On Search Powered Navigation

Our paper "On Search Powered Navigation", with Glorianna Jagfeld, Hosein Azarbonyad, Alex Olieman, Jaap Kamps, Maarten Marx, has been accepted as a short paper at . \o/
Knowledge graphs and other hierarchical domain ontologies hold great promise for complex information seeking tasks, yet their massive size defies the standard and effective way smaller hierarchies are used as a static navigation structure in faceted search or standard website navigation. As a result, we see the only limited use of knowledge bases in entity surfacing for navigational queries, and fail to realize their full potential to empower search. Seeking information in structured environments consists of two main activities: exploratory browsing and focused searching.
Exploratory browsing refers to activities aimed at better defining the information need and increasing the level of understanding of the information space, while focused searching includes activities such as query rewriting and comparison of results, which are performed after the information need has been made more concrete. Based on the interplay of these two actions, a search system is supposed to provide a connected space of information for the users to navigate, as well as search to adjust the focus of their browsing towards useful content.

In our paper, we introduce the concept of Search Powered Navigation (SPN), which enables users to combine navigation with the query based searching in a structured information space, and offers a way to find a balance between exploration and exploitation. We hypothesize that SPN enables users to exploit the semantic structure of a large knowledge base in an effective way. We test this hypothesis by conducting a user study in which users are engaged in exploratory search activities and investigate the effect of SPN on the variability in users’ behavior and experience. We employed an exploratory search system on parliamentary data in two modes, pure navigation and search powered navigation, and tested two types of tasks, broad- and focused-topic tasks.

Beating the Teacher: Neural Ranking Models with Weak Supervision

Our paper "Neural Ranking Models with Weak Supervision", with Hamed Zamani, Aliaksei Severyn, Jaap Kamps, and W. Bruce Croft, has been accepted as a long paper at The 40th International ACM SIGIR Conference on Research and Development in Information Retrieval (SIGIR2017). \o/
This paper is on the outcome of my pet project during my internship at Google Research.

Despite the impressive improvements achieved by unsupervised deep neural networks in computer vision, natural language processing, and speech recognition tasks, such improvements have not yet been observed in ranking for information retrieval. The reason may be the complexity of the ranking problem, as it is not obvious how to learn from queries and documents when no supervised signal is available. In our paper, we propose to train neural ranking models using weak supervision, where labels are obtained automatically without human annotators or any external resources e.g., click data.

To this aim, we use the output of a known unsupervised ranking model, such as BM25, as a weak supervision signal. We further train a set of simple yet effective ranking models based on feed-forward neural networks.  We studied their effectiveness under various learning scenarios: point-wise and pair-wise models, and using different input representations: from encoding query-document pairs into dense/sparse vectors to using word embedding representation. Our findings also suggest that supervised neural ranking models can greatly benefit from pre-training on large amounts of weakly labeled data that can be easily obtained from unsupervised IR models.

We have three main research Questions:

  • RQ1. Is it possible to learn a neural ranker only from labels provided by a completely unsupervised IR model such as BM25, as the weak supervision signal, that will exhibit superior generalization capabilities?
  • RQ2. What input representation and learning objective is most suitable for learning in such a setting?
  • RQ3. Can a supervised learning model benefit from weak supervision step, especially in cases when labeled data is limited?


SIGIR2017 Tutorial on “Neural Networks for Information Retrieval”

We will be giving a full day tutorial on "Neural Networks for Information Retrieval", with Tom Kenter, Alexey Borisov, Christophe Van Gysel, Maarten de Rijke, Bhaskar Mitra at The 40th International ACM SIGIR Conference on Research and Development in Information Retrieval (SIGIR2017). \o/

The aim of this full-day tutorial is to give a clear overview of current tried-and-trusted neural methods in IR and how they benefit IR research. It covers key architectures, as well as the most promising future directions. It is structured as follows:

  • Basic concepts:
    • Main concepts involved in neural systems will be covered, such as back propagation, distributed representations/embeddings, convolutional layers, recurrent networks, sequence-to-sequence models, dropout, loss functions, optimization schemes like Adam.
  • Semantic matching:
    • Different methods for supervised, semi- and unsupervised learning for semantic matching will be discussed.
  • Learning to Rank with Neural Networks:
    • Feature-based models for representation learning, ranking objectives and loss functions, and training a neural ranker under different levels of supervision are going to be discussed.
  • Modeling user behavior with Neural Networks:
    • Probabilistic graphical models, Neural click models, and modeling biases using neural network will be described.
  • Generating Models:
    • The ideas on machine reading task, question answering, conversational IR, and dialogue systems will be covered.

hummm…got existed?  Join us at SIGIR2017 🙂
The material from our SIGIR 2017 tutorial on Neural Networks for Information Retrieval (NN4IR) is available online at http://nn4ir.com.

Modeling Retrieval Problem using Neural Networks

Despite the buzz surrounding deep neural networks (DNN) models for information retrieval, the literature is still lacking a systematic basic investigation on how generally we can model the retrieval problem using neural networks.
Modeling the retrieval problem in the context of neural networks means the general way that we frame the problem with regards to the essential components of a neural network, including what we consider as the objective function, and which kind of architecture we employ, how we feed the data to the network, etc.

Here, in this post, I try to present different general architectures that can be considered for modeling the retrieval problem. First, I provide a categorization of different models based on their objective function, and then I will discuss different approaches with regards to their inference time. Note that in the figures, I use the fully connected feed-forward neural network, while it can be replaced by more complex or more expressive neural models like LSTMs, or CNN.

Categorizing Models by the Type of Objective Function

There are different models that the retrieval problem can be generally formulated in the neural network framework in terms of the objective function which is defined to be optimized: Retrieval as Regression, Retrieval as Ranking, and Retrieval as Classification. I am going to explain these models and discuss their pros and cons.

Retrieval as Regression

The first architecture would be framing the retrieval problem as the scoring problem which can be phrased as the regression problem. In the regression model (left most model in above figure), given the query Latex formula and the document Latex formula, we aim at generating a score, which could be for example interpreted as the probability that the document Latex formula is relevant given the query Latex formula. In this model, network learns to produce calibrated scores, which at the end, these scores are used to rank documents. This model is also referred as the point-wise model in the learning to rank literature.


Hierarchical Re-estimation of Topic Models for Measuring Topical Diversity

Our paper "Hierarchical Re-estimation of Topic Models for Measuring Topical Diversity", with Hosein Azarbonyad, Tom Kenter, Maarten Marx, Jaap Kamps, and Maarten de Rijke, has been accepted as a long paper at The 39th European Conference on Information Retrieval (ECIR'17). \o/

Quantitative notions of topical diversity in text documents are useful in several contexts, e.g., to assess the interdisciplinarity of a research proposal or to determine the interestingness of a document. An influential formalization of diversity has been introduced in biology. It decomposes diversity in terms of elements that belong to categories within a population and formalizes the diversity of a population Latex formula as the expected distance between two randomly selected elements of the population:

Latex formula

where Latex formula and Latex formula  are the proportions of categories Latex formula andLatex formula in the population and Latex formula is the distance between Latex formula and Latex formula.

This notion of diversity had been adapted to quantify the topical diversity of a text document. Words are considered elements, topics are categories, and a document is a population. When using topic modeling for measuring topical diversity of text document Latex formula, We can model elements based on the probability of a word Latex formula given Latex formula, Latex formula, categories based on the probability of Latex formula given topic Latex formula , Latex formula, and populations based on the probability of Latex formula given Latex formula, Latex formula. In probabilistic topic modeling, at estimation time, these distributions are usually assumed to be sparse.

  1. First, the content of a document is assumed to be generated by a small subset of words from the vocabulary (i.e., Latex formula is sparse).
  2. Second, each topic is assumed to contain only some topic-specific related words (i.e.,  Latex formula is sparse).
  3. Finally, each document is assumed to deal with a few topics only (i.e., Latex formula is sparse).

When approximated using currently available methods,  Latex formula and Latex formula are often dense rather than sparse. Dense distributions cause two problems for the quality of topic models when used for measuring topical diversity: generality and impurity. General topics mostly contain general words and are typically assigned to most documents in a corpus. Impure topics contain words that are not related to the topic. Generality and impurity of topics both result in low quality Latex formula distributions.

Different topic re-estimation approaches. TM is a topic modeling approach like, e.g., LDA. DR is document re-estimation, TR is topic re-estimation, and TAR is topic assignment re-estimation.


Telling how to narrow it down: Effect of Browsing Path Recommendation on Exploratory Search

Our paper "Telling how to narrow it down: Effect of Browsing Path Recommendation on Exploratory Search", with Glorianna Jagfeld, Hosein Azarbonyad, Alex Olieman, Jaap Kamps, Maarten Marx, has been accepted as a short paper at The ACM SIGIR Conference on Human Information Interaction & Retrieval (CHIIR'17). \o/

There are several information needs requiring sophisticated human-computer interactions that currently remain unsolved or poorly supported by major search applications. One of these cases is exploratory search, which refers to search tasks that are open-ended, multi-faceted, and iterative, like learning or topic investigation. This type of search often occurs in a domain unknown or poorly known to the searchers which can make it hard for them to formulate proper queries for retrieving useful documents.

Exploratory search is composed of two main activities, exploratory browsing and focused searching . Exploratory browsing refers to activities that aim at better defining the information need and raising the understanding of the information space. Focused searching corresponds to activities like query refining and results’ comparisons after the information need has been shaped more clearly. Based on this composition, an exploratory search system needs to provide its users a connected space of information to browse and investigate, as well as facilities to adjust the focus of their search towards useful documents.

Using structured data to organize unstructured information is one of the promising approaches for supporting complex search tasks, including exploratory search. Structure in the data provides overviews at different levels of abstraction and empowers the users to explore the data from different points of view. However, it may still be difficult to find useful paths of exploration and clues can help the users.

The main aim of this research is to investigate the user behavior in exploratory search when a recommendation engine for browsing paths is provided along with the browsing system.To do so, we have employed the ExPoSe-Browser (Exploratory Political Search Browser) as the baseline system and built a recommendation engine as a supplementary feature for the system. We have conducted a user study involving exploratory search tasks which revealed general differences of the browsing behavior of the subjects using the two different systems.


Poison Pills and Antidots: Inoculating Relevance Feedback

"Poison Pills and Antidots: Inoculating Relevance Feedback", an article published in Amsterdam Science Magazine as one of the cool contributions of our CIKM2016 paper. We also have a extended abstract describing this part, accepted to be presented in DIR2016 "Inoculating Relevance Feedback Against Poison Pills", with Hosein Azarbonyad, Jaap Kamps, Djoerd Hiemstra and Maarten Marx.

Relevance Feedback (RF) is a common approach for enriching queries, given a set of explicitly or implicitly judged documents either explicitly assessed by the user or implicitly inferred from user behavior,
to improve the performance of the retrieval.
Although it has been shown that on average, the overall performance of retrieval will be improved after relevance feedback, for some topics, employing some relevant documents may decrease the average precision of the initial run. This is mostly because the feedback document is partially relevant and contains off-topic terms which adding them to the query as expansion terms results in loosing the retrieval performance. These relevant documents that hurt the performance of retrieval after feedback are called “poison pills”. In this article, we discuss the effect of poison pills on the relevance feedback and present Significant Words Language Models as an approach for estimating feedback model to tackle this problem.

Significant Words Language Models are family of models aiming to estimate models for a set of documents so that all, and only, the significant shared terms are captured in the models(see here and here). This makes these models to be not only distinctive, but also supported by all the documents in the set.

poisonpillsPut loosely, SWLM iteratively removes two types of words from the model: general words, i.e., common words used frequently across all the documents, and page-specific words, i.e., words mentioned in some of the relevant documents, but not the majority of them (see the above Figure). This approach prevents noise words interfering with the relevance feedback, and thus successfully improves the retrieval performance by protecting relvance feedback against Poison Pills.