Scheduling of inventory releasing jobs to minimize a regular objective function of delivery times Abstract In this note we provide new complexity and algorithmic results for scheduling inventory releasing jobs, a new class of single machine scheduling problems proposed recently by Boysen et al. We focus on tardiness related criteria, while known results are concerned with inventory levels between fixed delivery points. Our interest is motivated by the fact that deciding whether a feasible schedule exists is NP-hard in the strong sense, provided that all delivery deadlines are fixed, and there are no restrictions on the amount of products released by the jobs, nor on the job processing times. We will establish NP-hardness results, or provide polynomial or pseudo-polynomial time algorithms for various special cases, and describe a fully polynomial approximation scheme for one of the variants with the maximum tardiness criterion. In this paper we study new variants of the problem of scheduling inventory releasing jobs, recently proposed by Boysen et al. [1] . The problem has been motivated by JustIn-Time manufacturing, where a set of inventory releasing jobs have to be sequenced on a single machine (or server) in order to meet a set of delivery requests. However, as Boysen et al. observed, with fixed deadlines it is NP-hard in the strong sense to decide whether a feasible solution exists even if there is only one product type, but the job sizes and the quantities of products released are arbitrary. Therefore, M. Drótos · T. Kis Computer and Automation Research Institute, Hungarian Academy of Sciences, H1111 Budapest, Kende str. 13-17, Hungary Tel.: +36 1 2796156; Fax: +36 1 4667503 E-mail: marton.drotos@sztaki.hu, tamas.kis@sztaki.hu Boysen et al. consider special cases where the existence of feasible schedules can be decided in polynomial time, and they aim at minimizing stock level related criteria.. In this paper we focus on the problem of meeting the due-dates of deliveries, i.e., late delivery is permitted, and we seek a schedule which minimizes a regular function of the delivery completion times. An optimal or suboptimal solution can be used to set hard deadlines, and then in a second round one can apply the methods of Boysen et al. to minimize the stock levels. In a combined approach, one may consider the two types of criteria together in a multi-criteria optimization framework, but this is out of the scope of the present paper.. As a concrete application, consider a manufacturing workshop assembling and welding metal pieces together to satisfy customer orders. Each product consists of several pieces cut out from steel slabs. After some pieces are cut out from a steel slab, the remaining part becomes waste. This preparatory work transforms raw material into an inventory of various components. Cutting operations are inventory releasing jobs that may produce metal pieces (intermediate products) of several forms and sizes from the same metal sheet to economize on steel slabs. The due dates and inventory levels are dictated by an MRP system that computes the material requirements of the customer orders for the final assemblies over time. The scheduling models studied in this paper can handle a single cutting machine. Since pieces of various types may be cut out from the same steel slab, a cutting operation cannot be replaced by several cutting operations, and since the various components cannot replace one-another, this problem does not fit the framework of Boysen et al. [1] , where a job always produces only one product type. The problem of minimizing the inventory levels while satisfying all the external demands on time is studied in [1] . In that paper, the delivery requests have strict deadlines, and special cases where the existence of a feasible schedule is decidable in polynomial time are considered with the objective of minimizing some stock level related criteria. Polynomial algorithms or NP-hardness proofs are provided for several special cases.. The opposite problem, in which jobs consume nonrenewable resources has been studied e.g. in [5, 6, 8] . In these models a job may be started only if the requirements of the job do not exceed the available quantities from each nonrenewable resource. If a job is started, the available quantities of the non-renewable resources are instantly decreased by the requirements of the job. Moreover, non-renewable resources are supplied over time at given time points. For the special case when there are only non-renewable resourceand precedence constraints, Carlier and Rinnooy Kan [5] gave polynomial solution methods. If, in addition, the jobs have to be sequenced on a machine, the problem has been shown to be NP-hard [6] . In [8] , the complexity of various sequencing problems on a single machine is studied subject to non-renewable resource constraints. The authors provide NP-hardness proofs, and approximation algorithms for the hard problems, or polynomial time algorithms for the tractable ones.. In a more general setting jobs may produce and consume a common set of materials, and a basic question is whether a feasible sequence of producers and consumers exists. This problem has been shown NP-hard in the strong sense by Kellerer et al. [9] . In the same paper, the authors consider the minimization of maximum stock level and propose three different approximation algorithms with relative error 2, 8/5, 3/2, respectively. Some numerical results complement the theoretical findings. This line of work has been taken up by Briskorn et al. [2] , where several variants are studied, and either an NP-hardness proof is presented, or a polynomial time algorithm is devised. In [3] , an exact branch-and-bound based method is developed and numerical results are provided for the general problem with 5 to 20 jobs.. Finally, Neumann and Schwindt [10] study project scheduling problems with inventory constraints. They analyze the feasible region of job starting times, and propose to add temporary constraints between pairs of jobs to resolve resource conflicts in a branch-and-bound algorithm.

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


Energy-efficient instruction set synthesis for application-specific processors Several techniques have been proposed to enhance the energy-efficiency of ASIPs (Application-Specific Instruction set Processors). While those techniques can reduce the energy consumption with a minimal change in the instruction set (IS), they fail to exploit the opportunity of designing the entire IS from the energy-efficiency perspective. In this paper, we present an energy-efficient IS synthesis technique that can comprehensively reduce the energy-delay product (EDP) of ASIPs through optimal instruction encoding, considering both the instruction bitwidth and the dynamic instruction count. Experimental results with a typical embedded RISC processor show that our technique can generate application-specific IS's that are up to 40% more energy-efficient over the native IS for several application benchmarks. It is well known that CISC IS's (Instruction Sets) are more energyefficient than RISC IS's for the same microarchitecture [1] . However, it is not well known how we can utilize this observation to generate more energy-efficient IS's, especially when we are given the freedom to modify an IS on an application (or application domain) basis. With the recent development in soft IP's (Intellectual Properties) and configurable processors, IS customization has become possible and even necessary to make differentiation in today's competitive markets. Nonetheless, previous work on lowpower ASIPs (Application-Specific Instruction Set Processors) has not been so ambitious as to fully exploit the flexibility of ASIPs and redesign the IS from the energy-efficiency perspective.. In this paper, we present an energy-efficient IS synthesis approach for application-specific processors. We optimize IS's under given microarchitectural constraints, as the design change in the datapath may incur significant engineering cost and thus not be desirable. With a fixed microarchitecture, specialization can be made in such areas as instruction encoding, the number of instructions, and the instruction bitwidth, all of which can be considered as instruction encoding in a broad sense. Thus, our objective is to find the best instruction encoding (manifested by RISC vs. CISC) that leads to the maximal energy-efficiency through fewer number of instructions fetched (reducing the instruction memory energy) or fewer number of execution cycles (reducing the processor core energy) or a balance of the two.. One of the critical elements of the proposed energy-efficient IS synthesis is reducing the instruction fetch energy through multiple dimensions of the code volume (the number of instructions fetched multiplied by the instruction bitwidth). While some previous lowpower techniques can also have similar effects of reducing the code volume, only one dimension has typically been considered. 1 Our technique, on the contrary, addresses the multiple factors of the code volume and provides a comprehensive optimization framework for energy-efficient IS's. Also, our scheme generates a single IS as opposed to dual IS's (compressed, uncompressed) as the code compression techniques do; thus, it avoids the problems of dual IS's such as requiring an instruction decompressor (or re-map table) and, for some techniques, having to take care of the changes in the branch target addresses. It should be noted, however, that our IS customization framework assumes minor architectural changes in the datapath, allowed by the given architectural constraints, such as inserting additional muxes in front of functional units, as well as changing the instruction decoder logic. Our experimental re- sults show that our technique can generate application-specific IS's that outperform the native IS of a typical embedded RISC processor, not only in performance but also in energy and the EDP, up to about 40% with each metric.. The rest of the paper is organized as follows. In Section 2 we briefly discuss the previous work for energy-efficient ASIPs and in Section 3 we highlight the key elements of the encoding-oriented IS synthesis for ASIP customization. In Section 4 we derive the contribution of each instruction to the overall energy-efficiency based on an ASIP energy consumption model. We present our experimental results in Section 5 and conclude the paper. We have presented an energy-efficient IS synthesis technique that is based on an encoding-oriented IS synthesis framework. To comprehensively reduce the code volume, our technique optimizes the instruction encoding, considering both the instruction bitwidth and the dynamic instruction count. To apply the IS synthesis framework for energy-efficiency optimization, we formulated the EDP change due to IS customization and derived the contribution of each complex instruction. The experimental results show that our technique can generate application-specific IS's that outperform the native IS of a typical embedded RISC processor, in performance, energy, and the EDP, up to about 40% with each metric.. Our methodology to improve the IS of a processor from the energy-efficiency perspective focuses on the flexibility of ASIPs at the instruction level. In the future, we plan to investigate customization techniques at higher-levels (e.g., loops, functions), to exploit more opportunity available in future complex systems-onchips. Previous work on low power techniques for ASIPs has mostly concentrated on bit pattern assignment of instructions, without changing the number of instructions in the IS. To reduce the switching activity and the dynamic energy consumption in IF (Instruction Fetch) registers of ASIPs, it was proposed to re-encode the opcode part of instructions so that the most frequent opcode sequences can have the smallest Hamming distances [5] [6] . Or, exploiting the asymmetric energy consumption of some memory devices, even whole instructions can be re-encoded [7] [8] . Also, for a more aggressive approach, removing unused or less useful instructions from the IS has been suggested [9] .. While these techniques may fit well where only minimal changes can be made in the architecture, they are too conservative when a more aggressive IS redesign is preferred to seize the opportunity afforded by configurable processors. Contrastingly, we consider redesigning the IS from the energy-efficiency perspective to better exploit the flexibility of configurable processors. In [10] , an IS synthesis technique is proposed considering instruction encoding, which is, however, developed for performance improvement and does not consider energy-efficiency. Our energy-efficient IS synthesis is based on this technique, but significantly extends it by considering various optimization goals and their efficacy. For our experiments, we used the MIPS microprocessor architecture [11] , from which we defined a basic IS annotated with resource and timing information. For deriving complex instruction sets, we used a number of realistic benchmark applications covering multimedia (e.g., h.263 decoder, JPEG encoder), controlintensive (e.g., ADPCM coder/decoder), and cryptography (e.g., DES) domains. The benchmark applications were preprocessed using the EXPRESS retargetable compiler [12] targeting the basic IS to generate preliminary assembly code, which was used for the rest of the IS synthesis process.. While the MIPS architecture has 32-bit instructions, the native IS [11] of the MIPS uses the code space of only about 2 30 , meaning that the native IS essentially uses only 30 bits, reserving the rest of the code space for future versions. Since the basic IS for the MIPS was defined with the code space of about 1.42 × 10 8 , we used the code space of 2 30 − 1.42 × 10 8 for the complex IS synthesis.. After the IS synthesis process, the application was recompiled using the same retargetable compiler targeted for the synthesized IS. The execution cycle counts and the instruction fetch counts were obtained through cycle-accurate simulation (at the basic block level) and profiling. We assume that the ID energy is the same for all IS's, as we compare the synthesized IS's with the native IS, which also has many complex instructions.. For the energy consumption estimation, we made the following assumptions on the architecture. We assumed that the instruction memory is large enough to fit each application so that there is no off-chip memory access for instruction fetch. To further simplify, we assumed that there is no instruction cache; thus, instruction memory energy consumption only depends on the number of instruction fetch. For the energy consumption ratio between IF, ID, and EX stages, we assumed that the ratio between E B IF + E B ID and E EX is 1:1 for all applications. 4 Note that this assumption also allows for an easy comparison of the EDP values for different IS's; that is,. where R EDP , R #IF , and R #CYC are the ratios of the EDP, #IF, and the cycle count values (respectively) of two IS's.

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


Simulation of land use spatial pattern of towns and villages based on CA-Markov model Firstly, this paper analyzes the basic principles and processes of the spatial pattern changes of land use in towns and villages, and the result shows that the land resource demands of urban development and population growth lead to the spatial pattern changes. Secondly, in order to grip land use changes better, the paper proposes a method for the simulation of spatial patterns. The simulating method can be divided into two parts: one is a quantitative forecast by using the Markov model, and the other is simulating the spatial pattern changes by using the CA model. The above two models construct the simulative model of the spatial pattern of land use in towns and villages. Finally, selecting Fangshan which is a district of Beijing as the experimental area, both the quantity and spatial pattern changing characteristics are investigated through building a changing dataset of land use by using spatial analysis methods based on the land use data in 2001, 2006 and 2008; CA-Markov is used to simulate the spatial pattern of land use in Fangshan for 2015. Rapid advances in geospatial models have made it increasingly possible to design and simulate spatial patterns for land use change (LUC). An approach commonly used in the simulation model for LUC is based on cellular automata theory and the GIS framework [1, 2] . So far, the establishment of simulation models to monitor and adjust the changes of land use is a local and global issue of great concern. Mainly simulation methods include two aspects: the first one is the number of prediction, and the other one is simulating for the spatial patterns of the future. Spatial patterns of land use changes in the dynamic simulation and analysis relating to the impact of land use changes in many drivers is a very complex process [3] . Models based on the simulation of the spatial pattern of land use change processes are used to understand and explain the process of regional land use changes and trends in effective ways. However, the current real land use changes and the spatial distribution of the combination in different scales of land use, spatial and temporal dynamic model of the evolution rule are rare.. Both cellular automata (CA) and the Markov model have great advantages in the study on land use changes, while both of them have respective disadvantages. The Markov model for land use changes has been widely used, but with the traditional Markov model it is difficult to predict the spatial pattern of land use changes. The CA model with powerful spatial computing can be used to simulate the spatial variation of the system effectively. A CA-Markov model is a robust approach in the spatial and temporal dynamic modeling of land use changes because geographic information systems (GIS) and remote sensing (RS) can be efficiently incorporated [4] . The CA-Markov model absorbs the benefits from the time series and spatial

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


TWiki a collaboration tool for the LHC At the European Laboratory for High Energy Physics, CERN[1], the Large Hadron Collider (LHC) [2] accelerator is colliding beams of protons at energies of 3.5 TeV, recreating conditions close to those at the origin of the Universe. The four main LHC experiments, Alice, Atlas, CMS and LHCb are complex detectors with millions of output channels. These experiment detectors, "large as cathedrals", have been designed, built and are now operated by collaborations of physicists from universities and research institutes spread across the world.Wikis are a perfect match to the collaborative nature of CERN experiments and since TWiki [3] was installed at CERN in 2003 it has grown in popularity and the statistics from April 2011 show nearly 10000 registered editors and about 110000 topics (Figure 1 ). Since the start-up of the LHC more and more users are accessing TWiki requiring better server performance as well as finer control for read and write access and more features. This paper discusses the evolution of the use of TWiki at CERN. The World Wide Web was invented at CERN to improve sharing of documents among collaborating physicists on diverse computer systems. Wiki pages, where the user has the possibility to edit the page directly from the browser, is very much in the original democratic spirit of the web. For scientific organizations like CERN, this allows collaborations where users are in different buildings, cities or even countries a convenient way of working together on projects and documents.. TWiki, one of many available Wikis, is a structured one targeting mainly corporate intranets. TWiki was originally chosen because of its project oriented focus and simple setup on computing resources that were readily available at CERN. TWiki runs on Linux machines with the Apache web server and is written in Perl. To keep track of changes to web pages, an RCS (revision control system) back end is used. There are a number of Perl "plugins" available for TWiki that provide additional functionality. The TWiki service quickly became popular at CERN following its introduction and as figure 1 shows the number of topics has grown at a steady rate over the past years. TWiki has proven to be a simple and easy tool to use for the creation and development of collaborative documents. The Wiki approach is a perfect match to the collaborative nature of the experiment communities at CERN. New members of the LHC experiments can easily access information and do not need to follow a course in order to contribute.

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


Composing architectural aspects based on style semantics The lack of architecturally-significant mechanisms for aspectual composition might artificially hinder the specification of stable and reusable design aspects. Current aspect-oriented approaches at the architecture-level tend to mimic programming language join point models while overlooking mainstream architectural concepts such as styles and their semantics. Syntax-based pointcuts are typically used to select join points based on the names of architectural elements, exposing architecture descriptions to pointcut fragility and reusability problems. This paper presents style-based composition, a new flavor of aspect composition at the architectural level based on architectural styles. We propose stylebased join point models and provide a pointcut language that supports the selection of join points based on styleconstrained architectural models. Stability and reusability assessments of the proposed style-based composition model were carried out through three case studies involving different styles. The interplay of style-based pointcuts and some style composition techniques is also discussed. Architectural aspects are components that modularize widely-scoped properties that naturally cut across one or more of the elements in a given architectural decomposition [1, 7, 9] . The importance of taming architectural aspects is attested by the recent interest of the software architecture community on understanding how aspects influence architectural descriptions (ADs) [11, 9] and by the growing number of aspect-oriented (AO) architecture description languages (ADLs) [7, 2] . In this context, aspect composition requires the identification of architecturally-relevant join points in which aspects and other architectural elements are naturally combined together.. However, current AO ADLs overlook mainstream architectural concepts such architectural styles, and aspect composition resorts to join point models that mimic low-level programming language join point models. This may lead to a conceptual misalignment between the techniques, models and ADLs used by architects to document architectures and the expressiveness of AO approaches. For instance, architects commonly organize the components of large software systems on the basis of one or more architectural styles. An architectural style encapsulates important decisions about architectural elements and emphasizes important constraints on these elements and their relationships. Architectural styles allow architects to reuse and apply successful design knowledge to a particular class of systems, with the support of style-specific tools, analysis, and implementations [10] . Moreover, syntax-based pointcuts are typically used by current AO ADLs to select join points based on the names of architectural elements, exposing AD to pointcut fragility [21, 19] and reusability problems. The characteristics and limitations of low-level join point models and syntax-based pointcuts that affect aspect composition at the architectural level are also discussed (Section 2).. In this context, we present style-based composition, a new flavor of aspect composition at the architectural level based on the semantics of architectural styles. Style-based aspect composition is defined in terms of style-based join point models (Section 3), high-level join point models that stand for abstract models of system behaviour at the architectural level. Such abstract models entail significantly different sets of join points from those supported by existing AO ADLs and AspectJ. For each style, a join point model needs to be defined and documented. The documentation makes the style semantics explicit so that the style-based joint point models can be used for architectural composition and analysis. In style-based aspect composition, pointcut definitions are inevitably based on querying over multiple style-based join point models. They also require an open-ended pointcut language that takes into account these join point models (Section 4).. Style-based join point models are expected to facilitate aspect specification and composition in the context of real large-scale and complex systems which are seldom homogeneous. Style-based pointcuts are expected to reduce pointcut fragility and promote reuse. Stability and reusability assessments of the style-based composition model are presented, based on the outcomes of three case studies involving different styles and application domains: the Health Watcher (HW) system [33] , the Conference Management (CM) system [29] , and the MobileMedia (MM) [12] product line for data manipulation in mobile devices. Our analysis also discusses the interplay of style-based composition and some existing techniques for composing architectural styles in the context of the HW system (Section 5). Finally, our proposal is compared with related work (Section 6) before disclosing final remarks and future work directions (Section 7). The definition of pointcut languages plays a central role in aspect-oriented approaches [23, 21] . Although it has been known that the abstraction level of pointcuts must be lifted [21, 34] , syntax-based pointcuts are typically used to select join points based on the names of architectural elements, exposing architectural description to pointcut fragility [21, 19] and reusability problems.. We propose style-based join point models and provide a pointcut language that supports the selection of join points based on the semantics of architectural styles. Style-based join point models and the composition approach proposed here are meant to be language-independent and adaptable to different ADLs and formalisms to define style-specific behaviors. In this paper, architectural descriptions are expressed in AspectualACME and formal behavioural descriptions in CSP. We plan to exploit the proposed approach with other languages and formalisms in future work.. The definition and the rationale behind style-based join point models emerged from our analysis of existing AO ADLs [2, 14] and our experience on designing and assessing AO architectures for a number of distinct application domains. AO applications include a reflective middleware system [5] , multi-agent systems [16] , a CVS system [13] , product lines for quality control measurements [24] and J2ME games [24] .. In this paper, our main claim is that style-sensitive composition promotes the development of architectural aspects that are more reusable and stable in face of syntactic changes to the architecture. Our systematic comparison of style-based composition against syntax-based composition in three case studies has provided initial evidences that support our claim. We also discussed briefly the interplay of some techniques for style composition and style-based pointcuts in the context of our exploratory studies; we certainly need to gather more empirical evidence that may allow us to characterize other benefits and liabilities related to these issues. Future experimental work is also needed to assess the adequacy of style-based pointcuts to express architect's design intent and composition rationale, and the challenges of their adoption by the Software Architecture community. The Health Watcher (HW) design (Section 2.1) is a reallife case study that involves several architectural styles and different architectural aspects, including exception handling (Section 2.2). Architectural descriptions for the HW system are provided in AspectualACME [14] , an AO ADL that extends ACME [17] for expressing aspectual interactions and configurations (Section 2.3). The HW design is used to discuss characteristics and limitations of low-level join point models and syntax-based pointcuts for composing aspects at the architectural level (Section 2.4). In previous work [29] , we presented an exploratory study of the influence exerted by style-based composition on the stability of architectural modules addressing error handling and security, in the context of alternative designs for the CM system. Each design adopted a different style (blackboard, reflective blackboard, reactive coordination and stigmergic coordination). In this work, stability and reusability assessments of the style-based composition model were carried out by means of three case studies involving different architectural styles and different application domains.. Style-based join points and existing ADLs. Existing AO approaches at the architecture level do not support stylebased pointcut specifications. The exploitation of stylebased join point models seems to address at the architectural level the recurring problem of pointcut fragility, a common concern in conventional programming-level join point models. As discussed in Section 5, in previous empirical studies on architecture stability [25, 19] using the HW system, we observed that style-based pointcuts tended to be more stable in the presence of widely-scoped design changes because the syntactical changes in ADs occur more often than modifications on the stylistic architectural choices [25] . Certainly, AO ADLs may resort to conventional pointcut designators in conjunction with style-based designators.. Semantics-based composition in requirements and design. The drawbacks of syntax-based AO compositions have already been discussed [8] from the perspective of AO requirements engineering. The similarities with our work are the discussions about the disadvantages of syntax-based compositions in contrast with the expressiveness of semanticsbased composition in early aspects. However, the main dif-ferences are that of focus (ours is on ADLs) and the use of a formal language (CSP) versus natural language to express join point models and compositions.. Klein et al. [23] argue in favor of a semantics-based approach for pointcut languages at a more abstract level. They propose a semantics-based weaving algorithm for hierarchical message sequence charts, a scenario formalism, and assess its benefits and limitations. In our work, we propose a semantics-based approach for pointcut languages at the architectural level. We resort to style-based join point models and a pointcut language to support style-based composition in ADs and provide initial experimental assessment on the stability and reuse of such ADs.. Stein et al. [34] point out that most pointcut languages at the modeling level are based on existing AOP languages and that there are no means to express join point selection criteria with respect to the behavior of a system. They provide graphical visualization of join point selections via Join Point Designation Diagrams (JPDDs), where each visualization can be examined with respect to the selection's underlying conceptual model (control flow-oriented, data flow-oriented, or state-oriented conceptual model). In our work, we have also defined an early aspects approach that is independent of existing AOP languages. However, instead of focusing on visualization diagrams and conventional join point models, we propose style-based join point models and provide a textual pointcut language to express the selection of join points based on the semantics of architectural styles.. Application-specific models and pointcuts. Kellens et al. [21] propose model-based pointcuts, defined in terms of a conceptual model of the base program, and show how such pointcuts can be less fragile with respect to changes in the base program. Brichau et al. [3] extend the model-based pointcuts technique and use a logic-based pointcut language to express application-defined pointcut predicates. In this point their work is similar to ours as it exploits the expressive power of a logic language to declare pointcuts and to address the pointcut fragility problem. However, instead of addressing application-specific join point models, our proposal focuses on and argues in favor of more high-level, stylespecific join point models and enforces style semantics on every application that adheres to those architectural styles.

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


Information Systems Offshore Outsourcing: An Exploratory Study of Motivations and Risks in Large Spanish Firms Information systems offshore outsourcing is motivated by such factors as globalization, technological development and the possibility to explore new markets. However, both the geographical and the cultural distance create more risks than in onshore outsourcing. The aim of this article is to develop a typology of firms based on the specific motivations and risks associated with offshore outsourcing in large Spanish firms. This article seeks to understand the motivations and risks in offshore outsourcing by conducting an exploratory field survey in the largest Spanish firms and establishing a typology of firms involved in offshore outsourcing. We first examine the position of Spanish firms in connection with onshore as well as offshore outsourcing. We then describe determining factors for offshore outsourcing with a special focus on the motivations and the risks linked to it. Next, we present our methodology along with results and conclusions. Several theories have been put forth in the past 15 years to explain IS outsourcing, both offshore and onshore, including outsourcing motivations and risks. We examine offshore outsourcing motivations and risks which are related with factors like costs, technology and infrastructure, time, quality, and also international and employment factors (see Appendix A- Table 1 ). Based on the assumption that larger-sized firms are the most likely to outsource (Lee, Miranda, & Kim, 2004) , we distributed a questionnaire to the largest Spanish enterprises. The '5,000 Largest Firms' Directory of the Actualidad Económica magazine-later collated with other databases such as Duns and Bradstreet's 'The 50,000 Most Important Spanish Firms'-established the target population for the study. We removed 893 of the 5,000 firms with higher turnovers included in the first database because their address and telephone coincided with those of others, which suggested that they were subsidiary or affiliate companies.. The remaining 4,107 firms received questionnaires along with a stamped self-addressed envelope. The questionnaire derives from a previous one prepared by the same authors and constructed, like this one, from the literature on the topic as a reference. Additionally, some experts in IS management analysed the questionnaire. 3 We included only eight of the 26 questions in the final questionnaire in the present article, as this is part of a larger study which deals with a wide range of issues related to IS outsourcing (see Appendix B). Of those eight questions, one pertains to the extent of outsourcing, both nationally or globally; five pertain to the general profile of the firms in the study as well as their IS departments and managers; and two questions deal with offshore outsourcing motivations and risks. Table 2 shows the measurements for the main variables analysed in the study.. The questionnaire addressee was the IS manager of the selected firms. Unfortunately, no lists of these managers are available in Spain, leaving the identity of the questionnaire addressee unknown. We later elaborated upon the questionnaire using the statistical program SPSS for Windows, and treated it with univariate and multivariate methods. Table 3 shows the technical specifications of the empirical work.. Three-hundred twenty-nine valid questionnaires were received, which represents an 8% response rate. This ratio may seem low, but it is actually similar or even superior to others in comparable studies of IT outsourcing (Bahli & Rivard, 2005; Ma, Pearson, & Tadisina, 2005; Shi, Kunnathur, & Ragu-Nathan, 2005) . It is also difficult to obtain responses to surveys carried out among executives, especially IS executives, because rapid technological change, considerable IT-related investments by firms and the great interest in outsourcing have made these executives the target of many surveys (Poppo & Zenger, 1998) . The firms that answered the questionnaire reflect the total population in terms of size (sales and number of employees) and sector. A T-test verified the possible differences in the number-of-employees mean both for firms that answered the survey and for those that did not, with T having a value of -1.080 with a 0.280 significance level. In the case of sales, we used a non-parametric test-Mann-Whitney's U-test⎯ with a value of 444732.5 and a 0.338 significance level. A Chi-square test helped to check the possible connection between the industrial sector and the response or lack of response by firms. The Chi value was 2.802 and the significance level 0.246. These results imply the existence of a non-response bias in relation to these three variables. 4 Because as discussed in the next section, most of the interviewed firms did not use offshore outsourcing, the number of answers about offshore outsourcing motivations and risks was low. One-hundred seventy-seven firms answered these Table 4 shows the general features of the interviewed firms and of their IS departments and managers. We identified possible differences between firms which practice offshore outsourcing and those that do not. The study confirms that IT outsourcing has become a widespread phenomenon on a national scale, as 83.6% of the interviewed firms outsource some of their IS activities to a national provider, and only 54 firms (16.4%) do not. Global outsourcing continues to be an isolated phenomenon in Spain, though, since only 54 of the firms analysed (16.4%) look for IS providers abroad. A significant dependence relationship exists with respect to whether firms outsource inside or outside their country (the chi-square statistic detects dependence between both variables with a 0.000 significance level). Only one firm uses international outsourcing without national outsourcing. The rest of the firms that use offshore outsourcing have national providers too.

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


Collaborative sketching with distributed displays and multimodal interfaces In this paper we describe a system design for supporting creative group activities using distributed displays and multimodal interaction. We describe the rationale behind our approach and proposed interaction techniques for supporting collaborative sketching. Our goal is to understand how the interface metaphor, display space and interaction modalities may influence exploration and communication in collaborative settings. When designers are creating and revising ideas during early design stages, they often harness the spatial properties of the environment [1] . Design sketches are shared on large whiteboards or spread out on tables and walls for comparison and discussion with other designers. In design studio environments, the room itself is an important tool that allows organizing information in an informal and spatial way. Especially during group activities, accessibility and visibility of artifacts is crucial for efficient communication. This is one of the reasons why designers often prefer to work with pen and paper during creative group activities [2] . Paper provides a private workspace while sharing is as simple as pinning the paper on the wall or spreading it out on the table. However, when using desktop-based electronic tools, the artifacts that are created are often hidden in file systems. At the same time, multiple devices are required to work simultaneously in group settings. Even when using electronic whiteboard systems, exchanging sketches to other displays is awkward and can lead to breakdowns of the creative flow. In the following, we examine existing approaches to these issues before describing the rationale and proposed interaction techniques of our alternative approach. We are currently extending the system with groupware features. This includes an automatic locking mechanism of objects that are currently manipulated to cope with concurrency problems. In addition, we are also adding a location tracking system for identification of users and their display association. In future work, we want to integrate this metadata for analytical visualizations of design sessions and for presenting passive information on displays that are not actively used by the group.

O 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


Differential approximation results for the traveling salesman and related problems Abstract. This paper deals with the problem of constructing a Hamiltonian cycle of optimal weight, called T SP . We show that T SP is 2/3-differential approximable and can not be differential approximable greater than 649/650. Next, we demonstrate that, when dealing with edge-costs 1 and 2, the same algorithm idea improves this ratio to 3/4 and we obtain a differential non-approximation threshold equal to 741/742. Remark that the 3/4-differential approximation result have been recently proved by a way more specific to the 1, 2-case and with another algorithm in the recent conference (symposia on Fundamentals of Computation Theory 2001) [18] . Based upon these results, we establish new bounds for standard ratio: 5/6 for M ax T SP [a, 2a] and 7/8 for M ax T SP [1, 2] . We also derive some approximation results on partition graph problems by paths.Keywords: Approximate algorithms; Differential ratio; Performance ratio; Analysis of Algorithms;A current and very active research area coping with N P −Completeness is polynomial approximation theory; the main objective is either finding a good approximation algorithm or establishing a nonapproximation threshold for a given N P O optimization problem. The goal of an N P O-optimization problem π = (D, sol, m, goal) 1 with respect to an instance I is to find an optimum solution We focus on the design of approximation algorithms with guaranteed performance ratios, that run within polynomial time and produce sub-optimal solutions. Usually, the scientific community uses the worst-case standard ratio [14] ,[1], [7] . However, we mainly refer in this article to another ratio called differential ratio. This measure, studied in [2],[13] and more recently in [11] , leads to new algorithms taking into account the extreme solutions of the instance, and provides the opportunity to better understand these problems. Besides, we show that there are tight links between both measures for our problems. Definition 1.1. Let π be an N P O problem and x be a feasible solution of an instance I. We define the performance ratios of x with respect to the instance I asThe performance ratio is a number less than or equal to 1, and is equal to 1 when m[I, x] = OP T (I). The performance of A with respect to R ∈ {δ, ρ} on the instance I is the quantity R A [π](I) = 1 D is the set of instances, sol is the set of feasible solutions, m is the objective function and goal ∈ {M ax, M in}.2 If goal = M ax, then goal = M in and goal = M ax. Routing design problems are of major importance in combinatorial optimization, and related works have been numerous during the last twenty years (see [6] , [13] , [17] and [12] ). We will be concerned with the Traveling Salesman problem formally defined as follows. Definition 2.1. Consider a complete graph K n with non-negative costs d(x, y) for each vertices pairs of K n . We want to find an optimal-cost Hamiltonian cycle, where the cost of a path is the sum of the weights on its edges. We call T SP this problem. When the edge-weights are in the set {a, a + 1, ..., b − 1, b}, we called this problem T SP [a, b] .. If goal = M ax, the problem is called M ax T SP , else M in T SP . We use the notation T SP when we consider without distinction the cases goal = M ax or goal = M in. ♦. A lot of standard ratio approximation results have been obtained until now for both goal = M in and goal = M ax. The first negative approximation result [22] states that it is not possible to approximate M in T SP within 1/f (|I|) where f is any integer function computable within polynomial time unless P = N P . Nevertheless, M in metric T SP is approximable within 2/3 [6] , M in T SP [1, 2] is 6/7-approximable and is APX-complete [20] . Finally, the result of [12] proves that it is N P -hard to approximate M in T SP [1; 6] within a standard ratio strictly greater than 130 131 . For M ax T SP , results are more optimistic since M ax T SP is 3/4-standard approximable [23] .. We show that T SP is 2/3-approximable with the differential ratio and we improve the ratio to 3/4 for T SP [1, 2] . We can deduce from lemma (1.

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


Distributed topology control of wireless networks Abstract-We propose and analyze a distributed control law that will maintain prescribed local properties of a wireless ad hoc network in the presence of node mobility, MAC layer power control and link fades. The control law uses a simple and intuitive power adaptation mechanism. We consider as an example the topology requirement of maintaining the out degrees of each node at prescribed values and keeping the in degree close to the out degree. The topology objective is achieved by adapting the transmission power based only on local information. This power adaptation algorithm is analyzed using the o.d.e. approach to stochastic approximation. Simulation results verify the analysis and demonstrate its effectiveness. We also study the ability of the proposed objective to maintain connectivity. Although many heuristics are described in the literature to maintain local topological properties, the algorithm proposed in this paper is the first one that has proven convergence properties. Power control in ad hoc wireless networks can be used by different layers of the communication stack, possibly simultaneously. At the physical layer it can be used to maintain channel quality (for example, bit error rates through signal to interference ratio) at acceptable values by adjusting the transmission power. This has been addressed extensively in the context of cellular or infrastructure based networks. See, e.g., [8] . Power control can be used to reduce MAC latency [17] by using, if possible, lower power levels to connect to neighbors without disturbing ongoing transmissions that have forced it to not transmit by a CTS of the CSMA/CA MAC layer protocol. Transmission power determines the radio range of a node thereby defining its connectivity and hence the topology of the network. Thus power control can also be used for topology control by the network layer [22] , [21] , [25] , [9] , [13] , [14] . Power control can even be mapped to the transport layer where it can impact the congestion control algorithms [18] . [22] , [21] , [25] , [9] describe a local topology objective to achieve a connected network. The topology so obtained is further optimized by eliminating the links to nodes that can be reached in multiple hops with less power.. Our goal in this paper is not to propose a new local property objective. Rather, it is to obtain a control law that will maintain the prescribed objective to obtain the 'working topology' in the presence of changing network conditions. We describe and analyze such a control law based on power, and hence range, adaptation. This control law is aimed at maintaining the prescribed local property objective while the number of active nodes and their locations change, due possibly to MAC layer energy conservation algorithms that switch off a node's radio when it is inactive [23] , node movement and channel conditions. We note that there are many heuristics described in the literature to maintain local properties, e.g., [21] , but, to the best of our knowledge, this is the first algorithm that has proven convergence properties.. The power control algorithm that we propose is in the spirit of adaptive 'learning' schemes of adaptive signal processing and makes incremental corrective adjustments to the transmission power and hence the transmission range, based on a noisy 'error' signal that is calculated using only local information. It does not aim to find an exact or near-exact optimum transmission range. Thus our treatment of the problem is along the lines of a 'regulation' or 'tracking' problem in control where the objective is to stay close to a prescribed operating point (here the prescribed local property objective) rather than to achieve an optimum. The optimality is built into the choice of the local property objective. The simple scheme can be seen to be totally distributed and extremely easy to implement. The scheme has overtones of the transmission power adaptation scheme of [8] that is aimed at maintaining a specified SIR at the receivers using a distributed control scheme. In our analysis we use only some very gross properties of the scheme such as some natural monotonicities that arise, and do not require the detailed structure of the adaptive scheme. This makes it very robust with respect to the modeling assumptions and hence a potentially powerful tool that may find applications well beyond the present scheme.. The rest of the paper is organized as follows. In the next section we review existing local topology objectives and in Section III we describe the power adaptation scheme with reference to one topology objective and the analysis of the algorithm. Section IV presents some numerical results from simulations. We conclude with a discussion in Section V where we discuss some implementation issues, performance implications of the topology control scheme and application of the controller to achieve other local topology objectives. . Since the transmission range is a direct function of the transmission power, we will consider range adaptation to imply power adaptation and deal only with the range. Let be the prescribed outdegree for node " which is to be achieved through transmission power adaptation. We will assume that the transmission range can be varied continuously in the interval. adjusts the power at times. according to the adaptation equation is the projection onto the interval. being the maximum range which the node can achieve and % a small number corresponding to the minimum range which the node should have. Thus. w is a weight factor. The idea is as follows. The adaptation equation will strive to maintain the term inside the outer square brackets in Eqn. (1) near on the average. The term in the first inner square bracket will increase the transmission power if the out-degree is less than the prescribed value and decrease it otherwise. The term in the second inner square bracket will increase the transmission power if the out-degree is less than the in-degree and decrease it otherwise. Using an odd integer for @ ¥ will enhance the difference between the actual and desired values and will make the convergence faster, likewise for Y . Ideally, the terms in both the square brackets are to be maintained near , i.e., the out-degree should be equal to the prescribed value and the in-degree should be equal to the out-degree. The proposed scheme does not ensure this a priori. However, we have arranged the two terms so that an excessively low, respectively high, out-degree should give the same sign to both the terms and thus we may expect both to remain low on the average. As we see later, simulations confirm this intuition. Note that increasing the transmission power can cause interference at other nodes thus decreasing their SIR. However, we ignore this effect and assume that the only source of interference is through collisions due to simultaneous transmissions.. Assuming a stationary environment, let. be defined by:. , where . (We are implicitly assuming that the ambient random processes such as channel characteristics, mobility patterns, the MAC layer power control behavior, etc., are quasi-stationary.) Then our theoretical analysis below shows that under reasonable hypotheses, The continuous differentiability is an assumption for mathematical convenience in our analysis to follow. It will typically hold if the underlying probability distributions have sufficiently nice densities. Note that an increase in the output power of~will tend to cause an increase in the in-degree , which will correspondingly tend to increase. Thus this condition is quite natural. In this paper we have described a power adaptation scheme for use in an ad hoc network at the network layer that can be used to achieve topology control objective. We have analyzed the scheme to show that under fairly general assumptions, the adaptation scheme will converge. Extensive simulation results show that the topology control objectives are indeed achieved fairly efficiently and accurately. The adaptation scheme is also fairly general and can be easily adapted to achieve other, more detailed, topology objectives. We remark once again that Eqn. (1) can be used to obtain the 'working topology' and further optimization mechanisms can be used alongside to fine-tune the topology.

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On information rates of the fading Wyner cellular model via the thouless formula for the strip We apply the theory of random Schrödinger operators to the analysis of multi-users communication channels similar to the Wyner model, which are characterized by short-range inter-cell broadcasting. With H the channel transfer matrix, HH † is a narrow-band matrix and in many aspects is similar to a random Schrödinger operator. We relate the per-cell sum-rate capacity of the channel to the integrated density of states of a random Schrödinger operator; the latter is related to the top Lyapunov exponent of a random sequence of matrices via a version of the Thouless formula. Unlike related results in classical random matrix theory, limiting results do depend on the underlying fading distributions. We also derive explicit results in the high-SNR regime for some particular cases. We study communication channels similar to the Wyner model, a simplistic model that captures inter-cell interference which is considered to be a central factor in cellular networks. See [1] for a tutorial review.. The model is characterized by short-range inter-cell broadcasting, thus making possible the use of random Schrödinger operator techniques. Note that standard random matrices techniques ( [2] ) are not applicable because they concern random matrices built from a number of independent random variables of the order of the number of entries. Moreover, due to the particular (sparse) structure of the underlying random channel matrix, limiting results presented here do depend on the underlying distributions as opposed to standard results in random matrices theory.. The full proofs of the results are given in [3] . The rest of the paper is organized as follows. In Section II, we present the problem statement. In Section III, we prove the convergence of the per-cell sum-rate capacity when the number of cells and Base Stations (BSts) goes to infinity and we express the limit in terms of the Lyapunov exponent of a sequence of random matrices (Theorem III.2). In Section IV, we give a reformulation of this result. In Section V, we specialize the results and make them explicit in some particular cases. The relevant background on the theory of Lyapunov exponents is given in Section B of the Appendix, and the relevant background on exterior products is given in Section C of the Appendix.

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Structural theorems for symbolic summation Abstract Starting with Karr's structural theorem for summation-the discrete version of Liouville's structural theorem for integration-we work out crucial properties of the underlying difference fields. This leads to new and constructive structural theorems for symbolic summation. E.g., these results can be applied for harmonic sums which arise frequently in particle physics. In [21, 22] Karr developed a summation algorithm in which indefinite nested sums and products can be simplified. More precisely, such expressions are rephrased in a -field F, a very general class of difference fields, 1 and first order linear difference equations defined over F are solved by Karr's algorithm. In this way, one can decide constructively, if a given indefinite sum or product with a summand or multiplicand f from F can be expressed in terms of F. For instance, given F = Q(k)(S 1 (k), S 2 (k), S 3 (k)) where S r (k) = k i=1 1 i r denotes the generalized harmonic numbers of order r ≥ 1 and given 1 Throughout this article all fields contain the rational numbers Q as subfield.. Supported by the grant P16613-N12 of the Austrian FWF. Starting with Karr's structural theorem, we obtained various refined versions for reduced, completely reduced and depth-optimal * -extensions. In particular we worked out one essential draw back of Karr's version of reduced * -extensions if one wants to reduce, e.g., the nesting depth of sum expressions: his optimality depends on the order how the elements are adjoined in the field. In particular, if one reorders the tower of extensions w.r.t. the nesting depth given by the shift-operator, Karr's structural theorem usually cannot be applied: only if the difference field is reorganized by expensive transformations, one gets back a reduced * -extension of the desired ordered shape; compare Theorem 39.. In contrast to that, in the recently defined depth-optimal * -fields any possible reordering (as a * -field) gives again a depth-optimal * -field. As a consequence we could show structural properties that are independent of the extension order.. We emphasize that the presented theorems for telescoping (1) can be immediately carried over to Zeilberger's creative telescoping paradigm [54] used for definite summation; for more details in the setting of * -fields we refer to [46] . More generally, we obtain structural results for parameterized telescoping. For illustrative purposes we rephrase Theorems 9 and 56 explicitly.. Theorem 55 (Karr's structural theorem for parameterized telescoping) Let (E, σ ) be a reduced * -extension of (F, σ ) with E = F(t 1 ) . . . (t e ) and σ (t i ) = a i t i + f i (where either a i = 1 or f i = 0), and define S by (8) ; let φ 1 , . . . , φ n ∈ F. If there are κ 1 , . . . , κ n ∈ const σ F and g ∈ E such that the parameterized telescoping equation (g) = κ 1 φ 1 + · · · + κ n φ n (34) holds, then there are w ∈ F and c i ∈ const σ F such that (9) holds; in particular, for any such g there is some c ∈ const σ F such that (10) holds. (10) for some c, c i ∈ K and w ∈ E with δ F (w) ≤ d.. By concluding, we remark once more that Karr's structural theorem in [21, 22] (Theorem 9) is closely related to Liouville's theorem (Theorem 1) and Rosenlicht's algebraic proof [38] in the language of differential fields. A natural question is how our new results can be carried over to the differential field case. A positive answer should throw new light on the differential theory of elementary extensions.

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Instantly indexed multimedia databases of real world events Abstract-We introduce a new paradigm for real-time conversion of a real world event into a rich multimedia database by processing data from multiple sensors observing the event. Real-time analysis of the sensor data, tightly coupled with domain knowledge, results in instant indexing of multimedia data at capture time. This yields semantic information to answer complex queries about the content and the ability to extract portions of data that correspond to complex actions performed in the real world. The power of such an instantly indexed multimedia database system, in content-based retrieval of multimedia data or in semantic analysis and visualization of the data, far exceeds that of systems that index multimedia data only after it is produced.We present LucentVision, an instantly indexed multimedia database system developed for the sport of tennis. This system analyzes video from multiple cameras in real time and captures the activity of the players and the ball in the form of motion trajectories. The system stores these trajectories in a database along with video, three-dimensional (3-D) models of the environment, scores, and other domain-specific information. LucentVision has been used to enhance live television and Internet broadcasts with game analysis and virtual replays in more than 250 international tennis matches.

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Missing pattern discovery In this paper, we study the missing patterns problem: Find the shortest pair of patterns that do not occur close to each other in a given text, i.e., the distance between their occurrences is always greater than a given threshold α. We present various solutions to this problem, as well as to the case where the patterns in the pair are required to be of the same length. This work is motivated by optimizing the sensitivity of PCR. Experiments show that our algorithm is practical enough to handle human genome data. This paper presented efficient algorithms to solve the missing pattern discovery problems. Table 3 summarizes the results of this paper.. We implemented Bijective Mapping Algorithm 1 and made experiments for the human genome and the baker's yeast genome, and we succeeded in finding shortest missing pairs of length 8 for both human and yeast genomes. In addition, we studied an extended version of the problem where patterns in the pair occur at certain positions at a distance at most α, but do not occur α-close anywhere else, in the input string.. Independently of our work, Li [25] proposed an algorithm that solves the problem of listing all the shortest missing pattern pairs in O (min{αn log n, n 3/2 }) time. The algorithm assumes that the alphabet size σ is constant.. As a generalization of the missing pattern discovery problem, the following problem that allows mismatches is worth to consider: Given string T , distance α, and error parameter e, find pattern pair (A, B) such that any occurrence of A and B within e mismatches in T is not α-close. [28] presented some algorithms to discover structured motifs with errors in the Hamming distance metric. Since the algorithms of [28] and our algorithms in Section 3 are both based on suffix trees, it might be possible to solve the above general missing pattern discovery problem by combining these approaches. We have performed tests with the baker's yeast (Saccharomyces cerevisiae) genome and the human genome. 2 We set the distance α to 5000, which is a realistic value in terms of the speed of the polymerase reaction and duration of the PCR cycle. We then searched for shortest missing pattern pairs of the same length k. There were solutions with k = 8 for the yeast genome (i.e. both patterns of the pair are of length 8), in fact there were over 16 million such pairs. From the human genome data, we found 238 missing pattern pairs with k = 8. This is an interesting result, since the human genome is about 250 times larger than the yeast genome. Of the 238 pattern pairs, 20 pairs are missing from both the human and the baker's yeast genome. Table 1 summarizes these missing pairs and the shortest distance between the patterns (or their reverse complements) of each pair in the corresponding genomes. For reference, the shortest single missing patterns from the human genome are of length 11 and are listed in Table 2 . This is also surprising since the human genome length is roughly equal to 4 16 .. The program needed about 3 hours to process the baker's yeast genome on a 1 GHz machine, and about 30 hours for the human genome. The stop condition of Step 3 of the algorithm of Section 4.2.1, namely when all pattern pairs are discovered for the current pattern, provides a significant optimization in practice which allows the software to run only 10 times slower (rather than 250 times) for the human genome compared to the yeast genome.

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On the evolution of the yahoo! answers QA community While question answering communities have been gaining popularity for several years, we wonder if the increased popularity actually improves or degrades the user experience. In addition, automatic QA systems, which utilize different sources such as search engines and social media, are emerging rapidly. QA communities have already created abundant resources of millions of questions and hundreds of millions of answers. The question whether they will continue to serve as an effective source of information for web search and question answering is of vital importance. In this poster, we investigate the temporal evolution of a popular QA community -Yahoo! Answers, with respect to its effectiveness in answering three basic types of questions: factoid, opinion and complex questions. Our experiments show that Yahoo! Answers keeps growing rapidly, while its overall quality as an information source for factoid question-answering degrades. However, instead of answering factoid questions, it might be more effective to answer opinion and complex questions. Categories and SubjectRecently, community question answering (CQA) emerged as a popular alternative to finding information online. It has attracted millions of users who post millions of questions and hundreds of millions of answers, producing a huge knowledge repository of all kinds of topics, so many potential applications can be possibly made on top of it. For example, automatic question answering systems, which try to find the information to questions directly instead of giving a list of related documents, might use CQA repositories as a useful information source. However, it is not clear what information needs these CQA portals serve, and how these communities are evolving. In this poster we study a popular CQA portal -Yahoo! Answers-as our test case to quantify relative effectiveness for different types of queries such as factoid question, opinion queries, and complex question. As another motivation for our exploration, we examine how Yahoo! Answers has evolved recently and try to identify some trends in its development.We analyze the temporal changes of the Yahoo! Answers contents during the years of 2006 and 2007, so that we may get an idea of how it has progressed and to quantify potential uses of the services. Also we can gain a deeper understanding of community question answering phenomenon as it evolves over time. For this, we initially study CQA performance for simple factoid questions, and evaluate the potential utility for using CQA for opinion and complex questions.Yahoo! Answers: To obtain enough information for a better analysis, we crawled a large portion of Yahoo! Answer, resulting in a local archive of 96,000 questions and 1,150,000 answers, which cover about 125 categories. We divide all the questions and answers equally by posting time, resulting in 4 time periods of 2006.8 ~ 2006.11, 2006.12 ~ 2007.3, 2007.4 ~ 2007.7 and 2007.8 ~ 2007.11.In order to examine what type of questions Yahoo! Answers is best for, we prepared three datasets: factoid questions, opinion questions and complex questions, all acquired from the NIST TREC website.For factoid questions, we selected a sample of 1250 questions from the TREC question-answering track (years 1999-2006) that have at least one matching question was found in Yahoo! Answers database. This way we could focus on the quality and relevance of the CQA content instead of the artifacts of the current version of the Yahoo! Answers question retrieval engine. Note that from 1999 to 2003, the TREC factoid questions were independent of each other; however, starting in 2004 the TREC questions were organized in groups with a common target for each group. For the latter, we submit its question text as well as its target. In order to demonstrate Yahoo! Answers capability to provide related knowledge for factoid questions, we submit the factoid questions to Yahoo! Answer's web service and check the answers are correct or not.We submit all the factoid questions to Yahoo! Answers with minimal rewording.Relevance for factoid questions: TREC makes available "unofficial" answer patterns for factoid questions. We check every answer's content, and if the answer pattern is included by regular expression, we say this answer is 'matched', and is considered relevant for our purposes. For these preliminary experiments we focus only on whether the correct information is contained somewhere within a page and not on stylistic or ease-of-use issues (e.g., long vs. short answer), which we will explore in the future. Recently, community question answering (CQA) emerged as a popular alternative to finding information online. It has attracted millions of users who post millions of questions and hundreds of millions of answers, producing a huge knowledge repository of all kinds of topics, so many potential applications can be possibly made on top of it. For example, automatic question answering systems, which try to find the information to questions directly instead of giving a list of related documents, might use CQA repositories as a useful information source. However, it is not clear what information needs these CQA portals serve, and how these communities are evolving. In this poster we study a popular CQA portal -Yahoo! Answers-as our test case to quantify relative effectiveness for different types of queries such as factoid question, opinion queries, and complex question. As another motivation for our exploration, we examine how Yahoo! Answers has evolved recently and try to identify some trends in its development.. We analyze the temporal changes of the Yahoo! Answers contents during the years of 2006 and 2007, so that we may get an idea of how it has progressed and to quantify potential uses of the services. Also we can gain a deeper understanding of community question answering phenomenon as it evolves over time. For this, we initially study CQA performance for simple factoid questions, and evaluate the potential utility for using CQA for opinion and complex questions. Yahoo! Answers is rapidly growing. Our experiments suggest that searchers increasingly turn to Yahoo! Answers for opinion and complex questions. We can also see as the size grows, the overall quality in terms of answering factoid questions degrades. Finally, it appears that the form of participation in the Yahoo! Answers community is becoming more passive: users increasingly vote on other users' content and provide fewer answers. Finally, our findings suggest that while Yahoo! Answers is not optimal for factoid QA, it is becoming the destination of choice for complex information needs such as opinion or advice. We report the MRR, and the KL-divergence for factoid questions in Figure 1 As we can see, for the first three time periods, KL-Divergence initially increases, but drops during the final period. The MRR values appear to slightly decrease. This suggests that the questions posted on Yahoo! Answers increasingly diverge from the typical TREC factoid questions, and the CQA content is becoming less valuable as a source of factoid information.. Next we compare whether Yahoo! Answers content is evolving to be more similar to TREC factoid questions, opinion questions, or complex questions. These were obtained by calculating the KLDivergence between the TREC factoid, opinion, and complex questions respectively, and the Yahoo! Answers snapshots for the different time periods. Figure 1 (b) shows that the Yahoo! Answers corpus of questions is far more similar to the TREC opinion and complex questions, than to TREC factoid questions Last, we investigate the site-level evolution of the Yahoo! Answers community (Figure 1 (c) ). The three bars indicate the numbers of newly posted questions, answers, and the number of votes per each time period. For number of votes, we use the sum of both positive votes and negative votes. The number of newly produced questions and answers during each time period remained steady, though their speed of growth decreases. It is worth noting that the number of votes increases faster than the content. This implies that instead of contributing more answers, Yahoo! Answers participants are becoming more interested rating the existing answers. In order to demonstrate Yahoo! Answers capability to provide related knowledge for factoid questions, we submit the factoid questions to Yahoo! Answer's web service and check the answers are correct or not.

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