This dissertation is devoted to the development of new flow-based formulations for the asymmetric traveling salesman problem (ATSP) and to the demonstration of their applicability in effectively solving some scheduling problems. The ATSP is commonly encountered in the areas of manufacturing planning and scheduling, and transportation logistics. The integration of decisions pertaining to production and shipping, in the supply chain context, has given rise to an additional and practical relevance to this problem especially in situations involving sequence-dependent setups and routing of vehicles. Our objective is to develop new ATSP formulations so that algorithms can be built by taking advantage of their relaxations (of integer variables, thereby, resulting in linear programs) to effectively solve large-size problems. In view of our objective, it is essential to have a formulation that is amenable to the development of an effective solution procedure for the underlying problem. One characteristic of a formulation that is helpful in this regard is its tightness. The tightness of a formulation usually refers to the quality of its approximation to the convex hull of integer feasible solutions. Another characteristic is its compactness. The compactness of a formulation is measured by the number of variables and constraints that are used to formulate a given problem. Our formulations for the ATSP and the scheduling problems that we address are both tight and compact. We present a new class of polynomial length formulations for the asymmetric traveling salesman problem (ATSP) by lifting an ordered path-based model using logical restrictions in concert with the Reformulation-Linearization Technique (RLT). We show that a relaxed version of this formulation is equivalent to a flow-based ATSP model, which, in turn, is tighter than the formulation based on the exponential number of Dantzig-Fulkerson-Johnson (DFJ) subtour elimination constraints. The proposed lifting idea is applied to derive a variety of new formulations for the ATSP, and a detailed analysis of these formulations is carried out to show that some of these formulations are the tightest among those presented in the literature. Computational results are presented to exhibit the relative tightness of our formulations and the efficacy of the proposed lifting process.> While the computational results demonstrate the efficacy of employing the proposed theoretical RLT and logical lifting ideas, yet it remains of practical interest to take due advantage of the tightest formulations. The key requirement to accomplish this is the ability to solve the underlying LP relaxations more effectively. One approach, to that end, is to solve these LP relaxations to (near-) optimality by using deflected subgradient methods on Lagrangian dual formulations. We solve the LP relaxation of our tightest formulation, ATSP6, to (near-) optimality by using a deflected subgradient algorithm with average direction strategy (SA_ADS) (see Sherali and Ulular [69]). We also use two nondifferentiable optimization (NDO) methods, namely, the variable target value method (VTVM) presented by Sherali et al. [66] and the trust region target value method (TRTV) presented by Lim and Sherali [46], on the Lagrangian dual formulation of ATSP6. The preliminary results show that the near-optimal values obtained by the VTVM on solving the problem in the canonical format are the closest to the target optimal values. Another approach that we use is to derive a set of strong valid inequalities based on our tighter formulations through a suitable surrogation process for inclusion within the more compact manageable formulations. Our computational results show that, when the dual optimal solution is available, the associated strong valid inequalities generated from our procedure can successfully lift the LP relaxation of a less tight formulation, such as ATSP2R¯, to be as tight as the tightest formulation, such as ATSP6. We extend our new formulations to include precedence constraints in order to enforce a partial order on the sequence of cities to be visited in a tour. The presence of precedence constraints within the ATSP framework is encountered quite often in practice. Examples include: disassembly optimization (see Sarin et al. [62]), and scheduling of wafers/ ICs on automated testing equipments in a semiconductor manufacturing facility (see Chen and Hsia [17]); among others. Our flow-based ATSP formulation can very conveniently capture these precedence constraints. We also present computational results to depict the tightness of our precedence-constrained asymmetric traveling salesman problem (PCATSP) formulations. We, then, apply our formulations to the hot strip rolling scheduling problem, which involves the processing of hot steel slabs, in a pre-specified precedence order, on one or more rollers. The single-roller hot strip rolling scheduling problem can be directly formulated as a PCATSP. We also consider the multiple-roller hot strip rolling scheduling problem. This gives rise to the multiple-asymmetric traveling salesman problem (mATSP). Not many formulations have been presented in the literature for the mATSP, and there are none for the mATSP formulations involving a precedence order among the cities to be visited by the salesmen, which is the case for the multiple-roller hot strip rolling scheduling problem. To begin with, we develop new formulations for the mATSP and show the validity of our formulations, and present computational results to depict their tightness. Then, we extend these mATSP formulations to include a pre-specified, special type of precedence order in which to process the slabs, and designate the resulting formulations as the restricted precedence-constrained multiple-asymmetric traveling salesman problem (rPCmATSP) formulations. We directly formulate the multiple-roller hot strip rolling scheduling problem as a rPCmATSP. Furthermore, we consider the hot strip rolling scheduling problem with slab selection in which not all slabs need to be processed. We model the single-roller hot strip rolling scheduling problem with slab selection as a multiple-asymmetric traveling salesman problem with exactly two traveling salesmen. Similarly, the multiple-roller hot strip rolling scheduling problem with slab selection is modeled as a multiple-asymmetric traveling salesman problem with (m+1) traveling salesmen. A series of computational experiments are conducted to exhibit the effectiveness of our formulations for the solution of hot strip rolling scheduling problems. Furthermore, we develop two mixed-integer programming algorithms to solve our formulations. These are based on Benders΄ decomposition [13] and are designated Benders΄ decomposition and Modified Benders΄ methods. In concert with a special type of precedence order presented in the hot strip rolling scheduling problems, we further introduce an adjustable density ratio of the associated precedence network and we use randomly generated test problems to study the effect of various density ratios in solving these scheduling problems. Our experimentation shows the efficacy of our methods over CPLEX. Finally, we present a compact formulation for the job shop scheduling problem, designated as JSCD (job shop conjunctive-disjunctive) formulation, which is an extension of our ATSP formulations. We use two test problems given in Muth and Thompson [53] to demonstrate the optimal schedule and the lower bound values obtained by solving the LP relaxations of our formulations. However, we observe that the lower bound values obtained by solving the LP relaxations of all variations of our JSCD formulation equal to the maximum total processing time among the jobs in the problem. / Ph. D.

This dissertation develops efficient solution techniques for general and problem-specific applications within nonconvex optimization, exploiting the constructs of the Reformulation-Linearization Technique (RLT). We begin by developing a technique to enhance general problems in nonconvex optimization through the use of a new class of RLT cuts, called semidefinite cuts. While these cuts are valid for any general problem for which RLT is applicable, we demonstrate their effectiveness in optimizing a nonconvex quadratic objective function over a simplex. Computational results indicate that on average, the semidefinite cuts have reduced the number of nodes in the branch-and-bound tree by a factor of 37.6, while decreasing solution time by a factor of 3.4. The semidefinite cuts have also led to a significant reduction in the optimality gap at termination, in some cases producing optimal solutions for problems that could not be solved using RLT alone. We then narrow our focus to the class of mixed-integer programming (MIP) problems, and develop a modification of Benders' decomposition method using concepts from RLT and lift-and-project cuts. This method is particularly motivated by the class of two-stage stochastic programs with integer recourse. The key idea is to design an RLT or lift-and-project cutting plane scheme for solving the subproblems where the cuts generated have right-hand sides that are functions of the first-stage variables. An illustrative example is provided to elucidate the proposed approach. The focus is on developing a first comprehensive finitely convergent extension of Benders' methodology for problems having 0-1 mixed-integer subproblems. We next address a specific challenging MIP application known as the facility layout problem, and we significantly improve its formulation through outer-linearization techniques and concepts from disjunctive programming. The enhancements produce a substantial increase in the accuracy of the layout produced, while at the same time, providing a dramatic reduction in computational effort. Overall, the maximum error in department size was reduced from about 6% to nearly zero, while solution time decreased by a factor of 110. Previously unsolved test problems from the literature that had defied even approximate solution methods have been solved to exact optimality using our proposed approach. / Ph. D.

Sans formation spécialisée en rédaction, des adultes utilisent leurs habiletés rédactionnelles en tant qu'étudiants, chercheurs d'emploi, employés ou entrepreneurs. Nous les appelons rédacteurs fonctionnels. Ces derniers publient leurs textes sur un blogue, dans un magazine ou dans un livre édité. Ces textes font souvent l'objet d'une révision linguistique. Au moment d'en effectuer la lecture, les réviseurs doivent parfois relire des passages pour saisir la relation entre des informations. Cette difficulté de lecture semble provoquée parfois par l'absence d'un connecteur, parfois par l'emploi d'un connecteur qui ne permet pas au lecteur d'identifier une relation vraisemblable entre les évènements. Les connecteurs sont des outils linguistiques servant à marquer les relations (ex. cause, restriction, but). Leur présence, bien qu'elle ne soit pas toujours requise, et leur emploi judicieux contribuent à faire en sorte que l'arrimage des énoncés au niveau évènementiel soit réussi. Or, dans certains cas, l'absence ou l'emploi d'un connecteur fait en sorte que le lecteur doit déployer un grand effort cognitif pour identifier cette relation entre les énoncés. Ces phénomènes engendrent une rupture de cohérence au niveau évènementiel. Dans ce mémoire, nous avons voulu comprendre les conditions dans lesquelles la cohérence au niveau évènementiel peut être perturbée par l'absence ou l'emploi plus ou moins adéquat de connecteurs. Pour ce faire, nous avons analysé 18 rédigés par 12 rédacteurs fonctionnels québécois francophones. Il ressort de notre analyse que la compétence des rédacteurs de notre corpus, en ce qui a trait à l'emploi des connecteurs, est très inégale. Si des ruptures ont été observées dans 12 textes (d'une à huit ruptures par texte), il reste que six textes ne présentent aucune rupture. Nos résultats font état de 41 ruptures, dont 33 résultent de l'absence d'un connecteur. De ce nombre, 13 ruptures touchent l'articulation de l'addition et 9, l'articulation de la conclusion.

本篇論文的目的在於探討兒童在親子對話中行使重新請求 (request reformulation) 的情況，研究問題如下: 1.兒童採取哪些重新請求的策略以達到請求的目的? 2.親子對話中，常見的重新請求的序列模式（patterns of request reformulation sequences）為何？ 2.如何從兒童重新請求的使用反映出角色取代能力 (perspective-taking ability )的發展? 研究對象為一位三歲和一位六歲的男孩。研究結果顯示隨著年紀的增長，兒童能使用更多元的重新請求策略。研究也發現造成請求失敗的原因隨著不同年齡的兒童有所差異。隨著年紀的增長，兒童面臨的失敗原因和挑戰日漸複雜、困難，兒童會依據不同的失敗原因採取重新請求的策略。最後，研究顯示不同年齡兒童採取的重新請求策略可以展現出他們不同階段的角色取代能力的發展。三歲的兒童無法跳脫自己的觀點而從別人的角度來看待自己的請求，所以重新請求著重於強調自己的需求。六歲的兒童較能夠從別人的立場看待自己的請求，所以他較有能力在考量對方的觀點和利益之後採用對雙方有益的策略。 / The purpose of this study is to explore how children at different age make reformulation to compensate for an unsuccessful request. Firstly, we aim to investigate what reformulation strategies children apply and the patterns of reformulation sequences. Second, we further aim to explore how children’s use of reformulation strategies reveals the development of perspective-taking ability. The data analyzed are natural conversations of two Mandarin-speaking mother-child dyads. Subjects in this present study are two male children. One subject is three years and six months old and the other is six years old. The strategies of request reformulation adopted in this study are mainly based on Levin and Rubin’s (1984) categorization. The results show that children would have a greater variety of reformulation strategies as they get older. Furthermore, aggravation and explanation are both children’s main strategies of reformulation. With the growth of age, children decrease the use of aggravation and increase the use of bargain and mitigation. Furthermore, the results of reformulation sequences reveal that the two children are confronted with different causes of the failure to obtain compliance, which influences their adoption of reformulation strategies. The younger child faced the communicative breakdown and his mother’s ignorance while the older child encountered his mother’s queries and disagreements. Finally, the two children’s application of reformulation strategies revealed their different ability to take the other’s perspectives. The younger child’s reliance on aggravation and speaker-oriented negotiation reveals that he is embedded in his own viewpoints and is less able to view his request from the hearer’s viewpoints while the older child is more able to view the request from the hearer’ perspective and take her benefits into account. Our findings throw some light on children’s use of request reformulation strategy and the development of the perspective-taking ability.

Durante as décadas de 70 e 80, desenvolveram-se métodos baseados em penalidades exatas diferenciáveis para resolver problemas de otimização não linear com restrições. Uma desvantagem dessas penalidades é que seus gradientes contêm termos de segunda ordem em suas fórmulas, o que impede a utilização de métodos do tipo Newton para resolver o problema. Para contornar essa dificuldade, utilizamos uma ideia de construção de penalidade exata para desigualdades variacionais, introduzida recentemente por André e Silva. Essa construção consiste em incorporar um estimador de multiplicadores, proposto por Glad e Polak, no lagrangiano aumentado para desigualdades variacionais. Nesse trabalho, estendemos o estimador de multiplicadores para restrições gerais de igualdade e desigualdade, e enfraquecemos a hipótese de regularidade. Como resultado, obtemos uma função penalidade exata continuamente diferenciável e uma nova reformulação do sistema KKT associado a problemas não lineares. A estrutura dessa reformulação permite a utilização do método de Newton semi-suave, e a taxa de convergência local superlinear pode ser provada. Além disso, verificamos que a penalidade exata construída pode ser usada para globalizar o método, levando a uma abordagem do tipo Gauss-Newton. Por fim, realizamos experimentos numéricos baseando-se na coleção CUTE de problemas de teste. / During the 1970\'s and 1980\'s, methods based on differentiable exact penalty functions were developed to solve constrained optimization problems. One drawback of these functions is that they contain second-order terms in their gradient\'s formula, which do not allow the use of Newton-type methods. To overcome such difficulty, we use an idea for construction of exact penalties for variational inequalities, introduced recently by André and Silva. This construction consists on incorporating a multipliers estimate, proposed by Glad and Polak, in the augmented Lagrangian function for variational inequalities. In this work, we extend the multipliers estimate to deal with both equality and inequality constraints and we weaken the regularity assumption. As a result, we obtain a continuous differentiable exact penalty function and a new equation reformulation of the KKT system associated to nonlinear problems. The formula of such reformulation allows the use of semismooth Newton method, and the local superlinear convergence rate can be also proved. Besides, we note that the exact penalty function can be used to globalize the method, resulting in a Gauss-Newton-type approach. We conclude with some numerical experiments using the collection of test problems CUTE.

The presented thesis discusses bilevel programming problems with the focus on solution algorithms. Bilevel programming problem is a hierarchical programming problem, where constraints contain another programming problem. We formulate basic bilevel optimization theory and describe three types of so- lution algorithms for bilevel programming problems: Algorithms based on KKT reformulation where the lower level is replaced by its KKT conditions, algorithms based on optimal value function where the bilevel programming problem is re- duced to a single level problem using the optimal value function of the lower level problem, and algorithms solving linear bilevel programming problems. Using real data for portfolio optimization bilevel programming problems, we compare ability to solve the problems and computing time of some of the pre- sented algorithms. 1

Durante as décadas de 70 e 80, desenvolveram-se métodos baseados em penalidades exatas diferenciáveis para resolver problemas de otimização não linear com restrições. Uma desvantagem dessas penalidades é que seus gradientes contêm termos de segunda ordem em suas fórmulas, o que impede a utilização de métodos do tipo Newton para resolver o problema. Para contornar essa dificuldade, utilizamos uma ideia de construção de penalidade exata para desigualdades variacionais, introduzida recentemente por André e Silva. Essa construção consiste em incorporar um estimador de multiplicadores, proposto por Glad e Polak, no lagrangiano aumentado para desigualdades variacionais. Nesse trabalho, estendemos o estimador de multiplicadores para restrições gerais de igualdade e desigualdade, e enfraquecemos a hipótese de regularidade. Como resultado, obtemos uma função penalidade exata continuamente diferenciável e uma nova reformulação do sistema KKT associado a problemas não lineares. A estrutura dessa reformulação permite a utilização do método de Newton semi-suave, e a taxa de convergência local superlinear pode ser provada. Além disso, verificamos que a penalidade exata construída pode ser usada para globalizar o método, levando a uma abordagem do tipo Gauss-Newton. Por fim, realizamos experimentos numéricos baseando-se na coleção CUTE de problemas de teste. / During the 1970\'s and 1980\'s, methods based on differentiable exact penalty functions were developed to solve constrained optimization problems. One drawback of these functions is that they contain second-order terms in their gradient\'s formula, which do not allow the use of Newton-type methods. To overcome such difficulty, we use an idea for construction of exact penalties for variational inequalities, introduced recently by André and Silva. This construction consists on incorporating a multipliers estimate, proposed by Glad and Polak, in the augmented Lagrangian function for variational inequalities. In this work, we extend the multipliers estimate to deal with both equality and inequality constraints and we weaken the regularity assumption. As a result, we obtain a continuous differentiable exact penalty function and a new equation reformulation of the KKT system associated to nonlinear problems. The formula of such reformulation allows the use of semismooth Newton method, and the local superlinear convergence rate can be also proved. Besides, we note that the exact penalty function can be used to globalize the method, resulting in a Gauss-Newton-type approach. We conclude with some numerical experiments using the collection of test problems CUTE.

Made available in DSpace on 2015-04-22T22:16:06Z (GMT). No. of bitstreams: 1 daiana santos.pdf: 1011976 bytes, checksum: 0d1f23d4c01774fbad224c1c0fbe0359 (MD5) Previous issue date: 2013-09-23 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / In this dissertation, we present a proximal point method for solving problems balance in Hilbert spaces proposed by Alfredo Iusem and Wilfredo Sosa in [1]. We analyzed the convergence of this mehtod for troubleshooting balance. We verified the sequence generated by the method of classical proximal point and generated sequence the proximal point method to balance problems are the same. These results were obtained using variations of monotonicity of the function that defines the balance problem. In the final analysis is made on the weakening of the hypothesis assumed by function. / Nesta dissertação, apresentamos um método de ponto proximal para resolução de problemas de equilíbrio em espaços de Hilbert proposto por Alfredo Iusem e Wilfredo Sosa em [1]. Analisamos a convergência deste método para soluções de problemas de equilíbrio. Verificamos que a sequência gerada pelo método de ponto proximal clássico e a sequência gerada pelo método de ponto proximal para problemas de equilíbrio coincidem. Esses resultados foram obtidos usando variações de monotonicidade sobre a função que define o problema de equilíbrio. Uma análise final é feita sobre o enfraquecimento das hipóteses assumidas pela função.

In many institutional settings in today’s globalized job market, people have to deal with different role asymmetries in the co-construction of meaning. In this study, institutional, cultural and linguistic asymmetries are focused on in interviews at an employment agency in Sweden. Interviews between a recruiter and fourteen female job candidates with an academic background from other countries were video taped. Three sequences on personality were analysed: What do you consider to be your strengths? What personal characteristics do you want to improve? and What has made an impact on you? The general aim of the study was to gain knowledge of the processes whereby self-presentations are co-constructed and how participants try to reach common understanding when they do not share common linguistic and cultural resources. Theoretically, the study has a dialogical framework. Discourse is seen as the place where society, culture, situation, individual and language meet and where meaning is constructed through social action. Within an interactional sociolinguistics framework, an holistic approach to methods combines ethnography of communication with ethnomethodology and conversation analysis. The results show that the meaning-making project in this institutional situation is institutionally framed, culturally hidden, socially constrained by face-work and interactionally embedded. The recruiter orients to the institutional frame by embedding reformulations of the candidates’ answers in her uptake, often an adjective, which is filled in on a form and later transferred to a data base. The recruiter also takes on the face-work of the communicative dilemmas that the questions exhibit, for example by using explanations when candidates admit to low self-confidence. It is also shown that for some candidates the hidden agenda of the situation is concealed and that their communicative styles clash with the recruiter’s expectations. The asymmetrical situation can for the candidates be seen as both a resource and a constraint. The linguistic asymmetry is not foregrounded. Instead, the negotiation of meaning concerns the institutional and cultural frame rather than linguistic meanings. On the other hand, the recruiter shows a tendency to normalize the candidates according to her own institutional and cultural knowledge. This dynamic interplay between heterogenization and homogenization tendencies is an important feature in the interviews.

Tα τελευταία χρόνια, η εξάπλωση του διαδικτύου και το εύρος της πληροφορίας που διατίθεται στο χρήστη, καθιστούν αναγκαία τη χρησιμοποίηση σημασιολογικών τεχνικών προσωποποίησης, προκειμένου να βελτιώσουν την εμπειρία του χρήστη στο διαδίκτυο. Στις μηχανές αναζήτησης, οι χρήστες βελτιώνουν το επερώτημά τους με την προσθήκη, την αφαίρεση ή την αντικατάσταση των λέξεων. Παρ 'όλα αυτά , εκτός από την αλληλεπίδραση με μια μηχανή αναζήτησης, η εμπειρία ενός χρήστη στο διαδίκτυο κατά την αναζήτηση της σωστής πληροφορίας, περιλαμβάνει και την περιήγησή του σε σελίδες ενός δικτυακού τόπου ή μια σειρά από δικτυακούς τόπους. Κατά τη διάρκεια της συνεδρίας του, ο χρήστης αναδιαμορφώνει την αναζήτησή του. Ωστόσο, τόσο ο καθορισμός της σημασιολογίας της αναζήτησής του, όσο και ο προσανατολισμός της αναζήτησής του (γενίκευση ή εξειδίκευση σε ένα σημασιολογικό πεδίο) με βάση την πλοήγηση μέσα από τις σελίδες, δεν είναι τόσο εύκολοι. Κάθε σελίδα περιέχει περισσότερες από μία έννοιες. Επιπλέον, η επιλογή των αντιπροσωπευτικότερων είναι πολύπλοκη διαδικασία. Σκοπός της παρούσας εργασίας είναι η παρουσίαση της μεθοδολογίας SOSACT. Η μεθοδολογία SOSACT αποτελεί μια σημασιολογική μεθοδολογία εξατομίκευσης που παρακολουθεί τις επιλογές του χρήστη κατά τη συνεδρία του και καθορίζει αν ο χρήστης ειδικεύει ή γενικεύει την πλοήγηση του μέσα από τη σημασιολογική ανάλυση των σελίδων, σε ένα εννοιολογικό πεδίο. Η μεθοδολογία SOSACT ορίζει το σημασιολογικό προσανατολισμό της πλοήγησης του χρήστη. Επιπλέον, στην παρούσα εργασία προτείνεται ο αλγόριθμος SOSACT, ο οποίος εντοπίζει το σημασιολογικό προσανατολισμό του χρήστη με τη βοήθεια μίας ταξινομίας. Η μεθοδολογία SOSACT υλοποιείται από το σύστημα SOSACT. Το σύστημα SOSACT εφαρμόζει τον αλγόριθμο SOSACT και προτείνει χρήσιμες συστάσεις προς το χρήστη για τη βελτίωση της διαδικτυακής αναζήτησής του . Το σύστημα SOSACT αξιολογήθηκε με τη χρησιμοποίηση πραγματικής δραστηριότητας χρηστών σε μια ιστοσελίδα, για ορισμένο χρονικό διάστημα. Η μεθοδολογία SOSACT μπορεί να εφαρμοστεί και σε ένα σώμα κειμένων και όχι μόνο σε διαδικτυακές πηγές. Μπορεί να γίνει ένα χρήσιμο εργαλείο για τη βελτίωση της πλοήγησης στο διαδίκτυο. Επιπλέον, η προτεινόμενη μεθοδολογία μπορεί να γεφυρώσει τις τεχνικές αποσαφήνισης του επερωτήματος στις μηχανές αναζήτησης και τις τεχνικές αναδιαμόρφωσης του αντικειμένου περιήγησης. Η μεθοδολογία SOSACT θα μπορούσε να χρησιμοποιηθεί σε μια συγκριτική μελέτη μεταξύ των δύο αυτών τομέων και να οδηγήσει σε νέες τεχνικές και στις δύο περιοχές έρευνας του Σημασιολογικού Ιστού. / In recent years, the spread of the World Wide Web, as well as the range of information available to the user make the use of semantic personalization techniques a necessity in order to enhance the user experience on the web. In search engines, users refine their query by adding, removing or replacing the keywords in their query. Thus, query refinement is easy to be detected and tell whether a user generalizes or specializes his web search. Nevertheless, besides interaction with a search engine, a user web search involves browsing and navigating through the pages of a web site or a number of web sites while seeking the right information. During this session the user reformulates his search. But, defining search orientation (generalization or specialization) based on navigation through web pages is not that easy. Each page contains more than one concept. Furthermore, the concepts may be developed in the same extend and it is difficult to tell about the representative semantics of a certain page and thus a user session’s orientation. In order to define user navigation’s orientation a semantic web personalization methodology is developed, the SOSACT methodology, which tracks user’s hits through a session and defines whether a user specializes or generalizes his navigation through semantics analysis of the pages in his session window. Moreover, the SOSACT algorithm is proposed of capturing user session orientation based on concept taxonomy. The SOSACT methodology is implemented by the SOSACT system. The SOSACT system applies the SOSACT algorithm and proposes useful recommendation to the user to improve his web search. The SOSACT system is evaluated on real user activity in a web site for a certain period of time. The experimental outcomes satisfied the prospective results. The SOSACT methodology could become a useful tool for navigation refinement. Furthermore, this work is proved to bridge search engine query refinement and browsing reformulation techniques. It could be a comparative study between these two fields and lead to new techniques in both areas or migration techniques between both areas.