Fragment-based approximate retrieval in highly heterogeneous XML collections Due to the heterogeneous nature of XML data for internet applications exact matching of queries is often inadequate. The need arises to quickly identify subtrees of XML documents in a collection that are similar to a given pattern. Similarity involves both tags, that are not required to coincide, and structure, in which not all the relationships among nodes in the tree structure are strictly preserved.In this paper we present an efficient approach to the identification of similar subtrees, relying on ad-hoc indexing structures. The approach allows to quickly detect, in a heterogeneous document collection, the minimal portions that exhibit some similarity with the pattern. These candidate portions are then ranked according to their actual similarity. The approach supports different notions of similarity, thus it can be customized to different application domains. In the paper, three different similarity measures are proposed and compared. The approach is experimentally validated and the experimental results are extensively discussed. Interoperability among systems is commonly achieved through the interchange of XML documents that can represent a great variety of information resources: semi-structured data, database schemas, concept taxonomies, ontologies, etc. Most XML document collections are highly heterogeneous from several viewpoints. The first level of heterogeneity is tag heterogeneity: vocabulary discrepancies may occur in the element tags. Two elements representing the same information can be labelled by tags that are stems (e.g., author and authors), that are one substring of the other (e.g., authors and co-authors), or that are similar according to a given thesaurus (e.g., author and writer). The second level of heterogeneity is structural heterogeneity that results in documents with different hierarchical structures. Structural heterogeneity can be produced by the different schemas (i.e. DTDs or XML Schemas) behind the XML documents. Moreover, as schemas can also include optional, alternative, and complex components, structural heterogeneity can appear even for a single schema collection.. Highly heterogeneous XML collections can be found in a great variety of application domains, most of them related to the discovery and integration of semi-structured information coming from disparate and autonomous sources. Semantic Web Services is one of these application domains, which has been used for experimental evaluation. In this application, services are described according to concepts from one or several ontologies. In this way, service descriptions can be represented as trees expressing the hierarchical relationships that can appear in service methods and input/output parameters. Notice that these parameters usually have complex types (e.g., address) which can be defined in different ways across services. For example, in the ASSAM Web service collection, address and personal data present several structural relationships. In this context, user requests cannot account for all these structural variations as users do not a priori know how data are organized. Instead, the user expresses her request by arranging the elements of interest as she considers it is most likely to find them (pattern). In other words, she expresses an approximation of what she wishes to find, although the final results are not required to exactly comply to the given pattern.. A more complex and specific scenario is that of biomedical information exchange. Sharing clinical data among clinicians is crucial for the development of their researches and daily tasks, see e.g. [6] . Contrary to hospital information systems, where a great effort on data standardization has been produced (e.g. HL7 and IHE), clinical data managed within hospital departments has not been standardized at all because these data are quite irregular and dynamic. Clinical data cover many aspects of a patient: visits, examinations, diagnosis, symptoms, and a long etcetera. Also clinical procedures use to change over time as new findings over medical evidences are discovered (e.g., new treatments, new lab tests, etc.). Irregularity and dynamicity are two features of semi-structured data that are well supported by XML technology, therefore current biomedical projects like myGRID, 1 PEDRo 2 and caBIG 3 propose different XML-based models for clinical data exchange. Heterogeneity increases dramatically when several departments share their clinical records, since they can consider different detail levels and some clinical variables are more relevant than others. Also the structure of patient records can differ notably from one department to another depending on the particular use of the data. In this context, clinicians need a flexible retrieval tool for discovering interesting information from all the available data sources (e.g., local patient records, external patient records as well as public databases). For example, given a patient record, a clinician might wish to search not only similar patient records published within her department but also other document portions describing similar cases or reporting interesting findings with respect the patient at hand.. To sum up, in this paper we stress the tag and structural heterogeneity of XML document collections. This can lead to search a very large amount of highly heterogeneous documents. In this context, we propose an approach for identifying the portions of documents that are similar to a given pattern. In our context a pattern is a labelled tree whose labels are those that should be retrieved, preferably with the relationship imposed by the hierarchical structure, in the collection of documents (that for simplicity is named the target collection). We develop a two-phase approach where, in the first phase, tags occurring in the pattern are employed for identifying the portions of the target in which the nodes of the pattern appear. Exploiting the ancestor/descendant relationships existing among nodes in the target, subtrees (named fragments) are extracted having common/similar tags to those in the pattern, but eventually presenting different structures. The structural similarity between the pattern and the fragments is evaluated as a second step, for two purposes. First, for merging fragments in a region when the region exhibits a higher structural similarity with the pattern than the fragments it is originated from. Then, for ranking the identified fragments/regions and producing the result. In this second phase, different similarity measures can be considered, thus accounting for different degrees of document heterogeneity, depending on the application domain and on the heterogeneity degree of the target collection.. The proposed approach is thus highly flexible. The problem is however how to perform the first step efficiently, that is, how to efficiently identify fragments, that is portions of the target containing labels similar to those of the pattern, without relying on strict structural constraints. Our approach employs ad-hoc data structures: a similarity-based inverted index (named SII) of the target and a pattern index extracted from SII on the basis of the pattern labels. Through SII, nodes in the target with labels similar to those of the pattern are identified and organized in the levels in which they appear in the target. Fragments are generated by considering the ancestor-descendant relationship among such vertices. Then, identified fragments are combined in regions, allowing for the occurrence of nodes with labels not appearing in the pattern, as described above. Finally, some heuristics are employed to avoid considering all the possible ways of merging fragments into regions and for the efficient computation of similarity, thus making our approach more efficient without loosing precision.. In the paper, we formally define the notions of fragments and regions and propose the algorithms allowing their identification, relying on our pattern index structure. The use of different structural similarity functions taking different structural constraints (e.g., ancestor-descendant and sibling order) into account is discussed. The practical applicability of the approach is finally demonstrated, both in terms of quality of the obtained results and in terms of space and time efficiency, through a comprehensive experimental evaluation. The contribution of the paper can thus be summarized as follows: (i) specification of an approach for the efficient identification of regions by specifically tailored indexing structures; (ii) characterization of different similarity measures between a pattern and regions in a collection of heterogeneous semi-structured data; (iii) realization of a prototype and experimental validation of the approach. The paper is an extended version of [7] . With respect to [7] , the presentation of the approach has been deeply revised, all the underlying concepts are clearly and formally defined, and the corresponding algorithms, only sketched in [7] , are detailed and their correctness and complexity are discussed. Moreover, the experimental evaluation considerably extends the preliminary results presented in [7] .. The remainder of the paper is organized as follows. Section 2 formally introduces the notions of pattern, target, fragments, and regions the approach relies on. Section 3 is devoted to the discussion of different approaches to measure the similarity between the pattern and a region identified in the target. Section 4 discusses how to efficiently identify fragments and regions. Section 5 presents experimental results while Section 6 compares our approach with related work. Finally, Section 7 concludes the paper. In this paper we have developed an approach for the identification of subtrees similar to a given pattern in a collection of highly heterogeneous semi-structured documents. In this context, the hierarchical structure of the pattern cannot be employed for the identification of the target subtrees but only for their ranking. Peculiarities of our approach are the support for tag similarity relying on a thesaurus, the use of indexing structures to improve the performance of the retrieval, and a prototype of the system.. As future work we plan to compare different similarity measures in order to identify those more adequate depending on the application context and the heterogeneity of the considered data. Such measures can be col-lected in a framework of functions that a user can select, compose, and apply depending on her needs. Moreover we plan to consider more sophisticated patterns in which further constraints on vertices and edges can be stated. For instance, an element or a portion of the pattern could be requested to mandatorily appear in the target regions, or the difference between the levels in which two elements appear could be constrained by fixing a threshold. The constraints should then be considered in the similarity evaluation. Finally, we wish to consider subtree identification in a collection of heterogeneous XML Schemas. In this context, the proposed approach should be tailored to the typical schema constraints (e.g., optionality and repeatability of elements, groups, types).. Appendix A. Details of similarity evaluation Detailed match-based similarity (see Example 9) . Let x p be the vertex tagged article in the pattern P in Fig. 5 and x 1 r ; x 2 r ; x 3 r the corresponding vertices in the regions R 1 , R 2 , R 3 . In R 1 , article appears with the same label then the match-based similarity is 1, whereas in the other two regions a similar tag appears, then the match-based similarity is 1 À d.. Consider now Table 2b . Since R 1 has two perfect node matches over three nodes in the pattern, the resulting similarity is nodes are those that can occur at level l in the pattern index for the creation of a fragment F. The following situations can arise.. (1) If head(PI(l)) = t is a left relative of F, t is the root of another fragment. Indeed, all the fragments whose roots precede root(F) have been removed. Therefore, t cannot belong to other fragments and it is the root of a new fragment. (2) If head(PI(l)) = u is a descendant of root(F), but not of v, u is left relative of all internal nodes of F. If this is not true, there would be a vertex p in F (in a level between level(root(F)) and l) that precedes v for which u would have been added as child of p. Therefore, u can only be the direct child of root(F). (3) If head(PI(l)) = w is a descendant of v, for the same reasons of previous item, w can only be a direct child of v. (4) If head(PI(l)) = n is a right relative of F, no elements of F can be identified at this level. Indeed, n and the nodes that follows it have a higher rank than that of root(F). h Proof sketch of Proposition 2. The proposition directly follows from Proposition 1 and the considerations of how Algorithm 2: CreateListOfFragments works. Indeed, if a node v at a given level of the current PI is not removed by the recursive calls of Algorithm 1: CreateFragments on nodes at level m < level(v), it means that it is the root of a fragment and will be removed along with all its descendants when Algorithm 2: CreateListOfFragments is invoked on its level. h Proof Sketch of Proposition 3. The number of operations for the entire process of region construction is the maximum between the number of operations required for the construction of the pattern index and those required for the extraction of regions from the pattern index. Therefore, exploiting the complexity specified for these operations, the process of region construction is in OðmaxfjP j Á K Á MÞ; N Á jP jgÞ. h The need of shifting from exact queries with boolean answers to proximity queries with ranked approximate results is a relevant requirement of XML query languages for searching the Web and several approaches in this direction have been developed. These approaches share the goal of integrating structural conditions typical of database queries with weighted and ranked approximate answers typical of Information Retrieval (IR). Work from the IR area [13] is mainly concerned with the retrieval of XML documents, by representing them with known IR models. These approaches mainly focus on the textual part of XML documents and structure is only used to guide user queries.. A crucial issue in ranked approximate querying is how to score results. A great variation of XML similarity measures have been proposed for different applications (see [14, 15] for a survey). In this section, we will briefly discuss the similarity measures the most meaningful approaches to XML approximate querying rely on to rank results. Further specific structural similarity measures have been proposed in the areas of Schema Match- ing [16] and more recently Ontology Alignment [17] . In the former, tree/graph-matching techniques allow determining which schema portions from the target schema can be mapped to the source ones. In this context, data types and domain constraints are used to decide if two nodes match. However, schemas usually exhibit simple structures that seldom exceed three depth levels (relation-attribute-type). In the latter, the problem consists in finding out which concepts of a target ontology can be associated to concepts of the source ontology.. In this section, we focus on approximate query answering for XML documents taking both vocabulary and structural heterogeneity into account. First, we discuss the kind of heterogeneity taken into account and the similarity measures employed to score results. Then, algorithmic approaches to query relaxation and to compute the top-k results are reviewed.. Heterogeneity degree and similarity evaluation. An early approach for XML approximate retrieval is ELIXIR [18] that allows approximate matching in data content (tree leaves), and ranks the results according to the matching degree, disregarding structure in the evaluation. No structural heterogeneity is considered, and vocabulary heterogeneity is allowed only for data content elements, not for tags.. More sophisticated approaches, like XIRQL [19] and XXL [20] , accept approximate matching at nodes and then discuss how to combine weights depending on the structure. Vocabulary heterogeneity is supported for content and element tags, but no structural heterogeneity is allowed: conditions on document structure are interpreted as filters, thus they need to be exactly satisfied. XXL supports a similarity operator and, to use this operator, the user should be aware of the occurrence of similar keywords or element tags.. In the approach proposed by Damiani and Tanca [21] both XML documents and queries are modeled as graphs labeled with fuzzy weights capturing the information relative relevance. They propose to employ both structure related weighting (weight on an edge) and tag related weighting (weight on a node). Some criteria for weighting are proposed such as the weight decreases as moving far away from the root, the weight depends on the dimension of the subtree. Shortcut edges are considered, thus allowing the insertion of nodes, which weight is function of weights of edges. The match score is a normalized sum of weight of edges.. In the tree relaxation approach [2] exact and relaxed weights are associated with query nodes and edges. The score of a match is computed as the sum of the corresponding weights, and the relaxed weight is function of the transformations applied to the tree. The considered transformations are: relax node, replacing the node content with a more general concept; delete node, making a leaf node optional by removing the node and the edge linking it to its parent; relax edge, transforming a parent/child relationship to an ancestor/descendant relationship; promote node, moving up in the tree structure a node (and the corresponding subtree).. The approXQL [5] approach can also handle partial structural matchings. All the paths in the query are however required to occur in the document. The allowed edit operations on the document tree are delete node, insert intermediate node, relabel node. The score of match is function of the number of transformations, each one of which is assigned with a user-specified cost.. Amer-Yahia et al. in [3] account for both vocabulary and structural heterogeneity and propose scoring methods that are inspired by tf * idf and rank query answers on both structure and content. Specifically, twig scoring accounts for all structural and content conditions in the query. Path scoring, by contrast, is an approximation of twig scoring that loosens the correlations between query nodes when computing scores. The key idea in path scoring is to decompose the twig query into paths, independently compute the score of each path, and then combine these scores. [21] On content and tag Node insertion Structure dependent [2] On content and tag Delete node, relax edge, promote node Structure dependent approXQL On content and tag Node insertion, node deletion Structure dependent [3] On content and tag Edge generalization, leaf deletion, subtree promotion Structure dependent. The main differences among the considered approaches are summarized in Table 5 . Note how approaches to XML approximate queries have progressively shifted to higher degrees of heterogeneity, and to cope also with structural heterogeneity. Our approach allows for more significant structural variations and can be considered as a step forward in the treatment of structural heterogeneity in the context of XML. All the considered approaches, indeed, enforce at least the ancestor-descendant relationship in pattern retrieval, whereas our approach also allows to invert and relax this relationship. Our approach, moreover, is highly flexible because it allows choosing the most appropriate structural similarity measures according to the application semantics.. Tree embedding and top-k processing. A different perspective from which approaches to XML approximate querying started, is that of looking for approximate structural matches, allowing the structure of the document and query trees to partially match. Kilpeläinen [1] discusses ten different variations of the tree inclusion problem, that is, the problem of locating instances of a query tree Q in a target tree T. He orders these different problems, ranging from unordered tree inclusion to ordered subtrees, highlighting the inclusion relationships among them. Moreover, he gives a general schema of solution, and instantiates it for each problem, discussing the resulting complexities. His goal, however, is not to measure the distance, nor to rank results. All the instances of the pattern in the data tree are returned.. Another approach aimed at identifying the matches but that does not rank them, is by Kanza and Sagiv [22] . They advocate the need of more flexible query evaluation mechanisms in the context of semi-structured data, where both queries and data are modeled as graphs. They propose mapping query paths to data paths, so long as the data path includes all the labels of the query path; the inclusion needs not to be contiguous or in the same order.. Sub-optimal approaches for ranked tree-matching have been proposed for dealing with the NP complexity of the tree inclusion problems widely discussed and analyzed in [1] . In these approaches, instead of generating all (exponentially many) candidate subtrees, the algorithms return a ranked list of ''good enough'' matches. For example, in [23] a dynamic programming algorithm for ranking query results according to a cost function is proposed. In [2] a data pruning algorithm is presented where intermediate query results are filtered dynamically during evaluation process. ATreeGrep [24] , instead, uses as basis an exact matching algorithm, but allowing a fixed number of ''differences'' in the result. [4] proposes an adaptive query processing algorithm to evaluate approximate matches where approximation is defined by relaxing XPath axes. In adaptive query processing, different plans are permitted for different partial matches, taking the top-k nature of the problem into account.. Starting from the user query, the approaches [2] [3] [4] [5] , for structural and content scoring of XML documents, generates relaxations of the query structure that preserve the ancestor-descendant relationships existing among nodes in the query. These relaxations do not consider the effective presence of such a structure in the collection of documents. The number can also be really high when the number of nodes in the query is high. The novelty of our approach relies on the employment of ad-hoc indexing structures. By exploiting such auxiliary information, only the variations on the pattern that occur in the target are considered. The number of variations to be evaluated is thus considerably reduced, still allowing for greater structural heterogeneity, as discussed in the previous section. Finally, in [2] [3] [4] [5] constraints in the user queries are relaxed to augment the obtained results, whereas in our approach, we start from a completely relaxed query. We follow this approach because of the high degree of heterogeneity of the collection of documents we work on and we apply indexing structures for improving the performance.

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In the Fall of 2002, the ANP had shown a better way to deal with Iraq In 2003, the United States launched a pre-emptive strike against Iraq which was largely defended by the Bush Administration as an act to protect national security. In the months leading up to the attack, however, the US was still in the decision-making process -should we work with the UN on enforcing sanctions? go in only with Allied support? launch a pre-emptive strike with mainly US forces? During this time, the Analytic Network Process [T.L. Saaty, The Analytic Network Process, Fundamentals of Decision Making and Priority Theory, second ed., RWS Publications, Pittsburgh, 2001] was used to determine the best course of action. Working with the UN to ensure weapons inspections was found to be the best choice; the model showed that other alternatives, such as a pre-emptive attack on Iraq or attacking Iraq with Allied help would increase the possibility of such risks as increased oil prices, increased terrorism, decreased domestic support for the war, and high economic costs of sustaining the war itself. Without question, foreign policy decisions necessitate the consideration of all possible options. In the case of the United States and Iraq, however, the decision was one of prime importance, given the future repercussions of both countries' actions in 2002. At the time, we felt that the decision of the United States would be based on an educated guess as to whether Iraq possessed either nuclear WMD or the means to make them. We now know that faulty intelligence was used to convince the public that Iraq was harboring WMD. Regardless, the ANP was successfully used in 2002 to examine the short-term, and possible long-term, effects of engaging Iraq in war, unilaterally or not.. In 2002, the following conclusion was reached by the author of this paper: President Bush's insistence on viewing the United States in the context of a unipolar world, rather than conceding that a larger picture exists, may in fact stifle any progressive foreign policy decisions. In general, he and his administration have shown little concern for the rest of the world's response to his protectionist policies. Further, his consistent movement toward unilateral action should be alarming at least, and should incite a dialogue that is currently absent. Repeated public opinion polls demonstrate that the American public is uncertain at best when faced with whether or not to engage Iraq -is this the shaky foundation on which a military campaign should be launched? At the very least, these are questions that must be asked, despite the current American climate of patriotism and, perhaps, superiority. Unilateral action against Iraq, coupled with other recent protectionist policies, may serve only to portray US interests as superior and valid, and our needs and wants as the exception to every rule, inviting only disdain and opposition from the rest of the world.. In short, using pre-emptive, unilateral force has a high potential of both alienating allies and negatively affecting America's long-term interests. In addition, pre-emptive action might incite the use of WMD in retaliation, as well as create further instability in the Middle East and within Iraq, as the country is left in the hands of warring factions with Iraqi citizens at their mercy. It cannot be denied that Iraq poses a threat to both the United States and the world, and that Hussein is a leader that must be contended with. Unchecked, he represents the quintessential example of both absolute power and absolute corruption, unfettered by the reins of conscience, ethics, morality or religious beliefs. However, the question, as stated at the beginning of this paper, is not whether to engage Iraq, but rather, how and when.. Weapons inspectors have not been in the country since 1998; surely, the US could take the time necessary to carry out the appropriate dialogue in both the public and political/diplomatic arenas in order to gain both allied and public support, fully consider both the depth and scope of the operation (including anticipated costs), as well as to formulate a plausible plan for what will become of an Iraq absent of the Hussein regime. The logistics of this operation are being glossed over by the Bush administration. The importance of allied and public support is being dangerously underplayed. The Administration is spouting the rhetoric of "force as a last resort", even as it dismisses UN authority through House resolutions. There is no good faith here, on the part of either country.. In the end, there is only one plan that is truly in the best interests of both the United States and the world. The UN must move to expediently pass a resolution calling for a new, tougher inspection regime. Absent Iraqi cooperation, there must be a multilateral move to forcefully search out and destroy Iraqi WMD and related programs. Simultaneously, the Arab world must be actively engaged and consulted, as the West should be mindful that Westernled authority will neither have legitimacy nor longevity, and that Iraq, left entirely to her own devices, would likely dissolve into the hands of warring factions. There are goals here: protecting oil reserves, improving life for Iraqi civilians, building bridges with the Arab world, maintaining focus on the domestic economy, and strengthening our ties both with our allies and IGOs. Simply put, there is not enough support, at home or worldwide, for pre-emptive unilateral action, and the US cannot afford the risks involved. The wisest choice remains to first exhaust diplomatic measures . . . hoping for the best, but preparing for the possible necessity of allied intervention.. There is a larger picture here, however, that must be considered. Yes, Iraq must comply with inspections. Yes, Iraq must be rid of WMD and related programs. Yes, the days of Saddam Hussein's regime ought to be numbered. However, the shaping of foreign policy never hinges on one single decision at one moment in time. There is a definite shift to unilateralism and a push for American hegemony. There is a noticeable absence of dialogue and debate regarding the past, current and future actions of a "wartime" president. There are too many decisions being made and accepted in the name of fear -breeding protectionist, isolationist policies cloaked in patriotism and politics. There is, very nearly, a policy of paralysis regarding common sense, active debate, prudent fiscal decisions and long-term repercussions. Not attacking pre-emptively is a message that will give the US a better response on many fronts, and in the long-term. If Iraq must be engaged militarily, then let it be by a multilateral allied force, sharing in both the costs and the risks.. The results and conclusion, as stated above and composed in 2002, have proven to be quite prophetic in nature. In the years since Operation Iraqi Freedom began, American public support has indeed diminished and the costs of the war have risen to over 300 billion dollars, with the total cost project to surpass one trillion dollars [13] . The risks of US and Iraqi casualties have materialized; since the war began in March 2003, almost 2700 Americans have died, over 20,000 have been wounded, and over 40,000 Iraqi civilians have died [14] . The cost of the war is also seen in high oil prices and increased terrorism, as well as further destabilization of the Middle East. While the US-led pre-emptive strike was justified largely with the rationale of overcoming security risks to the US, in our current situation, one could ask whether we are indeed more secure today than four years ago. It would have been far better to work with the UN than to be the leader of a few allies. Iraq would have thought that they were fighting the whole world instead of just the United States. At this point, the United States remains in an unyielding Catch-22: withdraw troops, leaving Iraq to be ruled by whichever faction emerges victorious from the current state of civil war, or maintain troops, even as support for the war diminishes and the monetary and casualty toll grows higher. Given the current state of affairs, 'winning' no longer seems to be an option.

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 B I I 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 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 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


OntoVIP: An Ontology for the Annotation of Object Models Used for Medical Image Simulation Abstract This paper describes works carried out in the Virtual Imaging Platform (VIP) project to create a comprehensive conceptualization of object models used in medical image simulation and suitable for the major imaging modalities and simulators. The goal is to create an application ontology that can be used to annotate the models in the VIP platform's model repository, to facilitate their sharing and reuse. Such annotations allow making the anatomical, physiological and pathophysiological content of the object models explicit. The Virtual Imaging Platform (http://vip.creatis.insalyon.fr) provides researchers with a platform gathering several image simulators of various modalities [1] . This work focuses on the sharing and reuse of the models used for medical image simulation. Currently, a barrier to the widescale use of these techniques is the difficulty of creating realistic models that are suited to the researchers' specific needs. Thus the VIP project aims at setting up a model repository to facilitate their sharing and reuse. This paper describes an ontology for medical image simulation models, tailored to the needs of the SINDBAD, SIMRI, SORTEO and FIELD-II simulators integrated in VIP, but easily extensible to other simulators. This ontology, called OntoVIP is used to semantically annotate the models files (images, meshes, etc.) The ontology allows precise semantics to be associated to information depicted in the images or meshes that compose a model. It models consistently all kinds of medical image simulation object models, especially with regards to the different imaging modalities (CT, MR, PET, US). The major features of the model are: (1) an organization in layers, allowing representing the various facets of a model, each of them represented by a model layer (e.g. anatomy, pathology, presence of an external agent, presence of a foreign body); (2) links with various physical properties of tissues or materials, which is required by simulation software; (3) capability to represent time-varying phenomena; (4) definition of a rich taxonomy of models facilitating their indexing, retrieval and use in image simulations.

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 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 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 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 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 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


Structural methods for the synthesis of speed-independent circuits Abstract Petri nets (PNs) are a powerful formalism to model concurrent systems. As a model, their most interesting feature is the capability of implicitly describing a vast state space by a succinct representation, which gracefully captures the notions of causality, concurrency and conflict between events. Petri nets have also been chosen by many authors as a formalism to describe the behavior of asynchronous circuits by interpreting the events as signal transitions coining the term Signal Transition Graph (STG) 114, 31.. Each reachable marking of an STG is assigned a binary code with the value of the circuit signals in that marking. Deriving logic equations from an STG requires the generation of the binary codes for all markings. Currently, most synthesis tools [15, 161 perform an exhaustive token flow analysis to obtain the complete reachability graph of the PN and all binary codes.. Even for small STGs, the reachability graph of highly concurrent systems can be extremely large and, in the worst case, exponential in the size of the STG. Some efforts have been devoted to propose structural methods for synthesis [IO, 171, but they have been usually devised for restricted classes of PNs that compromise the potential expressiveness of this formalism.. In this paper we present structural techniques to synthesize speed-independent (SI) circuits from STGs. In this framework, "structural" means "at Petri net level" without requiring the explicit generation of the reachability graph. The techniques have polynomial complexity if the underlying PN is free choice [6, 4] , and can be efficiently extended to the class of PNs that can be covered by State Machines (SM) [5] . We aim at complementing the existing tools by providing alternative and efficient synthesis methods for SM-coverable STGs, which account for a large fraction of the set of benchmarks we have used.. This work improves the techniques presented in [ 1 1,121 in two directions: (1) by providing new methods to calculate covers for the boolean functions needed for synthesis and (2) by extending these methods to the synthesis of SI-circuits. Let us assume that we want to derive a logic function for signal y in Fig.l(a) and, in particular, for the set of markings in which transition y+ is enabled--excitationregion of y+ (ER(y+)). This region corresponds to all the markings in which placepsis marked,

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


Counting the Faces of Randomly-Projected Hypercubes and Orthants, with Applications Abstract. Let A be an n by N real valued random matrix, and H N denote the N -dimensional hypercube. For numerous random matrix ensembles, the expected number of k-dimensional faces of the random n-dimensional zonotope AH N obeys the formula Ef k (AH N )/f k (H N ) = 1 − P N−n,N−k , where P N−n,N−k is a fair-coin-tossing probability:The formula applies, for example, where the columns of A are drawn i.i.d. from an absolutely continuous symmetric distribution. The formula exploits Wendel's Theorem [19] .Let R N + denote the positive orthant; the expected number of k-faces of the random coneARThe formula applies to numerous matrix ensembles, including those with iid random columns from an absolutely continuous, centrally symmetric distribution.The probabilities P N−n,N−k change rapidly from nearly 0 to nearly 1 near k ≈ 2n − N . Consequently, there is an asymptotically sharp threshold in the behavior of face counts of the projected hypercube; thresholds known for projecting the simplex and the cross-polytope, occur at very different locations. We briefly consider face counts of the projected orthant when A does not have mean zero; these do behave similarly to those for the projected simplex. We consider non-random projectors of the orthant; the 'best possible' A is the one associated with the first n rows of the Fourier matrix.These geometric face-counting results have implications for signal processing, information theory, inverse problems, and optimization. Most of these flow in some way from the fact that face counting is related to conditions for uniqueness of solutions of underdetermined systems of linear equations. a) A vector in R N + is called k-sparse if it has at most k nonzeros. For such a k-sparse vector x 0 , let b = Ax 0 , where A is a random matrix ensemble covered by our results. With probability 1 − P N−n,N−k the inequality-constrained system Ax = b, x ≥ 0 has x 0 as its unique nonnegative solution. This is so, even if n < N , so that the system Ax = b is underdetermined. b) A vector in the hypercube H N will be called k-simple if all entries except at most k are at the bounds 0 or 1. For such a k-simple vector x 0 , let b = Ax 0 , where A is a random matrix ensemble covered by our results. With probability 1 − P N−n,N−k the inequality-constrained system Ax = b, x ∈ H N has x 0 as its unique solution in the hypercube. There are 3 fundamental regular polytopes in R N , N ≥ 5: the hypercube H N , the cross-polytope C N , and the simplex T N −1 . For each of these, projecting the vertices into R n , n < N , yields the vertices of a new polytope; in fact, every polytope in R n can be generated by rotating the simplex T N −1 and orthogonally projecting on the first n coordinates, for some choice of N and of N -dimensional rotation. Similarly, every centro-symmetric polytope can be generated by projecting the cross-polytope, and every zonotope by projecting the hypercube.

O O O O O O O O O O O O O O O O O O O O O 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 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 B O O O O


A

system

for

the

static

analysis

of

XPath

XPath

is

the

standard

language

for

navigating

XML

documents

and

returning

a

set

of

matching

nodes.

We

present

a

sound

and

complete

decision

procedure

for

containment

of

XPath

queries,

as

well

as

other

related

XPath

decision

problems

such

as

satisfiability,

equivalence,

overlap,

and

coverage.

The

considered

XPath

fragment

covers

most

of

the

language

features

used

in

practice.

Specifically,

we

propose

a

unifying

logic

for

XML,

namely,

the

alternation-free

modal

μ-calculus

with

converse.

We

show

how

to

translate

major

XML

concepts

such

as

XPath

and

regular

XML

types

(including

DTDs)

into

this

logic.

Based

on

these

embeddings,

we

show

how

XPath

decision

problems,

in

the

presence

or

absence

of

XML

types,

can

be

solved

using

a

decision

procedure

for

μ-calculus

satisfiability.

We

provide

a

complexity

analysis

of

our

system

together

with

practical

experiments

to

illustrate

the

efficiency

of

the

approach

for

realistic

scenarios.

XPath

[Clark

and

DeRose

is

the

standard

declarative

language

for

querying

an

XML

tree

and

returning

a

set

of

nodes.

It

is

increasingly

popular

due

to

its

expressive

power

and

compact

syntax.

These

advantages

have

given

XPath

a

central

role

both

in

other

key

XML

specifications

and

XML

applications.

It

is

used

in

XQuery

as

a

core

query

language;

in

XSLT

as

a

node

selector

in

transformations;

in

XML

Schema

to

define

keys;

and

in

XLink

and

XPointer

to

reference

portions

of

XML

data.

XPath

is

also

used

in

many

applications,

such

as

update

languages

[Sur

et

al.

and

XML

access

control

[Fan

et

al.

.Several

XPath

decision

problems

arise

naturally

in

these

use

cases.

The

most

basic

decision

problem

for

a

query

language

is

satisfiability

whether

or

not

an

expression

yields

a

nonempty

result.

XPath

Author's

addresses:

P.

Genevès,

N.

Layaïda,

INRIA

Rhône-Alpes,

Avenue

de

l'Europe,

Montbonnot,

St

Ismier

Cedex,

France;

email:

Pierre.geneves@inria.fr.

Permission

to

make

digital

or

hard

copies

of

part

or

all

of

this

work

for

personal

or

classroom

use

is

granted

without

fee

provided

that

the

copies

are

not

made

or

distributed

for

profit

or

direct

commercial

advantage,

and

that

copies

show

this

notice

on

the

first

page

or

initial

screen

of

a

display

along

with

the

full

citation.

Copyrights

for

components

of

this

work

owned

by

others

than

ACM

must

be

honored.

Abstracting

with

credit

is

permitted.

To

copy

otherwise,

to

republish,

or

to

post

on

servers,

to

redistribute

to

lists,

or

to

use

any

component

of

this

work

in

other

works

requires

prior

specific

permission

and/or

a

fee.

Permission

may

be

requested

from

Publications

Dept.,

ACM,

Inc.,

Penn

Plaza,

Suite

New

York,

NY

USA,

fax:

or

permission@acm.org.

P.

Genevès

and

N.

Layaïda

satisfiability

is

important

for

optimization

of

host

language

implementations:

For

instance,

if

we

can

decide

at

compile-time

that

a

query

is

not

satisfiable,

then

subsequent

bound

computations

can

be

avoided.

Another

basic

decision

problem

is

that

of

XPath

equivalence:

whether

or

not

two

queries

always

return

the

same

result.

It

is

important

for

reformulation

and

optimization

of

the

query

itself

[Genevès

and

Vion-Dury

which

aim

at

enforcing

operational

properties,

while

preserving

semantic

equivalence

[Abiteboul

and

Vianu

Levin

and

Pierce

These

two

decision

problems

are

reducible

to

XPath

containment:

whether

or

not,

for

any

tree,

the

result

of

a

particular

query

is

included

in

the

result

of

another.

Query

containment

is

itself

critical

for

the

static

analysis

of

XML

specifications

and

especially

for

type-checking

transformations

[Martens

and

Neven

Tozawa

Such

applications

introduce

XPath

decision

problems

in

the

presence

of

XML

types

such

as

DTDs

[Bray

et

al.

or

XML

schemas

[Fallside

and

Walmsley

Other

decision

problems

needed

in

applications

include,

for

example,

XPath

overlap

(whether

two

expressions

select

common

nodes)

and

coverage

(whether

nodes

selected

by

an

expression

are

always

contained

in

the

union

of

the

results

selected

by

several

other

expressions).In

the

literature,

much

attention

has

been

paid

to

classifying

the

containment

problem

for

simple

XPath

subfragments

in

complexity

classes.

This

allowed

the

identification

of

subsets

of

XPath

for

which

the

containment

can

be

efficiently

decided.In

this

article,

our

goal

is

to

describe

sound,

complete,

and

efficient

decision

procedures

that

are

usable

in

practice

for

a

large

XPath

fragment

in

the

presence

or

absence

of

XML

types.

We

first

briefly

introduce

the

XPath

language,

and

present

the

approach

and

outline

of

the

article.XPath

[Clark

and

DeRose

has

been

introduced

by

the

as

the

standard

query

language

for

retrieving

information

in

XML

documents.

It

allows

navigation

in

XML

trees

and

returning

a

set

of

matching

nodes.

In

their

simplest

form,

XPath

expressions

look

like

"directory

navigation

paths."

For

example,

the

XPath

navigates

from

the

root

of

a

document

(designated

by

the

leading

slash

through

the

top-level

"book"

element

to

its

"chapter"

child

elements

and

on

to

its

"section"

child

elements.

The

result

of

the

evaluation

of

the

entire

expression

is

the

set

of

all

the

"section"

elements

that

can

be

reached

in

this

manner,

returned

in

the

order

they

occurred

in

the

document.

At

each

step

in

the

navigation,

the

selected

nodes

for

this

step

can

be

filtered

using

qualifiers.

A

qualifier

is

a

Boolean

expression

between

brackets

that

can

test

path

existence.

So,

if

we

ask

for

[citation]

then

the

result

is

all

the

"section"

elements

that

have

a

least

one

child

element

named

"citation."

The

situation

becomes

more

interesting

when

combined

with

XPath

[Clark

and

DeRose

is

the

standard

declarative

language

for

querying

an

XML

tree

and

returning

a

set

of

nodes.

It

is

increasingly

popular

due

to

its

expressive

power

and

compact

syntax.

These

advantages

have

given

XPath

a

central

role

both

in

other

key

XML

specifications

and

XML

applications.

It

is

used

in

XQuery

as

a

core

query

language;

in

XSLT

as

a

node

selector

in

transformations;

in

XML

Schema

to

define

keys;

and

in

XLink

and

XPointer

to

reference

portions

of

XML

data.

XPath

is

also

used

in

many

applications,

such

as

update

languages

[Sur

et

al.

and

XML

access

control

[Fan

et

al.

Several

XPath

decision

problems

arise

naturally

in

these

use

cases.

The

most

basic

decision

problem

for

a

query

language

is

satisfiability

whether

or

not

an

expression

yields

a

nonempty

result.

XPath

XPath's

capability

of

searching

along

"axes"

other

than

the

shown

"children

of

axis.

Indeed,

the

aforementioned

XPath

is

a

shorthand

for

[child::citation]

where

it

is

made

explicit

that

each

path

step

is

meant

to

search

the

"child"

axis

containing

all

children

of

the

previous

context

node.

If

we

instead

asked

for

/child::book/descendant::*[child:

:citation]

then

the

last

step

selects

nodes

of

any

kind

that

are

among

the

descendants

of

the

top

element

"book"

and

have

a

"citation"

subelement..

Previous

examples

are

all

absolute

XPath

expressions.

The

meaning

of

a

relative

expression

(without

the

leading

is

defined

with

respect

to

a

context

node

in

the

tree.

A

key

to

XPath

success

is

its

compactness

due

to

the

powerful

navigation

made

possible

by

the

various

axes.

Starting

from

a

particular

context

node

in

a

tree,

every

other

node

can

be

reached.

Axes

define

a

partitioning

of

a

tree

from

any

context

node.

Figure

illustrates

this

on

a

sample

tree.

More

informal

details

on

the

complete

XPath

standard

can

be

found

in

the

specification

[Clark

and

DeRose

A

variety

of

factors

contribute

to

the

complexity

of

XPath

decision

problems,

such

as

the

operators

allowed

in

XPath

queries

and

their

combination.

We

present

here

the

common

distinctions

between

XPath

fragments

found

in

the

literature,

taken

from

-positive

vs.

nonpositive:

depending

whether

the

negation

operator

is

considered

inside

qualifiers;

-downward

vs.

upward:

depending

whether

queries

specify

downward

or

upward

traversal

of

the

tree,

or

both;.

P.

Genevès

and

N.

Layaïda

-recursive

vs.

nonrecursive:

depending

whether

XPath

transitive

closure

axes

(e.g.,

"descendant"

or

"ancestor")

are

considered;

-qualified

vs.

nonqualified:

depending

whether

queries

allow

filtering

qualifiers;

and

-with

vs.

without

data

values:

depending

whether

comparisons

of

data

values

expressing

joins

are

allowed..

From

the

results

of

and

Schwentick

we

know

that

the

combination

of

some

previous

factors

with

data

values

may

lead

to

undecidability

of

decision

problems

such

as

containment.

In

the

remaining

part

of

the

article,

we

focus

on

a

large

XPath

fragment

covering

all

previous

factors,

except

data

values.

This

fragment,

detailed

in

Section

is

the

largest

considered

so

far

in

the

literature,

and

covers

most

features

of

XPath

We

propose

a

new

logical

approach

for

XPath

decision

problems.

XPath

queries

and

regular

tree

types

are

translated

into

the

μ-calculus.

XML

decision

problems

are

expressed

as

formulae

in

this

logic,

then

decided

using

an

efficient

decision

procedure

for

μ-calculus

satisfiability.

This

article

makes

several

contributions..

P.

Genevès

and

N.

Layaïda

First,

we

propose

a

specific

variant

of

the

μ-calculus,

namely,

alternation-free

modal

μ-calculus

with

converse,

as

the

appropriate

logic

for

reasoning

on

XML

trees,

XPath

queries,

and

XML

types.

As

a

valuable

outcome,

we

show

how

both

XPath

and

regular

tree

types

can

be

linearly

translated

in

the

μ-calculus..

Second,

we

take

advantage

of

these

translations

to

reduce

several

XML

decision

problems

to

satisfiability

in

L

μ

We

obtain

effective

EXPTIME

decision

procedures

that

are

usable

in

practice.

The

considered

XPath

fragment

includes

union,

intersection,

path

composition

(together

with

all

downward

and

upward

axes),

branching,

Boolean

connectives,

wildcards,

and

negation,

in

the

presence

or

absence

of

DTDs.

This

fragment

is

far

more

complete

than

other

fragments

addressed

in

previous

studies.

We

provide

practical

experiments

and

detailed

results

that

corroborate

our

claim

that

this

approach

is

efficient

in

practice

for

real-world

XPath

expressions

and

DTDs.

Our

system

has

been

fully

implemented

[Genevès

and

Layaïda

and

can

be

used

for

the

static

analysis

of

XML

specifications.

This

strengthens

the

hope

for

an

effective

analysis

of

standard

XML

transformations

in

the

near

future..

Eventually,

an

additional

advantage

of

the

technique

is

to

allow

generation

of

XML

tree

examples

when

the

containment

does

not

hold.

We

believe

this

makes

our

method

of

special

interest

for

many

applications,

including

debuggers

or

applications

that

can

benefit

from

a

precise

reporting

during

static

analysis

stages..

One

direction

of

future

work

consists

in

specifically

tuning

the

μ-calculus

satisfiability

solver

for

XML.

Incorporating

XML

peculiarities

directly

into

the

core

of

the

μ-calculus

solver

(instead

of

general

Kripke

structures)

may

yield

even

more

efficient

decision

procedures.

Relatively

close

in

spirit

to

our

work

is

the

constructive

connection

between

XPath

and

formal

logics,

which

is

actively

studied

[Marx

Barceló

and

Libkin

From

Marx

and

Genevès

and

Vion-Dury

we

know

that

XPath

expressive

power

is

close

to

first-order

logic

(FO).

However,

FO

does

not

fully

capture

regular

tree

types

[Benedikt

and

Segoufin

Thus,

attempts

to

characterize

XPath

subfragments

in

terms

of

FO

variants

such

as

computational

tree

logic

(CTL)

[Marx

Miklau

and

Suciu

which

is

equivalent

to

FO

over

tree

structures

[Marx

Barceló

and

Libkin

are

not

intended

to

support

regular

XML

types.

The

work

found

in

Afanasiev

et

al.

proposes

a

variant

of

propositional

dynamic

logic

(PDL)

[Fischer

and

Ladner

with

a

similar

EXPTIME

complexity

for

reasoning

about

ordered

trees,

but

its

exact

expressive

power

is

still

under

study..

One

of

the

most

expressive

(yet

decidable)

known

logics

is

monadic

secondorder

logic

(MSO)

over

tree

structures,

which

extends

FO

by

quantification

over

sets

of

nodes.

Specifically,

the

appropriate

MSO

variant

which

exactly

captures

regular

tree

types

is

the

weak

monadic

second-order

logic

of

two

successors

[Thatcher

and

Wright

Doner

From

Arnold

and

Niwinski

and

Kupferman

and

Vardi

we

know

that

is

exactly

as

expressive

as

the

alternation-free

fragment

(AFMC)

of

the

propositional

modal

μ-calculus

introduced

in

Kozen

However,

the

satisfiability

problem

for

is

nonelementary

while

in

EXPTIME

AFMC.

Moreover,

We

recall

that

the

term

elementary

introduced

by

Grzegorczyk

refers

to

functions

obtained

from

some

basic

functions

by

operations

of

limited

summation

and

limited

multiplication.

Consider

the

function

tower()

defined

by:

tower(n,

n

tower(n,

k

tower(n,k)

Grzegorczyk

has

shown

that

every

elementary

function

in

one

argument

is

bounded

by

λn.tower(n,

c)

for

some

constant

c.

Hence,

the

term

nonelementary

refers

to

a

function

that

grows

faster

than

any

such

function.

The

complexity

class

EXPTIME

is

the

set

of

all

decision

problems

solvable

by

a

deterministic

Turing

machine

in

p(n)

time,

where

p(n)

is

a

polynomial

function

of

the

input

size

n..

AFMC

subsumes

all

early

logics,

such

as

CTL

[Clarke

and

Emerson

and

PDL

[Fischer

and

Ladner

Furthermore,

the

work

in

Vardi

adds

converse

programs

to

propositional

modal

μ-calculus

and

shows

that

the

resulting

logic

still

admits

an

EXPTIME

decision

procedure

for

satisfiability.

It

follows

that

alternation-free

modal

μ-calculus

with

converse

sounds

like

an

appropriate

logic

for

XML:

It

is

expressive

enough

to

capture

a

significant

class

of

XPath

decision

problems,

while

potentially

providing

efficient

and

practically

effective

decision

procedures.

From

the

point

of

view

of

computational

complexity,

some

EXPTIME

upper

bounds

are

already

known

for

the

satisfiability

and

containment

of

specific

subsets

of

our

XPath

fragment.

The

complexity

of

XPath

satisfiability

in

the

presence

of

DTDs

is

studied

in

XPath

containment

has

specifically

attracted

a

lot

of

research

attention

[Amer-Yahia

et

al.

Deutsch

and

Tannen

Miklau

and

Suciu

Neven

and

Schwentick

Schwentick

Wood

Prior

work

concentrated

on

various

combinations

of

the

previous

factors

for

obtaining

complexity

results

(see

Schwentick

for

an

overview).

Specifically,

the

focus

was

given

to

restricted

positive

XPath

subfragments

without

upward

axes.

In

particular,

Neven

and

Schwentick

proves

an

EXPTIME

upper

bound

for

containment

(in

the

presence

of

DTDs)

of

queries

containing

the

"child"

and

"descendant"

axes,

and

union

of

paths.

Deutsch

and

Tannen

consider

XPath

containment

in

the

presence

of

DTDs

and

simple

XPath

integrity

constraints

(SXICS).

They

maintain

that

this

problem

is

undecidable

in

general

and

in

the

presence

of

bounded

SXICs

and

DTDs.

Containment

for

the

fragment

XP

is

shown

to

be

coNP-complete

in

Miklau

and

Suciu

where

the

containment

mapping

technique

relies

on

a

polynomial-time

tree

homomorphism

algorithm

that

gives

a

sufficient,

but

not

necessary,

condition

for

containment

of

XP

in

general.

Additionally,

the

containment

problem

is

shown

to

be

in

EXPTIME

for

the

fragments

XP

XP

XP

in

the

presence

of

DTDs

in

Wood

Compared

to

all

these

previous

works,

the

XPath

fragment

we

consider

is

far

more

complete

and

much

more

realistic.

We

also

present

a

single

unifying

logical

framework

in

which

all

major

XPath

features,

but

also

regular

tree

types,

fit

together.

Moreover,

our

framework

yields

effective

decision

procedures

that

are

usable

in

practice

for

real-world

scenarios

(whereas

no

usable

working

system

has

been

reported

in

prior

work)..

Finally,

from

a

theoretical

perspective,

we

see

the

connection

between

XML

and

μ-calculus

as

a

simple

way

of

deriving

the

precise

upper

bound

time

complexity

O(n·log

n)

of

XML

decision

problems,

where

n

is

the

combined

size

of

considered

XPath

queries

and

tree

types.

O O O O O O O B B 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 B O O O O O O B O O O O O B O O O O O B O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O B O O O B O O B O O O O O B O O O O O O O B 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 B 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 B O O O O O O O B O O B O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O B O B O O O O O O O O O B O O O O O B O O O O O O O B 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 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 B O O O 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 B 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 B O O O O O O O O O O O B O O O O O O O B B 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 O O O O O O B 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 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 B O O O B O O O O O O O O O O O B 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 B O O O O O O O B 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 B O O O O O B O O O O O B O O O O O O O O O O O O B 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 B 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 B O O O O O O O B O O B O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O B O B O O O O O O O O O B O O O O O B O O O O O O O O B 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 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 O O O O O O O O O O O O O O O O O O O O O O O O O O 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 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 B 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 B 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 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 B 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 B O O O O O O O O O B O O B O O O O O O O O O O B 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 B O O O B O B O O B 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 B 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 B 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 O O O O O O O O O O O O O O O O O B 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 B 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 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 B 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 B 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 B 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 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 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 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Hypermedia on the Web: what will it take? Researchers in the hypermedia field often lament that the World Wide Web does not support many of hypermedia's rich structuring, navigation and annotation features. What would it take for everyday Web applications to be fully hypermedia compliant, now that the basic hypermedia building blocks exist on the Web? The following four capabilities are the most critical for integrating hypermedia support in the Web environment: edit-capable browsers, storing document content and link anchors separately, external linkbases, and displaying link spans, node and link attributes. Individual developers cannot decide autonomously on how to resolve many of the outstanding issues. Developers need agreed-upon conventions and tools built upon today's Web standards to fully incorporate hypermedia functionality into everyday applications. Researchers in the hypermedia field often lament that the World Wide Web does not support many of hypermedia's rich structuring, navigation and annotation features ], [Bieber 1997a ] developed over the last 40 years since Engelbart's NLS system Engelbart 1968] . Structuring features include semantically typed anchors, links and nodes; attributes and keywords on these; links to and from content spans within any medium; bidirectional links; __________________________ Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Publications Dept, ACM Inc., fax +1 (212) 869-0481, or permissions@acm.org ACM Computing Surveys, Vol. 31, Number 4es, December 1999 links recursively to links and to other hypermedia constructs; transclusions and inclusions providing access to all uses of the same span of content; versioning of hypermedia constructs; landmarks; automatic link propogation; trails and guided tours; and local and global overviews. Navigation features include link traversal; visual feedback upon link arrival; search based on the hypermedia structure (as opposed to content); process enactment through link traversal; backtracking strategies; backjumping; and history mechanisms. Annotation features include comments, bookmarks and reader-authored links with private, workgroup and public access. People can annotate any hypermedia construct, including other annotations recursively.. In fact, standard Web data formats and protocols recently introduced can facilitate many of these. So what is really standing in the way? What would it take for everyday Web applications to be fully hypermedia compliant? Now that the basic hypermedia building blocks exist, hypermedia and WWW researchers must now figure out how to deploy them to create an infrastructure for seamlessly integrating hypermedia techniques into the Web environment and making them pervasive in everyone's daily Web activities.. We believe that the following four capabilities are the most critical for integrating hypermedia support to the Web environment:. • edit-capable browsers. • storing document content and link anchors separately

B O O O O O O O O O O B 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 B O O O O O B O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O B 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 B O O O O O O O B 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 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 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 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 B O O O O O B O O O B 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 B O O O O O O O B O O O O O O O O


On the Role of Shared Entanglement Despite the apparent similarity between shared randomness and shared entanglement in the context of Communication Complexity, our understanding of the latter is not as good as of the former. In particular, there is no known "entanglement analogue" for the famous theorem by Newman, saying that the number of shared random bits required for solving any communication problem can be at most logarithmic in the input length (i.e., using more than O(log n) shared random bits would not reduce the complexity of an optimal solution).In this paper we prove that the same is not true for entanglement. We establish a wide range of tight (up to a polylogarithmic factor) entanglement vs. communication tradeoffs for relational problems. The low end is: for any t > 2, reducing shared entanglement from log t n to o(log t−2 n) qubits can increase the communication required for solving a problem almost exponentially, from O(log t n) to Ω( √ n). The high end is: for any ε > 0, reducing shared entanglement from n 1−ε log n to o(n 1−ε / log n) can increase the required communication from O(n 1−ε log n) to Ω(n 1−ε/2 / log n). The upper bounds are demonstrated via protocols which are exact and work in the simultaneous message passing model, while the lower bounds hold for bounded-error protocols, even in the more powerful model of 1-way communication. Our protocols use shared EPR pairs while the lower bounds apply to any sort of prior entanglement.We base the lower bounds on a strong direct product theorem for communication complexity of a certain class of relational problems. We believe that the theorem might have applications outside the scope of this work. Suppose that Alice, Bob and Charlie play the following game: Alice receives an n-bit binary string x, Bob receives a string y of the same length, they both send some information to Charlie, who then tries to guess (based on the received messages) whether x = y or not. The goal is for Alice and Bob to send as short messages as possible, such that Charlie would still be able to answer correctly with probability at least 3/4. Assume that before the game starts Alice and Bob choose two random binary strings r 1 and r 2 , of length 2 n each. Then they treat their n-bit inputs as indices in the range [1..2 n ] and send to Charlie the bits which are on the positions x and y of r 1 and r 2 (i.e., Alice and Bob send 2 bits each). Eventually, Charlie decides that x = y if the pairs of bits received from Alice and Bob are the same, otherwise he declares that x = y. It is clear that if Charlie guesses that x = y then he is correct with probability 3/4 and if he says that x = y then he is certainly right. So, we see that the problem can be solved by communicating only 4 bits (for any input length n). On the other hand, Newman and Szegedy [NS96] have shown that if Alice and Bob do not share random bits then they must communicate at least Ω ( √ n) bits in order to win the game with any constant probability greater than 1/2. We can let our players use the laws of quantum mechanics in order to further increase their strength. Specifically, they can share entanglement. 1 In this case they are allowed to apply any quantum-mechanical operation to their subspaces of the common Hilbert space. In particular, they can perform measurements and their behavior may depend on the outcomes of the measurements.. If the players share a sequence of random bits (chosen uniformly and independently) we say that they are using shared or public randomness (also called a public coin). If the players share a quantum state we say that they are using shared entanglement (note that it would be useless to share a state which is not entangled w.r.t. the players' local subspaces). It is easy to see that in the model of shared entanglement the players are at least as strong as they are in the model of shared randomness (k independent shared EPR pairs can be measured locally in order to get k perfect random bits).. In this paper we will deal with a longstanding open question regarding the power of quantum entanglement in communication. In this paper we solve one of the open question regarding the power of quantum entanglement in communication complexity: we show that no general sublinear upper bound on the required amount of shared entanglement can be put in the models of classical communication with either 1-way or simultaneous message passing. Can similar results be obtained for other communication models?. In Section 5 we showed a simple modification of our entanglement bounding ideas which leads to some nontrivial statement regarding the power of 2-prover proof systems with shared entanglement. Can we find other applications of our technique outside the domain of communication complexity? Possible applications to other communication complexity models might be interesting too. Given that the power of entanglement is one of the most important longstanding open problems in the area, it is very tempting to look for other applications of our technique.. There are some more technical questions. Can we find more uses for our strong direct product theorem for relations? It would be interesting to find applications other than HMP, though even with that relation it might probably lead to more results in communication complexity. The importance of HMP stems from the fact that this is the only problem we know today which demonstrates superpolynomial (in fact, exponential) separation between quantum and classical 1-way communication models.. It would be also interesting to see whether results similar to ours can be demonstrated through functional problems, either total or partial (the latter means that some combinations of (x, y) can never appear in the input).. The last question we would like to mention is whether independent EPR pairs provide a universal source of entanglement in the contexts of 2-party communication complexity and 2-prover proof systems.

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


Sensor-driven agenda for intelligent home care of the elderly The exponential increase of home-bound persons who live alone and are in need of continuous monitoring requires new solutions to current problems. Most of these cases present illnesses such as motor or psychological disabilities that deprive of a normal living. Common events such as forgetfulness or falls are quite common and have to be prevented or dealt with. This paper introduces a platform to guide and assist these persons (mostly elderly people) by providing multisensory monitoring and intelligent assistance. The platform operates at three levels. The lower level, denominated ''Data acquisition and processing'' performs the usual tasks of a monitoring system, collecting and processing data from the sensors for the purpose of detecting and tracking humans. The aim is to identify their activities in an intermediate level called ''activity detection''. The upper level, ''Scheduling and decision-making'', consists of a scheduler which provides warnings, schedules events in an intelligent manner and serves as an interface to the rest of the platform. The idea is to use mobile and static sensors performing constant monitoring of the user and his/her environment, providing a safe environment and an immediate response to severe problems. A case study on elderly fall detection in a nursery home bedroom demonstrates the usefulness of the proposal. Elderly population growth is a concerning situation. The latest census collected in developed countries show that elderly population is increasing very fast, whilst on the contrary younger population is decreasing. This means that the overall population is getting older, thus triggering scenarios that were unknown in the recent past. The new situation reveals new challenges, mostly related to health, economy and society issues. Medical advances permit the providence of better services to the attendants, as well as the availability of an improved health care to the general public. This translates to better services, procedures and cures to current illnesses. The main beneficiaries of these improvements are persons -most likely elderly persons -whose health condition is more fragile. This population group frequently suffers from illnesses; and severity is more intense than in younger persons (Weil, 2006) . Although chronic and constant pain are quite common, new medical approaches to these diseases help people in improving their daily life. The described factors contribute to an increased life expectancy and quality. As aforementioned, the abrupt reverse of the population age pyramid brings adverse economical situations. There is no doubt that costs involved in elderly care are elevated. On the other hand, families and public social care are less able to provide services as less money is available to date. Moreover, young working people might support persons in retirement, but currently there is a lack of balance, revealing that about three workers are needed to economically support a single elderly person. The economic problems also lead to social problems (United Nations, 2009). Indeed, health care services, such as daycare centers and retirement houses, are insufficient to accommodate all the needy persons. A more familiar solution is to look after a person at his/her relatives' home. But, this carries an economic and personal burden. The family has to support one more person who normally makes little money as income and much attention has to be spent on the elderly. Such timely or economic sacrifices are usually not assumable by the families (Beard, 2010) .. In contrast, elderly persons tend to prefer living at their own homes. But it is difficult to provide the necessary safety and assistance when nobody is monitoring them. Also, as loneliness sets in, the elderly become more reclusive, and the probability of being unassisted when a problem arises increases. In this sense, technology can be the solution to the described problems. The rapid decrease of technological devices' cost and the exponential increase of capabilities and computing power leads to a multipurpose use in new domains. The availability of software that provides intelligent and proactive actions, according to sensor data capture, enables the use of complex functions in simple sensors and actuators. Ambient Assisted Living (AAL) is an area that has been intrinsically joined to this concept. AAL describes user-home interactions using sensors and actuators. It also defines the interfaces and devices needed by the user in case of disabilities and illnesses. This paper has presented an information and communications technology (ICT) solution towards facing the current problem of attending home-bound persons who live alone and are in need of continuous monitoring. In this sense, the concept of Ambient Assisted Living (AAL), which consists of applying technology in a user's home environment, transforming it into a seamless interactive sphere adapted to the user's needs, has inspired the approach offered in this proposal. Indeed, the paper has presented a platform to guide and assist these persons (mostly elderly people) by providing multisensory monitoring and intelligent assistance.. A three-level platform has been described extensively. The lower level (''Data acquisition and processing'') performs the usual tasks of a monitoring system, collecting data from the sensors and processing it for the purpose of detecting and tracking humans in order to identify their activities. Initially, a Data acquisition component translates the data captured by the sensors. The Blob detection component filters the spots that are candidates to be objects of interest. The next component is in charge of Object identification, tracking & classification, raising the information abstraction from blobs to objects. Then, the proposal incorporates external knowledge about the problem domain into the expected structure of an ''Activity detection'' module. Motion-based image features are explicitly linked to a symbolic notion of hierarchical activity through several layers of more abstract activity descriptions. Here, atomic actions are detected and fed to handcrafted grammars to detect activity patterns of interest. Besides, we work with shape and trajectory to indicate the events related to moving objects. Now, the upper level, ''Scheduling and decision-making'', consists of a scheduler which provides warnings, intelligently schedules events and serves as an interface to the rest of the platform. The scheduling interface with the user is developed following the principles established in the iGenda project. Intelligent scheduling goes beyond the normal conception of traditional scheduling. The intelligent agenda contains several events in charge of actions that persons normally carry out, such as taking medication, but at the time are difficult to remember for a memory impaired person. Currently, the components of the ''Scheduling and decision-making'' are Agenda manager, Conflicts manager, Free time manager, profiling system, Clinical guidelines, Medication reminder and Sensing manager.. Moreover, the approach uses mobile and static sensors performing constant monitoring of the user and his/her environment, providing a safe environment and an immediate response to severe problems. The mobile platform is optimally developed to interact with the users, providing visual and audible information, as well as warnings. Also, the mobile platform enables everywhere availability to the user. This means that it is easier to the user to provide feedback to the platform when required, without having to even move from where he/she is. Also, the mobile platform serves as a direct input to an emergency situation. If the user is inactive for a period of time, the platform is prompted to present a question to the user, collecting different aspects beyond the answer itself. The lack of response from the user points out that something happened to the user. Also it can serve as a panic button that calls to a relative or an emergency service, providing automatically the user's location.. Lastly, a case study on elderly fall detection in a nursery home bedroom has shown the usefulness of the proposal. It is our intention to install our platform at different locations of a nursery home and increase the current capacities of the platform. And, although the initial consideration and development was made to face the problems inherent in the elderly, as future work we propose to enhance the functionalities in the mobile platform. We consider working for persons with visual or hearing difficulties. In this sense, we envisage to engage in adaptive interfaces, which is an important approach to build a system that is welcomed by the users, by providing more and more intuitive interfaces.

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