Boosting topic-based publish-subscribe systems with dynamic clustering We consider in this paper a class of Publish-Subscribe (pub-sub) systems called topic-based systems, where users subscribe to topics and are notified on events that belong to those subscribed topics. With the recent flourishing of RSS news syndication, these systems are regaining popularity and are raising new challenging problems.In most of the modern topics-based systems, the events in each topic are delivered to the subscribers via a supporting, distributed, data structure (typically a multicast tree). Since peers in the network may come and go frequently, this supporting structure must be continuously maintained so that "holes" do not disrupt the events delivery. The dissemination of events in each topic thus incurs two main costs: (1) the actual transmission cost for the topic events, and (2) the maintenance cost for its supporting structure. This maintenance overhead becomes particularly dominating when a pub-sub system supports a large number of topics with moderate event frequency; a typical scenario in nowadays news syndication scene.The goal of this paper is to devise a method for reducing this maintenance overhead to the minimum. Our aim is not to invent yet another topic-based pub-sub system, but rather to develop a generic technique for better utilization of existing platforms. Our solution is based on a novel distributed clustering algorithm that utilizes correlations between user subscriptions to dynamically group topics together, into virtual topics (called topic-clusters), and thereby unifies their supporting structures and reduces costs. Our technique continuously adapts the topic-clusters and the user subscriptions to the system state, and incurs only very minimal overhead. We have implemented our solution in the Tamara pub-sub system. Our experimental study shows this approach to be extremely effective, improving the performance by an order of magnitude. The amount of information available to Internet users is increasing rapidly. The need of users to be constantly updated with an up-to-date, accurate, and relevant data, out of this ocean of information, makes the publish-subscribe interaction scheme (pub-sub, for short) particularly appealing. In a pub-sub system, subscribers express their interest in certain events (e.g. the appearance of new relevant data item), and are subsequently notified of any event, generated by a publisher (information provider), that belongs to their registered interest. Pub-sub systems have raised considerable interest in the research community over the years. In this paper we focus on a relatively simple class of such systems, called topic-based systems, where users subscribe to topics and are notified on events that belong to those subscribed topics. With the recent flourishing of RSS news syndication, these systems are regaining popularity and are raising new challenging problems.. In most of the modern platforms for topic-based event notification, the events in each topic are delivered to the subscribers via a supporting, distributed, data structure (typically a multicast tree). Since peers in the network may come and go frequently, this supporting structure must be continuously maintained so that holes do not disrupt the delivery of events. The dissemination of events in each topic thus incurs two main costs: (1) the actual transmission cost for the topic events, and (2) the maintenance cost for its supporting structure. This maintenance overhead becomes particularly dominating when a pub-sub system supports a large number of topics with moderate event frequency; a typical scenario in nowadays news syndication scene.. The goal of this paper is to devise a method for reducing this maintenance overhead to the minimum. Our aim is not to invent yet another topic-based pub-sub system, but rather to develop a generic novel technique for better utilization of existing platforms. Our solution takes advantage of correlations between user subscriptions to group topics together, into virtual topics (called topic-clusters), and thereby unifies their supporting structures and reduces costs.. Before presenting our results let us briefly highlight some of the main properties of pub-sub systems in general, and topic-based ones in particular, and explain how a good solution to the problem addressed in this paper can contribute to better performance of such systems.. Background. Pub-sub is a distributed computing paradigm that consists of three principal components: subscribers, publishers, and an infrastructure for event delivery. Subscribers express their interest in an event or a pattern of events (say, the publication of new sports news). Publishers (e.g. CNN's sport department) generate events (e.g. post news). The infrastructure is responsible for matching events with the interests and sending them to the subscribers. Based on the way the subscribers specify their inter-est, pub-sub systems can be classified into two main categories: topic-based and content-based. In topic-based pub-sub systems, subscribers specify their interest by subscribing to a topic, also known as feed, channel, subject, or group. Each event produced by the publisher is labeled with a topic and sent to all the topic subscribers. In other words, publishers and subscribers are connected together by a predefined topic. In content-based systems, on the other hand, subscribers specify their interest through event filters, which are boolean queries on the events content. Published events are matched against the filters and sent to the subscribers if they satisfy their specified filters.. Topic-based pub-sub is rather static and basic compared to a content-based one. Its simplicity however has the advantage of allowing for a very efficient implementation and a simple, intuitive, user interface. Content-based pub-sub typically requires more sophisticated protocols with higher runtime overhead, as well as more sophisticated user interaction. Because of this additional complexity, one generally prefers to use a topic-based pub-sub in contexts where events divide naturally into groups that correspond to users interest. A typical example is the increasingly popular RSS news syndication [16] . An RSS system is a simple topic-based pub-sub system. Publishers publish their news by putting them into an RSS feed and providing the URL for the feed on their website. RSS users subscribe to an RSS feed by specifying its URL to their RSS readers. It is interesting to note that most existing RSS applications rely on a rather primitive implementation where RSS readers poll the feeds periodically. But with the continuous dramatic increase in the number of RSS users, it is anticipated that, for scalability, future implementation will move to push-based platforms.. To allow for scalability, most modern topic-based platforms [4, 30, 18, 22] are based on a Peer-to-Peer architecture. More specifically, they often run over Distributed Hash Table (DHT) systems [21, 24, 29] and manage their operative layer using the DHT exported functions (API). In that sense, the DHT acts as a mediator layer between the underneath network and the system core. For each topic the system allocates a dedicated distributed structure (essentially a multicast tree) over the DHT, which serves as medium for delivering the events. Since peers may leave the network unexpectedly, the structure must be continuously maintained so that the delivery of events is not disrupted.. In all the topic-based pub-sub systems that we are aware of, the structures are built and kept separately for each topic, and the maintenance cost of each structure is proportional to the number of subscribers. A large number of topics each having a large number of subscribers entails a high overall maintenance cost. So the question motivating the present work is can this overhead be avoided or at least be significantly reduced?. It turns out that the answer is often positive. The key observation is that, in practice, one can typically detect correlations between users subscriptions, which can be used to group topics and reduce the overall maintenance cost. As a simple example, consider two popular news websites, CNN.com and FoxNews.com, each providing, among others, a Headlines feed. In a typical pub-sub system, each of the feeds would be modeled as a distinct topic, and the system would keep (and maintain) two separate structures for disseminating their corresponding events. Now, assume that we have a large number of "news addicts" that are subscribed to both topics. If we create a topic that is the union of the two and subscribe those users directly to the merged topic, instead of the individual ones, the redundancy in the underlying structures would be eliminated. The overall structures size would be reduced and hence also the maintenance cost. Furthermore, if it happens that a majority of CNN Headlines subscribers are also subscribed to FoxNews headlines, and the events frequency in FoxNews is not too high, it may be cost effective to eliminate the individual CNN topic all together, subscribing all its users to the merged CNN-FoxNews topic and simply provide those few users not interested in FoxNews a local filter that filters out the redundant events. In the above example the correlation between the user subscriptions is due to the fact that the topics provide semantically similar information. In general, there may be many other reasons for such correlations. For instance, users that are subscribed to updates for a given piece of software (say the free bitmap image editor GIMP [25] ) are likely to be also subscribed to updates of other software pieces on which the given software depends (e.g. GTK+, libart and Pango [9] ).. Challenges. To improve performance, we would like to form the "best" topic-clusters, (and correspondingly determine to which topics/topic-clusters each users should subscribe), so that the overall cost of events delivery and structures maintenance in the system is minimized. While this may appear to be a traditional clustering problem, there are three requirements, derived from the specific context, which together make the problem particularly challenging. Adaptivity. A P2P pub-sub environment has a dynamic nature: users, topics and publishers may come and go; users may change interests; the events frequency in the various topics may change over time. A good solution thus must have a dynamic nature, continuously adapting the topic-clusters and the user subscriptions to the current system state. Distribution. The decentralized P2P nature of pub-sub systems, where no central coordinator has full knowledge about the system's state and the users subscriptions, calls for a corresponding distributed clustering algorithm. Low overhead. Finally, the continuous clustering efforts, as well as the adjustment of users subscription, should incur only very minimal overhead for the saving it brings to be meaningful.. While each of these aspects have been addressed, often separately, by previous research in the area of clustering (see Section 6 for an overview), to our knowledge none of these works provides a comprehensive solution that can be employed in the given context. In particular, many works aim at forming disjoint clusters, which is not a requirement here (and may indeed lead to inferior performance, as shown in our experiments.). Results. The contributions of this paper are the following.. • We introduce a simple generic model for describing the cost of events delivery and structures maintenance in a pub-sub system with topic-clusters.. • Based on this model we present a dynamic distributed clustering algorithm that continuously adapts the topic-clusters and, resp., the user subscriptions, to the changing system state. The algorithm employs local cluster updates to change the overall system configuration. Each local update is performed only when it is estimated to be (globally) cost effective. Furthermore, to minimize the overhead involved in gain estimations, a probabilistic component is employed to guarantee that (with high probability) gain estimation are computed only for updates that are likely to be beneficial.. • We have implemented the above algorithm in the Tamara pub-sub system. Tamara uses a standard popular topic-based pub-sub platform (Scribe [4] ) to manage topics, topic-clusters, and user subscriptions. Our new dynamic topic-clustering algorithm is used to automatically group topics together, into virtual topics, and redirect the publishers' event notifications, as well as the users subscriptions, to these virtual topic. Our experiments shows that, compared to the standard use of Scribe, Tamara improves the performance by an order of magnitude.. It should be stressed that while our implementation uses Scribe to manage topics and user subscriptions, the technique that we propose is generic and can similarly be used to boost the performance of other existing topic-based pub-sub platforms. The grouping of topics into sets has been previously proposed in the literature in a different context: To provide users with varying subscription granularity it was suggested to group topics into sets forming a sub-set hierarchy [26] . A main difference with the present work is the static nature of that grouping. In contrast our solution adapts continuously the topic-clusters to the user needs, guaranteeing, as we shall see, stable good performance even when users interests shift significantly.. The paper is organized as follows. Section 2 provides the necessary background for our study and presents the cost model used in the rest of the paper. Section 3 presents our dynamic distributed clustering algorithm and Section 4 describes the users subscription process. Section 5 describes the system implementation and experiments. Finally, Section 6 concludes with related and future work. We have implemented the above ideas in the Tamara pub-sub system. Tamara was developed in Java on top of the popular topicbased pub-sub platform Scribe [4] (which is itself built on top of the DHT system Pastry [21] ). Tamara exposes to users the same API as Scribe for defining topics, publishing events, and (un)subscribing. It uses our new dynamic clustering algorithm to automatically group topics into clusters and redirect the publishers' event notifications, as well as the users subscriptions, accordingly. Figure 4 illustrates the layered architecture that we adopted in our design, starting from the highest level -the application that utilizes Tamara through its API, and ending with the Network itself. Although our current implementation runs on top of Scribe and Pastry, our design (i.e. Tamara core, see next paragraph) is generic and can be applied to other pub-sub systems sharing similar standard features. Tamara leverages the basic event notification qualities of Scribe for creating and managing its topics and its clusters, and utilizes the Pastry's capabilities for locating nodes of interest. On initiation, a Tamara peer first tries to recognize the underneath Network, and to connect to an already established Pastry ring. Upon success, it further allocates a new Scribe instance using the created Pastry node ID. In that sense, both Scribe and Pastry act as mediator layers between Tamara and the underneath network.

O O B O O B I O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Information Dissemination in Unknown Radio networks with Large Labels We consider the problems of deterministic broadcasting and gossiping in completely unknown ad-hoc radio networks. We assume that nothing is known to the nodes about the topology or even the size of the network, n, except that n > 1. Protocols for vanilla model, when n is known, may be run for increasingly larger estimates 2 i on the size of the network, but one cannot determine when such a protocol should terminate. Thus, to carry this design paradigm, successfull completion or incompletion of the process should be detected, and this knowledge circulated in the network. In radio networks litertaure, this setting is referred to as Acknowledged broadcasting and gossiping. An important feature of dynamic ad-hoc radio networks is that radio nodes become ineffective due to a variety of reasons and new nodes are introduced from time-to-time. Thus, the new nodes have to assigned labels in a much larger range, say polynomial in the size of the network, e.g., [1, . . . , n c ], for some constant c. For the above setting, we present the following results for strongly connected networks: (a) A deterministic protocol for acknowledged broadcasting which takes N RG(n, n c ) rounds, where N RG(n, n c ) is the round complexity of deterministic gossiping for vanilla model. (b) A deterministic protocol for acknowledged gossiping, which takes O(n 2 lg n) rounds when collision detection mechanism is available. The structure of the transmissions of nodes in the network, to enable them to infer collisions, and discover existence of unknown in-neighborhood as a result, is abstracted as a family of integral sets called Selecting-Colliding family. We prove the existence of Selecting-Colliding families using the probabilistic method and employ them to design protocol for acknowledged gossiping when no collision detection mechanism is available. Finally, we present a deterministic protocol for acknowledged broadcasting for bidirectional networks, with a round complexity of O(n lg n) rounds. Mobile ad-hoc radio networks play an important role in a wide range of fields, ranging from agriculture and automobiles to hazardous environments and defense. Often enough, the connectivity of radio networks is not planned ahead precisely and there is no centralized system to coordinate the deployed radio stations. Thus, radio networks form a classical distributed setting in which the nodes have to rely solely on the communication received by them from other nodes, their own label values (possibly knowledge of some other parameters) and environment stimulus to determine their action at any time. Complex communication activities rely in turn on fundamental communication primitives like broadcasting and gossiping. In the broadcasting problem, a message from a distinguished source node is to be communicated to the rest of the nodes of the network, while in the gossiping problem each node of the network possesses a message which is to be disseminated to the entire network. Needless to say, gossiping can be achieved only on strongly connected networks. For both these primitives, the most important design consideration is the total time lapsed from initiation of a task to its completion. In this work, we assume that nodes are synchronized with respect to a clock, there are no faulty nodes and that nodes can communicate messages of arbitrary sizes in a single time unit. Computation is organized in rounds. In every round, each node acts either as a transmitter or as a receiver but not both. Whether a node is actually able to receive a message or the message sent by it is received by an out-neighbor depends on the following salient feature of radio networks: If two in-neighbors of a node transmit any message in the same round, then a collision occurs and the receiving node receives nothing. Furthermore, the receiving node cannot distinguish it from the case when all of its in-neighbors are silent. It is this feature of radio networks that makes even a simple task of broadcasting non-trivial. Two metrics by which the complexity of broadcasting and gossiping protocols are usually measured are round complexity and message complexity. These metrics are typically defined in terms of the number of nodes in the network n, the diameter of the network, maximum in-degree of a node etc. The most important and prevalent complexity measure under which broadcasting and gossiping problem has been studied is round complexity, which is the criterion used to calibrate protocols in this work. The broadcasting and gossiping problem in radio networks have been studied under different assumptions about the knowledge of topology. In the centralized setting, the topology of the network is known to all the nodes. In a stricter model, nodes are given the labels of their immediate neighbors and the more general setting is one when the network is directed and nodes know only their own labels and the number of nodes in the network. However, the ad-hoc nature of the radio networks is most closely modeled by the setting in which even the number of nodes in the radio network is not known. Radio nodes have batteries which run for a short duration and whose life is largely restricted by the number of radio transmissions made by a node. Once the battery is consumed the radio node itself may be discarded or forgotten. Older nodes lying in the field for long duration are likely to die out, may be ignored and stop participating in future computations. In a truly dynamic setting, nodes do not have any estimate of the size of the network to which they belong. Also, many nodes in the field may not respond, may possess small labels which cannot be reused. Thus, the ad-hoc nature of radio networks imposes the constraint that the nodes are allowed to take polynomially large labels i.e., within some range [1, . . . , n c ], for some large constant c (The reader is referred to [43] for a detailed motivation for studying the case of large labels). A protocol designed for the vanilla setting can be adapted to work for this model, by running it for multiplicatively larger estimates on the size of the network in every new phase. For this phase-wise design methodology nodes cannot determine when a particular task has completed. Hence, it is required that nodes receive some form of an ACK (acknowledgment) or NACK (negative acknowledgment) about the completion of certain task at the end of a phase. In the literature, these problems for completely unknown networks are called acknowledged broadcasting and acknowledged gossiping. They are known to be impossible, to achieve, for arbitrary n. If n is guaranteed to be greater than 1, then possibility results are known, [8] , [42] . Secondly, the impossibility result in [20] rigorously formalizes the intuition that for acknowledged broadcasting, players must wake-up spontaneously and start participating on their own. Thus, we assume sponatenous transmissions and n > 1. The question of acknowledged broadcasting and gossiping was initially formulated and explored in [8] . Most recently, [44] and [20] considered this problem. [44] give protocols for acknowledged broadcasting (ARB) and acknowledged gossiping (ARG) for bidirectional and strongly connected networks. For ARB on bidirectional and strongly connected networks, [44] present protocols of round complexity O(n) andÕ(n 4/3 ), respectively. For ARG, the authors design protocols of round complexity O(n lg 3 n) andÕ(n 4/3 ) for bidirectional and strongly connected networks, respectively. For strongly connected networks, [20] improve the round complexity for deterministic acknowledged broadcasting to O(n lg n lg lg n) rounds. Acknowledged protocols proposed in [8] , [42] , [44] and [20] , for the setting of small labels, are very inefficient when the nodes can take polynomially large labels; and not much useful in practice. From a theoretical point of view, the assumption of small labels, allows protocol designers to use a simple round-robin phase where all nodes transmit their IDs, in separate rounds corresponding to their labels and learn about their in-neighborhoods etc.. This considerably simplifies the construction of these protocols. However, when nodes The study of broadcasting has received considerably more attention then gossiping. For directed graphs, a series of works improved the trivial upper bound of O(n 2 ) for broadcasting (when nodes have small labels), to O(n 11/16 ) in [8] ,Õ(n 5/3 ) in [24] , O(n 3/2 ) in [10] , O(n lg 2 n) in [11] , O(n lg 2 D ) in [14] and most recently O(n lg n lg lg n) in [23] . [6] show that for any deterministic algorithm A for broadcasting in ad-hoc radio networks, there are networks on which A requires Ω(n lg n) rounds. The first sub-quadratic deterministic algorithm for the gossiping problem in ad-hoc radio networks was O(n 3/2 ) time algorithm proposed in [11] . Subsequently, [46] improved this bound by a poly-logarithmic factor obtaining O(n 3/2 ) bound. For small diameter D, the gossiping time was later improved in [22] toÕ(nD 1/2 ). These algorithms assume that the node labels are linear in n. [13] present aÕ(D∆ 2 )-time deterministic algorithm, which was improved toÕ(D∆ 3/2 ) in [22] , for polynomially large labels. [29] improved the result on deterministic gossiping fromÕ(n 5/3 ) in [28] toÕ(n 4/3 ) in [29] . An excellent survey of results on deterministic gossiping problem is presented by Gasieniec in [21] . For bounded size messages deterministic gossiping was studied in [9] and for unit size messages gossiping protocols were given in [26] and [41] . [11] propose an O(n lg 4 n) time randomized gossiping algorithm, which was improved to O(n lg 3 n) rounds in [40] and O(n lg 2 n) rounds in [14] . [8] , [42] , [44] study the problem of acknowledged broadcasting and gossiping. [20] improve a result in [44] and present a O(n lg n lg lg n)-time deterministic algorithm for acknowledged broadcasting. As pointed above the shortcoming of these works is that the nodes can take small labels only. For the centralized setting, the topology of the radio network is known to all the nodes of the network. For this setting, a deterministic broadcasting protocol of O(D lg 2 n) is given in [17] , for networks of radius D. For the centralized setting, a lower bound of Ω(D + lg 2 n) rounds was proved in [1] . This was shown to be tight in a recent work [37] , where a matching upper bound of O(D + lg 2 n) rounds was proved, after a series of improvements from O(D lg 2 n) rounds in [17] ), O(D lg n + lg 2 n) in [36] , O(D + lg 4 ) in [19] and O(D + lg 5 n) in [25] .

O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Who and what links to the Internet Archive The Internet Archive's (IA) Wayback Machine is the largest and oldest public Web archive and has become a significant repository of our recent history and cultural heritage. Despite its importance, there has been little research about how it is discovered and used. Based on Web access logs, we analyze what users are looking for, why they come to IA, where they come from, and how pages link to IA. We find that users request English pages the most, followed by the European languages. Most human users come to Web archives because they do not find the requested pages on the live Web. About 65 % of the requested archived pages no longer exist on the live Web. We find that more than 82 % of human sessions connect to the Wayback Machine via referrals from other Web sites, while only 15 % of robots have referrers. Most of the links (86 %) from Websites are to individual archived pages at specific points in time, and of those 83 % no longer exist on the live Web. Finally, we find that users who come from search engines browse more pages than users who come from external Web sites. A variety of research has been conducted for studying Web archives to answer questions related to user needs and to present Web archive data to users [22, 34, 43, 67] . However, no previous work has been carried out to answer these questions: What do Wayback Machine users look for in the context of languages of the pages they request? Why do users come to Web archives? Do they come because they cannot find the Web pages on the live Web, or do they come because they want a copy of a Web page at a specific time? Where do Web archive users come from? Who links to Web archives? How do sites link to Web archives? Do sites link deeply to specific archived pages or link to the repository? Why do sites link to the past? Is there a relationship between the referrer and the time spent in the archive? Is there a relationship between the referrer and the number of browsed archived pages?. The Internet Archive [39] is the first Web archiving initiative attempting global scope and currently holds over 360 billion Web pages with archives as far back as 1996 [46] . It allows traveling back in time for traversing archived versions of Web pages through the Wayback Machine [61] . In this paper, we examine the requests of Web archive users, both humans and robots, to gain insight into what users look for, in the context of the language of the requested pages, through an analysis of the server logs of the Internet Archive's Wayback Machine. We deduce the reason for using the Web archives by checking the status of requested Web pages on the live Web. We also provide an analysis of referring pages of human users to investigate how humans discover the Wayback Machine, why the referrers link to Web archives, and how they link to Web archives. Finally, we investigate if there is a relationship between the referrer and the session length and duration.. We found that users of Internet Archive's Wayback Machine request English pages the most, followed by several European languages. We also found that most human users come to the Wayback Machine via links or direct address presumably because they did not find the requested pages on the live Web. Of the requested archived pages, 65 % do not currently exist on the live Web, which we believe implies that many users come to Web archives because they do not find the Web pages on the live Web. From analyzing the referrers, we found that more than 82 % of human sessions have referrers, while only 15 % of robot sessions have referrers. We also found that 86 % of the referrers link deeply to archived pages at specific times, and of those 83 % no longer exist on the live Web. In terms of linking, there is an overall preference for linking to the recent past. Finally, we found that the users who come from search engines and the Internet Archive's home page have longer sessions in terms of the number of browsed pages than users who come from external Web sites. Most of the sessions that are composed of one request come from external web sites.. This paper is organized as follows. Definitions of important terms and a review of related work on Web usage mining and Web archive studies are presented in Sect. 2. Section 3 contains a description of the Wayback Machine's Web server logs, the sampling methodology, and the dataset we used in the analysis. The methodology of this study and the methodology of the analysis are presented in Sect. 4. Section 5 contains the results from analyzing the Wayback Machine access logs in terms of the content language of the requested pages and the existence of these pages on the live Web. Section 6 presents a detailed analysis of the referrers of human users. Future work and conclusions for the findings are presented in Sect. 7. To the best of our knowledge, no prior study has analyzed where Web archive users come from or what they look for in terms of the linguistic context. Furthermore, the usage of Web archives in general has not been widely studied. The characterization of search behavior and the information needs of Web archive users have been studied by Costa et al. [21, 22] based on quantitative analysis of the Portuguese Web Archive (PWA) search logs.. In a previous study [9] , we provided the first analysis of user access to a large Web archive. We discovered four basic access patterns for Web archives through analysis of Web server logs from the Internet Archive's Wayback Machine. In the study, we applied heuristics for robot detection after data filtering and found that robot sessions outnumber human sessions 10:1. Robots outnumber humans 5:4 in terms of raw, unfiltered requests, and 4:1 in terms of megabytes transferred.. Many studies have investigated what is missing from digital libraries and Web archives, in addition to the effect of this on the satisfaction of users' needs and expectations [17, 51, 60, 68] . In [60] , the Internet Archive's coverage of the Web was investigated. The results showed an unintentional international bias in the archive coverage through uneven representation of different countries in the archive. The reason of unbalanced representation of countries is visibility of the Websites (i.e., the number of inlinks of Websites). The results also showed that the language of a Website does not have an effect on how Internet Archive indexes it.. Ainsworth et al. [8] estimated the coverage of Web resources in Web archives in "How Much of the Web Is Archived?" They sampled 4,000 URIs from DMOZ, Delicious, Bitly, and search engines and measured their coverage in the public Web archives and the number and frequency of archived versions. They found that, according to the URI source, the archived percentage varies from 16 to 79 %.. AlSum et al. [10] studied the coverage of 12 Web archives on 3 data sets from the live Web, web server access logs of the archives, and fulltext search of the archives to create profiles for the 12 archives. They discovered that IA has the largest and widest coverage of all the archives. This finding matches our results of checking the coverage of other archives in Sect. 5.. Carmel et al. [17] suggest a tool to dynamically analyze the query logs of a digital library system, identify the missing content queries, and then direct the system to obtain the missing data.. We investigate what is missing through an analysis of requests with an HTTP 404 status in the Wayback Machine Web server logs.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I


Estimating 3D Human Shapes from Measurements The recent advances in 3-D imaging technologies give rise to databases of human shapes, from which statistical shape models can be built. These statistical models represent prior knowledge of the human shape and enable us to solve shape reconstruction problems from partial information. Generating human shape from traditional anthropometric measurements is such a problem, since these 1-D measurements encode 3-D shape information. Combined with a statistical shape model, these easy-to-obtain measurements can be leveraged to create 3D human shapes. However, existing methods limit the creation of the shapes to the space spanned by the database and thus require a large amount of training data. In this paper, we introduce a technique that extrapolates the statistically inferred shape to fit the measurement data using nonlinear optimization. This method ensures that the generated shape is both human-like and satisfies the measurement conditions. We demonstrate the effectiveness of the method and compare it to existing approaches through extensive experiments, using both synthetic data and real human measurements. Many applications require realistic 3D human shapes. For instance, 3D human models are used to design products that fit a target population. Typically, these shapes need to have certain characteristics or to be samples from a population. Although it is possible to digitize humans using 3D imaging technologies, it is impractical to find and scan suitable human subjects for each individual application. On the other hand, there is a long history of using anthropometric measurements to describe the human shape. These measurements are linear and curvilinear distances between anatomical landmarks or circumferences at predefined locations. In spite of providing limited shape information, they are readily available, and therefore widely used.. Intuitively, the linear measurements should encode information about the body shape. If accurate 3D human shape can be inferred from a simple set of measurements, traditional anthropometric data can be leveraged to create 3D datasets without resorting to expensive scanning equipment.. The early attempts at solving this problem deform a generic human model to fit the measurement data. However, the models thus obtained are not necessarily human forms because generating a human shape from a sparse set of measurements is an under-constrained problem. More sophisticated methods use knowledge of the human shape learned from a database of 3D scans. A statistical model can be built from a set of registered 3D scans and a relationship between the measurements and the shape space can be established. In doing so, detailed 3D shapes can be predicted from sparse and partial shape data. Apart from predicting 3D shapes from measurements [19, 1] , other partial shape information, such as marker positions [3] and 2D images [14, 7] , has also been used to reconstruct 3D shapes.. Existing methods that predict the 3D shapes using a statistical model limit the generated shapes to the space spanned by the shape model (more specifically, within two standard deviations of the shape variability) and local variations of human shapes that are outside this space cannot be predicted accurately. This means that these methods require a 3D database that accurately represents a target population (for instance, human subjects of different ethnicities and different weight classes must be present in the database). To apply these techniques, one must carefully choose a target population and acquire a representative database. In reality, the acquisition of a 3D anthropometry data that represents a target population well is complicated and expensive (the acquisition of the Civilian American and European Surface Anthropometry Resource took 4 years and cost $6 Million 1 ). In this paper, we address the problem of estimating 3D human body and face shapes given a set of anthropometric measurements. Our main goal, in contrast to previous work, is to predict shapes that are inside the space of human shapes, but still account for local variations not captured by the training data. This extrapolation allows us to create human shapes based on relatively small 3D databases.. As most of the previous approaches, our method does not take posture or expression changes into account. That is, we assume that all of the training data is in a standard pose. This scenario is commonly assumed since in a typical 3D anthropometry survey, the human subjects are asked to maintain a standard posture.. The rest of the paper is organized as follows. Section 3 gives an overview of the approach, and Section 4 outlines the details of a shape refinement step, which constitutes the main contribution of this paper. We aim for design applications in engineering where accuracy is essential. We show, through experiments, that straightforward application of existing techniques does not produce satisfactory results (Section 5). We conducted experiments based on human face and body shapes using both real and synthetic data. We conducted an extensive evaluation by estimating 600 face shapes and over 650 body shapes. In summary, we demonstrated experimentally that our method has the following properties.. • Our method estimates realistic body or face shapes that are outside of the learned shape space.. • Our method yields results that are more accurate than SGPLVM, and that, unlike feature analysis, always stay within the shape space of human body or face shapes.. • Our method accurately predicts local shape variations not present in the training set (which accounts for accurate predictions of the waist shapes in Figure 5 ).. • Our method yields visually pleasing results even when a small database is used for training. This is important in practice because the acquisition of a large database for training is costly.. • Even for inaccurate input measurements acquired by non-experts, our method is able to find visually consistent results.. • Our method is computationally efficient. The running time of the optimization steps is linear in the number of vertices. To predict one human body shape, our (non optimized) implementation takes about 35 seconds on a standard PC with a dual core CPU and 8GB of RAM. We presented a novel approach to estimate human body and face shapes based on measurements. We demonstrated that the approach can produce a large variety of likely shapes based on a relatively small training set and a small number of measurements. We showed experimentally that, unlike feature analysis, the approach always produces shapes that are inside the space of human shapes. Furthermore, the approach yields higher accuracy than SGPLVM. That is, unlike previous approaches, our approach predicts shape variations not present in the training data while maintaining a realistic human body shape. This allows to generate accurate body shape estimates based on simple modalities without the need to acquire a large-scale 3D database that represents the target population.. (a) (b) (c) (d) Figure 5 : Predicted body shapes: (a) shows the result using our approach, (b) shows the result using SGPLVM, (c) shows the result using feature analysis, and (d) shows the ground truth. Each mesh is shown using a color coding corresponding to the signed distance from the parameterized body scan that was used to compute the measurements in S real . Figure 7 . The first row shows the ground truth, the second row shows the result using our approach, the third row shows the result using SGPLVM, and the last row shows the result using feature analysis. This section reviews existing work that aims to estimate 3D human shapes based on partial input information. We categorize the related literature by the type of input data that is used to predict human shapes. This section demonstrates the effectiveness of our method using both synthetic experiments and experiments with real data.. We implemented the proposed algorithm using C++. The implementation uses Dijkstra's algorithm [10] to compute geodesic distances, the quickhull algorithm [5] to compute the convex hull to determine circumferences, and the limited-memory Broyden-FletcherGoldfarb-Shanno scheme [17] to solve the optimization problems. We choose these standard algorithms for their ease of use. To parameterize the database used for training, the efficient approach by Xi et al. [25] is employed.. We compare our results to the results obtained using feature analysis and to the results obtained by using a SGPLVM mapping from the space of the measurements to the PCA space of the models. Both approaches are reviewed in Section 2. We use the code by Ek et al. [12] to compute the SGPLVM.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Crossing textual and visual content in different application scenarios Abstract This paper deals with multimedia information access. We propose two new approaches for hybrid text-image information processing that can be straightforwardly generalized to the more general multimodal scenario. Both approaches fall in the trans-media pseudo-relevance feedback category. Our first method proposes using a mixture model of the aggregate components, considering them as a single relevance concept. In our second approach, we define trans-media similarities as an aggregation of monomodal similarities between the elements of the aggregate and the new multimodal object. We also introduce the monomodal similarity measures for text and images that serve as basic components for both proposed trans-media similarities. We show how one can frame a large variety of problem in order to address them with the proposed techniques: image annotation or captioning, text illustration and multimedia retrieval and clustering. Finally, we present how these methods can be integrated in two applications: a travel blog assistant system and a tool for browsing the Wikipedia taking into account the multimedia nature of its content. Information, especially digital information, is no longer monomodal: web pages can have text, images, animations, sound and video; we have audiobooks, photoblogs and videocasts; the valuable content within a photo sharing site can be found in tags and comments as much as in the actual visual content. Nowadays, it is difficult to visit a page within a popular social network without finding a large variety of content modes surrounded by a rich structure of social information such as profiles, interest groups, consumer behaviour or simple conversations. This major shift in the way we access content and what type of content we access is largely due to the connected, easily accessible, global nature of the internet. The democratization of the tools of production and delivery have also strongly contributed to this situation, e.g. low cost camera-phones combined with accessible publishing tools. This scenario poses a strong need for tools that enable interaction with multimodal information.. Multimodal information processing strongly needs trans-media similarity measures that can effectively bridge the gap between the co-existing modes. Such tools will enable applications whose relevance can already be perceived today: accessing an image repository from a textual query, automatic illustration, content creation and document generation, captioning, multimodal summarization, hybrid categorization and indexing, content personalization, etc. In this article, we explore such measures and propose two new approaches for hybrid text-image information processing, an important particular case of the more general multimodal scenario.. Within multimodal information processing an important family of approaches is constituted by the so-called "trans-media" pseudo-relevance feedback approaches (Section 3). The basic idea is to first use one of the media types to gather relevant multimedia information and then, in a second step, use the dual type to perform the final task (retrieve, annotate, etc). These approaches can be seen as an "intermediate level" fusion as the media fusion takes place after a first mono-media retrieval step based on mono-modal similarities (see Sections 2.1 and 2.2).. We describe two methods, both falling in the "trans-media" pseudo-relevance feedback category. In our proposed approaches, similarly to [21] , we need to define similarities between an aggregate of objects and a new multimodal object. In our first approach (Section 3.1), we build a model inspired by the mixture model [38] of the aggregate. In our second approach (Section 3.2), we define trans-media similarities as an aggregation of mono-modal similarities between the elements of the aggregate and the new multimodal object.. We first provide an overview of the state-of-the-art in hybrid text and image information processing, emphasizing work on trans-media relevance feedback (Section 1.1). Then we introduce our monomodal similarity measures for images (Section 2.1) and for text (Section 2.2). We then focus on our two main contributions (Section 3). An important part of our article is dedicated to show how these techniques can be applied to a number of scenarios such as unsupervised text illustration (Section 4.3.2); image annotation or captioning (Section 4.3.1); ranking and retrieval (Section 4.1); cross-media clustering and improved visualisation (Section 4.4). Finally, we share some details of a system we developed for assisting in the creation of travel blogs (TBAS) in Section 5.1. This system illustrates the way many of these techniques can interact in a real world content creation example. Similarly, we present another tool for browsing multimedia corpora, such as Wikipedia in Section 5.2. We have presented a framework for accessing multimodal data. First of all, the theoretical contribution is the extension of the principle of trans-media feedback, into a metric view: the definition of trans-media similarities. As it was shown, these new similarity measures of cross-content enables to find illustrative images for a text, to annotate an image, cluster or retrieve multi-modal objects. Moreover, the trans-media similarities are not specific to image and text: they can be applied to any mixture of media ( speech, video, text ) or views of an object. Most importantly, we have shown how these techniques can be used in two use cases: the travel blog assistant system and the multimedia browsing tool. These two applications stress the necessity of cross-media systems, where no monomedia systems can solve the user's problem, nor address all the different user's need at the same time.. recognition, particularly when dealing with uncontrolled environments. Prior to Xerox, several of his contributions in these fields were applied to a variety of scenarios including biometric solutions, data mining, CBIR and industrial vision. Dr

O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Recurrence

Relationships

for

the

Mean

Number

of

Faces

and

Vertices

for

Random

Convex

Hulls

A

general

recurrence

identity

(see

equation

below)

for

this

expected

count

is

conjectured.

Consider

the

experiment

where

points

P

P

P

n

are

placed

randomly

and

independently

in

R

d

(d

according

to

a

common

probability

law.

This

law

is

defined

by

the

(induced)

probability

measure

µ

defined

on

B

d

the

Borel

sets

of

R

d

Let

the

convex

hull

of

the

first

n

points

be

denoted

by

H

n

The

d-dimensional

volume

of

H

n

is

given

by

V

n

whilst

µ

n

is

defined

as

the

probability

content

(that

is,

µ-measure)

of

H

n

The

convex

hull

H

n

is

a

convex

polytope.

We

denote

the

number

of

i-faces

of

H

n

by

F

n,i

When

i

however,

we

follow

the

practice

of

other

authors

and

use

the

notation

N

n

F

for

the

number

of

vertices.

We

also

introduce

F

n

F

as

the

number

of

facets..

Combining

the

power

of

three

distinct

ideas

-the

Efron/Buchta

identity

an

integral

technique

of

Rényi/Sulanke

modified

to

suit

our

purpose,

and

an

identity

involving

µ

n

that

follows

from

recent

work

of

the

author

-we

derive

various

new

recurrence

identities

for

EN

n

EF

n

and

EF

To

be

more

precise,

we

note

that

these

identities

are

only

partial

recurrences

as

there

are

parity

conditions

on

them.

We

do

not,

however,

use

the

word

'partial'

in

further

descriptions..

Mostly

we

focus

on

the

case

where

µ

gives

zero

probability

mass

to

every

j-dimensional

hyperplane

(for

all

j

d)

and,

in

particular,

to

any

one-point

set.

This

implies

that

the

polytope

H

n

is

almost

surely

simplicial

with

dimension

equal

to

min(d,

n

We

refer

to

this

constraint

on

µ

as

the

hyperplane

condition;

we

note

that

it

is

weaker

than

absolute

continuity

with

respect

to

Lebesgue

measure

as

it

allows

µ

to

have

positive

mass

on

some

types

of

Lebesguemeasure-zero

sets.

For

example,

when

d

we

allow

a

measure

which

is

positive

on

a

curve

no

part

of

which

is

a

line-segment..

In

the

hyperplane-conditioned

case

our

results

are

as

follows.

For

vertices,

EN

n

n

if

n

d

whilst.

For

facets,.

Employing

the

Dehn-Sommerville

identities

and

in

combination

with

and

we

find

a

recurrence

for

(d

and

a

complete

list

of

recurrences

for

i-faces

when.

All

of

our

new

results

have

a

common

form,

namely,

for

i

d,.

This

suggests

to

us

that

The

paper

concludes

with

a

brief

discussion

of

the

difficulties

that

arise

when

µ

does

not

satisfy

the

hyperplane

condition.

The

discussion

suggests

that

this

condition

is

the

most

appropriate

for

the

current

study..

Some

detail

which

has

been

omitted

from

the

published

version

is

available

on

the

author's

website

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Regular Polytopes of Nearly Full Rank Abstract An abstract regular polytope P of rank n can only be realized faithfully in Euclidean space E d of dimension d if d ≥ n when P is finite, or d ≥ n − 1 when P is infinite (that is, P is an apeirotope). In case of equality, the realization P of P is said to be of full rank. If there is a faithful realization P of P of dimension d = n + 1 or d = n (as P is finite or not), then P is said to be of nearly full rank. In previous papers, all the at most four-dimensional regular polytopes and apeirotopes of nearly full rank have been classified. This paper classifies the regular polytopes and apeirotopes of nearly full rank in all higher dimensions.

O O O B I I O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O B I I O O O O O O O O O O O O B I I O O O O


Privacy-aware identity management for client-side mashup applications This paper concerns the problem of identity management in modern Web-2.0-based mashup applications. Identity management supports convenient access to information when mashups are used in sensitive environments, such an banking, investment and online shopping, by providing services such as single sign-on.We present Web2ID, a new identity management protocol tailored for mashup applications. Web2ID leverages a secure mashup framework and enables transfer of credentials between a service provider and a consumer. We also describe a new relay framework in which communication between two service providers is mediated by a relay agent within the mashup. We show that Web2ID is privacy-preserving and prevents service providers from learning a user's surfing habits.We present an implementation of Web2ID and the relay framework using a JavaScript-based library that executes within the browser. Our implementation does not require client-side changes and is therefore fully compatible even with legacy browsers. We also highlight the key challenges faced in creating a portable, inbrowser library to support identity management in mashups. Mashup applications integrate information from multiple autonomous data sources within the Web browser. For example, iGoogle allows users to create a personal page containing "gadgets" from multiple Web domains, such as NYTimes, Weather.com and Google Maps. As such, mashups have gained in popularity because they provide a seamless browsing experience.. Despite their popularity, mashups are still not in widespread use for sensitive Web applications, such as banking, investment, online shopping and bill payment. Such mashup applications currently require user authentication to prevent unauthorized access to sensitive information. A Web user who includes such sensitive applications in a mashup must authenticate herself individually to each of these applications. For example, mint.com and yodlee.com allow users to view a summary of their financial activities by accessing back-end services such as banks and credit card companies. However, they require the user to authenticate with each of these services and grant the mashup service provider access to her private financial information. Studies show that users who manage multiple Web identities often use weak passwords, or write them down to alleviate the burden of having to memorize their passwords for each domain-both of which can potentially compromise security.. Existing techniques to ease user authentication leverage federated identity management solutions, such as Single Sign-On (SSO). In conventional SSO, a user authenticates herself to an identity provider (IdP) website. The IdP allows the user to sign into other participating service provider (SP) 1 websites without requiring her to authenticate again. For example, suppose that Alice authenticates using a secure logon session with an identity provider IdP.com. She may later wish to access services provided at CarRental.com and Airline.com. Instead of requiring Alice to authenticate herself again to CarRental.com and Airline.com (the SPs), IdP.com could assert Alice's identity to these websites. IdP.com, which acts as the IdP in this case, can provide Alice's user name and other attributes that verify her identity to CarRental.com and Airline.com. Note that in this case, because of direct communication between the IdP and SPs, IdP.com may learn that Alice has accounts at CarRental.com and Airline.com and her usage pattern. Moreover, CarRental.com may query user's flight schedule (or other attributes) from Airline.com. However, using any conventional communication over network (e.g. HTTP) enables Airline.com to learn which car rental service is being used by the user.. Unfortunately, two key difficulties prevent existing identity management protocols from being directly applicable to modern Web-2.0-based mashup environments. First, these protocols implement SSO via a series of HTTP redirections within the user's browser. These redirections perform inter-domain communication between the IdP and SP and transmit the user's credentials from the IdP to the SP. However, redirections are ill-suited for stateful AJAX-based applications, such as Web desktops and Web-based office applications, because they involve unloading/reloading the application upon each redirection. Without application-level support, unloading/reloading operations will result in the loss of unsaved data. Second, the identity provider used to manage users' credentials and personal information causes privacy concerns. It can learn a lot about a user's online activities because IdPs are involved whenever a user authenticates herself to a service provider.. There have been several existing identity management work addressing IdP-related privacy concerns by anonymizing user credentials, defining privacy policies, or hiding a user's digital trail [4, 7, 11, 21, 23] . There are two main differences between these privacy-aware identity management solutions and our work. First, we study identity management in the client-side mashup environment through a secure and efficient in-browser framework. Second, we propose a novel single sign-on protocol without requiring the participation of a trusted party identity provider.. We present Web2ID, a new protocol for identity management (and SSO) in mashup applications. By leveraging a secure mashup framework, Web2ID enables transfer of credentials without requiring webpage redirections, and works seamlessly with AJAX-based Web-2.0 applications. We also describe a new relay mashup framework, based on which a trusted, client-side relay application can be built in the mashup to transmit credentials between providers. Our Web2ID protocol offers the following main benefits:. • Privacy. We protect user privacy by eliminating the requirement of a trusted party identity provider in online single sign-on process. To realize this property, we utilize publickey cryptography, in our authentication protocol. Moreover, we provide a client-side communication framework called mashlet relay which enables a service provider to send a query to another service provider without revealing its identity. A mashlet is a HTML page hosted by an iframe in the browser (described in Section 2). The mashlet-relay framework protect user privacy in mashup environments because service providers that host user's data cannot learn how user consumes her data. This feature is especially important when the user wants to provide her identity attributes (certified by a trusted party) to another service provider.. • Compatibility with legacy browsers and modern AJAX oriented mashups. Our framework is implemented as a JavaScript library that is incorporated with mashup applications. It does not require browser modifications or specialized plugins to operate and is fully portable across browsers and execution platforms. We illustrate the portability of our framework by incorporating it with several popular browsers, including Firefox, Opera, Apple Safari, IE and Google Chrome. Moreover, we avoid using HTTP redirections for communication; consequently, our protocol is compatible with modern AJAX-based Web applications.. Our implementation of the relay framework required inbrowser support for both symmetric and asymmetric cryptography in the form of a JavaScript library. We highlight the key difficulties in creating such a library for a legacy browser and also consider this library as an independent contribution of this paper. As mashup applications increase in popularity, we expect that they will also be used with sensitive Web services, such as financial and banking applications. When mashups are used in such scenarios, it is key to provide features such as identity management and SSO. Existing identity management protocols are ill-suited for modern AJAX-based Web applications This paper presented Web2ID, an identity management protocol for mashup applications. Web2ID preserves the privacy of the end user and eliminates the need for a trusted identity provider in the online single sign-on process. We described how this feature can be realized with conventional public-key cryptography. We also described a mashlet-relay framework that enables efficient yet indirect communication between two server mashlets via a local relay mashlet controlled by the user. Such a relay framework allows for attribute exchange without disclosing the user's surfing habits to service providers. Our implementation of Web2ID and the relay framework is implemented as an in-browser library and is fully compatible with commodity browsers. Our Web2ID protocol can be realized with any secure mashup frameworks. They provide general infrastructure and environments for content providers to communicate in our identity management applications. There have been a couple of recent work that proposed secure mashup solutions including MashupOS [25] , SMash [15] , PostMessage method [3] , and OMOS [27] . The main goal of these solutions is two-fold: to isolate contents from different sources in sandbox structures such as frames and to achieve frame-frame communication. SMash [15] uses the concepts in publish-subscribe systems and creates an efficient event hub abstraction that allows the mashup integrator to securely coordinate and manage contents and information sharing from multiple domains. SMash mashup integrator (i.e., the event hub) is assumed to be trusted by all the web services. MashupOS [25] applies concepts in operating systems in mashup and develops sophisticated browser extensions and environments that enable the separation and communication of frames similar to inter-process communication management in the operating system. As mentioned earlier, the OpenMashupOS (OMOS) framework contains a key-based protocol providing secure frameto-frame communication [27] .. Camenisch et al. presented the architecture of PRIME (Privacy and Identity Management for Europe), which implements a technical framework for processing personal data [7] . PRIME focuses on enabling users to actively manage and control the release of their private information. Privacy policies for liberty single sign-on [17, 8] have been presented [21] by Pfitzmann. The paper identifies a number of privacy ambiguities in Liberty V1.0 specifications [18] and propose privacy policies for resolving them. A good article on the issues and guidelines for user privacy in identity management systems was written by Hansen, Schwartz, and Cooper [12] .. In the federated identity management (FIM) solution by Bhargav-Spantzel et al., personal data such as a social security number is never transmitted in cleartext to help prevent identity theft [4] . Commitment schemes and zero-knowledge proofs are used to commit data and prove the knowledge of the data. BBAE is the federated identity-management protocol proposed by Pfitzmann and Waidner [23] . They gave a concrete browser-based single sign-on protocol that aims at the security of communications and the privacy of user's attributes. Goodrich et al. proposed a notarized FIM protocol that uses a trusted third-party, called notary server, to effectively eliminate the direct communication between identity provider and service provider [11] . The main difference with these proposed privacy-aware ID management solutions and our approach is that we study ID management in the client-side mashup environment through a novel and efficient mashlet relay framework.. In the access control area, the closest work to ours is the framework for regulating service access and release of private information in web-services by Bonatti and Samarati [5] . They study the information disclosure using a language and policy approach. We designed cryptographic solutions to control and manage information exchange. Another related work aiming to protect user privacy in web-services is the point-based trust management model [26] , which is a quantitative authorization model. Point-based authorization allows a consumer to optimize privacy loss by choosing a subset of attributes to disclose based on personal privacy preferences. The above two models mainly focus on the client-server model, whereas our architecture include two different types of providers. In this section we report on the performance of in-browser cryptographic operations that are required for the implementation of Web2ID. Our goal is to study feasibility and overhead of using in-browser cryptographic operations. We ran experiments on a machine with the following configurations. Intel The most expensive cryptographic operation that is required by Web2ID is asymmetric-key generation. Figure 6 shows the runtime of our RSA keypair generation function for keys of size 512 and 1024 bits. Since asymmetric key generation is a probabilistic process, the values reported are averaged results over ten runs. As this Figure shows, Google Chrome, which uses a fast JavaScript Engine (V8), generates a 1024-bit key pair in under 4 seconds. The slowest browser was IE, which took about one minute to generate a 1024-bit key pair. Because key generation is a one-time operation and the browser stays responsive during this time, we feel that this delay is acceptable. Figure 7 shows the performance of RSA encryption/decryption using keys of length 1024 bits. As expected, decryption is more costly compared to encryption and the performance is quite reasonable for web applications. Of the browsers that we tested, Google Chrome had the best performance (less than 100ms for decryption using 1024-bit key).

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A New Lower Bound on the Maximum Number of Satisfied Clauses in Max-SAT and its Algorithmic Applications AbstractA CNF formula is unit-conflict free (UCF) if it contains no pair of conflicting unit clauses. Lieberherr and Specker (J. ACM 28, 1981) showed that for each UCF CNF formula with m clauses we can simultaneously satisfy at leastφm clauses, whereφ = ( √ 5 − 1)/2. We improve the LieberherrSpecker bound by showing that for each UCF CNF formula F with m clauses we can find, in polynomial time, a subformula F ′ with m ′ clauses such that we can simultaneously satisfy at leastφm + (1 −φ)m ′ + (2 − 3φ)n ′′ /2 clauses (in F ), where n ′′ is the number of variables in F which are not in F ′ . We consider two parameterized versions of MAX-SAT, where the parameter is the number of satisfied clauses above the bounds m/2 and m( √ 5 − 1)/2. The former bound is tight for general formulas, and the later is tight for UCF formulas. Mahajan and Raman (J. Algorithms 31, 1999) showed that every instance of the first parameterized problem can be transformed, in polynomial time, into an equivalent one with at most 6k + 3 variables and 10k clauses. We improve this to 4k variables and (2 √ 5 + 4)k clauses. Mahajan and Raman conjectured that the second parameterized problem is fixed-parameter tractable (FPT). We show that the problem is indeed FPT by describing a polynomial-time algorithm that transforms any problem instance into an equivalent one with at most (7 + 3 √ 5)k variables. Our results are obtained using our improvement of the Lieberherr-Specker bound above. Let F = (V, C) be a CNF formula, with a set V of variables and a multiset C of non-empty clauses, m = |C| (i.e., m is the number of clauses in C; each clause is counted as many times as it appears in C), and sat(F ) is the maximum number of clauses that can be satisfied by a truth assignment. With a random assignment of truth values to the variables, the probability of a clause being satisfied is at least 1/2. Thus, sat(F ) ≥ m/2 for any F . This bound is tight when F consists of pairs of conflicting unit clauses (x) and (x). Since each truth assignment satisfies exactly one clause in each pair of conflicting unit clauses, it is natural to reduce F to the unit-conflict free (UCF) form by deleting all pairs of conflicting clauses. If F is UCF, then Lieberherr and Specker [11] proved that sat(F ) ≥φm, whereφ = ( √ 5 − 1)/2 (golden ratio inverse), and that for any ǫ > 0 there are UCF CNF formulae F for which sat(F ) < m(φ + ǫ). Yannakakis [19] gave a short probabilistic proof that sat(F ) ≥φm by showing that if the probability of every variable appearing in a unit clause being assigned true iŝ ϕ (here we assume that for all such variables x the unit clauses are of the form (x)) and the probability of every other variable being assigned true is 1/2, then the expected number of satisfied clauses isφm.. A formula. ′ denotes the subformula obtained from F by deleting all clauses of F ′ . A formula F = (V, C) is called expanding if for each X ⊆ V , the number of clauses containing at least one variable from X is at least |X| [17] . It is known (this involves so-called matching autarkies, see Section 2 for details) that for each CNF formula F = (V, C) a subformula F ′ = (V ′ , C ′ ) can be found in polynomial time such that sat(F ) = sat(F \F ′ )+|C ′ | and the subformula F \F ′ is expanding. In this paper, the main technical result is that sat(F ) ≥φ|C|+ (2 − 3φ)|V |/2 for every expanding UCF CNF formula F = (V, C). Combining this inequality with the previous equality for sat(F ), we conclude that for each UCF CNF formula. The last inequality improves the Lieberherr-Specker lower bound on sat(F ). Mahajan and Raman [14] were the first to recognize both practical and theoretical importance of parameterizing maximization problems above tight lower bounds. (We give some basic terminology on parameterized algorithms and complexity in the next section.) They considered Max-SAT parameterized above the tight lower bound m/2:. SAT-A(m/2) Instance: A CNF formula F with m clauses. Parameter: A nonnegative integer k. Question: Decide whether sat(F ) ≥ m/2 + k.. Mahajan and Raman proved that SAT-A(m/2) is fixed-parameter tractable by obtaining a problem kernel with at most 6k + 3 variables and 10k clauses.. We improve on this by obtaining a kernel with at most 4k variables and 8.47k clauses.. Sinceφm rather than m/2 is an asymptotically tight lower bound for UCF CNF formulae, Mahajan and Raman [14] also introduced the following parameterization of Max-SAT:. SAT-A(φm) Instance: A UCF CNF formula F with m clauses. Parameter: A nonnegative integer k. Question: Decide whether sat(F ) ≥φm + k.. Mahajan and Raman conjectured that SAT-A(φm) is fixed-parameter tractable. To solve the conjecture in the affirmative, we show the existence of an O(k)-variable kernel for SAT-A(φm). This result follows from our improvement of the Lieberherr-Specker lower bound.. The rest of this paper is organized as follows. In Section 2, we give further terminology and notation and some basic results. Section 3 proves the improvement of the Lieberherr-Specker lower bound on sat(F ) assuming correctness of the following lemma: if F = (V, C) is a compact CNF formula, then sat(F ) ≥φ|C| + (2 − 3φ)|V |/2 (we give definition of a compact CNF formula in the next section). We prove this non-trivial lemma in Section 4. In Section 5 we solve the conjecture of Mahajan and Raman [14] in the affirmative and improve their result on SAT-A(m/2). We conclude the paper with discussions and open problems. A CNF formula I is t-satisfiable if any subset of t clauses of I can be satisfied simultaneously. In particular, a CNF formula is unit-conflict free if and only if it is 2-satisfiable. Let r t be the largest real such that in any t-satisfiable CNF formula at least r t -th fraction of its clauses can be satisfied simultaneously. Note that r 1 = 1/2 and r 2 = ( √ 5 − 1)/2. Lieberherr and Specker [12] and, later, Yannakakis [19] proved that r 3 ≥ 2/3. Käppeli and Scheder [9] proved that r 3 ≤ 2/3 and, thus, r 3 = 2/3. Král [10] [8] showed that lim t→∞ r t ≤ 3/4 and Trevisan [18] proved that lim t→∞ r t = 3/4 (a different proof of this result is later given by Král [10] ).. In the preliminary version of this paper published in the proceedings of IPEC 2010 we asked to establish parameterized complexity of the following parameterized problem: given a 3-satisfiable CNF formula F = (V, C), decide whether sat(F ) ≥ 2|C|/3 + k, where k is the parameter. This question was recently solved in [7] by showing that the problem has a kernel with a linear number of variables. Unlike this paper, [7] uses the Probabilistic Method. Similar question for any fixed t > 3 remains open.

O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O