hillerström graduates on Deep Verification Learning

Tuesday, December 13th, 2016, posted by Djoerd Hiemstra

by Fieke Hillerström

Deep Verification Learning

Deep learning for biometrics has increasingly gained attention over the last years. Due to the expansion of computational power and the increasing sizes of the available datasets, the performance has surpassed that of humans on certain verification tasks. However, large datasets are not available for every application. Therefore we introduce Deep Verification Learning, to reduce network complexity and train with more modest hardware on smaller datasets. Deep Verification Learning takes two images to be verified at the input of a deep learning network, and trains directly towards a verification score. This topology enables the network to learn differences and similarities in the first layer, and to involve verification signals during training. Directly training towards a verification score reduces the number of trainable parameters significantly. We applied Deep Verification Learning on the face verification task, also it could be extended to other biometric modalities. We compared our face verification learning topology with a network trained for multi-class classification on the FRGC dataset, which contains only 568 subjects. Deep Verification Learning performs substantially better.


IP&M Best Paper Award for A cross-benchmark comparison of 87 learning to rank methods

Monday, November 7th, 2016, posted by Djoerd Hiemstra

We are proud of the Information Processing & Management Best Paper Award 2015 for our paper: A cross-benchmark comparison of 87 learning to rank methods.

IPM Best Paper Award Certificate

Published in Information Processing and Management 51(6), pages 757–772

[download preprint]

Solving the Continuous Cold Start Problem in E-commerce Recommendations

Wednesday, August 3rd, 2016, posted by Djoerd Hiemstra

Beyond Movie Recommendations: Solving the Continuous Cold Start Problem in E-commerce Recommendations

by Julia Kiseleva, Alexander Tuzhilin, Jaap Kamps, Melanie Mueller, Lucas Bernardi, Chad Davis, Ivan Kovacek, Mats Stafseng Einarsen, Djoerd Hiemstra

Many e-commerce websites use recommender systems or personalized rankers to personalize search results based on their previous interactions. However, a large fraction of users has no prior interactions, making it impossible to use collaborative filtering or rely on user history for personalization. Even the most active users may visit only a few times a year and may have volatile needs or different personas, making their personal history a sparse and noisy signal at best. This paper investigates how, when we cannot rely on the user history, the large scale availability of other user interactions still allows us to build meaningful profiles from the contextual data and whether such contextual profiles are useful to customize the ranking, exemplified by data from a major online travel agent
Our main findings are threefold: First, we characterize the Continuous Cold Start Problem (CoCoS) from the viewpoint of typical e-commerce applications. Second, as explicit situational context is not available in typical real world applications, implicit cues from transaction logs used at scale can capture essential features of situational context. Third, contextual user profiles can be created offline, resulting in a set of smaller models compared to a single huge non-contextual model, making contextual ranking available with negligible CPU and memory footprint. Finally we conclude that, in an online A/B test on live users, our contextual ranker increased user engagement substantially over a non-contextual baseline, with click-through-rate (CTR) increased by 20%. This clearly demonstrates the value of contextual user profiles in a real world application.

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Niek Tax wins the ENIAC thesis award

Tuesday, December 15th, 2015, posted by Djoerd Hiemstra

Another thesis prize for Niek Tax: Best master thesis in computer science in 2014/2015 at the University of Twente, awarded by Alumni Association ENIAC. Photo: Niek Tax receives the award from Johan Noltes on behalf of the ENIAC jury. Congrats, Niek! Other nominees were Justyna Chromik (DACS), Vincent Bloemen (FMT), Maarten Brilman (HMI), Tim Paauw (IEBIS), and Moritz Müller (SCS).

Niek Tax

Niek Tax runner-up in Ngi-NGN thesis awards

Monday, November 30th, 2015, posted by Djoerd Hiemstra

Niek Tax was awarded today for his master thesis Scaling Learning to Rank to Big Data: Using MapReduce to Parallelise Learning to Rank by the Dutch association for ICT professionals and managers (Nederlandse beroepsvereniging van en voor ICT-professionals en -managers, Ngi-NGN). More information at Ngi-NGN and UT Nieuws. Congratulations, Niek!

Niek Tax

Twente Cooperation on Machine Learning

Tuesday, November 3rd, 2015, posted by Djoerd Hiemstra

Machine Learning Research at the University of Twente focusses on the application of Machine Learning in Social Signal Processing, Biometric Pattern Recognition, and Text mining. Have a look at our new web site at:

Zhemin Zhu defends PhD thesis on Co-occurrence Rate Networks

Friday, October 16th, 2015, posted by Djoerd Hiemstra

Co-occurrence Rate Networks: Towards separate training for undirected graphical models

by Zhemin Zhu

Dependence is a universal phenomenon which can be observed everywhere. In machine learning, probabilistic graphical models (PGMs) represent dependence relations with graphs. PGMs find wide applications in natural language processing (NLP), speech processing, computer vision, biomedicine, information retrieval, etc. Many traditional models, such as hidden Markov models (HMMs), Kalman filters, can be put under the umbrella of PGMs. The central idea of PGMs is to decompose (factorize) a joint probability into a product of local factors. Learning, inference and storage can be conducted efficiently over the factorization representation.
Two major types of PGMs can be distinguished: (i) Bayesian networks (directed graphs), and (ii) Markov networks (undirected graphs). Bayesian networks represent directed dependence with directed edges. Local factors of Bayesian networks are conditional probabilities. Directed dependence, directed edges and conditional probabilities are all asymmetric notions. In contrast, Markov networks represent mutual dependence with undirected edges. Both of mutual dependence and undirected edges are symmetric notions. For general Markov networks, based on the Hammersley–Clifford theorem, local factors are positive functions over maximum cliques. These local factors are explained using intuitive notions like ‘compatibility’ or ‘affinity’. Specially, if a graph forms a clique tree, the joint probability can be reparameterized into a junction tree factorization.
In this thesis, we propose a novel framework motivated by the Minimum Shared Information Principle (MSIP): We try to find a factorization in which the information shared between factors is minimum. In other words, we try to make factors as independent as possible.
The benefit of doing this is that we can train factors separately without paying a lot of efforts to guarantee consistency between them. To achieve this goal, we develop a theoretical framework called co-occurrence rate networks (CRNs) to obtain such a factorization. Briefly, given a joint probability, the CRN factorization is obtained as follows. We first strip off singleton probabilities from the joint probability. The quantity left is called co-occurrence rate (CR). CR is a symmetric quantity which measures mutual dependence among variables involved. Then we further decompose the joint CR into smaller and indepen dent CRs. Finally, we obtain a CRN factorization whose factors consist of all singleton probabilities and CR factors. There exist two kinds of independencies between these factors: (i) a singleton probability is independent (Here independent means two factors do not share information.) of other singleton probabilities; (ii) a CR factor is independent of other CR factors conditioned by singleton probabilities. Based on a CRN factorization, we propose an efficient two-step separate training method: (i) in the first step, we train a separate model for each singleton probability; (ii) given singleton probabilities, we train a separate model for each CR factor. Experimental results on three important natural language processing tasks show that our separate training method is two orders of magnitude faster than conditional random fields, while achieving competitive quality (often better on the overall quality metric F1).
The second contribution of this thesis is applying PGMs to a real-world NLP application: open relation extraction (ORE). In open relation extraction, two entities in a sentence are given, and the goal is to automatically extract their relation expression. ORE is a core technique, especially in the age of big data, for transforming unstructured information into structured data. We propose our model SimpleIE for this task. The basic idea is to decompose an extraction pattern into a sequence of simplification operations (components). The benefit by doing this is that these components can be re-combined in a new way to generate new extraction patterns. Hence SimpleIE can represent and capture diverse extraction patterns. This model is essentially a sequence labeling model. Experimental results on three benchmark data sets show that SimpleIE boosts recall and F1 by at least 15% comparing with seven ORE systems.
As tangible outputs of this thesis, we contribute open source implementations of our research results as well as an annotated data set.

[download pdf]