Proactive AP Selection Method Considering the Radio Interference Environment In the near future, wireless local area networks (WLANs) will overlap to provide continuous coverage over a wide area. In such ubiquitous WLANs, a mobile node (MN) moving freely between multiple access points (APs) requires not only permanent access to the Internet but also continuous communication quality during handover. In order to satisfy these requirements, an MN needs to (1) select an AP with better performance and (2) execute a handover seamlessly. To satisfy requirement (2), we proposed a seamless handover method in a previous study. Moreover, in order to achieve (1), the Received Signal Strength Indicator (RSSI) is usually employed to measure wireless link quality in a WLAN system. However, in a real environment, especially if APs are densely situated, it is difficult to always select an AP with better performance based on only the RSSI. This is because the RSSI alone cannot detect the degradation of communication quality due to radio interference. Moreover, it is important that AP selection is completed only on an MN, because we can assume that, in ubiquitous WLANs, various organizations or operators will manage APs. Hence, we cannot modify the APs for AP selection. To overcome these difficulties, in the present paper, we propose and implement a proactive AP selection method considering wireless link condition based on the number of frame retransmissions in addition to the RSSI. In the evaluation, we show that the proposed AP selection method can appropriately select an AP with good wireless link quality, i.e., high RSSI and low radio interference. Wireless local area networks (WLANs) based on the IEEE 802.11 specification [1] provide high data transmission and simple, low-cost installation. For this reason, WLANs have been spreading rapidly in both private and public spaces, so that these WLANs will overlap to provide continuous and wide coverage as the underlying basis of ubiquitous networks. In such ubiquitous WLANs, mobile nodes (MNs) can access the Internet from everywhere and at anytime.. In WLANs, an MN requires not only permanent access to the Internet, but also seamless movement between access points (APs) without degradation of communication quality, i.e., seamless mobility is essential. Furthermore, in such ubiquitous WLANs, each AP will independently provide wireless Internet connectivity based on IEEE 802.11 technology. That is, the APs have a different IP subnet due to independent management of different organizations and operators. In such a situation, if a mobility support technology is developed and standardized for APs in the future, it will be difficult to replace all APs, which have been spreading, with new APs that support mobility technology. Moreover, since existing APs may not be able to accept such technologies due to restrictions such as lower CPU performance or less memory, update of APs' software for supporting mobility technology is also not realistic. Therefore, it is desirable to provide a seamless mobility technology without modification of APs. To achieve such seamless mobility, the following two requirements must be satisfied: (1) selection of an AP with better performance from among multiple candidate APs and (2) preservation of communication quality during handover. For (2), we proposed a handover management scheme based on the number of frame retransmissions [2] - [4] . In the proposed scheme, an MN is assumed to move between WLANs with different IP subnets. In [2] , we first employed multihoming architecture to prevent a disruption period due to handover processes. That is, since an MN with two WLAN interfaces (a multi-homing MN) can connect to two APs before starting handover, an MN never experiences a disruption period due to handover processes. Next, to properly switch the two associating APs based on each wireless link quality, the number of frame retransmissions was introduced as an indicator for detecting the wireless link condition. Although the Received Signal Strength Indicator (RSSI) is generally used as an indicator of a wireless link quality, we showed that the RSSI is insufficient to detect wireless link condition because it is incapable of detecting the degradation of communication quality due to radio interference [5] . On the other hand, we showed that the number of frame retransmissions could promptly and reliably detect the performance degradation due to reduction of the RSSI and radio interference. Therefore, the proposed handover management method based on the number of frame retransmissions can preserve communication quality during a handover.. Selection of an AP with better performance from among multiple candidate APs, however, remains unresolved. For example, in the method proposed in [2] , even if an MN has two WLAN interfaces to eliminate a disruption period due to handover process, there is no guarantee that the MN can select an AP with better performance for a Copyright c 2009 The Institute of Electronics, Information and Communication Engineers handover. In ubiquitous WLANs, the MN may find multiple candidate APs at one time and needs to select an appropriate AP from among them. At this time, if an AP of good quality is not selected appropriately, the communication quality may degrade after a handover. In the current general AP selection, an MN selects an AP based on the strongest RSSI. However, since numerous APs and MNs will exist in high-density ubiquitous WLANs, radio interference, which degrades communication quality, occurs frequently due to both the lack of the number of channels and heavy traffic in the AP. Thus, in order to achieve seamless mobility, it is essential that an AP selection consider not only RSSI reduction but also radio interference caused by other WLAN devices.. In the present paper, we propose a new proactive AP selection method based on RSSI and frame retransmissions and then demonstrate the experimental results of a prototype system. The proposed AP selection method enables an MN to select an AP with better performance taking radio interference into consideration by exploiting the number of frame retransmissions in addition to the RSSI. Note that, in this paper, we especially focus on the radio interference caused by packet transmission from other WLAN devices. Therefore, the proposed method is designed to avoid degradation of communication quality due to collisions between hidden terminals and/or simultaneous transmission from neighboring MNs. Furthermore, our handover management system [2] , [6] is extended to introduce our AP selection method, which requires no modification of AP.. The present paper is organized as follows. Section 2 surveys related research for existing AP selection methods. Section 3 describes the proposed proactive AP selection method. In Sect. 4, we then explain an implementation and system parameters used in the proposed AP selection method. Section 5 describes the experimental topology and presents the demonstration in a real environment and screenshots of the prototype system. After introducing our future work in Sect. 6, concluding remarks are presented in Sect. 7. In the present paper, we focus on a proactive AP selection for a radio interference environment. In the handover method we proposed in a previous study [6] , as described in Sect. 1, a multi-homed MN appropriately switches WLAN interfaces (WIFs) according to wireless link condition. formed on the WIF2 during communicating through the WIF1. On the other hand, after a handover, since the communication switched to the WIF2, the AP selection is next executed on the WIF1. That is, the AP selection is executed on an idle interface. In the present paper, we showed that our proposed method can select an AP with better performance with high RSSI and low radio interference. However, to adapt the method to more realistic environments, the following problems remain. We here describe them as the future work. a) APs with Auto-Rate Fallback (ARF): In the present experimental environment, we disabled ARF function because it makes our basic evaluation complex. However, since almost APs enable it in a real environment, we intend to study the influence of various ARF algorithms in order to demonstrate practical use in actual ubiquitous WLAN environment. b) Network load: Since our proposed method employs an active scan to collect the number of frame retransmissions, it may contribute to network load. In the present configuration, 50 probe packets with 1,500-byte size are sent in 3-milliseconds interval at every 5 seconds, that is the network load generated by one MN is 120 (= (8 × 5 )/1000) kbps. As the network load increases depending on the number of MNs, it is important to reduce network traffic of probe packets. To solve the problem, we consider the following approach. An MN can capture frames sent by another MN even if the frames are not destined for itself. As proposed in [14] , a representative MN among MNs associating with an AP sends probe packets. Then, MNs around the representative MN detect condition of an AP based on the captured frames. Thus, this approach has a possibility to be able to reduce the network load. In the present paper, in order to select an AP with better performance from among multiple candidate APs in ubiquitous WLANs, we proposed a proactive AP selection method based on frame retransmissions and the RSSI. In an AP selection based on only the RSSI, an MN cannot always select an AP with better performance in ubiquitous WLANs, because the RSSI alone cannot detect the degradation of wireless link quality due to radio interference. We therefore used the number of frame retransmissions as an index for detecting radio interference in addition to the RSSI and then proposed an AP selection method for the proposed handover management system. Moreover, to evaluate its effectiveness in a real environment, we also implemented the proposed AP selection method on a prototype system. Experimental results in a real environment revealed that an MN could avoid an AP disturbed by radio interference and select the AP with a good wireless link condition due to the number of frame retransmissions. Therefore, we consider that the number of frame retransmissions has potential as an effective metric to select an AP with low radio interference. So far, there have been numerous discussions on AP selection for improving the communication performance of MNs in WLANs. As described in Sect. 1, in ubiquitous WLANs, since an MN must be able to freely connect with all APs for an inter-domain handover, it is desirable that an AP is not modified in order to maintain compatibility with existing APs. Almost all existing AP selection methods [7] - [9] , however, necessitate some modifications of APs, e.g., additional information is needed in the beacon frame transmitted from the AP. Moreover, the modification needs to be implemented in both an AP and an MN. Such approaches have focused on the enhancement of communication performance in some limited areas where a network operator can manage the all APs. However, if the modified APs are introduced into ubiquitous WLANs, MNs without the modification may not be able to connect to the modified APs or obtain sufficient performance for AP selection. Thus, in the present paper, we focus on an AP selection method with no modification of an AP, i.e., only an MN is modified.. In [10] , [11] , AP selection methods only on an MN were proposed. In [10] , the proposed method measures potential uplink/downlink bandwidth by exploiting beacon frames. However, the experiments were carried out under low noise conditions only, and their effectiveness under radio interference conditions have not been investigated. On the other hand, although the method proposed in [11] selects an AP with the best quality using active scanning, the authors did not focus on periodical AP selection. Continuous selection of an AP with better performance is essential for inter-domain handover in ubiquitous WLANs.. In ubiquitous WLANs, communication quality on MNs could degrade due to radio interference and hidden mobile nodes. A number of studies [12] , [13] proposed methods to avoid such types of degradation. In [12] , the authors showed the communication performance under radio interference and proposed an AP selection scheme considering radio interference. However, as this scheme is an extension of [9] , the modification of an AP is still necessary. On the other hand, [13] explained that the effects from hidden mobile nodes severely impacts throughput degradation. In the method proposed herein, although modification of an AP is unnecessary, the method is applied to only IEEE 802.11e, which has not yet become widespread. Therefore, in the present paper, we focus on a proactive AP selection method considering the wireless link condition with no modification of APs for inter-domain handover. In this section, we describe the details of our implementation. We first explain the implementation environment. We employed CentOS 4.3 with Linux kernel version 2.6.9 as an operating system and a madwifi driver as a WLAN interface driver. Note that the madwifi driver can obtain the number of frame retransmissions per packet on an Atheros chipset. In order to obtain the number of frame retransmissions, we select a laptop PC (ThinkPad X60) with a built-in WLAN interface (P/N: 40Y7028) employing an Atheros chipset. In addition, in the proposed method, since we focus on a multihomed MN, i.e., an MN equipped with two WIFs, a WIF of a PC card type (corega WLCB54AG2) is prepared as another WIF.. As described in Sect. 1, the proposed AP selection method requires no modification of an AP. That is, the proposed AP selection method only requires modification of an MN. Figure 4 shows the architecture of the proposed AP selection method on an MN. Note that our AP selection method is implemented as an extension of on the prototype system described in [6] . In [6] , the prototype system uses a shared memory to collect the number of frame retransmissions. A handover manager on the transport layer then obtains the number of frame retransmissions from the shared memory and controls the execution of handovers based on the information. That is, the shared memory connects the transport layer with the MAC layer (cross-layer architecture). In the cross-layer mechanism used herein, whenever a data frame is successfully transmitted, i.e., an MN receives an ACK frame on the MAC layer, the modified madwifi driver writes the number of frame retransmissions to the shared memory. The shared memory is allocated for each WIF and forms a ring buffer for storing the number of frame retransmissions. As depicted in Fig. 4 , since our AP selection mechanism works as a daemon process in userland, we also implement a socket to obtain the number of frame retransmissions in the shared memory from userland applications. Moreover, since the AP selection mechanism cooperates with the proposed handover management system, we also implement a function to control the execution of handovers during the AP selection process.

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Robust Authentication Scheme between User and Remote Autonomous Object in Telecommunications System Autonomous objects represent active database objects which can be distributed over the Internet. This paper proposes a robust authentication scheme for the remote autonomous object based on AES (Advanced Encryption Standard) symmetric cryptosystem. Compared with related schemes, the proposed scheme not only resists various security attacks but also provides computation and communication efficiency. In the telecommunications system environment, a remote autonomous object acts with its own thread of control. In general, the conduct of an autonomous object is defined by methods, rules and dynamic constraints [1] , [2] . Therefore, it needs to communicate securely and authenticate between a user and the remote autonomous object [3] . The authentication scheme is commonly used to verify the identities of users. Remote access control is one of the important applications to ascertain whether the user is legal and whether he/she can access the remote resources.. In 2003, Novikov-Kiselev [4] proposed an authentication scheme of the user from the remote autonomous object with public key cryptosystem [5] which is applicable to perform secure authentication between the user and the remote autonomous object in the telecommunications system. However, Yang et al. [6] pointed out that the scheme is not secure against man-in-the-middle attack. That is, a certain attacker can displace a user's identity by performing the attack. Awasthi [7] also pointed out that the scheme is not secure against man-in-the-middle attack and reflection attack. This paper proposes a new authentication scheme based on the AES symmetric cryptosystem to overcome such security problems of the Novikov-Kiselev scheme. We adopt time-stamp techniques to prevent the man-inthe-middle attack and the reflection attack. We also adopt the AES symmetric cryptosystem to provide computation efficiency. Moreover, the proposed scheme needs only three communication rounds. Therefore, it can reduce two communication rounds compared with Novikov-Kiselev's scheme. As a result, the proposed scheme resists various security attacks, while also providing computation and communication efficiency because it can be executed faster than Novikov-Kiselev's. This paper proposed a new authentication scheme of the user from the remote autonomous object that overcomes the weaknesses of the Novikov-Kiselev scheme. The proposed scheme is based on the AES symmetric cryptosystem to provide better computational efficiency than that of the Novikov-Kiselev scheme. Moreover, the proposed scheme requires three communication rounds. As a result, the proposed authentication scheme resists various security attacks, while also providing more efficiency because it can be executed faster than Novikov-Kiselev scheme.

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Bounds from a Card Trick We describe a new variation of a mathematical card trick, whose analysis leads to new lower bounds for data compression and estimating the entropy of Markov sources.Keywords: empirical entropy, estimating entropy, Markov sources Several years ago, an article in the popular press [1] described the following mathematical card trick: the magician gives a deck of cards to an audience member, who cuts the deck, draws six cards and lists their colours; the magician then says which cards were drawn. The key to the trick is that the magician prearranges the deck so that the sequence of the cards' colours is a substring of a binary De Bruijn cycle of order six, i.e., so that every sextuple of colours occurs at most once. Although the trick calls only for the magician to name the cards drawn, he or she could also name the next card, for example, with absolute certainty. At the time we ran across the article, we were studying empirical entropy, and one way to define the kth-order empirical entropy of a string s is as our expected uncertainty about the character in a randomly chosen position when given the preceding k characters [2] . After reading the trick's description, it occurred to us that the kth-order empirical entropy of any De Bruijn cycle of order at most k is 0. Using this and other properties of De Bruijn cycles, we were able to prove several lower bounds for data compression [3, 4] . For example, since σ-ary De Bruijn cycles of order k have length σ k , there arecounting argument proves the following theorem.Theorem 1 (Gagie, 2006 [6]). If k ≥ log σ n then, in the worst case, we cannot store a σ-ary string s of length n in λnH k (s) + o(n log σ) bits for any coefficient λ.In this paper we consider a variation of the trick described above, that has led us to some new bounds. This time, suppose the magician does not bother to prearrange the deck, but shuffles it instead and has the audience member draw seven cards; after the audience member lists the cards' colours, the magician has him or her replace the cards, cut the deck again and return it; the magician

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Test data compression and test time reduction using an embedded microprocessor Abstract-Systems-on-a-chip (SOCs) with many complex intellectual property cores require a large volume of data for manufacturing test. The computing power of the embedded processor in a SOC can be used to test the cores within the chip boundary, reducing the test time and memory requirements. This paper discusses techniques that use the computing power of the embedded processor in a more sophisticated way. The processor can generate and reuse random numbers to construct test patterns and selectively apply only those patterns that contribute to the fault coverage, significantly reducing the pattern generation time, the total number of test applications and, hence, the test time. It can also apply deterministic test patterns that have been compressed using the characteristics of the random patterns as well as those of the deterministic patterns themselves, which leads to high compression of test data. We compare three fast run-length coding schemes which are easily implemented and effective for test-data compression. We also demonstrate the effectiveness of the proposed approach by applying it to some benchmark circuits and by comparing it with other available techniques.Index Terms-Built-in self test (BIST), data compression/decompression, embedded core testing, processor-based testing, random pattern generation, system-on-a-chip (SOC), test time. We have proposed a technique that can reduce the number of test applications by selectively applying those random patterns that contribute to the fault coverage. The technique can be easily combined with the random number reusing method to reduce the required total number of random words to be generated, significantly reducing the test time. We have also presented a new test pattern compression method in which test data can be decoded fast on the embedded processor in a SOC. The deterministic patterns are compressed by utilizing the random patterns as well as the deterministic patterns themselves. Experimental results on the ISCAS benchmark circuits show that the proposed technique is very efficient, and superior to other published approaches.

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Generalized Unequal Error Protection LT Codes for Progressive Data Transmission Abstract-The original design of standard digital fountain codes assumes that the coded information symbols are equally important. In many applications, some source symbols are more important than others, and they must be recovered prior to the rest. Unequal error protection (UEP) designs are attractive solutions for such source transmissions. In this paper, we introduce a more generalized design for the first universal fountain code design, Luby transform (LT) codes, that make it particularly suited for progressive bit stream transmissions. We apply the generalized LT codes to a progressive source and show that it has better UEP properties than other published results in the literature. For example, using the proposed generalization, we obtained up to 1.7-dB peak signal to noise ratio gain in a progressive image transmission scenario over the two major UEP fountain code designs.Index Terms-Fountain codes, iterative decoding, lossy channels, progressive sources, unequal error protection (UEP), unequal iteration time (UIT), unequal recovery time (URT). Fountain codes are a type of erasure-correcting code with simple encoding and decoding structures used both for pointto-point communications and for multicasting information. The initial design of such codes was aimed at recovering the entire information block, and therefore might not be the best choice when different parts of the data have different levels of importance, such as image or video files compressed in a progressive or scalable fashion. In this paper, we introduced a generalized version of UEP LT codes having a larger set of parameters and hence a more flexible rateless coding scheme. We also introduced a progressive transmission scheme using this generalized version of UEP LT codes. We compared the proposed scheme with two other major UEP LT codes in the literature for the progressive transmission scenario. Simulations show that the proposed coding scheme outperforms these previous schemes by providing improved UEP, URT, and UIT properties. As a future work, we plan to investigate the asymptotic analysis of the proposed generalization. Unequal protection for progressive sources is usually achieved by joint source channel coding (JSCC), in which more important contents are encoded with stronger codes (see [7] [8] [9] [10] ). Those studies assume that channel state information is available at the transmitter. When the channel erasure rate or the channel fading coefficients are unknown and nonuniform, one JSCC mechanism targets the worst-case error rate as the primary design criterion in choosing the optimal code rate/s [11] . An optimal fixed code rate for a good state is typically unable to perform well when the channel is bad. At the other end, when the code rate is optimized for the bad state, there will typically be many unnecessary redundant bits. Rateless codes, such as LT codes [3] , Raptor codes [12] , and Online codes [13] do not assume any information about the channel and, therefore, are good matches for transmitting data over time varying channels with unknown parameters. Similarly, such codes can be very good candidates for multicast transmissions because there is no prior assumption about the channels.. In the original study of LT codes, EEP of all the information symbols is assumed. The degree of a coded symbol d is assigned according to a suitable distribution called the degree distribution (DD). After choosing the degree for each coded symbol, a d-element subset of the information block is chosen randomly according to another distribution called the selection distribution (SD). It is shown in a series of studies [14] [15] [16] [17] that UEP LT codes can be produced simply by allowing coded symbols to make more edge connections with more important parts of the information bit stream with high probability by modifying the DD and SD. This way, the unrecovered symbol probability becomes lower for the high priority content of the original source. The ideas presented in those studies are successfully applied to various transmission scenarios [18] , [19] .. In [16] , a structured LT code graph is constructed. Then the proposed code is randomized using a degree assigner and a random selector. Although the terminology in [16] is different from that in [14] , the unequal protection is achieved essentially the same way using a fixed DD and a non-uniform SD. In other studies such as [20] , the authors introduced the use of overlapped windows to allow one to have a virtually extended block for superior performance compared to fixed-window encoding. Although the main objective was to increase the virtual block size of the LT codes for a better performance, it is recognized that such block size enhancement can be used to provide UEP. Later, a similar idea is used in [21] , called block duplication, for the EEP of a two-layer source. It is shown that under certain assumptions, the method of [21] provides slightly better performance than [14] . The gains reported in [17] over [14] are greater due to using different DDs for each window. This shows the combined choice of degree and SD had a great impact on the final performance of the fountain code. Last, the algorithm presented in [22] chooses degree-one coded symbols from the high priority class of source symbols, and the edge connections of degree-two coded symbols are selected non-uniformly similar to the weighted approach of [14] . Unequal protection is achieved by this slight modification and a fixed DD, and the rest of the encoding is exactly the same as in original LT coding. Although all of these studies ( [14] [15] [16] [17] [18] [19] [20] [21] [22] ) consider fountain codes with a UEP property for a given application scenario, a joint optimization of degree and SD remains untouched. In this section, we first review progressive source coding. Then, we review fountain codes and review the original encoding and decoding structures for LT codes. Last, we briefly discuss the previous UEP designs.

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Implementing the Main Functionalities Required by Semantic Search in Decision-Support Systems This paper exploits different semantic web technologies and builds a prototype of semantic web mashup functionality based on an architecture proposed by us. The main scope is to improve decision-making processes. In this paper, we are focusing on querying different ontologies in order to improve decision-making semantic search. As a conclusion, we demonstrate that in order to improve decision-making semantic search there is a need of special constructions that a query language must support. The main problem treated by the present article is: improving Decision Support Systems (DSS) means improving search which leads to the semantic interoperability problem.. There is a main problem and, in the same time, a controversy here. When discussing enterprise decision support systems data exists, data comes from different sources (internal and external to enterprise) but they are differently described. There is an open world (the Web) and a closed world (the enterprise). If in the open world we discuss search engines and queries made by Internet users on existent data from www space, in the closed world we discuss databases and answers to queries that are priory represented. In the first case the answers to queries seems to be poorly represented in the aspect of semantics, in the second case the answers seems to be perfectly represented but not relevant. In this closed world of enterprise, usually decision-makers need answers to queries formulated by them and these queries are ad-hoc, very often cannot be anticipated. Their answers need a mixture of information that comes from the both worlds.. Even if all computer-based solutions are well intended the practical use shows that user satisfaction is low due to many reasons analyzed by studies that have been realized. There are many identified reasons: poor maintainability, poor flexibility and less reusability (see [22] ). Much of the implicit information remains undiscovered thereby resulting in sub-optimal business decisions.. Web-based technologies are having a major impact on design, development, and implementation processes for all types of decision support systems (see [1] ).. Therefore it is our goal to solve this problem by this article. We consider in this study two main important reasons: (1) the possibility to apply knowledge in the decision-making moment at the decision-making place by the decision-maker; (2) semantic integration of information.. As a solution to the problem identified by us we propose practical implementations of semantic web search functionalities with existent Decision Support Systems. We present scenarios, technical requirements, and the architecture of a semantic web based application in decision support systems.. The scope of this paper is to present a method to improve search at the decision-making level. The main idea consists in using ontologies and semantic search technologies. The motivation is 908 S.C. Necula given by lack of interoperability and semantic consistency of different formats for the same content. In order to discuss differences of our approach we present the related achieved work in the field of adopting semantic web standards and the related achieved work in the field of developing applications in the context of decision-making.. Decision-making has been considered as one of the main concern in practice as in theory (see [19] , [3] , [13] and [10] Most of all previous studies focus on success factors of information systems (see [4] , [5] , [12] and [17] ).. Describing big data sets according to schema(s) and accessing data by overlapping schemas is the big problem that Semantic Web is trying to address. Its main applications are in the field of managing the currently linked data, learning how to extract information from currently linked data (Linked Data Browsers), sense-making of events (there is a lot of life data streams like tweets) in order to provide a solution able to gather, collect and analyze in real time a large number of live data streams (e.g. twits), to extract the information contained and to map any reference to both a) geographical location/point of interest, etc. and b) domain specific facts (e.g. music events or violence/ demonstration). The goal is to identify events happening in a specific area (e.g. a specific city) in a short time (e.g. some hours). Sense making of the events is provided via mapping events over location and time. There is a lot of use for social purposes like emergency operators, governmental bodies. We must say that Semantic Web is intended to be used by people in the way which web intended to be at its origins.. Semantic web technologies are by far most often used for data integration and for improving the search (see [9] ). The use of ontologies for knowledge sharing, heterogeneous database integration, and semantic interoperability has been long realized (see [8] , [11] and [18] ).. Metadata (data about data)/ ontology promises to overcome the problem of interoperability. An accepted standard for representing metadata should provide information about the syntax, the structure and the semantic context of data. Many standards have been proposed. For the moment the World Wide Web Consortium recommends RDF (S) (Resource Description Framework -Schema), and OWL (Ontology Web Language) for representing linked web data.. A number of query languages have been developed to query RDF and OWL. SPARQL (SPARQL Protocol and RDF Query Language) is currently the de facto standard RDF query language. Since OWL can be serialized as RDF, SPARQL can be used to query it. There is thus a need for an expressive OWL query language that supports comprehensive querying of OWL (see [14] ). These authors proposed SQWRL (Semantic Query-enhanced Web Rule Language) built on SWRL (Semantic Web Rule Language).. A mashup is a Web page or application that uses and combines data, presentation or functionality from two or more sources to create new services. Mashup techniques retrieve content from several sources to create a new service or application.

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Compact Formulations of the Steiner Traveling Salesman Problem and Related Problems The Steiner Traveling Salesman Problem (STSP) is a variant of the Traveling Salesman Problem (TSP) that is particularly suitable when dealing with sparse networks, such as road networks. The standard integer programming formulation of the STSP has an exponential number of constraints, just like the standard formulation of the TSP. On the other hand, there exist several known compact formulations of the TSP, i.e., formulations with a polynomial number of both variables and constraints. In this paper, we show that some of these compact formulations can be adapted to the STSP. We also briefly discuss the adaptation of our formulations to some closely-related problems. The Traveling Salesman Problem (TSP), in its undirected version, can be defined as follows. We are given a complete undirected graph G = (V, E) and a positive integer cost c e for each edge e ∈ E. The task is to find a Hamiltonian circuit, or tour, of minimum total cost. The best algorithms for solving the TSP to proven optimality, such as the ones described in [1, 28, 32] , are based on a formulation of the TSP as a 0-1 linear program due to Dantzig et al. [7] , which we present in Subsection 2.1 of this paper.. The Dantzig et al. formulation has only one variable per edge, but has an exponentially-large number of constraints, which makes cutting-plane methods necessary (see again [1, 28, 32] ). If one wishes to avoid this complication, one can instead use a so-called compact formulation of the TSP, i.e., a formulation with a polynomial number of both variables and constraints. A variety of compact formulations are available (see the surveys [18, 29, 31, 33] and also Subsection 2.2 of this paper).. When dealing with routing problems on real-life road networks, however, one often encounters the following variant of the TSP. The graph G is not complete, not every node must be visited by the salesman, nodes may be visited more than once if desired, and edges may be traversed more than once if desired. This variant of the TSP was proposed, apparently independently, by three sets of authors [6, 13, 30] . (The special case in which all nodes must be visited was considered earlier in [20, 26] .) We will follow Cornuéjols et al. [6] in calling this variant the Steiner TSP, or STSP for short.. As noted in [6, 13] , it is possible to convert any instance of the STSP into an instance of the standard TSP, by computing shortest paths between every pair of required nodes. So, in principle, one could use any of the abovementioned TSP formulations to solve the STSP. If, however, the original STSP instance is defined on a sparse graph, the conversion to a standard TSP instance increases the number of variables substantially, which may be undesirable. For this reason, we have decided in this paper to present and analyse some compact formulations for the STSP.. The paper is structured as follows. We review the relevant literature on TSP and STSP formulations in Section 2. In Section 3, we show how to adapt so-called commodity-flow formulations of the TSP to the Steiner case, and make some remarks about the relative strength of the resulting formulations. In Section 4, we adapt the so-called time-staged formulation of the TSP to the Steiner case, and present a key theorem, which enables one to reduce the number of variables substantially. Then, in Section 5, we briefly discuss the possibility of adapting our compact formulations to some other vehicle routing problems, when sparse graphs are involved rather than complete graphs. Finally, some concluding remarks appear in Section 6. Observe that we have not adapted the MTZ formulation to the Steiner case. This is because the MTZ formulation is based on the idea of determining the order in which the nodes are visited. Since nodes can be visited multiple times in the Steiner case, a unique order cannot be determined. As a result, it does not appear possible to adapt the MTZ formulation. This is not a problem, though, given the extreme weakness of the MTZ formulation mentioned in Subsection 2.2. Our motive for looking at the 'Steiner' version of the TSP and its variants was that many real-life vehicle routing problems are defined on road networks, rather than complete graphs as normally assumed in the literature. Moreover, 'compact' formulations are of interest, not only for their elegance, but also because one can just feed them into a standard branchand-bound solver, without having to implement complex solution methods such as branch-and-cut.. We have seen that the classical, single-commodity flow, multi-commodity flow and time-staged formulations of the Traveling Salesman Problem can all be adapted to the Steiner Traveling Salesman Problem, the Steiner Orienteering Problem and the Steiner Capacitated Profitable Tour Problem. In some cases, we can characterise the projections of the resulting LP relaxations into the space of the 'natural' variables. Moreover, in some cases, the formulations can be easily strengthened, without increasing their size.. On the other hand, it does not seem possible to adapt the above formulations to the Steiner Traveling Salesman Problem with Time Windows. Nevertheless, we have produced a compact formulation of this problem which is of reasonable size.. We believe that all of the formulations presented in this paper are potentially of practical use. Possible topics for future research would be the derivation of smaller and/or stronger compact formulations for the problems mentioned, the derivation of useful compact formulations for the Steiner version of other variants of the TSP, and exploring the potential of extending the approach to problems with multiple vehicle and/or depots.

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Towards an Agile Approach to Adapting Dynamic Collaboration Support to Student Needs Abstract This paper investigates the use of conversational agents to scaffold on-line collaborative learning discussions through an approach called Academically Productive Talk (APT). In contrast to past work on dynamic support for collaborative learning, where agents were used to elevate conceptual depth by leading students through directed lines of reasoning (Kumar & Rosé, IEEE Transactions on Learning Technologies, 4(1), 2011), this APT-based approach uses generic prompts that encourage students to articulate and elaborate their own lines of reasoning, and to challenge and extend the reasoning of their teammates. This paper integrates findings from a series of studies across content domains (biology, chemistry, engineering design), grade levels (high school, undergraduate), and facilitation strategies. APT based strategies are contrasted with simply offering positive feedback when the students themselves employ APT facilitation moves in their interactions with one another, an intervention we term Positive Feedback for APT engagement. The pattern of results demonstrates that APT based support for collaborative learning can significantly increase learning, but that the effect of specific APT facilitation strategies is context specific. It appears the effectiveness of each strategy depends upon factors such as the difficulty of the material (in terms of being new conceptual material versus review) and the skill level of the learner (urban public high school vs. selective private university). In contrast, Feedback for APT engagement does not positively impact learning. In addition to an analysis based on learning gains, an automated conversation analysis technique is presented that effectively predicts which strategies are successfully operating in specific contexts. Implications for design of more agile forms of dynamic support for collaborative learning are discussed. With the recent press given to online education and increasing enrolment in Internetbased courses, the need for scaling up quality educational experiences online has never been so urgent. The biggest limitations are related to the human side of effective educational experiences. While instructor time is a scarce commodity in many such courses, students are plentiful. Thus, one important contribution the field of intelligent support for group learning can make is to develop technologies to structure interactions between students in order to maximize the benefit students receive from one another. Effective collaborative learning experiences are known to provide many benefits to learners in terms of cognitive, metacognitive, and social impact (Kirschner et al. 2009; Bereiter 1993, 2006; Webb and Palinscar 1996) . These experiences offer a potentially valuable resource for massively open online courses, if affordances can be provided that facilitate high quality collaborative learning interactions in the absence of human facilitators that can keep up with the high enrolment in such courses. Effective, automated support for such interactions is the key.. In this paper, we build on a paradigm for dynamic support for group learning that has proven effective for improving interaction and learning in a series of online group learning studies. In particular we refer to using tutorial dialogue agent technology to provide interactive support within a synchronous collaborative chat environment (Kumar et al. 2007; Chaudhuri et al. 2008 Chaudhuri et al. , 2009 Kumar et al. 2010; Ai et al. 2010; Kumar and Rosé 2011) . This form of support can be called dynamic for two reasons. First, the conversational agents are interactive. They have the capability of conducting multi-turn directed lines of reasoning with students that respond to the particulars of student input in response to their prompts (Rosé et al. 2001; Rosé and VanLehn 2005) . Second and more importantly, they can be triggered through real time analysis of the collaborative discussion as it unfolds (Kumar et al. 2007 Adamson et al. 2013; Dyke et al. 2013 ). The decision making process for identifying triggers in the ongoing collaboration in real time and then launching a specific supportive behaviour at the appropriate time in response to those triggers can be thought of as a strategy. In our prior work, each study described a single strategy that was meant to behave dynamically, according to the same context-sensitive rules for all student groups. In the current work, we explore the ways the dynamic support strategy itself might need to be adapted depending upon the characteristics of the student population. In particular, we build on prior work in triggering support based on real time analysis of collaborative discourse and work towards a new characteristic of dynamic support. Specifically, we are building an empirical foundation for adapting the strategy taken by the support technology to the specific, contextual needs of different student populations. We refer to the concept of strategy adaptation that we work towards in this article as agile support for collaborative learning. This paper integrates findings from a series of studies across content domains (biology, chemistry, engineering design), grade levels (high school, undergraduate), and facilitation strategies. In each study, each experimental condition makes use of only one strategy. As we observe the pattern of results across studies, where the studies differ in domain and grade level, we see that the ranking among strategies in terms of the relative effectiveness of alternative strategies differs depending on the student population and learning task. We also observe a characteristic pattern in the interaction between students within successful conditions that can be detected with high reliability through automated collaborative process analysis. Thus we offer this series of studies along with the automated process analysis technique as an initial empirical foundation for the development of a more agile approach to dynamic support for group learning. In particular, the choice of facilitation strategy can be adapted in response to an assessment of the patterns of interaction, i.e., whether the characteristic pattern indicating a successful intervention is present.. In the remainder of the paper we first describe a theoretical foundation from prior work in the literature on computer supported collaborative learning, tutorial dialogue agents, and classroom discourse. We then describe our technical approach, which is a publically available architecture for dynamic support for collaborative learning called Bazaar. Next we describe the set of experimental studies we present in this article. Finally, we integrate across the results presented in the individual studies in order to motivate a research agenda for future work in the area of intelligent support for group learning. We conclude with a discussion of the limitations of this study and remaining research questions. The pattern of results across studies is consistent with what we expected to see given the connection between types of transactive discussion behavior and how they are related to the three different discussion facilitation behaviors we explored in this paper. In particular, we contrasted Revoicing, which is meant to elicit self-oriented, consensusoriented transacts, which we have argued should be less demanding and to some extent logically prior to other-oriented, conflict-oriented transacts, which are elicited by Agree-Disagree facilitation moves. It would therefore be consistent to expect that Revoicing moves would be most needed by younger, less sophisticated learners, whereas Agree-Disagree moves would be more appropriate for more advanced learners. In prior studies of the effect of transactivity on learning (Azmitia and Montgomery 1993) , the effect was only observed in material that was difficult for learners, thus we would expect that learners who were close to mastery would not benefit substantially from APT. Thus, where material is easy for learners, we would not predict a difference between conditions where we test APT in comparison with other facilitation behaviors or even no facilitation. A summary of results across studies is given in Table 9 .. In study 1 where we test Revoicing against Feedback for APT with young learners on material that was difficult for them, we observe a positive effect of Revoicing. In Significant negative effect of Revoicing, no effect of feedback Significant positive effect of agreedisagree study 2, we test Revoicing again, but this time with material that was easy for the students. Here there was no significant difference between conditions. This contrast is consistent with what we argued above. It is true that since the group of learners was the same in the two studies, the difference in effect could have potentially been related to the fact that the students were already familiar with the support agents. It is clear, however, that re-exposure to the same manipulation does not completely explain the difference in results across these two studies. In the first study, we observed a significant pre to post test gain across all conditions, including the condition where no support was offered beyond the macro level structuring of the activity. In the second study, no significant pre to post test gain was observed in any condition. Rather, both pre and post test scores were high across conditions, which highlights the fact that the material was easy for the students. Studies 3 and 4 involve more advanced learners on material that was moderately familiar to them. More advanced learners are already good at articulating their own ideas. Thus, Revoicing support is unneeded support for them. Rather, they need to be pushed beyond that to connect to the reasoning of their partner students. We expect then not to see a positive effect in study 3 where we test Revoicing on these advanced learners, and we do expect to see a positive result with Agree-Disagree, which we test in the final study. And we do see this.. The pattern of results with learning gains is as expected from prior work. What is more striking is the picture that emerges when we compare the pattern of results from the learning gains analysis with that from the process analysis. What we see from the series of studies presented in this paper is that the effect of condition on learning gains and on collaborative process provide largely converging evidence across studies. This convergence highlights the value of the simple form of process analysis presented in this article for evaluating in process effect of collaboration support. It shows that this process analysis can be used to gauge whether an intervention is working appropriately with a group of learners. If the process analysis indicates that the strategy is not a good match for the learners, the strategy can be adjusted. The new strategy can then be evaluated in process the same way, and further adjustments can be made. Thus, this simple automated process analysis technique could form the foundation for a new, more agile approach to dynamic support for group learning where the strategy itself can adapt to the needs of the population of learners. As in the Diffusion Lab study, we evaluated pre-to-post test learning and the effect of condition on learning and on the collaborative process. However, the material appears to have been too easy for the students. Post-test scores were higher on average than pre-tests scores, but not significantly. And although the trend was for students in the Revoicing condition to learn more than students in the Control condition, the difference was not significant or even marginal. Thus we do not elaborate on the learning gains analysis here.. While the learning gains analysis does not allow us to draw new insights about learning, we can observe how the collaborative processes play out with the same student population used in Study 1, but with material that appears to be less challenging for them. The process analysis using the random intercept and slope model showed an interesting contrast between this study and the Diffusion lab study. Similar to the Diffusion study, there was no significant difference in intercept between conditions, confirming again that there was no difference in absolute number of revoicable assertions between conditions. This time, however, there was a significant correlation between the number of revoicable assertions of a student and that of his partner students in both conditions (R=0.31, z=3.59, p<.001), and no difference in slope between conditions. Thus, we have confirming evidence that there was no difference in effect between conditions. Students were interacting productively in both conditions regardless of support, possibly because the material was easy for them and thus they may not have needed the revoicing support.. The results of this study were strikingly different from the two conducted in 9th grade Biology. In particular, rather than achieving a positive effect, the Revoicing manipulation had a significant negative effect on learning within the APT Feedback condition with this more advanced population of learners.. As in the earlier studies, we began our analysis by first verifying that students learned between pre and posttest. For this analysis, we treated Test as a repeated measure, with Pre and Post being the two time points. We conducted an ANOVA test with Test as the dependent variable. Time point, Revoicing, and Feedback were independent variables. We included all two-way interaction terms as well as the three-way interaction term. There was a significant main effect of Time point F(1,210)=9.28, p<.005, demonstrating that students learned. None of the interaction terms were significant. Thus students learned between pre and posttest regardless of condition.. Next we tested for differences in learning between conditions. For this analysis, we conducted an ANCOVA with Post-test as the dependent variable and Pre-test as a covariate. Revoicing and APT Feedback were the two independent variables. We also included the interaction term in the model. Here there was almost no effect of APT Feedback F(1, 104)=0.03, p=.87. There was a trend for a negative effect of the Revoicing manipulation F(1, 104)=2.22, p=.13. The interaction between APT Feedback and Revoicing was not significant, however, it should be noted that within the APT Feedback condition, there was a significant negative effect of Revoicing (p <.05). Thus, there is some qualified evidence of a potential detrimental effect of Revoicing with this population.. Consistent with the negative trend, the process analysis using the random intercept and slope model showed an interesting contrast with the earlier studies when we evaluated the effect of the Revoicing manipulation. Similar to the earlier studies, there was no significant difference in intercept between conditions, confirming again that there was no difference in absolute number of revoicable assertions between conditions. There was, however, a significant correlation between the number of revoicable assertions of a student and that of his partner students in the control condition (R=0.1, z=3.7, p<.001), as well as an interaction between condition and slope. In contrast to the Diffusion study where we saw a positive effect of revoicing both on learning and on the slope, here we see a negative impact on slope based on the correlation on the interaction term. This echoes the trend for a negative effect on learning (R=−0.1, z= 2.4, p<.05). Thus, we have confirming evidence that there was a negative impact of the Revoicing manipulation with this population. When we do the same analysis to evaluate the effect of the APT Feedback condition, we see no effect of any variable.. Our hypothesis was that the introduction of the Agree/Disagree agent would intensify the interaction between students, which might increase critical thinking, and subsequently increase learning. Our analysis offers qualified support for the hypothesis.. As before, we began our analysis by first verifying that students learned between pre and posttest. For this analysis, we treated Test as a repeated measure, with Pre and Post being the two time points. We conducted an ANOVA test with Test as the dependent variable. Time point and Revoicing were independent variables. We included the interaction between Time point and Condition as well. There was a significant main effect of Time point F(1,31)=7.58, p<.01, demonstrating that students learned. The interaction term was not significant. Thus students learned between pre and posttest regardless of condition. As before, to evaluate the effect of condition on learning, we used an ANCOVA with posttest as the dependent variable, pretest as a covariate, Condition as an independent variable. In this analysis, there was a marginal effect of Condition on learning (F(1,11)=1.82, p<.1, effect size 0.55 standard deviations), such that students in the Agree/Disagree condition learned more. The effect was moderate.. Next we examined the intensifying effect of the intervention on the interaction between students using the same random intercept and slope model approach used in the earlier studies. The analysis showed the pattern that we expected. There was no significant difference in intercept between conditions, confirming that there was no difference in absolute number of revoicable assertions between conditions. More importantly, there was no significant correlation between the number of revoicable assertions of a student and that of his partner students in the control condition where there was not an Agree/Disagree agent. There was, however, a significant interaction between the condition variable and the number of revoicable assertions contributed by partner students (R=0.14, z=2.03, p<.05). This suggests that there was a significant positive correlation between the number of revoicable assertions contributed by a student and that contributed by partner students in the Agree/Disagree condition. Thus we do see evidence that the intervention had the effect of precipitating pockets of intensive discussion. The line of inquiry investigated in this article was prompted by the hypothesis that by incorporating intelligent agents to model, support, coach, and provide feedback for students using Academically Productive Talk (APT) moves, students will benefit in terms of learning and interaction. Note that we do not hypothesize that all APT moves are interchangeable. Rather, in this work we manipulate the usage of different APT moves in order to understand better their separate and joint effects on measures of learning and interaction. The experiments presented in this paper build on the early success of a form of APT, namely revoicing support, in a study with 9th grade biology students . The series of studies presented in this paper serve as a test of the generality of the effect.. As an advance organizer for the series of studies and analyses, what we will see in these studies is that the positive effect of APT facilitation behaviors is context specific. Thus, a more generalizable form of support would need insights into the contextual pre-conditions for the success of these facilitation strategies. The pattern of results across the studies begins to provide an empirical foundation for a more agile, more generalizable form of support that can use APT facilitation behaviors in a more nuanced, population sensitive way. Note that we are not claiming in our presentation of these studies that we already have this agile form of support. Rather, our investigations provide the initial empirical foundation for developing such an approach. In addition to the learning gains analysis for each study, we present an automated process analysis technique that proves surprisingly accurate in identifying which interventions were most successful in each context. An automated measure that provides an indication of the relative success of alternative intervention strategies within contexts can be used to discover new associations between contexts and facilitation strategies in real time. Thus, we will argue that beyond the insights into the individual contexts investigated in this series of studies, the results allow us to make cautious predictions beyond those contexts using the results from the process analysis we present as one of the contributions of this paper.

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


Dynamic

constrained

coalition

formation

among

electric

vehicles

Background:

The

use

of

electric

vehicles

(EVs)

and

vehicle-to-grid

technologies

have

been

advocated

as

an

efficient

way

to

reduce

the

intermittency

of

renewable

energy

sources

in

smart

grids.

However,

operating

on

sessions

in

a

cost-effective

way

is

not

a

trivial

task

for

EVs.

The

formation

of

coalitions

among

EVs

has

been

proposed

to

tackle

this

problem.

Methods:

In

this

paper

we

introduce

Dynamic

Constrained

Coalition

Formation

(DCCF),

which

is

a

distributed

heuristic-based

method

for

constrained

coalition

structure

generation

(CSG)

in

dynamic

environments.

In

our

approach,

coalitions

are

formed

observing

constraints

imposed

by

the

grid.

To

this

end,

EV

agents

negotiate

the

formation

of

feasible

coalitions

among

themselves.

Results:

Based

on

experiments,

we

show

that

DCCF

is

efficient

to

provide

good

solutions

in

a

fast

way.

DCCF

provides

solutions

whose

quality

approaches

of

the

optimum.

In

dynamically

changing

scenarios,

DCCF

also

shows

good

results,

keeping

the

agents

payoff

stable

along

time.

Conclusions:

Essentially,

DCCF's

main

advantage

over

traditional

CSG

algorithms

is

that

its

computational

effort

is

very

lower.

On

the

other

hand,

unlike

traditional

algorithms,

DCCF

is

suitable

only

for

constraint-based

problems.

Electric

power

is

an

essential

resource

for

modern

societies.

Strategic

sectors

of

economy,

such

as

telecommunications,

transportation

and

industrial

activities

directly

depend

on

electricity.

Electricity

networks,

or,

as

called,

grids,

play

a

key

role

on

making

energy

available.

Roughly

speaking,

the

electricity

network

is

the

infrastructure

that

connects

energy

producers

to

energy

consumers..

Despite

its

importance,

electricity

grids

have

evolved

very

little

since

they

were

created.

The

energy

demand,

in

turn,

has

grown

manifold.

In

order

to

meet

such

a

demand,

the

energy

industry

has

invested

mostly

in

the

construction

of

large

power

plants.

However,

such

policies

resulted

in

non-redundant

grids,

which

strongly

depend

on

non-renewable,

highly

polluting

energy

sources,

whose

availability

is

becoming

increasingly

scarce.

As

a

consequence,

such

an

infrastructure

has

lost

efficiency

and

Additionally,

EVs

can

make

a

profit

by

selling

their

energy

on

sessions..

Although

the

mechanism

has

several

advantages

to

the

grid,

participating

in

sessions

in

a

cost-effective

way

is

not

a

trivial

task

for

EVs.

According

to

the

authors

in

to

act

in

sessions,

EVs

must

commit

to

provide

a

given

amount

of

energy.

However,

when

operating

in

an

isolated

way,

EVs

are

not

able

to

fulfil

their

commitment

due

to

their

insufficient

energy

capacity

and

unpredictable

availability.

In

order

to

address

this

problem,

a

particularly

interesting

approach

is

the

formation

of

coalitions

among

EVs,

forming

virtual

power

plants

(VPPs)

By

operating

in

coalitions,

EVs

can

coordinate

in

order

to

provide

more

accurate

predictions

about

their

energy

availability.

Furthermore,

the

amount

of

available

energy

is

also

increased.

Therefore,

coalition

formation

has

shown

to

be

an

effective

way

of

increasing

the

profitability

of

EVs

Coalition

formation

is

a

research

topic

that

has

recently

received

great

attention

in

the

field

of

multiagent

systems.

A

coalition

can

be

defined

as

a

group

of

agents

that

decide

to

cooperate

in

order

to

achieve

a

common

goal.

According

to

the

authors

in

coalition

formation

includes

three

activities:

coalition

structure

generation

(CSG),

solving

the

optimization

problem

of

each

coalition

and

division

of

the

obtained

value

among

the

agents.

Among

these

activities,

CSG

is

the

most

interesting

one

for

the

multiagent

systems

community..

Traditional

CSG

algorithms

deal

not

only

with

grouping

agents

but

also

grouping

them

in

order

to

obtain

the

greatest

possible

reward.

Such

activity,

however,

has

been

proven

to

be

NP-complete

Moreover,

traditional

CSG

algorithms

do

not

deal

with

dynamically

changing

scenarios.

In

this

paper,

our

focus

is

not

on

finding

the

optimal

solution,

but

on

finding

a

good

one

(in

a

reasonable

amount

of

time)

in

dynamic

environments,

i.e.,

environments

that

change

constantly

(agents

can

enter

or

leave

the

system).

We

remark

that

traditional

methods

for

CSG

do

not

deal

with

this

issue..

In

this

paper

we

propose

the

formation

of

coalitions

among

EVs

in

order

to

form

VPPs.

As

stated

in

by

forming

coalitions,

EVs

can

increase

their

efficiency

and,

consequently,

their

profitability.

Therefore,

we

present

a

distributed

heuristic-based

method

for

CSG

in

dynamic

environments,

called

Dynamic

Constrained

Coalition

Formation

(DCCF

henceforth),

which

is

able

to

prevent

constrained

agents

to

form

a

coalition.

DCCF

was

designed

to

run

in

a

distributed

way,

in

order

to

be

fast

and

to

provide

reasonably

good

solutions.

We

show

that

compared

to

state

of

the

art

CSG

algorithms,

DCCF

outperforms

them

by

many

orders

of

magnitude,

providing

solutions

whose

average

quality

nears

of

the

optimal

(with

a

standard

deviation

of

in

all

tested

cases.

In

more

dynamic

environments,

DCCF

also

shows

good

results,

being

able

to

keep

the

agents'

payoff

sufficiently

stable

over

time.

Also,

agents

which

joined

coalitions

have

obtained

a

higher

profit

than

isolated

agents.

In

essence,

DCCF's

main

advantage

over

traditional

CSG

algorithms

is

that

its

computational

effort

is

very

low.

On

the

other

hand,

unlike

traditional

CSG

algorithms,

DCCF

is

suitable

only

for

constraint-based

problems..

The

remainder

of

this

paper

is

organized

as

follows.

In

'Background

on

coalition

formation'

subsection,

we

give

more

details

about

coalition

formation.

Related

work

about

coalition

formation

in

smart

grids

is

discussed

in

'Coalitions

in

smart

grids'

subsection.

In

'Problem

modelling'

and

'Dynamic

constrained

coalition

formation'

subsections,

we

present

the

problem

modelling

and

our

method,

respectively.

Then

in

'Results

and

discussion'

subsection,

we

present

the

experiments

and

analysis

of

our

approach.

Conclusions

and

future

work

directions

are

presented

in

'Conclusions'

section.

In

this

paper

we

have

presented

DCCF,

a

distributed

method

for

constrained

CSG

in

smart

grids.

The

proposed

approach

works

by

allowing

agents

to

negotiate

the

formation

of

coalitions

among

themselves.

On

this

basis,

the

agents

can

propose

coalitions

to

their

neighbours

or

be

invited

to

join

a

coalition

proposed

by

them..

Based

on

these

experiments,

we

showed

that

DCCF

is

really

effective

in

providing

good

solutions

in

a

fast,

distributed

way.

We

showed

that

compared

to

state-of-theart

algorithms,

our

approach

outperforms

them

in

terms

of

runtime

performance

by

several

orders

of

magnitude,

providing

solutions

whose

quality

was

on

average

of

the

optimum

in

tested

cases

(with

standard

deviation

of

In

dynamic

environments,

DCCF

also

showed

good

results,

being

able

to

keep

the

agents'

payoff

sufficiently

stable

over

time.

Also,

through

experiments

we

showed

that

compared

to

isolated

agents,

the

agents

who

joined

coalitions

have

obtained

a

higher

profit.

However,

it

is

important

to

note

that

although

the

results

are

promising,

when

compared

to

other

approaches,

DCCF

is

not

as

generic

as

them.

IP

and

IDP,

for

instance,

return

optimal

solutions.

Additionally,

with

an

increased

number

of

neighbours

(more

dense

graphs),

the

agents

can

take

longer

to

find

good

results..

For

future

work,

we

would

like

to

investigate

how

the

distance

constraint

could

be

replaced

by

a

more

robust

one.

In

this

work,

the

agent

constraints

are

governed

by

the

physical

distance

among

them.

However,

more

robust

alternatives

could

be

used.

For

example,

in

order

to

group

agents

by

the

compatibility

of

their

energy

profiles,

a

similarity

function

could

be

used.

Also,

the

model

could

be

extended

to

include

more

than

one

kind

of

constraint..

Another

promising

future

direction

would

be

to

extend

the

model

to

handle

agent

uncertainties,

e.g.,

regarding

availability.

In

such

scenarios,

penalties

could

be

imposed

on

coalitions

that

do

not

fulfil

their

commitment

with

the

grid.

Machine

learning

techniques

could

be

used

to

allow

the

agents

to

predict

their

owners'

behaviour..

Additionally,

reputation

mechanisms

could

be

used

to

rank

the

agents

based

on

their

predictions..

Finally,

some

changes

could

be

made

in

the

modelling.

First,

having

not

just

one

constraint,

but

a

few,

would

be

a

more

realistic

and

interesting

approach.

Second,

agents

that

are

in

coalitions

could

be

always

checking

whether

a

better

coalition

is

available

or

not.

Probabilistic

models

could

also

be

incorporated

to

this

end.

Finally,

other

kinds

of

DERs

could

be

incorporated

into

the

model,

allowing

the

formation

of

heterogeneous

coalitions.

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