Cyberbullying is an important issue for our society and has a major negative effect on the victims, that can be highly damaging due to the frequency and high propagation provided by Information Technologies. Therefore, the early detection of cyberbullying in social networks becomes crucial to mitigate the impact on the victims. In this article, we aim to explore different approaches that take into account the time in the detection of cyberbullying in social networks. We follow a supervised learning method with two different specific early detection models, named threshold and dual. The former follows a more simple approach, while the latter requires two machine learning models. To the best of our knowledge, this is the first attempt to investigate the early detection of cyberbullying. We propose two groups of features and two early detection methods, specifically designed for this problem. We conduct an extensive evaluation using a real world dataset, following a time-aware evaluation that penalizes late detections. Our results show how we can improve baseline detection models up to 42%.

Collaborative Filtering algorithms suffer from the so-called cold-start problem. In particular, when a user has rated few items, recommendations offered by these algorithms are not too accurate. Profile Expansion techniques have been described as a way to tackle this problem without bothering the user with additional information requests by increasing automatically the size of the user profile. Up to now, only collaborative approaches had been proposed for Profile Expansion. However, content-based techniques can also be used. We perform a manual analysis of a movie dataset to analyze how content features behave. According to this analysis, we propose a content-based approach, which is also combined with collaborative information. Concretely, we expose the advantages and disadvantages of the combination with a popularity feature. Moreover, a comparison to pure collaborative approaches is performed. Our approach is evaluated in a new system situation. That is, not only the active user has few ratings, but also most of the users. The results show that content-based information is useful for rating prediction. In addition, recommendations are less personalized as popularity feature acquires more relevance for item selection.

Network Intrusion Detection Systems (NIDS) are concerned with the discovery of unauthorized accesses to computer networks by analyzing the traffic in order to detect malicious activity. In the event of an intrusion, the time elapsed until the detection is a key factor to break the Cyber Kill Chain. State-of-the-art studies use a traditional evaluation based on standard accuracy metrics (e.g. precision or F-measure) without taking into account the time required to detect a threat. In this paper, we formally define the early intrusion detection problem. We perform a thorough evaluation adapting existing time-aware metrics to the early detection of threats on a computer network and we also propose a new metric (i.e. NormERDE). Our results show how a good performance on standard metrics may not correspond to good results on early detection metrics. For instance, a technique with a high level of precision could need too much time to detect a threat. Therefore, in this paper we propose taking into account time-aware metrics in NIDS evaluations due to the importance of this factor in a real world environment.

In this paper a systematic analysis of a public intrusion detection dataset has been developed in order to understand how the traffic behaves in this particular context. This analysis is used for avoiding common pitfalls introduced because of a misunderstanding of data peculiarities and for selecting and tailoring correctly the algorithms. Specifically, we have employed machine learning algorithms to classify the traffic into normal and attack flows. In addition, it is important to decide what features should be evaluated. Typically, standard metrics do not take into account time spent in the classification, what is essential in an intrusion detection system. This is the reason why we introduce a metric that considers both the accuracy and the delay to make the decision and that is employed for evaluating machine learning algorithms in other domains. The conclusions obtained from our dataset analysis can be used to develop new models that could fit the data better than existing approaches.

The use of queries to find products and services that are located nearby is increasing rapidly due mainly to the ubiquity of internet access and location services provided by smartphone devices. Local search engines help users by matching queries with a predefined geographical connotation (“local queries”) against a database of local business listings. Local search differs from traditional Web search because, to correctly capture users’ click behavior, the estimation of relevance between query and candidate results must be integrated with geographical signals, such as distance. The intuition is that users prefer businesses that are physically closer to them or in a convenient area (e.g., close to their home). However, this notion of closeness depends upon other factors, like the business category, the quality of the service provided, the density of businesses in the area of interest, the hour of the day, or even the day of the week. In this work, we perform an extensive analysis of online users’ interactions with a local search engine, investigating their intent, temporal patterns, and highlighting relationships between distance-to-business and other factors, such as business reputation, Furthermore, we investigate the problem of estimating the click-through rate on local search ( LCTR ) by exploiting the combination of standard retrieval methods with a rich collection of geo-, user-, and business-dependent features. We validate our approach on a large log collected from a real-world local search service. Our evaluation shows that the non-linear combination of business and user information, geo-local and textual relevance features leads to a significant improvements over existing alternative approaches based on a combination of relevance, distance, and business reputation [1].

Over the years the number of elements in a corporate network, the services and the amount of traffic have grown significantly. For this reason, it is increasingly important to analyze the traffic. Packet-based analysis is the traditional option but entails a high resources consumption. In order to palliate this, flow-based analysis arises. It usually implies to deploy a flow exporter, responsible of generating the flows from the network packets, and a flow collector, in charge of receiving, storing and preprocessing the exported flows. This paper provides a study on flow exporters and collectors. To the best of our knowledge, there is little work dealing with the resources consumed by this kind of tools. Specifically, available memory, CPU load and volume of traffic have been monitored. Using a well-known dataset, packets have been sent to exporters and collectors in order to observe how they behave.

With the ubiquity of internet access and location services provided by smartphone devices, the volume of queries issued by users to find products and services that are located near them is rapidly increasing. Local search engines help users in this task by matching queries with a predefined geographical connotation ("local queries") against a database of local business listings.

Collaborative Filtering algorithms are frequently employed in e-commerce. However, this kind of algorithms can also be useful in other domains. In an information system thousands of bytes are sent through the network every second. Analyzing this data can require too much time and many resources, but it is necessary for ensuring the right operation of the network. Results are used for profiling, security analysis, traffic engineering and many other purposes. Nowadays, as a complement to a deep inspection of the data, it is more and more common to monitor packet flows, since it consumes less resources and it allows to react faster to any network situation. In a typical ow monitoring system, flows are exported to a collector, which stores the information before being analyzed. However, many collectors work based on time slots, so they do not analyze the flows when they are just received, generating a delay. In this work we demonstrate how Collaborative Filtering algorithms can be applied to this new domain. In particular, using information about past flows, these algorithms can anticipate future flows before being captured. This way, time required for detecting and responding to different network situations is reduced.

For many search settings, distributed/replicated search engines deploy a large number of machines to ensure efficient retrieval. This paper investigates how the power consumption of a replicated search engine can be automatically reduced when the system has low contention, without compromising its efficiency. We propose a novel self-adapting model to analyse the trade-off between latency and power consumption for distributed search engines. When query volumes are high and there is contention for the resources, the model automatically increases the necessary number of active machines in the system to maintain acceptable query response times. On the other hand, when the load of the system is low and the queries can be served easily, the model is able to reduce the number of active machines, leading to power savings. The model bases its decisions on examining the current and historical query loads of the search engine. Our proposal is formulated as a general dynamic decision problem, which can be quickly solved by dynamic programming in response to changing query loads. Thorough experiments are conducted to validate the usefulness of the proposed adaptive model using historical Web search traffic submitted to a commercial search engine. Our results show that our proposed self-adapting model can achieve an energy saving of 33% while only degrading mean query completion time by 10 ms compared to a baseline that provisions replicas based on a previous day's traffic.

For increased efficiency, an information retrieval system can split its index into multiple shards, and then replicate these shards across many query servers. For each new query, an appropriate replica for each shard must be selected, such that the query is answered as quickly as possible. Typically, the replica with the lowest number of queued queries is selected. However, not every query takes the same time to execute, particularly if a dynamic pruning strategy is applied by each query server. Hence, the replica's queue length is an inaccurate indicator of the workload of a replica, and can result in inefficient usage of the replicas. In this work, we propose that improved replica selection can be obtained by using query efficiency prediction to measure the expected workload of a replica. Experiments are conducted using 2.2k queries, over various numbers of shards and replicas for the large GOV2 collection. Our results show that query waiting and completion times can be markedly reduced, showing that accurate response time predictions can improve scheduling accuracy and attesting the benefit of the proposed scheduling algorithm.

In the last years, recommender systems have achieved a great popularity. Many different techniques have been developed and applied to this field. However, in many cases the algorithms do not obtain the expected results. In particular, when the applied model does not fit the real data the results are especially bad. This happens because many times models are directly applied to a domain without a previous analysis of the data. In this work we study the most popular datasets in the movie recommendation domain, in order to understand how the users behave in this particular context. We have found some remarkable facts that question the utility of the similarity measures traditionally used in k-Nearest Neighbors (kNN) algorithms. These findings can be useful in order to develop new algorithms. In particular, we modify traditional kNN algorithms by introducing a new similarity measure specially suited for sparse contexts, where users have rated very few items. Our experiments show slight improvements in prediction accuracy, which proves the importance of a thorough dataset analysis as a previous step to any algorithm development.

The technique of collaborative filtering is especially successful in generating personalized recommendations. More than a decade of research has resulted in numerous algorithms, although no comparison of the different strategies has been made. In fact, a universally accepted way of evaluating a collaborative filtering algorithm does not exist yet. In this work, we compare different techniques found in the literature, and we study the characteristics of each one, highlighting their principal strengths and weaknesses. Several experiments have been performed, using the most popular metrics and algorithms. Moreover, two new metrics designed to measure the precision on good items have been proposed. The results have revealed the weaknesses of many algorithms in extracting information from user profiles especially under sparsity conditions. We have also confirmed the good results of SVD-based techniques already reported by other authors. As an alternative, we present a new approach based on the interpretation of the tendencies or differences between users and items. Despite its extraordinary simplicity, in our experiments, it obtained noticeably better results than more complex algorithms. In fact, in the cases analyzed, its results are at least equivalent to those of the best approaches studied. Under sparsity conditions, there is more than a 20% improvement in accuracy over the traditional user-based algorithms, while maintaining over 90% coverage. Moreover, it is much more efficient computationally than any other algorithm, making it especially adequate for large amounts of data.

The recommendation of queries, known as query suggestion, is a common practice on major Web Search Engines. It aims to help users to find the information they are looking for, and is usually based on the knowledge learned from past interactions with the search engine. In this paper we propose a new model for query suggestion, the Search Shortcut Problem, that consists in recommending "successful" queries that allowed other users to satisfy, in the past, similar information needs. This new model has several advantages with respect to traditional query suggestion approaches. First, it allows a straightforward evaluation of algorithms from available query log data. Moreover, it simplifies the application of several recommendation techniques from other domains. Particularly, in this work we applied Collaborative Filtering to this problem, and evaluated the interesting results achieved on large query logs from AOL and Microsoft. Different techniques for analyzing and extracting information from query logs, as well as new metrics and techniques for measuring the effectiveness of recommendations are proposed and evaluated. The results obtained clearly show the importance of several of our contributions, and open an interesting field for future research.

Giving suggestions to users of Web-based services is a common practice aimed at enhancing their navigation experience. Major Web Search Engines usually provide "Suggestions" under the form of queries that are, to some extent, related to the current query typed by the user, and the knowledge learned from the past usage of the system. In this work we introduce "Search Shortcuts" as "Successful" queries allowed, in the past, users to satisfy their information needs. Differently from conventional suggestion techniques, our search shortcuts allows to evaluate effectiveness by exploiting a simple train-and-test approach. We have applied several Collaborative Filtering algorithms to this problem, evaluating them on a real query log data. We generate the shortcuts from all user sessions belonging to the testing set, and measure the quality of the shortcuts suggested by considering the similarity between them and the navigational user behavior.

In this paper using the information obtained from the daily working of a Web directory, we attempt to expand the knowledge about the behavior of the users in order to improve and adapt the Internet search engines to their users. We have analysed more than 320,000 requests of the transaction log of a Spanish Web directory, focusing our attention, firstly, in the searches in order to confirm the main differences between Internet and traditional Information Retrieval systems. Furthermore, we have developed an exhaustive statistical analysis of searches, categories visited and documents viewed to achieve a mathematical pattern of behaviour for each one, and what it is more important, to establish a relationship between the variations in the behaviour of each one.