An efficient unstructured MUSCL scheme for solving the 2D shallow water equations The aim of this paper is to present a novel monotone upstream scheme for conservation law (MUSCL) on unstructured grids. The novel edge-based MUSCL scheme is devised to construct the required values at the midpoint of cell edges in a more straightforward and effective way compared to other conventional approaches, by making better use of the geometrical property of the triangular grids. The scheme is incorporated into a two-dimensional (2D) cell-centered Godunov-type finite volume model as proposed in Hou et al. (2013a,c) to solve the shallow water equations (SWEs). The MUSCL scheme renders the model to preserve the well-balanced property and achieve high accuracy and efficiency for shallow flow simulations over uneven terrains. Furthermore, the scheme is directly applicable to all triangular grids. Application to several numerical experiments verifies the efficiency and robustness of the current new MUSCL scheme. Two-dimensional (2D) shallow water models based on hydrostatic pressure assumption have been used to simulate a wide range of surface environmental flows including dam-or dike-break induced flood events (Viero et al., 2013; Wang et al., 2011) , urban flood inundations (Hunter et al., 2007; Liang, 2010) , rainfall-runoff processes (Esteves et al., 2000; Simons et al., 2014) , tidal hydrodynamics and ocean tsunami hazards (Sugawara and Goto, 2012; Pelling et al., 2013) , water quality and fluvial morphology (Kneis et al., 2009; Cao et al., 2006) , hurricane induced storm surges (Akbar and Aliabadi, 2013) , and even gravity currents (La Rocca et al., 2008) , among many others. These applications may involve numerical calculation of very complex flow hydrodynamics such as shock-type flow discontinuities, transcritical flows, wetting and drying over irregular topography. A robust numerical scheme is required in order to produce accurate and stable numerical solutions for these applications.. Allowing automatic shock-capturing when computing all of the aforementioned complex flow hydrodynamics, Godunov-type finite volume schemes have been widely used to solve the shallow water equations (SWEs) over the last two to three decades (Anastasiou and Chan, 1997; Chippada et al., 1998; Yoon and Kang, 2004; Liang and Borthwick, 2009; Liang and Marche, 2009; Liang, 2010; Wang et al., 2011; Sanders, 2002, 2005; Sanders, 2006, 2007; Begnudelli et al., 2008; Sanders et al., 2010; Song et al., 2011b,a; Simons et al., 2011; Delis et al., 2008 Delis et al., , 2011 Delis and Nikolos, 2013; Gallardo et al., 2007; George, 2010; Loukili and Soulaimani, 2007; Murillo et al., 2007; Skoula et al., 2006; Toro, 2009; Zhou et al., 2001 Zhou et al., , 2004 Murillo et al., 2006 Murillo et al., , 2008 Murillo et al., , 2009 Murillo and Garcia-Navarro, 2011; Benkhaldoun et al., 2010b,a; Zokagoa and Soulaimani, 2010; Hou et al., 2013a,c,b) . For most of the applications, first-order finite volume schemes may give rise to unacceptable numerical diffusion and hence poor numerical solutions, especially for flows containing discontinuities, e.g. tsunami and dam-break waves. It is therefore necessary to develop second-or higher-order schemes to predict more accurately the shallow flows. As an effective second-order scheme, the monotone upstream scheme for conservation law (MUSCL) (van Leer, 1979) has been widely recognized and applied in solving the SWEs within the framework of finite volume Godunov-type schemes (Benkhaldoun et al., 2007; Barth and Jespersen, 1989; Hubbard, 1999; Sanders, 2006, 2007; Begnudelli et al., 2008; Song et al., 2011b,a; Jawahar and Kamath, 2000; Yoon and Kang, 2004; Simões, 2011; Canestrelli et al., 2012; Hou et al., 2013c,b,a) . This technique is able to substantially reduce numerical diffusion without causing unphysical oscillations, by means of linearly reconstructing the values of flow variables within a cell or at cell interfaces. The MUSCL scheme was originally developed by van Leer (1979) for uniform grids, but substantial research effort has been devoted to extend its application on unstructured grids to allow better representation of complex domain geometries for real-world applications.. Two-dimensional unstructured MUSCL schemes may be generally classified into two categories according to the way the values of flow variables are reconstructed within a cell, i.e. cell-based and edge-based MUSCL schemes, which are also referred to as monoslope and multislope MUSCL schemes, respectively (Buffard and Clain, 2010) . The cell-based MUSCL schemes use unique limited gradients of variables to reconstruct the required values at edges. A number of cell-based MUSCL schemes have been derived for unstructured grids. Being the most efficient cell-based MUSCL scheme, the limited central difference scheme (LCD) has been widely reported for solving the SWEs on unstructured grids (Hubbard, 1999; Sanders, 2006, 2007; Begnudelli et al., 2008; Song et al., 2011b,a) . However, this scheme is known to suffer from excessive numerical diffusion (Hubbard, 1999) . A more accurate scheme was developed by Barth and Jespersen (1989) , which satisfied monotonicity and was adopted by Anastasiou and Chan (1997) in their shallow water flow model. As the limiting function of Barth and Jespersen (1989) is not differentiable and likely to cause numerical instabilities near to the solution regions with constant variables, the scheme fails to provide converged solution to steady state (Venkatakrishnan, 1995; Jawahar and Kamath, 2000; Venkatakrishnan et al., 2003) . To resolve the convergence problem, Venkatakrishnan (1995) devised a modified limiter which was applied by Simões (2011) to simulate shallow water flows. The schemes of Barth and Jespersen (1989) and Venkatakrishnan (1995) were incorporated into the multi-dimensional limiting process (MLP) by Park et al. (2010) to achieve a higher accuracy. The MLP based on Barth and Jespersen's limiting scheme was adopted in Canestrelli et al. (2012) to solve the SWEs. In spite of the increased accuracy, MLP requires a much wider stencil of cells and a more complicated solution procedure and hence is computationally more demanding. It should be noted that the above list of references covers only a small number of cell-based MUSCL schemes reported in literature and it is by no means exhaustive.. Unlike the cell-based MUSCL schemes that provide piecewise linear gradients at a cell, the edge-based MUSCL schemes compute the edge values by limiting 1D slopes at each edge of a cell (Buffard and Clain, 2010; Delis and Nikolos, 2013) . They may not give linear functions at each cell to preserve the mean values in the cell under consideration (Buffard and Clain, 2010; Delis and Nikolos, 2013) . However, it does not affect the accuracy of finite volume method because its kernel lies in computing the fluxes at the cell edges instead of the shape of the reconstructed functions at the cells (Buffard and Clain, 2010) . The limiting procedure for edge-based MUSCL schemes is carried out in the same loop of computing the fluxes over all edges of a cell. This eliminates the need of an additional loop as required for cell-based MUSCL schemes for selecting the best limiter of all faces. Hence the number of times that the limiter is invoked is largely reduced (Aftosmis et al.,1994 (Aftosmis et al., , 1995 Delis and Nikolos, 2013; Hou et al., 2013a) . Therefore, the edge-based MUSCL schemes are computationally more efficient and have been employed broadly by model developers for solving the SWEs on unstructured grids (Audusse and Bristeau, 2005; Benkhaldoun et al., 2007 Benkhaldoun et al., , 2010b Nikolos and Delis, 2009; Delis et al., 2011; Delis and Nikolos, 2013; Hou et al., 2013a,c; Simons et al., 2014) . As a simple edge-based MUSCL approach, the minmod scheme that essentially selects the smaller slope between the two alternatives has been widely implemented in unstructured SWE models due to its simple formulation and superior numerical stability (Skoula et al., 2006; Benkhaldoun et al., 2007) . However, it may sometimes lead to unacceptable numerical diffusion and gives the lowest order of accuracy among all MUSCL schemes. Delis et al. (2011) developed a more accurate scheme to compute the values at point D (the intersection of the edge under consideration and the line connecting two adjacent cell centroids, see Fig. 1 ). Another recent technique to evaluate flow information at D was presented in Kong et al. (2013) . Since D does not always coincide with the midpoint M of the edge where fluxes are evaluated ( Fig. 1) , this type of techniques may result in a loss of accuracy on poorly connected grids (Buffard and Clain, 2010; Delis et al., 2011; Delis and Nikolos, 2013) .. The reduced solution accuracy may be largely avoided by using extrapolated flow values at M to calculate the fluxes and the slope source terms (Delis et al., 2011; Buffard and Clain, 2010) . The technique proposed in Buffard and Clain (2010) calculates the values at M by constructing the slopes from the cell center to point M based on those from the cell center to point D. But this may affect the computational efficiency of the overall edge-based MUSCL scheme, as a result of a more complex reconstruction procedure. Delis et al. (2011) used unlimited gradients to compute the required values at M and so the monotonicity is not rigorously guaranteed. To increase numerical stability, a new approach was reported by Delis and Nikolos (2013) to limit the slope along DM (Fig. 1) . This technique prevents the potential numerical oscillations but may also lead to increased computational cost due to the necessity of involving a much wider stencil of cells on calculation. Based on the technique of Delis et al. (2011 ), Hou et al. (2013a proposed a more efficient method to prevent possible local extreme when extrapolating flow variables from D to M. As demonstrated by Hou et al. (2013a) , this improved scheme provides satisfactory numerical solutions for complex flows involving wetting and dying over complex terrains. However, the method is still not entirely straightforward since two steps are required to compute the values at M (firstly the values at D are computed and then they are used to extrapolate the values at M). In this work, a novel 2D edge-based MUSCL scheme for triangular grids is presented to extrapolate the required values at M directly from the cell center. This scheme is devised to be more efficient but maintains the same or slightly higher numerical accuracy as the one reported in Hou et al. (2013a) . The improved scheme is incorporated into a 2D Godunov-type cell-centered finite volume model to solve the SWEs in this work. The reconstructed values at the midpoints of the cell edges are modified by a non-negative water depth reconstruction (Hou et al., 2013c ) that preserves the well-balanced solution or so-called conservation property (C-property) (Greenberg and Leroux, 1996) . These reconstructed values are then employed to compute the fluxes using the Harten, Lax and van Leer approximate Riemann solver with the contact wave restored (HLLC) and to evaluate the slope source terms. The splitting point-implicit method proposed in Bussing and Murmant (1988) is adopted to discretize the friction source terms. To update the flow variables to a new time level, the two-stage explicit RungeeKutta approach is applied (Hubbard, 1999; Song et al., 2011a) . Implemented with the new MUSCL scheme, the current model is able to achieve second-order accuracy, converge to steady state and predict complex flow hydrodynamics that involves moving wet-dry fronts over uneven topography in an efficient way.. The remainder of the paper is organized as follows: Section 2 introduces the governing equations; Section 3 presents the novel 2D edge-based MUSCL scheme and the overall shallow flow model; Section 4 validates the model by applying it to simulate several benchmark tests; and finally brief conclusions are drawn in Section 5. In this paper, a new 2D edge-based MUSCL scheme has been developed on triangular grids to reconstruct the required values at the midpoints of the cell edges in a direct and easy way, by constructing the slopes of variables along the medians of a triangular cell. The new scheme was incorporated into a Godunov-type cellcentered finite volume model as proposed in Hou et al. (2013a,c,b) for solving the SWEs.. Extensive numerical experiments suggest that the SWE model implemented with the novel MUSCL scheme is able to converge to steady state, capture shocks and handle complex shallow flows involving wetting and drying over complex beds. Comparing with the existing approach recently reported in Hou et al. (2013a) , the current MUSCL scheme has a slightly higher accuracy for general shallow flow solutions, and offers a better well-balanced property indicated by a faster convergent rate to steady solutions on different triangular girds. Furthermore, the novel MUSCL scheme is able to save around 5% of the computational time comparing with the previous model presented by Hou et al. (2013a) . The new scheme is also flexible and easy to be implemented on all triangular grids. As a summary, due to its better solution accuracy, higher computational efficiency and simplicity, the proposed MUSCL scheme provides a favorable alternative to the existing approaches for solving the SWEs. It can also be directly extended to solve other hyperbolic equations, e.g. the advectionediffusion equation which is widely used in environmental flow simulations. In addition, the scheme, presented here for the 2D triangular grids, can be easily generalized into 3D tetrahedron grids for solving the 3D problems.

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


Development and application of efficient pathway enumeration algorithms for metabolic engineering applications j o u r n a l h o m e p a g e : w w w . i n t l . e l s e v i e r h e a l t h . c o m / j o u r n a l s / c m p b by applying these methods on three case studies of synthetic ME related to the production of non-native compounds in E. coli and S. cerevisiae: 1-butanol, curcumin and vanillin.Some targeted improvements are implemented, extending both methods to address limitations identified that impair their scalability, improving their ability to extract potential pathways over large-scale databases. In all case-studies, the algorithms were able to find already described pathways for the production of the target compounds, but also alternative pathways that can represent novel ME solutions after further evaluation. In the last decades, the quest for sustainable industrial processes has driven an increased interest in Industrial Biotechnology. Typically, to reach acceptable levels of process involving several steps, including the search for suitable hosts. In many cases, the selected hosts do not possess the ability to conduct the full set of necessary chemical transformations or these do not fulfill the desired properties (e.g., in terms of productivity or yield). In these cases, the insertion of heterologous pathways allows to augment the hosts' capabilities to produce non-native compounds. Advances in algorithms and computational tools have provided automated methods to predict viable pathways for either biodegradation or biosynthesis of valuable compounds [2] . However, the complexity of this task is quite challenging, given the dimension of the search spaces that are imposed by the growing size of the databases containing metabolic data, such as for instance the Kyoto Encyclopedia of Genes and Genomes (KEGG) [3, 4] and MetaCyc [5] .. Metabolic pathway optimization is not a novel topic and a few methods have been proposed over the past decades. Until now, most available literature is either based on graph-based methods or rule-based (or knowledge-based) systems. An alternative comes from the use of constraint-based modeling (CBM) approaches that have gained considerable importance within ME. These alternatives will be discussed below, highlighting their main features and limitations.. In graph-based representations, compounds and/or reactions are represented as graph nodes, being compounds connected to reactions through their role as substrates and products, defining the direction of the graph edges [6] . Path searching algorithms are used to extract minimal length sequences of transformations between compounds with the purpose of identifying viable pathways.. There are several limitations that arise from graph-based representations of metabolic networks. In most scenarios, the shortest path between two compounds in a graph does not represent a biological meaningful path, since chemical reactions usually contain cofactors and pool metabolites (e.g., ATP, NAD, H 2 O, H + ). The high connectivity of these compounds reroutes the shortest path (that is directly translated from a metabolic network) to favor pool metabolites, which in most cases leads to biologically meaningless solutions [7] .. Distinct alternatives have been proposed to address this issue. One solution to overcome this problem is to strip cofactors and pool metabolites (also known as currency metabolites) from the network, leaving most reactions with a single substrate and a single product. This, however, involves user expertise and manual curation of the network. Also, by removing the entire set of currency metabolites, it is impossible to obtain solutions that are able to synthesize these compounds (e.g., ATP).. An alternative is to apply weights to each compound node based on their degree [7] . Compounds with high degree are penalized, allowing shortest path methods to find the proper route avoiding currency metabolites. Nonetheless, false positives remain a problem, but compared to the previous solution, the usage of compound weights does not require chemical knowledge about the content of the network.. Perhaps the most accurate method is to use chemical knowledge about the compounds to induce the correct transition between the main substrates and products of a reaction, distinguishing from co-factors and other secondary metabolites. The atom tracking approach [8] [9] [10] uses the chemical structure of the compounds and identifies conservation of atoms in chemical reactions. This allows to track, for instance, the conservation of carbon atoms between substrates and products, and therefore the conservation of carbon atoms in an entire pathway. This approach is able to generate core substrate-product pairs that together assemble the full reaction. An example is provided by the KEGG RPAIR database which contains metabolite pairs of the KEGG Reaction database, which allow to prune the network [11] . In a biological sense, the use of this knowledge within shortest path algorithms leads to more meaningful solutions.. Alternatively to topological methods, rule-based approaches share a common trait with the atom tracking approach, as they both use chemical structures to infer pathways. These approaches apply rules over the chemical compounds to generate reactions. This allows not only to identify pathways but also to infer novel reactions [12, 13] . The advantage to infer novel pathways comes with the price of increased computational complexity due to large number of hypothetical reactions. Also, these systems require a higher degree of validation [13] .. Besides the issues related to network pruning discussed above, the graph-based systems analyzed are usually limited to linear paths over the graph. This is an important limitation since many relevant biochemical reactions have two or more substrates and/ or compounds. One alternative to overcome this limitation is the implementation of further techniques to infer branched pathways over regular graphs. One example is provided by the ReTrace method [14] .. The use of a more complex graph structure allows to overcome many problems related to directed graph search. Hypergraphs or process graphs (which are similar to directed bipartite graphs) are so called set systems representations, which are capable to model chemical reactions with higher detail. This allows to address the problem of multiple products and reactants, since edges connect to vertex sets instead of a single vertex.. Process graphs were used by Friedler et al. [15, 16] in an exhaustive approach for decision mapping in synthesis processes through the Solution Structure Generation (SSG) algorithm [17] , being later adapted for pathway identification [18] . More recently, the work of Carbonell et al. [19] introduced Find Path, an enumeration strategy to extract pathways using hypergraphs. Both algorithms are enumeration approaches that attempt to list all possible pathways towards the desired target. Given their core role in this work, they are further explored in detail in the next sections of the paper.. Orthogonally to the aforementioned approaches, constraint based modeling (CBM) has been often adopted for in silico analysis of genome-scale metabolic models (GSMM), since it does not require kinetic information. Using this approach, the system is subjected to several constraints, such as reaction stoichiometry and reversibility. Typically, mainly for phenotype simulation purposes, systems are assumed to be in pseudo-steady state [20] , allowing the computation of a feasible flux space. Flux Balance Analysis (FBA) is a popular method to determine the flux distribution that maximizes a target objective (e.g., related to cellular growth) using linear programming [21] .. Among many other applications within pathway optimization, FBA has been used to determine producible non-native compounds [22] by merging GSMMs with large databases such as KEGG, allowing to infer putative heterologous reactions for defined purposes. Also within the CBM framework, the OptStrain algorithm [23] searches within a domain of reactions and metabolites (e.g., coming from a database such as KEGG) for the pathway with the smallest number of heterologous reactions that allows to produce the target compound. Since the constrains used in this case are different, that determines the need to resort to mixed integer linear programming (MILP).. As their main advantage, CBM based approaches avoid the combinatorial explosion of possible pathways in graph-based methods, through optimization based on a selected objective function. Furthermore, the constraints imposed in the system are able to guarantee that the obtained solutions are stoichiometrically valid. However, a limitation is the capability to determine only a single solution and, therefore, in this regard have similar limitations to the shortest path approaches based in regular graphs. Indeed, these methods do not enumerate exhaustively other alternative solutions, which may offer valuable information on alternative routes.. Still within the CBM framework, Elementary Flux Modes (EFM) of a metabolic model are defined as non-reducible subsets of reactions that can maintain steady state. The enumeration of the EFMs in a network that include the desired target provides an enumeration of all possible pathways producing this compound. However, their computation is still restricted to small or medium models, being impossible to extend to GSMMs [24] . de Figueiredo et al. [25] propose an enumeration strategy to compute the k-shortest EFMs expanding the size of computable problems, but still the enumeration is computationally expensive and restricted to small values of k. Indeed, database size networks (e.g., KEGG or MetaCyc) still offer an impossible challenge for exhaustive EFM computation. For large-scale networks (e.g., GSMMs), the only option is to apply heuristics to reduce the search space or to use stochastic approaches [26] .. In this scenario, given the advantages and limitations of the proposed methods, researchers have to choose the best option for their particular task. The field of ME has been resorting to CBM approaches in their quest for improved microbial cell factories. However, in many cases, it is difficult to define a suitable objective function for pathway optimization as multiple criteria need to be taken into account. Also, given the complexity of the problems and underlying biological phenomena, it is highly desirable to be able to identify alternative solutions leading to the desired products. As a result, we opted to focus our attention in the most promising methods using set systems representations, in which a network is represented as explained above by a set of sets. Indeed, these are able to overcome limitations of shortest path approaches over regular graphs, while providing the means to address the enumeration of multiple solutions for pathway optimization problems.. In this work, two previously identified algorithms for multiple pathway enumeration are analyzed: the Solution Structure Generation (SSG) and the Find Path (FP) algorithms. Both operate over set system representations (process graphs and hypergraphs, respectively). These are implemented, evaluated and improved through three case studies, regarding the production of butanol, vanillin and curcumin, using as hosts the bacterium Escherichia coli and the yeast Saccharomyces cerevisiae, two model organisms for which there are available GSMMs. The results obtained by both are provided and discussed, being clear the need to introduce some improvements to allow the scalability of the methods.. The next section introduces a more formal definition of the problem and related concepts; the following section details the SSG and FP algorithms and the improvements developed in this work; the next section details the case studies, some implementation issues and the experimental setup; next, the results are presented and discussed; and the paper closes with some conclusions and further work.

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


Undergraduate students' gender differences in IT skills and attitudes The worldwide concern about the gender gap in information technology and the lack of woman participation in computer science has been attributed to the different cultural influences to which boys and girls are subject. In The University of Hong Kong, girls achieved greater improvements in their computer skills than their male counterparts after completing one year of studies. Recognising their own progress has, in turn, boosted their confidence in using IT. The young women's estimates of their skill levels have doubled over the years from 1998 to 2000. Despite this recorded acceleration at the end of the academic years, girls were less confident of their abilities and possessed lower IT skill levels than boys before starting their university education, as found in surveys of freshmen's computer skills. This study compares the responses of student participants of the HKU/IBM Notebook Computer Programme, which started in 1998, in the self-reported IT skills and attitudes of male and female students, in surveys conducted both at the beginning and again at the end of the freshman year. It also examines the achievement scores of the IT Proficiency Tests and the 'Foundations to Information Technology' courses administered for the student IT requirement for graduation. While the use of computers and information technology (IT) is becoming ubiquitous in everyday life, IT is also transforming educational settings. Following the widespread influence of IT inevitably came the issue of gender differences in access and use. The American Association of University Women Educational Foundation (AAUW, 1994) reported gender differences in the use of IT from synthesised results of over 1000 studies, labelling technology as the 'new boys' club', as boys use computers to program and solve problems while girls use IT for word processing. Even though information technology is so influential in our society and computers are so widely used in education, male and female students still tend to perform differently in IT skills. For whatever reasons, the larger proportions of female students who came to study at The University of Hong Kong rated themselves as less competent and less confident in computer use, and knew less software packages, than their male counterparts. Much smaller proportions of female students were confident enough to take the IT Proficiency Test and they scored lower marks than the male students did. Yet, this does not preclude other academic requirements as the factor of having contributed to students' decision whether to take the test.. Nonetheless, the change in profile between the male and female students over the years not only attests to an expeditious acceleration of female confidence in their own IT skills over the three years in question, but also suggests another angle to examine the issue of gender differences in IT skills and attitudes. That there is larger room for improvement by female students who have started out from a relatively lower point than their male counterparts in the scale of IT skills is not a bone of contention. Meanwhile, there might also be the possibility that the social factor of the gradual overall change in IT attitude in the society of Hong Kong has effected the change in the female students. Will this factor be instrumental to an eventual bridging of the present gap in IT skills among Hong Kong male and female students?. It will also be interesting to investigate what gender perceptions, especially those Gender differences in IT skills are not only experienced in this university. Such differences are also evident in American universities. Discovering a phenomenon similar to that in this university, the fall 2000 survey of UCLA unfolded a gap among the current freshmen as the largest in the 35 years of history of the survey in their self-rated computer skills (Sax et al., 2000) . Nevertheless, further investigation into the data from this university has yielded another picture that also merits attention. Despite the lower ratings that female students gave themselves in their computer skills, their lower level of comfort working with computers, and the smaller proportions of female students who took the IT Proficiency Test, there are indications that they have been quick in catching up.. Over the three years, the proportion of male respondents who rated themselves as being experts or having significant experience at the start of the year increased by 80%, whereas that of the female respondents by 129% (see Table 13 ).. Similarly, the proportion of male respondents who gave themselves the same ratings at the end of the year experienced an increase of 10% over the two years vs. 97% of the female respondents (see Table 13 ). Furthermore, the male proportion who has the experience of teaching someone to use a computer increased by 27% over the three years, when the female proportion increased by 44% (see Table 14 ).. The proportion of first year male undergraduate students who took the IT Proficiency Test increased by 91% between Cohort 1 and Cohort 2, whereas the female proportion changed by 297% (see Table 14 ). The change in profile between the male and female students as presented above illustrates acceleration in confidence of female students in IT, amidst the persistent phenomenon of their lower self-ratings and performance in IT skills, as compared to those of the male students. It is important to note here that female students have more possibility for change as they have started out from a lower level.

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


Planning and Design Considerations for Computer Supported Collaboration Spaces Architects have long been aware of the need to design for the behaviors a space is meant to support. However, neither the seminal works on architectural programming or collaborative engineering address the linkages between physical environment design and collaborative work practice. This paper posits that the design of collaboration environments should stand as a third pillar of collaboration engineering, suggests four ways in which physical environment design and collaboration engineering might mutually inform the other, and specifies several dimensions of physical environment affordance collaboration engineers might consider when developing requirements for collaboration space. Collaboration engineering is defined as an approach to designing collaborative work practices for high-value recurring tasks and deploying them to practitioners to execute for themselves without ongoing intervention from a professional facilitator (de Vreede and Briggs, 2005) . Up to now, collaboration engineering researchers focused on designing work practices, including processes teams could follow to achieve their goals, and collaboration technologies they could use to support those processes. Collaboration engineers focus on deploying their work practice designs in ways that create self-sustaining communities of practitioners for the designs. It is also important, however, that collaboration engineers turn their attention to the physical environments in which practitioners will execute their work practices. Physical environment considerations can profoundly impact both behavioral and affective outcomes in collaborative work (BOSTI, 2001) . Two examples from collaboration research aboard the USS CORONADO (Briggs, Adkins, Mittleman, Kruse, Miller, and Nunamaker, 1998-99) illuminate this point.. The first example, the Joint Air Operations Center (JAOC) of the CORONADO was designed to support a collaborative effort among approximately 80 officers who planned and coordinated military air operations in the Eastern Pacific. The space was not, however, designed with an awareness of collaboration issues. Most personnel worked at computers. The computers were secured to desks that faced the bulkheads, which meant that personnel had to choose between seeing information on their computers or seeing one another; they could not do both. The CMOC was equipped with projectors so officers could brief others on details of planning and operations. Lighting for the space, however, was tied to a single on/off switch, allowing no variations of lighting configurations. Personnel had to choose between seeing projected images when lights were off, or taking notes when the lights were on; they could not do both. Further, most of the personnel in the JAOC did not participate in most briefings, yet nobody in the JAOC had lights when the projectors were in use. Finally, like the rest of the ship, the JAOC had metal walls, floors, and ceilings. These were subjected to radiant heat from outside sources. To make the space livable, ship builders retrofitted the space with a new air conditioning system composed of a heavy fan pushing air through ventilation shafts.. Ventilation shafts were serpentine (Figure 1 ), weaving around pre-existing structures. Every curve in the ventilation shaft slowed the flow of air while generating additional noise. By the time air reached personnel in the JAOC, almost no air flowed from the vents. Ship builders, therefore, doubled the capacity of the fan. This, however, made almost no difference in air flow, but dramatically raised noise levels, which peaked at more than 100 decibels. Personnel could not hear one another when the air conditioning was on; they had to work in a room too hot for comfort or in a room too loud for participants to hear one another. This paper argues that the design of collaboration environments should stand as a third pillar of collaboration engineering, Applying a systems development lifecycle approach to the architectural programming process for developing space requirements yields a Collaboration Engineering Physical Environment Programming Process. This process provides a framework for integrating knowledge of specific anticipated patterns of collaboration with known workspace and technology affordances to produce and validate space design requirements. Relevant environment and behavior literature is reviewed and mapped to typical collaboration spaces and collaboration technology affordances for the purpose of guiding a design programmer. A checklist of about 100 requirements elicitation questions and suggestions are surfaced to further guide the programming process.. The insights and guidelines presented in this paper were derived from several sources. I conducted qualitative field observations of people using collaborative workspaces in North America, Europe, and Asia. These observations used Focus Theory as a lens for interpreting how the organization of design elements and affordances might impact the productivity of groups. The concepts codified during those observations were taken into the field by more than a dozen designers who used them as the basis for developing designs for new collaborative workspaces in a wide variety of domains, ranging from a 55-seat collaborative decision space for the commander of a large military command to classrooms in an inner-city elementary school to a strategic planning center for a multi-national corporation. Qualitative feedback from the designers and the users of these spaces helped to refine and clarify the approach. The collaboration engineering research is driven by a design science methodology informed by social science theory. Design science (Hevner, March, Park, and Ram, 2004 ) posits a cyclical model of design, build, and evaluate activities producing artifacts that inform both the original design problem and are extensible to the field literature in the form of constructs, models, or methods. Design evaluation can inform the cycle by either informing design theory or raising new design research questions; or it can be explanatory (testable) in itself (Moore, 1997) . Design science is grounded in both the Information Systems literature and in the architectural design literature (Gregory, 1967; Jones, 1980) . The author's immersion into the activities of design, build, and evaluation. This research began with a theory and intervenes in a number of situations to improve both the situation and the theory (Argyris, Putman, and Smith, 1985) . The principal theory guiding this research is Focus theory (Briggs R. O., 1994) ; the research is also informed by environment and behavior literature. This work is based on a set of 20 design interventions that I either led or participated in. These interventions include architectural programming (planning) and design for: dot.com work environments, Fortune 500 ideation spaces, military planning, decision making and training spaces, civilian government meeting spaces, high school and college classrooms, meeting rooms, and faculty officing environments. As these interventions are limited to North American projects, caution should be used when extending the findings to other national cultures. This work is also informed by observations in more than 100 other collaboration spaces --commercial, governmental, military, and academic -that were made after implementation. Finally, the work is informed by feedback from other designers who took these concepts into the field and used them for designing new collaborative work spaces, and by feedback from the users of those spaces.. This research demonstrates that the physical environment can be manipulated to support individuals and teams engaging in cognitive effort toward a shared goal by enhancing environmental affordances that reduce the cognitive load of deliberation, and communication and ease information access. Such enhancements can increase the likelihood that group members will be able to establish and maintain goal congruence. These manipulations come through both the minimizing of environmental distracters as well as by the construction of structures to advance the four cognitive functions proposed by Focus Theory.

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


Modeling lane-changing behavior in a connected environment: A game theory approach Vehicle-to-Vehicle communications provide the opportunity to create an internet of cars through the recent advances in communication technologies, processing power, and sensing technologies. A connected vehicle receives real-time information from surrounding vehicles; such information can improve drivers' awareness about their surrounding traffic condition and lead to safer and more efficient driving maneuvers. Lane-changing behavior, as one of the most challenging driving maneuvers to understand and to predict, and a major source of congestion and collisions, can benefit from this additional information. This paper presents a lane-changing model based on a game-theoretical approach that endogenously accounts for the flow of information in a connected vehicular environment. A calibration approach based on the method of simulated moments is presented and a simplified version of the proposed framework is calibrated against NGSIM data. The prediction capability of the simplified model is validated. It is concluded the presented framework is capable of predicting lane-changing behavior with limitations that still need to be addressed. Finally, a simulation framework based on the fictitious play is proposed. The simulation results revealed that the presented lanechanging model provides a greater level of realism than a basic gap-acceptance model. Game theory has been applied in different disciplines in order to understand, analyze and model decision-making processes (Petrosjan and Mazalov, 2012) . In addition to its application in the domains of economics, politics and sociology, the theory was adopted in the engineering field to explore the presence of more efficient wireless networkMSM based calibration approach is offered in section 4. The corresponding section is followed by a discussion on the model validation in section 5. Finally, section 6 illustrates the fictitious play based simulation approach before concluding with some summary remarks and future research needs in section 7. Connected Vehicles technology is expected to improve drivers' strategic, tactical, and operation decisions. At the operation level, this technology improves drivers' awareness about their surrounding traffic condition. Acceleration and lane-changing decisions are drivers' main operational decisions. However, unlike acceleration models, only few lane-changing models have been presented in the literature. Most of these models are rule-base models and do not explicitly take into consideration the dynamic interactions among drivers and the stochastic nature of lane-changing maneuver. Moreover, most of these models are not framed to consider the flow of information in a connected environment. Adopting a game-theoretical approach, this paper presents a lane-changing model that considers the flow of information in a connected vehicular environment. Accordingly, two game types are considered for modeling lanechanging behavior: a two-person non-zero-sum non-cooperative game under complete information in the presence of connected vehicle technology and a two-person non-zero-sum non-cooperative game under incomplete information in its absence. A calibration approach based on the method of simulated moments (Bajari et al., 2010 ) is adapted and presented. Since calibrating the presented framework is computationally burdensome, a simplified version of the lanechanging model is presented and calibrated; and developing a computationally efficient calibration approach has been left for future research. The validation results revealed the limited prediction capability of the simplified model.. Finally, a simulation framework based on fictitious play is proposed and a segment in Chicago, IL is simulated based on this framework. The simulation results revealed that the presented lane-changing model provides a greater level of realism than a basic gap-acceptance model and MOBIL. However, further analysis should be performed, the proposed model should be calibrated and included in the simulation framework. Moreover, considering "cognitive decision" features in this framework is essential and can be implemented through reformulating the game as an evolutionary game in which the outcome of a game depends on the drivers' experience. The final goal is to develop a robust simulation framework to capture driving behavior in a connected vehicular environment. In addition to the game theory applications in different science and engineering fields mentioned in Section 1, game theory has been adopted multiple times in transportation analysis (He et al., 2010) . The main game theory models used are: (1) ordinary non-cooperative game, (2) generalized Nash equilibrium game, (3) Cournot game, (4) Stackelberg game, (5) bounded rationality game and (6) repeated games. The corresponding transportation analysis types may be mainly classified as: (a) macro-policy analysis (including i-games between travelers and authorities, ii-games between authorities, and iii-games between travelers) and (b) micro-behavior simulation (including i-games between travelers and authorities, and ii-games between travelers). These studies focused mainly on vehicular traffic and on the strategic decision making level (i.e. route choice, departure time choice, destination choice and mode choice) (Bell, 2000; Fisk, 1984; Hollander and Prashker, 2006; Tosin, 2008) . As for the shorter tactical and operational decision making time frame, the studies approached the problem from a safety perspective, as the objective was to avoid conflicts and collisions between vehicles (Zhang, 2009; Zhe, 2013) .. Such operational level applications motivated the use of game theory to develop improved traffic control strategies (Yu and Faldini, 2004) , particularly signalization. The objective was to create decentralized and coordinated traffic signal control systems that respond in real time to the volume fluctuations in a given transportation network (ElTantawy and Abdulhai, 2010) . Other game theory applications involved ramp metering and speed harmonization (Ghods and Kian, 2008; Li and Fan, 2008) . Lately, the operational and the tactical level decisions (i.e. acceleration, turning, gap-acceptance, lane-changing and merging) involved in traffic flow control started to be translated into autonomous driving logics via agent-based simulation (Rakha et al., 2013) . The corresponding studies however suffer from two major limitations. First, the applicability of game theory to microscopic driving decisions modeling may create computationally slow algorithms rendering the adopted approach impractical for real-time simulation purposes (Hoogendoorn and Bovy, 2009 ). This limitation is even more manifested when dealing with more complex lanechanging models. Second, to examine the hypothesis that game theory may be applied to capture lane-changing behavior in a robust manner, calibration needs to be performed accurately using high resolution (space and time) trajectory data. Such data may not be readily available in different geographic locations for different roadway geometric and traffic control features. At this stage, the authors assume that such data would be available through newer generation sensing instruments. The main goal of this paper is then to show that game theory may be adopted to construct more robust lane-changing models than currently in use, and that such models may be implemented and simulated efficiently in order to be used in a connected vehicle environment.. Lane-changing decisions are latent in nature and one can just observe the outcome of this decision making process (Ahmed, 1999) . The time to make this decision is not observable either. Moreover, the whole process is continuous and the order of events in this process can change (e.g., available gap, in one case, can be a triggering factor for a lanechanging decision while, in another case, a driver may look for an acceptable gap to change lane) (Ahmed, 1999) . Most of the lane-changing models in the literature are rule-based models. Gipps' (1986) lane-changing model is a notable example of the rule-based models. It assumes that drivers are willing to keep their own desired speed while using a "correct lane" on their path from an origin to a destination. However, these two objectives may be conflicting; therefore several other adjustments (including the possibility of lane-changing maneuver, presence of heavy vehicles, and vehicles' speed and the target lane's speed) were considered in the model, which determines the possibility, necessity, and attractiveness of a lane-changing maneuver through a series of questions that need to be answered (i.e. if-then rules).. In an effort to capture the underlying behavioral mechanisms of lane-changing decisions, (Ahmed, 1999) presented a utility-based framework. This model divides lane-changing maneuvers into mandatory (MLC) and discretionary (DLC) and adopts a three step approach to model a lane-changing maneuver: decision to change lane, decision to select target lane, and decision to accept the gap in the target lane. This model used a discrete choice modeling framework where lane-changing decisions are made at discrete points in time. Moreover, each lane-changing decision was assumed to be independent from previous lane-changing decisions in DLCs. Choudhury et al. (Choudhury et al., 2006) enhanced this framework by incorporating forced merging in the model structure and calibrated the update framework using NGSIM data. They compared this framework with the original model (Ahmed, 1999) and found that the extended model performs significantly better than the original model.. Another lane-changing model that focused on interactions between a merging vehicle and through vehicles in an on-ramp location is Kita's model (Kita, 1999; Kita et al., 2002) . The corresponding game theoretical approach captures the interactions between modeling framework is a two-player non-zero-sum non-cooperative game where the merging vehicle chooses between merge and stay in the merge lane and the through vehicle chooses between give way and do not give way. The main assumption of this model is that drivers minimize their lane-changing risk (defined based on time-to-collision).. In light of the presented literature review, further work is needed to investigate the suitability of game theory as a basis for lane-changing algorithms in a connected vehicle environment. For this purpose, adequate model formulation and efficient calibration are needed. The corresponding model should then be tested through well-designed simulation sensitivity analysis.

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


Characterization and optimization of a permanent magnet synchronous machine Purpose -The first purpose of this paper is to identify -by an inverse problem -the unknown material characteristics in a permanent magnet synchronous machine in order to obtain a numerical model that is a realistic representation of the machine. The second purpose is to optimize the machine geometrically -using the accurate numerical model -for a maximal torque to losses ratio. Using the optimized geometry, a new machine can be manufactured that is more efficient than the original. Design/methodology/approach -A 2D finite element model of the machine is built, using a nonlinear material characteristic that contains three parameters. The parameters are identified by an inverse problem, starting from torque measurements. The validation is based on local BH-measurements on the stator iron. Findings -Geometrical parameters of the motor are optimized at small load (low-stator currents) and at full load (high-stator currents). If the optimization is carried out for a small load, the stator teeth are chosen wider in order to reduce iron loss. An optimization at full load results in a larger copper section so that the copper loss is reduced. Research limitations/implications -The identification of the material parameters is influenced by the tolerance on the air gap -shown by a sensitivity analysis in the paper -and by 3D effects, which are not taken into account in the 2D model. Practical implications -The identification of the material parameters guarantees that the numerical model describes the real material properties in the machine, which may be different from the properties given by the manufacturer because of mechanical stress and material degradation. Originality/value -The optimization is more accurate because the material properties, used in the numerical model, are determined by the solution of an inverse problem that uses measurements on the machine. Nowadays, compact permanent magnet synchronous motors (PMSM) are used for applications that require a high-power density, such as electric vehicles and compressors. Because the volume and weight are very critical, the magnetic material in these machines is exploited in a highly saturated state. In recent literature, the majority of the numerical models of such a motor takes into account the nonlinearity of the magnetic material. In Henneberger et al. (1997) , saturation effects were studied in a PMSM. In Stumberger and Hribernik (2000) , the characteristics of a PMSM are predicted by using a standard 2D finite element model (FEM). In Lee et al. (2006) , the motor is described using the voltage equation wherein the inductances of d-and q-axis are also determined by a nonlinear FEM. Another nonlinear FEM was developed in de Belie et al. (2006) for the study of the cross-saturation and stability of a surface PMSM. Vivier et al. (2005) couples the electromagnetic model with mechanic and acoustic models in order to study noise.. Most of the above-mentioned models use nonlinear material characteristics that are obtained from the manufacturer of the steel sheets, or from measurements of B-H characteristics performed in an Epstein frame or in a single sheet tester. However, these characteristics change inside the material due to mechanical stresses on the lamination and due to material degradation resulting from the cutting or punching of the yoke (Crevecoeur et al., 2007) . Therefore, it is more accurate to determine the material properties of the magnetic material when it is already inside the machine.. In this paper, the numerical model (Section 2) is used to characterize the material behaviour from an inverse problem (Section 3). The material behaviour is also identified by local measurements of magnetic field and magnetic induction -measured directly on the stator yoke -in Section 4, in order to validate the results found by the inverse problem. The paper concludes by two optimizations of geometrical parameters in Section 5.. The usefulness of the paper is that a geometrical optimization of the machine is carried out after the detailed characterization of the machine. The characterization is necessary in order to obtain a valid optimization with reliable results. It deals with the development of a numerical model that produces approximately the same values of torque and losses as the experimentally obtained values in the same working conditions of the machine. Such a numerical model makes it possible to carry out accurate simulations of the effect of a changed geometry to the machine performance and efficiency. By using this accurate model, the result of a geometrical optimization is reliable. The identification of the material parameters for a PMSM can be generalized to any type of electromagnetic device (electrical machines, transformers, inductors, etc.). Figure 1 shows the geometry of the modelled machine with four poles. Details can be found in Table I . The model is a 2D FEM with the vector potential A as unknown: From an inverse problem that uses suitable measurements as inputs, the material properties of a permanent magnet synchronous machine are identified. To eliminate inaccuracies in the measurements, the measurement inputs for the inverse problem are replaced by a more smooth analytical function fitted through the measurement data. The material characteristic obtained by the inverse problem is compared with the characteristic obtained by local magnetic measurements on the stator yoke. With the obtained material parameters, the 2D FEM predicts torques similar to the measured ones for all considered rotor angles and current amplitudes. For rather weak fields, the obtained characteristic deviates somewhat from the locally measured BH-characteristic, but for strong fields, the correspondence between both characteristics is good. With this model, an optimization of the geometry is carried out to obtain maximal torque for minimal losses. It is observed that in case that the machine is optimized for high-stator current, smaller stator teeth and thicker magnets are chosen than in case the machine is optimized for low-stator current.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Towards

interoperability

of

i*

models

using

iStarML

Goal-oriented

and

agent-oriented

modelling

provides

an

effective

approach

to

the

understanding

of

distributed

information

systems

that

need

to

operate

in

open,

heterogeneous

and

evolving

environments.

Frameworks,

firstly

introduced

more

than

ten

years

ago,

have

been

extended

along

language

variants,

analysis

methods

and

CASE

tools,

posing

language

semantics

and

tool

interoperability

issues.

Among

them,

the

i*

framework

is

one

the

most

widespread.

We

focus

on

i*-based

modelling

languages

and

tools

and

on

the

problem

of

supporting

model

exchange

between

them.

In

this

paper,

we

introduce

the

i*

interoperability

problem

and

derive

an

XML

interchange

format,

called

iStarML,

as

a

practical

solution

to

this

problem.

We

first

discuss

the

main

requirements

for

its

definition,

then

we

characterise

the

core

concepts

of

i*

and

we

detail

the

tags

and

options

of

the

interchange

format.

We

complete

the

presentation

of

iStarML

showing

some

possible

applications.

Finally,

a

survey

on

the

i*

community

perception

about

iStarML

is

included

for

assessment

purposes.

Requirement

Engineering

(RE)

has

been

defined

as

the

branch

of

software

engineering

(SE)

concerned

with

the

real-world

goals

for

functions

of,

and

constraints

on,

software

systems

RE

is

inherently

broad,

interdisciplinary

and

open-ended

because

it

embraces

from

real

life

situations

to

mathematical

specification

languages..

Goal-oriented

RE

methodologies

were

introduced

more

than

ten

years

ago.

They

have

been

recognized

to

play

a

crucial

role

to

model

the

domain

and

to

identify

the

requirements

of

a

new

software

system,

through

the

understanding

of

stakeholders'

domain

goals

and

of

their

strategic

dependencies

for

goal

achievement

Goal-oriented

approaches

have

been

formulated

either

as

formal

frameworks,

e.g.

KAOS

or

as

rigorous

(but

not

formal)

ones,

both

of

them

proposing

their

own

modelling

language,

with

a

specific

set

of

conceptual

entities,

a

graphical

notation

to

depict

models,

and

a

set

of

analysis

techniques.

Among

rigorous

frameworks,

the

i*

(pronounced

eye-star)

framework

is

one

of

the

most,

if

not

the

most,

widespread

and

adopted

by

the

RE

community.

Several

indicators

support

this

statement,

from

the

increasing

number

of

scientific

papers

and

experience

reports

on

i*

presented

in

RE&SE

journals

and

papers;

the

periodic

organization

of

an

i*

workshop;

the

construction

of

the

i*

wiki

with

more

than

universities

and

organizations

currently

registered;

the

imminent

publication

of

a

monograph

on

i*

the

recognition

of

an

i*-based

language

like

URN

as

a

telecommunication

standard

(standard

and

the

offering

of

tutorials

in

world-leading

conferences

like

IEEE

RE

The

i*

framework

provides

the

ability

to

model

concepts

such

as

actors,

roles

and

agents,

and

to

reason

about

them.

Also

relevant

in

this

kind

of

modelling

is

the

assignment

of

goals

to

actors

or

agents,

which

has

been

the

base

of

agent-oriented

software

methodologies

Combining

goals

and

agents

altogether

allows

labelling

the

i*

framework

both

as

agent-oriented

and

goal-oriented.

i*

is

one

of

the

most

widespread

modelling

languages

by

itself

and

also

as

part

of

the

Tropos

SE

methodology

As

a

side

effect

of

this

growing

interest

around

i*,

several

extensions

to

the

original

framework

have

been

defined;

a

summary

can

be

found

in

They

have

been

applied

not

only

to

RE

but

also

to

other

fields

as

organizational

patterns

agent

networks

simulation

and

agent

security

patterns

among

others.

These

more

recent

approaches

aim

at

dealing

with

the

increasing

complexities

in

developing

nowadays

software-intensive

systems,

which

need

to

operate

in

open,

heterogeneous

and

evolving

environments.

Also,

several

i*-related

tools

have

been

built.

They

offer

capabilities

for

editing

i*

models,

for

analyzing

them

and

for

applying

techniques

over

them..

Therefore,

problems

on:

(i)

the

consistency

of

the

semantics

of

the

different

language

variants,

and

on

(ii)

how

to

exploit

reasoning

services

offered

by

the

tools

each

one

requesting

specific

modelling

formats,

have

become

relevant..

The

first

of

these

two

problems

has

been

recently

addressed

by

different

approaches.

For

instance,

in

the

authors

propose

to

root

the

modelling

language

to

a

domain-independent

metamodel

that

takes

into

account

more

basic

entities

motivated

by

philosophical

cognitive

science

theories

(e.g.,

object,

event).

These

ideas

have

been

illustrated

with

respect

to

the

concept

of

goal.

In

the

problem

of

language

variants

is

analyzed

along

a

set

of

ten

concept

properties

like

reflexivity,

boundary,

symmetry,

with

the

aim

to

refine

the

syntax

of

i*-based

modelling

languages.

In

a

comparison

of

some

variants

of

i*

is

presented

and

a

metamodel

for

embracing

the

commonalities

is

proposed;

customization

on

the

source

variants

is

projected

by

using

refactoring

techniques.

In

the

Tropos

metamodel

includes

the

i*

constructs

and

its

use

has

promoted

both

extensions

to

Tropos

such

as

Secure

Tropos

and

tool

implementations

such

as

The

diversification

of

i*

applications

has

produced

semantic

variations

which

have

implied

practical

problems

concerning

interoperability

of

tools,

e.g.

goal-analysis

tools,

modelling

tools,

metric

calculation

tools,

etc.,

because

each

tool

works

over

a

particular

i*

variant.

This

prevents

sharing

models

among

tools

or

combining

two

of

them

for

providing

enhanced

functionalities.

This

problem

could

be

unsolvable

if

variants

were

radically

different

but

as

shown

in

this

is

not

the

case:

changes

are

either

minor

differences

on

basic

i*

constructs.

For

this

reason,

the

objective

of

overcoming

that

interoperability

limitation

seems

feasible..

In

our

work

we

focus

on

practical

issues

related

to

the

i*

tools

interoperability

problem.

In

particular,

our

main

objective

is

to

provide

a

representation

where

differences

and

similarities

among

i*

variants

are

explicit,

generating

a

common

representational

framework

for

the

i*

community

and,

in

spite

of

the

differences,

enabling

effective

communication

inside

the

community,

tool

interoperability

and

a

common

representation

for

repository

of

i*

models.

Our

proposal

is

based

upon

the

definition

of

an

XML

interchange

format

for

i*

diagrams,

called

iStarML.

iStarML

includes

six

basic

categories

of

core

concepts,

transformed

into

six

abstract

core

concepts,

common

to

all

of

i*-based

modelling

languages.

Using

XML

as

basic

infrastructure

makes

it

possible

to

have

other

goals,

specifically

to

take

advantage

of

the

XML

format

for

Internet

communication

and

also

to

use

general-purpose

XML

tools..

The

rest

of

the

paper

is

structured

as

follows.

In

Section

we

show

the

basic

features

of

the

i*-based

framework,

discuss

about

i*

variations

and

present

the

related

interoperability

problem.

Next,

in

Section

we

outline

a

set

of

requirements

for

an

interchange

format

showing

the

analysis

that

generated

the

essential

principles

of

the

language

design.

Also

in

this

section

we

explain

how

we

have

considered

both

stable

i*

concepts

and

variant

i*

concepts.

In

Section

we

illustrate

the

facilities

of

using

iStarML

showing

four

generic

application

scenarios

by

pointing

to

particular

technological

examples.

Finally,

in

Section

we

show

the

results

of

a

survey

applied

to

representative

members

of

the

i*

research

community

which

have

expressed

their

perception

about

the

tool

interoperability

problem

in

the

i*

community,

and

about

how

iStarML

could

solve

this

problem.

Conclusions

include

an

overview

of

benefits

and

drawbacks

of

the

proposal,

related

work

comments,

mainly

focused

on

XMI

and

MDA

proposals

and

the

planned

future

work.

In

this

paper,

we

have

provided

a

broad

justification

of

the

iStarML

proposal

as

a

conceptual

vehicle

enabling

interoperability

inside

the

i*

community,

both

from

a

model-oriented

perspective,

and

also

from

a

tool-oriented

perspective.

The

first

one

aims

to

provide

a

shared

interpretation

of

i*

core

constructs

and

variations

and,

the

second

one

aims

to

Agresti-Coull

"nor-answers"

included

Agresti-Coull

"nor-answers"

discarded

develop

and

share

i*

tools

enabling

a

common

way

of

storing

and

transmitting

i*

models.

The

practical

impact

of

iStarML

in

the

i*

community

may

be

summarized

as:

(i)

support

to

model

interchange

among

different

tools;

(ii)

composition

of

existing

tools

to

create

new,

complex

functionalities;

(iii)

extending

existing

tools

with

new

i*-based

analysis

components;

(iv)

developing

i*-based

analysis

algorithms

independently

of

dialect

issues;

(v)

representing

specific

additional

syntactic

constraints

to

specify

evolutions

or

new

variations;

(vi)

having

a

common

way

of

representing

the

differences

and

similarities

between

existing

i*

variations

Interoperability

can

be

reached

even

by

the

different

i*

variants

because

the

iStarML

proposal

is

abstractly

formulated

on

the

core

i*

concepts.

This

makes

possible

not

only

sharing

models

between

different

variants

but

also

with

new

variants

which

can

be

built

using

this

set

of

abstract

core

concepts.

Moreover,

we

have

carried

out

an

empirical

approach

to

assess

the

i*

community

perception

about

the

interoperability

problem

and

the

iStarML

proposal.

The

findings

confirm

our

initial

perception

about

the

existence

of

an

interoperability

problem

and,

moreover,

there

is

an

initial

positive

evaluation

about

iStarML

and

its

capability

of

tackling

the

referred

interoperability

problem.

Besides,

the

results

reveal

an

optimistic

scenario

for

future

adoptions.

At

this

respect

we

have

presented

two

local

adoptions

that

have

been

developed

on

our

research-related

tools

and

we

have

outlined

other

possible

cases..

In

terms

of

related

work,

as

far

as

we

know,

iStarML

is

the

first

proposal

aiming

in

this

direction

and

accounting

with

a

previous

approval

from

different

scholars

from

RE

and

agent-oriented

software

engineering

communities..

About

the

technological

implementation

it

is

necessary

to

mention

that

not

any

type

of

schema

can

be

applicable

for

the

XML

implementation

of

iStarML.

For

example

widespread

proposals

such

as

DTD

and

XSD

are

not

useful

for

the

iStarML

because

the

specification

power

of

these

proposals

is

restricted

to

elements

(tags)

but

they

do

not

allow

specifying

attribute

rules

which

is

necessary

in

order

to

express

the

different

i*

variations.

Derived

from

this,

the

XML

Metadata

Interchange

(XMI)

a

proposal

which

allow

specifying

generic

diagrams

interchange

formats,

is

not

a

choice

either.

That

is

because

XMI

requires

a

MOF

metamodel

which

does

not

allow

a

flexible

specification

of

dependencies

among

attributes.

The

only

choice

allowing

using

XMI

also

implies

to

explicitly

represent

intentional

elements

(e.g.,

as

our

Tropos

MOF

model

in

however

this

means

losing

flexibility

which

only

be

compensated

by

adding

tags,

which

would

made

the

language

more

complex

and

applicable

only

to

some

i*

variations.

On

our

previous

experiences

of

using

XMI

on

Tropos

tools

we

have

taken

into

account

the

benefits

of

its

technological

support,

but

also

of

its

difficulty,

not

for

generating,

transmitting

and

reading

the

information,

but

on

easily

understanding

its

contents

and

creating

queries

or

transformations

on

it.

Therefore

we

consider

this

proposal

an

evolution

from

our

first

attempts

using

XMI..

Also

in

term

of

related

work

Model

Driven

Architectures,

or

MDA

is

an

approach

for

software

development

for

building

and

transforming

models

along

the

software

life

cycle.

These

models

follow

a

set

of

specifications

such

as

UML

MOF

CWM

and

XMI

for

UML

Models.

All

of

them

have

been

generated

by

the

Object

Management

Group

As

far

as

we

know,

even

novel

domain

modelling

proposals

from

OMG

like

Business

Process

Modelling

Notation

(BPMN)

do

not

consider

neither

goal

modelling,

quality

cross

cutting

concerns

nor

agents'

intentionality

modelling.

That

is

because

goaloriented

and

agent-oriented

conceptual

frameworks

have

been

out

of

the

paradigmatic

modelling

boundaries

of

object

orientation.

Therefore

we

claim

that

iStarML

is

a

good

first

step

applying

modeldriven

principles

(models'

transformation

and

interoperability)

inside

the

i*

goal-oriented

and

agent-oriented

conceptual

frameworks.

On

the

boundary,

i.e.

on

the

transformation

of

i*

and

Tropos

models

to

object-oriented

modelling,

different

approaches

have

been

already

proposed

If

we

try

some

automatization

approach

of

these

transformation

proposals,

for

sure

that

iStarML

would

be

a

relevant

option

as

Platform

Independent

Language

(PIM).

Therefore,

we

claim

that

iStarML

enables

MDA

principles

beyond

object

orientation.

Besides,

if

we

consider

not

only

an

agent-oriented

design

but

also

an

agent-oriented

implementation,

iStarML

can

enable

MDA

principles

on

software

methodologies

which

consider

agent

or

goalorientation

as

methodological

choice..

As

the

main

barrier

to

overcome

for

adopting

iStarML,

of

course

semantic

integration

is

the

most

important.

First

of

all,

we

remark

again

that,

as

we

have

already

reported

in

differences

in

the

core

of

i*

are

minor.

For

those

cases

in

which

direct

translation

from

one

i*

framework

to

another

is

not

direct,

we

need

to

develop

point-to-point

translations

as

mentioned

in

Section

for

the

case

of

soft

goal

contributions.

Other

constructs

may

be

treated

similarly,

e.g.

trust

relationships

in

trust

models

may

be

translated

to

dependencies.

For

others,

they

may

be

just

discarded,

e.g.,

the

traceability

construct

"supports"

as

defined

in

is

just

syntactic

sugar

and

may

be

removed

without

losing

meaning.

However,

a

few

of

existing

proposals

have

not

an

obvious

treatment

(e.g.,

the

temporal

relationship

among

tasks

as

proposed

in

Formal

Tropos)

and

therefore

the

only

action

to

take

is

to

detect

and

report

these

situations,

probably

keeping

them

as

annotations

in

the

generated

models..

In

terms

of

future

work

we

will

keep

supporting

iStarML

adoptions

because

they

will

allow

materializing

interoperability

benefits

in

the

i*

community,

e.g.

using

goal-oriented

domain

models

on

agent-oriented

software

design,

implementing

repositories

of

requirements

patterns,

using

agentoriented

metric

tools

on

actor-oriented

business

modelling,

and

a

long

and

unpredictable

list

of

human

activities

resulting

of

the

capacity

of

sharing

models

and

tools

that

work

on

a

common

but

customizable

conceptual

framework.

Precisely,

in

order

to

clarify

these

possibilities,

we

have

already

started

a

study

about

interoperability

scenarios

for

using

iStarML

in

the

context

of

software

development

process.

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