Decentralized resource management for a distributed continuous media server Abstract-Distributed continuous media server (DCMS) architectures are proposed to minimize the communication-storage cost for those continuous media applications that serve a large number of geographically distributed clients. Typically, a DCMS is designed as a pure hierarchy (tree) of centralized continuous media servers. In an earlier work, we proposed a redundant hierarchical topology for DCMS networks, termed RedHi, which can potentially result in higher utilization and better reliability over pure hierarchy. In this paper, we focus on the design of a resource management system for RedHi that can exploit the resources of its DCMS network to achieve these performance objectives. Our proposed resource management system is based on a fully decentralized approach to achieve optimal scalability and robustness. In general, the major drawback of a fully decentralized design is the increase in latency time and communication overhead to locate the requested object. However, as compared to the typically long duration and high resource/ bandwidth requirements of continuous media objects, the extra latency and overhead of a decentralized resource management approach become negligible. Moreover, our resource management system collapses three management tasks, 1) object location, 2) path selection, and 3) resource reservation, into one fully decentralized object delivery mechanism, reducing the latency even further. In sum, decentralization of the resource management satisfies our scalability and robustness objectives, whereas collapsing the management tasks helps alleviate the latency and overhead constraints. To achieve a high resource utilization, the object delivery scheme uses our proposed cost function, as well as various object location and resource reservation policies to select and allocate the best streaming path to serve each request. The object delivery scheme is designed as an application layer resource management middleware for the DCMS architecture to be independent of the underlying telecommunication infrastructure. Our experiments show that our resource management system is successful in realization of the higher resource utilization for the DCMS networks with the RedHi topology.Index Terms-Distributed continuous media servers, decentralized resource management, distributed multimedia systems, content delivery networks, distributed information systems, video-on-demand. T HE advent of broadband access network technology that supports high-bandwidth connectivity for diversified end-user devices (e.g., PCs, wireless hand-held devices, settop boxes, etc.) on the one hand and introduction of effective encoding techniques, such as MPEG-4, that allow streaming of continuous media (e.g., video and audio) with reasonably low bandwidth requirements on the other hand enabled the emergence of an enormous number of multimedia applications such as video-on-demand (VOD) [1] , [2] , [3] , teleconferencing [4] , distance learning [5] , and interactive TV [6] . Researchers in academia and industry have been struggling for more than a decade to design highperformance centralized continuous media servers (CCMSs) [7] , [8] , [9] , [10] and provide facilities to support specific QOS requirements of continuous media communications on the network [11] , [12] , [13] , [14] , all motivated by a desire to realize wide-spread use of these applications.. Distributed continuous media applications (e.g. VOD) are expected to provide service to a large number of clients often geographically dispersed on a metropolitan, countrywide, or even global area. With a naive design, employing only one large CCMS to support these distributed clients results in inefficient resource allocations that renders the design virtually impractical. For instance, the overall bandwidth requirement to implement an interactive VOD system with such a design is estimated to be as high as 1.54 Pb/s for the continental United States [15] . The full economic potential of such applications will not be realized unless cost-effective solutions are achieved.. To address this problem, one group of researchers has focused on various techniques to either reduce bandwidth requirements of individual continuous media streams, with methods such as smoothing [16] , staging [17] , and bandwidth renegotiation [18] , or reduce overall bandwidth requirements of multiple streams via aggregation (or statistical multiplexing), for example, with batching and multicasting [19] , [20] . As an orthogonal solution, other researchers have proposed distribution of the service to manage dispersedness of clients, i.e., employing a number of CCMSs each to serve clients located in a certain locality and interconnecting them via a high-speed network infrastructure to be able to share/exchange the continuous media objects (it is important to note that, although serving clients locally will result in a dramatic reduction in the total communication bandwidth requirement of the system, unless servers are able to share the objects, the huge aggregated storage capacity requirement of the servers will render the no-sharing approach impractical, too). Systems designed based on this approach [21] , [22] , termed distributed continuous media servers (DCMSs), are shown to be able to provide the optimal solution, i.e., the minimum communication-storage cost for distributed continuous media streaming applications [23] , [24] .. In this paper, we focus on developing a novel object delivery scheme as one of the components of a DCMS architecture. In the remainder of this section, first we describe the components of a typical DCMS architecture. Second, we briefly review those components of our proposed DCMS architecture, introduced in our previous work [25] , in order to provide the context. Finally, we highlight the contributions of this paper by enumerating the characteristics of our object delivery scheme, the component of focus in this paper. In this study, we developed an object delivery scheme for a DCMS network assuming the RedHi topology. The unique characteristics of this scheme are as follows:. . Given the unique features of continuous media objects, our object delivery scheme is designed as a fully decentralized resource management system that guarantees scalability and robustness as well as negligible start-up latency and resource management overhead. . Our object delivery scheme collapses three different resource management tasks into one distributed mechanism that executes all tasks integrated. . Our object delivery scheme is designed as an application layer resource management middleware that is independent of the underlying telecommunication infrastructure of the DCMS network. It does not assume any specific capabilities (e.g., multicasting and anycasting) for the telecommunication infrastructure except for providing point-to-point communication between adjacent nodes of the DCMS network. With our object delivery scheme, we introduced a cost function as well as various object location and path reservation policies. We performed extensive experiments via simulation to evaluate performances of these policies as well as overall performance of our object delivery scheme. Results of our experiments show that:. . Inclusive, path freeBW average , and ERO outperform other propagation, cost evaluation, and reservation techniques, respectively. . Our delivery scheme with a RedHi DCMS network can achieve up to 50 percent improvement in resource utilization over a pure hierarchy. . The start-up latency and the communication overhead per each request can be as low as two seconds and 10b/s, respectively. We intend to extend this study in several ways. First, we would like to extend the object delivery mechanism to support VCR functions for interactive object delivery. Second, we also intend to merge the bandwidth renegotiation idea into our object delivery scheme to provide a hybrid solution for distributed continuous media applications. Finally, we are investigating techniques to incorporate self-configuration/warm-expansion capabilities into the resource management system.. (DARPA) and US Air Force under agreement no. F30602-99-1-0524, and unrestricted cash/equipment gifts from the Okawa Foundation, Microsoft, NCR and SUN. In this section, we review some related studies that investigate one or more of the three tasks we support with our object delivery scheme. The object location problem has been studied in various but closely related contexts such as tracking mobile users [39] , locating objects for distributed object programming [48] , locating nearby copies of replicated servers [49] , and resource discovery [50] . Directory service is a common mechanism often used for object location and many resource management systems include centralized directory servers [51] , [52] . These servers usually comprise object state databases and query servers for object location. All client requests for objects are redirected to the directory server, where the replicas of the requested object are located, via object state database and, usually, a particular cost function is used to select the most appropriate object server to respond the request. To enhance both scalability and robustness of the object location mechanisms (particularly for those used with large, distributed, and usually interconnected systems that carry many objects), many researchers have introduced various distributed (and possibly replicated) directory structures that maintain states of the objects in a distributed fashion among multiple directory servers. As discussed in Section 3, decentralization of the service can cause an increase in the response-time and resource management overhead of such systems. To address this problem, besides replication, these systems usually exploit the locality characteristic of user access patterns and map a hierarchy of regional directories to the network (i.e., the system carrying the objects) so that most read and update accesses to the object states within a region are responded to by the regional directory server [53] . Consequently, response-time and overhead of resource management are drastically reduced. For instance, Awerbuch and Peleg [39] introduce a distributed directory server that is able to locate migrating objects with a communication overhead within a polylogarithmic factor of the lower bound; however, their directory service does not support replicated objects. Bartal et al. [54] also propose a distributed directory service and a "competitive" access algorithm with optimal communication cost for mesh and pure tree network topologies. The hierarchy of directory servers developed by Steen et al. [48] considers the "stability" of objects in each region and dynamically adapts to object migrations, but, as far as resource utilization optimization is concerned, it cannot distinguish the most appropriate replica of an object to be served. Plaxton et al. [49] use a virtual tree of object location agents that maps one-to-one into the network to locate replicas of an object. For each object, there is a separate tree and each node of the tree keeps track of the object replicas located at the entire subtree rooted at the node. On a request for an object, if a node does not find any replica of the object at its subtree, it forwards the request to its parent and this process repeats until a replica of the object is located. Due to the limited "view" of each agent, this approach does not guarantee locating the most appropriate object replica (i.e., the one that results in optimal resource utilization). This drawback might not be important in a system with small objects that are served with a low amount of resources and a good response-time requirement, however, for streaming applications with continuous media objects, which have intensive resource requirements and longer tolerable start-up latency, it will result in low resource utilization.. Our object delivery scheme can be considered as an extreme case distributed directory service to achieve optimal scalability and robustness. As compared to a normal distributed directory service, as far as responsetime and resource management overhead are concerned this approach minimizes the overhead of the update to the states (updates local metadata only), while it results in increase in the read access overhead. As discussed in Section 3, we alleviate the overhead of the read access to negligible level by collapsion of the object delivery tasks. It is important to note that almost all distributed directory structures assume a pure tree or a mesh topology for the network that contains the objects, whereas our scheme assumes a RedHi topology for the DCMS network. Besides, some systems rely on specific capabilities of the underlying telecommunication infrastructures, such as anycasting and multicasting, as the main means for object location [55] . This approach makes these systems network dependent. Our application layer scheme does not assume any of these specific capabilities for the underlying infrastructure of the DCMS network rather than point-to-point communication between adjacent nodes. A hybrid system in which both normal unicast and multicast communications can be used for object location was recently introduced by Cranor et al. [56] .. The path selection problem is well studied with dynamic routing algorithms such as distance vector (e.g., RIP) [57] and link state (e.g., OSPF) [58] . These algorithms enable each node of a network to find the "best" path between itself and other nodes of the network. A cost function (e.g., hop count) is usually defined to evaluate the costs of all paths between two nodes and to select the best path (i.e., the path with minimum cost) among them. Our path selection algorithm is supposed to find the best path among the paths between a single node, a head-end, and multiple potential object server nodes of the DCMS network, which are located by the object location algorithm. With multiple object servers, each probably having multiple paths to the headend in the RedHi redundant topology, a simple cost function such as hop count cannot resolve the highly probable tie conditions in the costs of the paths efficiently so that it results in low resource utilization. To achieve high resource utilization, our cost function considers load balancing by breaking the ties based on the current traffic load of the paths. Moreover, our path selection algorithm runs at the application layer on the DCMS network, whereas normal routing algorithms run at the network layer within the underlying telecommunication infrastructures. Therefore, our cost measures relate to streaming resources rather than networking resources. For example, we consider CCMS available bandwidth rather than link propagation delay as a cost measure.. Finally, the resource reservation problem is also studied under protocols such as RSVP [59] and ST-2 [60] , which intend to provide communication links with guaranteed service by reserving resources across the network. These protocols assume the communicating peers are already known and describe the procedure to reserve the required resources across a path between the peers, whereas, since, with our approach, reservation is integrated into object location and path selection, the peers (particularly the selected object server) and the selected path between peers are not known in advance. Our resource reservation algorithm runs at the application layer to reserve resources in the DCMS network, whereas the reservation protocols mentioned above run at the network layer within the underlying telecommunication infrastructures. Cao et al. [61] and Huang et al. [62] propose two typical application layer centralized and semidistributed resource reservation schemes, respectively. Our object delivery scheme supports fully distributed resource reservation.

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


Toward a search architecture for software components The Grid and its related technologies enable large-scale sharing of resources of various types. We envision that in the near future applications will be completely built in a bottom-up fashion using software components deployed on various locations and interconnected to form a workflow graph. In this paper, we make some proposals on the design of a component search service, enabling users to locate the components they need to deploy an application. More and more, today's business and scientific applications are built as a complex network of services offered by different providers, on heterogeneous resources, constrained by administrative problems when crossing the borders of different organizations. Applications are no longer monolythic kernels running on a large computing cluster, but rather dynamic collections of computing entities.. This makes the age-old problem of component searching more important and central than ever: developers must be able to find the correct software component for their needs, choosing from a variety of vendors, service providers, computing departments, outsourcing firms. While FORTRAN programmers had to choose from a palette of library calls for their tasks, now Grid developers can potentially make use of any computer on the Internet.. Component searching for Grid-aware applications plays two major roles.. 1. At design time, programmers want to find the component that best fits with the structure of their application. The component must be the most appropriate and trusted for the job at hand.. • First of all, we believe that Open Source Grid applications will naturally appear. Their code could be made available through portals such as SourceForge ‡ , GridForge § , or FreshMeat ¶ .. • Moreover, on the Web there are many examples of popular services that publicize their use of other important and effective services, therefore the same will happen for Grid applications, in order to attract users' trust: AOL, for instance, claims that it uses the Open Directory Project (ODP [3] ) as its backbone for offering its search service. Translated to the Grid, the importance of an application could grow when it uses another popular component.. • Lastly, by publishing the links to external components, an application developer can support or promote standards and competition among vendors. This could have a very high commercial value. In this contribution, we presented our vision of a new tool allowing the design of workflow-based Grid applications where a composition of different workflows can be seen as a single autonomous metacomponent. The main issue presented in the work is the component search service, which allows users to locate the components they need. We believe that in the near future there will be a growing demand for ready-made software services, and current Web search technologies will help in the deployment of effective solutions. The search engine in our opinion should be able to rank components on the basis of their similarity with the place-holder description, their popularity among developers (something similar to the hit count), their use within other services (similarly to PageRank) etc.. Clearly, it is of primary importance that there exists a quick, efficient, automatic way to deploy software components out of existing code. In our opinion, there is the need for automatic tools able to extract signature information from legacy code, and able to create the bridging code needed to make the component communicate with other entities, designed with different languages or running on different platforms.. When all these services become available, building a Grid application will become a straightforward process. A non-expert user, aided by a graphical environment, will give a high-level description of the desired operations, which will be found, and possibly paid for, out of a quickly evolving market of services. At that point, the whole Grid will become like a virtual machine, tapping the power of a vast number of resources. In the last few years, thanks to technologies like the Internet and the Web, a number of interesting works [9, 10] have studied the problem of discovering, indexing and searching for software components. Also, a number of interesting papers have analyzed new and existing solutions [11, 12] .

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


Experimental evaluation of temporal and energy characteristics of an outdoor sensor network This paper revisits the link quality issue in Wireless Sensor Networks (WSN) by studying the temporal and energy characteristics of a 2,4Ghz sensor network in an outdoor environment. Using different values of output power and sampling period, we analyze battery behavior in motes placed at different distances and show that farther motes have a shorter battery life. Our experimental results suggest that when deployed in real world deployments, the sampling periods of sensor networks be adjusted according to distance to normalize battery lifetime and a more accurate energy-aware routing protocol be developed. The emergence of WSN as one of the dominant technologies in the coming decades has posed numerous unique challenges to researchers. These networks are designed to be composed of hundreds, and potentially thousands of small smart sensor nodes (called motes), functioning autonomously and self-organizing in a mesh-type network. When working with real-world deployments many new issues arise: Wireless links are unreliable and unpredictable, link quality varies in time, and motes need to be battery powered to run unattended for months or even years.. To implement reliable and robust sensor networks, we need to understand the variation of link quality and battery behavior in a real world environment. Low-power transmitters have a limited range, and it is important to understand communication patterns. Energy is the scarcest resource of WSN motes, and it determines the lifetime of WSNs. Motes are meant to be deployed in various environments, including remote and hostile regions; consequently, they must use little power and one need to make sure that all batteries last the same amount of time. Also, battery level has an impact on routing: Packets should be sent to motes with a higher battery level. We investigated the performance of link quality in WSN over time. We observed that it's related to the motes location by distance. Moreover, the battery lifetime duration is related to the location of the motes by distance as well as to the sampling period and the output power.. We found that the link quality varies over time and that PRR and RSSI are correlated. More interestingly, we discovered that LQI depends on the distance length and that the battery lifetime depends on the distance in a quasi-linear way using high power. Also, we studied the dependency on output power and on sampling period. In conclusion, we foresee several interesting applications as results from our findings. These include the development of a battery-level aware routing protocol for realworld WSN applications where (1) the sensor motes are deployed with a careful selection of the sending output power and (2) the motes closest to the base station are sampled more frequently than those located farther away from the base station. Comparing the link quality of the Sun SPOT motes to the link quality provided by other types of motes such as the open sensor motes SquidBee [15] is an extension to the work presented in this paper. Finally, this study was done in the context of a single-hop WSN, hence the generalization of the link quality in single-hop WSNs to multihop WSNs is another avenue for further research work. Previous studies on temporal models of radio propagation were carried out with a specific emphasis on the variability of Received Signal Strength Indicator (RSSI) and Link Quality Indicator (LQI) in respect to a particular location as well as the determination of the so-called "gray area", a region in which the packet loss rate varies considerably.. There have been many studies with deployments in various environments using low-power sensor motes [1, 2, 3, 4, and 5] . Most of these experiments used the TR1000 [1] and CC1100 [2] low power RF transceivers which are used by Mica 1 [3] and Mica 2 [4] motes respectively. Zhao et al [5] performed a temporal analysis of packet delivery in a dense sensor network deployment of motes placed in a straight line. They revealed heavy variability in packet reception rate (PRR), and showed the prevalence of the "gray area" within the communication range of sensor radios, and indicated significant link asymmetry. Reijers et al. [6] performed further investigation on the "gray area" and the environmental effects on the links. Their results showed that it was much less pronounced in the outdoor and open space environments than in the corridor but that it was perceptible. They interpreted this outcome as a result of the indoor multi-path effects.. Cerpa et al. [7] used two different hardware platforms consisting of Mica 1 and Mica 2 motes to perform experiments in three different environments under systematically different conditions. Among other things they concluded that there was no clear correlation between packet delivery and distance in an area of more than 50% of the communication range. Moreover, Aguayo et al. [8] performed some measurements on a 38-mote urban 802.11b mesh network. They found that link distance and S/N ratio had an effect on loss rates. They added that the correlation was weak.. Woo et al. [9] measured the PRR against the distances in a uniform grid WSN. They discovered that both the mean link quality and the variance in quality were a function of distance. Ganessan et al. [10] studied temporal behavior of a large-scale WSN (over 150 motes) in an obstructed parking lot at various transmission power settings. They focused on the packet delivery rate and link asymmetry at both the link and MAC layers. Srinivassan et al [11] conducted an evaluation to compare RSSI and LQI with second generation chips (CC2420). Their preliminary results indicated that RSSI for a given link had very small variation over time for a link. Also, the results showed that when RSSI was above the sensitivity threshold (about -87 dBm), the PRR was at least 85%. On the other hand, the results showed that LQI varies over a wider range over time for a given link (and that the mean LQI computed over many packets results in a better correlation for PRR).. Lal et al [12] state that an immediate marker of link quality is Signal to Noise Ratio (SNR). They define a good channel as one that has SNR greater than 25db for the most part of the observation period (one day), a moderate channel as one where SNR fluctuates between 25dB and 15dB. If SNR is less than 15 dB most of the time, then, they call it a bad channel. We used five Sun SPOT motes and one base station unit to construct our experiments on the roof of the Forum building of the Royal Institute of Technology (Kista campus) in Stockholm, Sweden.. It is an open space environment that offers a line of sight from the base station to all Sun SPOT motes. We placed the motes from 48m up to 100m far from the base station, at heights from 90cm to 277cm with respect to the base station. All the motes were in weatherproof, plastic enclosures. The attenuation of the enclosure is of about 3dB. The radio channels were selected to avoid collisions: Each Sun SPOT mote has its own time slot to broadcast within. In order to have significant results, experiments were performed over a long period of time. The base station was connected to a PC for data gathering, recording, and monitoring the link quality. Figure 2 represents a picture of the test-bed and Table 1 describes the positioning and configuration settings of the motes. In this section, we describe different experimental scenarios and analyze the results of the experiments.

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FIRST: a flexible and interactive resampling tool for CFD simulation data We introduce a flexible, variable resolution tool for interactive resampling of computational fluid dynamics (CFD) simulation data on versatile grids. The tool and coupled algorithm afford users precise control of glyph placement during vector field visualization via six interactive degrees of freedom. Other important characteristics of this method include: (1) an algorithm that resamples any unstructured grid onto any structured grid, (2) handles changes to underlying topology and geometry, (3) handles unstructured grids with holes and discontinuities, (4) does not rely on any pre-processing of the data, and (5) processes large numbers of unstructured grid cells efficiently. We believe this tool to be a valuable asset in the engineer's pursuit of understanding and visualizing the underlying flow field in CFD simulation results. We believe FIRST to be a valuable asset in the engineer's pursuit of understanding the underlying flow field in their CFD simulation models. FIRST reduces perceptual problems such as occlusion and visual complexity when visualizing a vector field, steady or unsteady, with all three vector field components. Searching for flow features by sliding a slice through the 3D volume is also hastened.. Future work can take multiple directions including the addition of more user-interaction controls, extending the algorithm to 3D, and porting the algorithm to Java for inclusion into the VisAD open source, scientific visualization library [4] . tached to the resampling grid. These handles, while attached to the grid, may be placed arbitrarily via the common clickand-drag paradigm resulting in user-specified grid placement or user-specified scaling.. interaction techniques. One such technique involves the addition of handles attached to the resampling grid ( Figure 12 ). The user can click-and-drag a handle and change the location or size of the resampling grid. Two different strategies are possible: (1) where the other corners of the resampling grid are held fixed while one handle is dragged resulting in a change of size or (2) where the other corners move with the grid retaining a constant size but specifying a new location.. One of goals is to extend the algorithm to handle 3D simulation data. We believe that the algorithm outlined in Section 4 can be extended to 3D in a very straightforward manner. The only difference would be a modification to the traversal part of the algorithm to include multiple layers. We realize, however, that performance time will be biggest challenge in realizing this goal. When describing grids, we follow the terminology of Yagel et al. [20] . Structured grids, including cartesian grids, regular grids, and rectilinear grids, all maintain an implicit neighborhood connectivity (Figure 4(a-d) ), i.e. the position of grid cells can be computed, rather than stored explicitly. In contrast, grids whose neighbors must be explicitly stored are categorized as unstructured grids. This distinction is important in understanding our claim that the resampling technique here can be used to represent any unstructured grid with any structured grid. We demonstrate this assertion with implementations of the resampler from unstructured triangular grids (Figure 4 (f)) to cartesian and polar grids ( Figure 4(a-d) ). The basis for this claim hinges on the supposition that cell positions in structured grids can be computed.. The literature dedicated to the topic of resampling spans multiple, sometimes disparate, goals. While we designed our resampler with the goal of a high level of user-control, other resampling techniques focus on the goals of volume rendering, surface reconstruction, and accurate surface normal representation. In contrast with these approaches, we concentrate on 2D slices through a 3D mesh from CFD. We contrast other resampling goals with ours.. Resampling techniques whose goal is to achieve faster volume rendering speeds may make use of the hardware capabilities offered by modern graphics cards.. Westermann presents a resampling technique for resampling scalar fields given on unstructured tetrahedral grids [19] . The goal of this research is to bring direct volume rendering towards interactive frame rates with the assistance of graphics hardware. Determining the visibility ordering of grid elements is a major challenge in this scenario. While the goal of this approach is dissimilar to ours, one similarity worthy of note is that Westermann's technique can be used to display timedependent unstructured grids with changing geometry and topology.. Weiler and Ertl [18] also present three resampling approaches and contrast the results with the work of Westermann [19] . Their goal is to minimize performance time via balancing the computing workload between the native processor and the graphics board processor.. In addition to resampling techniques for volume rendering, some resampling approaches are targeted at representing surfaces. Botch and Kobbelt [3] present a technique to resample feature regions of a given triangle mesh with the goal of reducing aliasing artifacts on surfaces, i.e., surface anti-aliasing. Similar the work here, there is a strong interaction component to their work.. The user chooses the areas on the surface to which the surface normal anti-aliasing algorithm is applied. To remodel the structure of a sample CFD grid can take an interactive session lasting one hour.. Rocchini et al. [14] present an algorithm whose goal is the removal of small topological inconsistencies and high frequency details from surfaces. One of their goals is the simplification of huge meshes, i.e., meshes composed of millions of faces.. It is also worthy of note that some resampling algorithms from the image processing domain magnify or minify the original image via sampling at regular intervals [11] . Our approach samples the original data irregular intervals and generates an evenly-spaced representation.

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Historiographic Mapping of Knowledge Domains Literature To better understand the topic of this colloquium, we have created a series of databases related to knowledge domains [dynamic systems (small world/Milgram), information visualization (Tufte), co-citation (Small), bibliographic coupling (Kessler), and scientometrics (Scientometrics)]. I have used a software package called HistCite ™ which generates chronological maps of subject (topical) collections resulting from searches of the ISI Web of Science ® or ISI citation indexes (SCI, SSCI, and/or AHCI) on CD-ROM. When a marked list is created on WoS, an export file is created which contains all cited references for each source document captured. These bibliographic collections, saved as ASCII files, are processed by HistCite in order to generate chronological and other tables as well as historiographs which highlight the most-cited works in and outside the collection.HistCite also includes a module for detecting and editing errors or variations in cited references as well as a vocabulary analyzer which generates both ranked word lists and word pairs used in the collection. Ideally the system will be used to help the searcher quickly identify the most significant work on a topic and trace its year-by-year historical development.In addition to the collections mentioned above, historiographs based on collections of papers that cite the Watson-Crick 1953 classic paper identifying the helical structure of DNA were created. Both year-by-year as well as month-by-month displays of papers from 1953 to 1958 were necessary to highlight the publication activity of those years..

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Modeling the evolution of operating systems: An empirical study In this paper, we report on an empirical experiment where we observe, record and analyze the evolution of selected operating systems over the past decades and derive a statistical model that captures relevant evolutionary laws. We use this model to highlight relevant statistical laws, as well as to predict the future evolution of operating systems. In addition to deriving predictions on the future of specific operating systems, we also focus on predicting emerging features of operating systems, thereby obtaining a profile of future operating systems.KEY WORDS: Operating Systems, Software Engineering Trends, Tech Watch, Unix, Solaris, Sun/OS, BSD, Windows, MS-DOS, MAC OS, Linux, Net Ware, HP-UX, GNU Hurd, IBM AIX, Compaq/ DEC VMS, OS/2.Operating systems have played a crucial role in the evolution of the computing field, adapting continuously to the evolution of hardware and to the evolving demands of user communities. They have been the subject of intense research since the early days of computing, and have given rise to some of the most important breakthroughs in the history of computing. In this paper, we report on an empirical experiment where we observe, record and analyze the evolution of selected operating systems over the past decades and derive a statistical model that captures relevant evolutionary laws.This work is part of a wider project whose purpose is to model and understand the evolution of software engineering trends [1] . In addition to the top down, deductive, approach advocated in [1], we have resolved to take a bottom up, inductive, approach, whereby we analyze / model evolutionary laws of specific families of trends, to subsequently derive more generic laws. In [2], Chen et al discuss the evolution of programming languages; in this paper, we apply the same methodology to another homogeneous family of products, namely operating systems. Operating Systems are an excellent test bed for our inductive approach, for the following reasons:

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Estimating Relative Camera Motion from the Antipodal-Epipolar Constraint Abstract-This paper introduces a novel antipodal-epipolar constraint on relative camera motion. By using antipodal points, which are available in large Field-ofView cameras, the translational and rotational motions of a camera are geometrically decoupled, allowing them to be separately estimated as two problems in smaller dimensions. We present a new formulation based on discrete camera motions, which works over a larger range of motions compared to previous differential techniques using antipodal points. The use of our constraints is demonstrated with two robust and practical algorithms, one based on RANSAC and the other based on Hough-like voting. As an application of the motion decoupling property, we also present a new structure-from-motion algorithm that does not require explicitly estimating rotation (it uses only the translation found with our methods). Finally, experiments involving simulations and real image sequences will demonstrate that our algorithms perform accurately and robustly, with some advantages over the state-of-the-art. THE problem of estimating relative camera motion (or relative pose) from two views has been extensively studied in the last few decades. The problem involves estimating the rigid body transformation-the translation and rotation-between two cameras using 2D image point correspondences viewed by the cameras (the distances to the 3D world points are unknown, and translation can be found up to an unknown scale only).. In this paper, we introduce new constraints on camera motion by exploiting the geometry of large Field-of-View (FOV) cameras. A useful concept for thinking about large FOV cameras is the image sphere, where world points are projected onto a spherical imaging surface (as opposed to the standard image plane) [1] , [2] , [3] . Note that using image spheres implicitly assumes calibrated cameras.. Central to the proposed constraints is the concept of antipodal rays, which are only available in central, large FOV cameras. Two rays are antipodal if they are collinear and point in opposite directions. For example, in Fig. 1 , p and Àp are antipodal in the camera coordinate system centered on C. Antipodal rays will intersect the image sphere at a pair of diametrically opposite points (analogous to the Earth's North and South poles). In practice, antipodal rays may be found in large FOV camera systems such as those shown in Fig. 2 .. As we shall see, the use of antipodal rays leads to the novel antipodal-epipolar constraint that decouples translation and rotation and allows them to be estimated separately, independent of each other. In the conventional epipolar constraint [4] , translation and rotation are entangled together in the essential or fundamental matrix. If differential camera motions are assumed, translation and rotation can be decoupled by an approximate linearization of the motion equations [5] , [1] . However, in the more general discrete motion case considered here, this "trick" does not work and decoupling translation and rotation is nontrivial. In fact, this has not been achieved by any other method that we know of.. Consequently, through the antipodal-epipolar formulation, we can express constraints that are linear in translation and, independently, constraints that are linear in rotation. In contrast, the conventional epipolar constraint is bilinear in translation and rotation. In other words, under the special condition of antipodal points, a problem that is nonlinear in general becomes linear (and this is not a mere approximation, as in the case of differential motions).. As a result of the decoupling of motion components, we find ourselves solving two smaller dimension problems instead of a single higher dimensional one. This simplifies the problem, leading to important consequences for designing algorithms that are robust to outliers and noise. Basically, it is easier to separate the inlier data from the outliers in a lower dimensional space than in a higher dimensional one. This naturally results in more efficient and robust algorithms, including ones which may be implemented to run in constant time, regardless of outlier proportions in the data. (Some existing methods (e.g., [6] , [7] ) attempt to solve translation and rotation separately; however, the two estimates are not truly decoupled since the methods were based on the conventional epipolar constraint.). Furthermore, since translation can be estimated independent of rotation, we propose a method by which one may reconstruct scene structure purely from translation estimates and without recovering relative camera rotation explicitly (the rotation is implicitly constrained). This translation-only structure-frommotion (SfM) algorithm was previously not a sensible option since past methods recovered rotation and translation simultaneously (in the form of the essential or fundamental matrices). The new SfM algorithm is not only of theoretical interest but also has practical advantages in terms of computation speed, compared to existing techniques. This paper is organized as follows: Below, we first review existing work. We then derive our geometrical constraints in Section 2. Robust algorithms are presented in Section 3 and scene reconstruction is discussed in Section 4. Section 5 demonstrates the performance of our methods with experiments and we end with some discussion in Section 6. These algorithms aim to demonstrate the viability of the geometrical constraints introduced, and as such, play an illustrative role rather than a definitive one. Many other algorithms utilizing the antipodal constraints are possible, and the reader may replace them with their favorite robust estimation method. We have presented novel constraints on relative camera motion by exploiting the geometry of antipodal points which are found in large FOV cameras. These constraints are linear and decoupled in the translational and rotational components of motion, thus simplifying the problem and leading to improved motion and structure algorithms. Future work will explore further applications of these constraints-e.g., rotation recovery is not strictly required for odometry, so skipping it will lead to speedier estimation.. Supplemental videos, which can be found on the Computer Society Digital Library at http://doi. ieeecomputersociety.org/ 10.1109/TPAMI.2010.113, provide translation estimates and ground truth, marked in the video "Sequence A (static).mpg" corresponding to Fig. 9a . "Sequence B (moving objects).mpg" is the corresponding video for Fig. 9c . These show the view from the forward facing camera. Other camera views are included for the reader's reference. A series of simulations tested performance under increasing outlier proportions and under increasing Gaussian noise. Two views of a 3D scene were generated with random translations and rotations between cameras. The translation magnitude varied randomly between 5 and 10 units; rotation angle varied randomly between 10 and 50 degrees, while distances to the randomly generated world points varied between 5 and 10 units. Results were averaged over 100 trials.. We tested on data contaminated with up to 60 percent outliers and on data under zero-mean Gaussian noise with standard deviations of up to 0.3 degrees (in a camera with viewing angle 60 degrees and a 640 Â 480 pixel image, 0.3 degrees corresponds to around 2 to 3 pixels). This corresponds to realistic noise levels in feature matching methods (e.g., SIFT), which are subpixel accurate and typically exhibit errors of at most a couple of pixels for correct matches. Outliers consisted of randomly mismatched rays, while Gaussian noise was simulated by perturbing the directions of image rays according to a Gaussian distribution.. Real image sequences were obtained from a Ladybug omnidirectional camera [47] . This is a camera rig consisting of five cameras arranged in a ring configuration and one camera (which we did not use) pointing upward. Using the calibration supplied by the manufacturers, image points from the five cameras are mapped into a single coordinate frame.. In Image Sequence A, the camera was placed on the ground, where it translated by about 4 cm and rotated by 10 degrees between frames. The scene was static. The motion was estimated and compared with ground truth values (manually measured with ruler and protractor). Figs. 10b, 10c, 10d , 10e, and 10f show the images captured by the Ladybug omnidirectional camera rig at one time instance in sequence A. In another experiment, Image Sequence B, the camera translated by 4 cm and rotated by 4 degees between frames; furthermore, the scene contained independently moving objects, leading to greater outlier probabilities. The fact that motion was planar, was not used by any of the algorithms to simplify estimation.. SIFT features (code from [48] ) were used to find point correspondences. Points that were within 0.5 degrees of being antipodal were approximated as antipodal. In the real images, several hundred antipodal points could typically be found, which was many more than the minimum needed.

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


Structuring the modeling space and supporting evolution in software product line engineering The scale and complexity of product lines means that it is practically infeasible to develop a single model of the entire system, regardless of the languages or notations used. The dynamic nature of real-world systems means that product line models need to evolve continuously to meet new customer requirements and to reflect changes of product line artifacts. To address these challenges, product line engineers need to apply different strategies for structuring the modeling space to ease the creation and maintenance of models. This paper presents an approach that aims at reducing the maintenance effort by organizing product lines as a set of interrelated model fragments defining the variability of particular parts of the system. We provide support to semi-automatically merge fragments into complete product line models. We also provide support to automatically detect inconsistencies between product line artifacts and the models representing these artifacts after changes. Furthermore, our approach supports the co-evolution of models and their respective meta-models. We discuss strategies for structuring the modeling space and show the usefulness of our approach using real-world examples from our ongoing industry collaboration. Support for structuring the modeling space and support for evolution are key requirements for model-based product line engineering which are not adequately addressed by current approaches. We presented a tool-supported approach that aims to treat evolution as the normal case and not as the exception. The approach has been validated using real-world models developed and evolved in an ongoing industry collaboration with Siemens VAI. While our tool support has mainly been developed for Siemens VAI, our approach (i.e., model fragments) is generally applicable to graph-like structures and models. Approach and tools are customizable and extensible and not constrained to a specific industrial environment.. Our approach works well with component-based development and provides model merging capabilities to support evolution in multi-team environments. We use model fragments as the units of evolution. This allows working with smaller models to reduce complexity during creation, maintenance, and evolution of variability models. As model fragments are of manageable size it is easier to keep them consistent with the architecture, in particular using tool features for detecting changes automatically. While component-based approaches rely on matching provided and required interfaces, our model merging approach relaxes this purely technical view and aims at giving teams more leeway through a lazy consistency approach (indirect references through placeholder elements). It also supports the evolution of different subsystems at different speeds.. We believe that model fragments have two benefits from the perspective of product line variability modeling: (a) They allow to define variability locally and in a bottom-up manner (e.g., by starting at the level of teams or individual subsystems). This was the case in strategy 1 described in our experience section. (b) They allow to define variability at different levels of abstraction and to separate those levels more clearly. This was relevant in strategy 2.. Our industrial experiences have revealed that such an approach must be supported by stable and compatible tools. It should also not introduce more complexity than it removes, as the users are usually reluctant to try new tools and technologies. Our approach can be used to resolve scability issues of model-driven development, at different levels (teams, subsytems, software features, etc). Apart from that, it also provides support in reducing the complexity of model-based applications by automating the enforcement of consistency, wherever required.. In future work we plan to develop guidelines helping product line engineers to decide in which model fragment a subsystem's variability should be modeled. We will work on methods aiding modelers in finding the right granularity for customization decisions in our variability models. We will also explore additional visualization support for different aspects of our approach such as the visualization of interdependencies among model fragments or the visualization of model fragment evolution over time. Finally, we plan to further validate the approach by applying in other domains and development environments. Having applied our approach and tools at Siemens VAI we have learned that it is important to find a balance between the separation of concerns and the complexity and effort of merging required when separating too much. Too many fragments and infrequent merging makes the approach infeasible. However, too few models or too frequent merging make the approach impractical too. One has to find a balance between the practicability of distributed modeling and the number of model fragments. The pay-off point strongly depends on the concrete domain or context. In our case, we have learned that it makes sense to reflect the architectural structure of the software to be modeled. It is also helpful to take the structure of the team into account (subsystem owners are model owners). Our experience shows that it is advisable to frequently merge the fragments to resolve conflicts early and often.. In a paper on the state-of-the-art of software merging Mens (2002) discusses six design criteria and their influence on the design of a merge tool. We use them to structure the discussion of the strengths and weaknesses of our tool-supported approach: Our discussion of related work covers the areas of model evolution, product line evolution, multi-team modeling, organizing modeling spaces, and model merging.

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


Why Linked Data is Not Enough for Scientists Abstract-Scientific data stands to represent a significant portion of the linked open data cloud and science itself stands to benefit from the data fusion capability that this will afford. However, simply publishing linked data into the cloud does not necessarily meet the requirements of reuse. Publishing has requirements of provenance, quality, credit, attribution, methods in order to provide the reproducibility that allows validation of results. In this paper we make the case for a scientific data publication model on top of linked data and introduce the notion of Research Objects as first class citizens for sharing and publishing. Changes are occurring in the ways in which scientific research is conducted. Within wholly digital environments, methods such as scientific workflows, research protocols, standard operating procedures and algorithms for analysis or simulation are used to manipulate and produce data. Experimental or observational data and scientific models are typically "born digital" with no physical counterpart. This move to digital content is driving a sea-change in scientific publication, and challenging traditional scholarly publication. Shifts in dissemination mechanisms are thus leading towards increasing use of electronic publication methods. Traditional paper publications are, in the main linear and human (rather than machine) readable. A simple move from paper-based to electronic publication does not, however, necessarily make a scientific output decomposable. Nor does it guarantee that outputs, results or methods are reusable.. Current scientific knowledge management serves society poorly where for example, the time to get new knowledge into practice can be more than a decade. The models used to support medical decisions are not dynamically linked to the body of knowledge that defines best practice. More than half of the effects of medical treatments cannot be predicted from the literature, because trials exclude women of child bearing age, people with other diseases or on other medications. Doctors audit the outcomes of their treatments using research methods yet the results are not captured and put back into medical research for the benefit of society [1] .. As an example from the medical field, there are multiple studies relating sleep patterns to work performance, each study has a slightly different design, and there is disagreement in reviews as to whether or not the overall message separates out cause from effect. Ideally the study-data, context information, and modelling methods would be extracted from each paper and put together in a larger model -not just a review of summary data. To do this well is intellectually harder than running a primary study -one that measures things directly. This need for broad-ranging "meta-science" and not just deep "mega-science" is shared by many domains of research, not just medicine. Studies continue to show that research in all fields is increasingly collaborative [2] . Most scientific and engineering domains would benefit from being able to "borrow strength" from the outputs of other research, not only in information to reason over but also in data to incorporate in the modelling task at hand. We thus see a need for a framework that facilitates the reuse and exchange of digital knowledge. Linked Data [3] provides a compelling approach to dissemination of scientific data for reuse. However, simply publishing data out of context would fail to respect research methodology nor would it respect the flow of rights and reputation of the researcher. Scientific practice is based on publication of results being associated with provenance to aid interpretation and trust, and description of methods to support reproducibility.. In this paper, we discuss the notion of Research Objects, semantically rich aggregations of resources that provide the "units of knowledge" which supply structure for delivery of information as Linked Data. A Research Object (RO) provides a container for a principled aggregation of resources, produced and consumed by common services and shareable within and across organisational boundaries. An RO bundles together essential information relating to experiments and investigations. This includes not only the data used, and methods employed to produce and analyse that data, but also the people involved in the investigation. In the following sections, we look at the motivation for linking up science, consider scientific practice and look to three case studies to inform our discussion. Based on this, we identify principles of ROs and map this to a set of features. We discuss the implementation of ROs in the emerging Object Reuse and Exchange (ORE) representation and conclude with a discussion of the insights from this exercise and critical reflection on Linked Data and ORE.

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


Retrieval constraints and word frequency distributions a log-logistic model for IR Abstract We first present in this paper an analytical view of heuristic retrieval constraints which yields simple tests to determine whether a retrieval function satisfies the constraints or not. We then review empirical findings on word frequency distributions and the central role played by burstiness in this context. This leads us to propose a formal definition of burstiness which can be used to characterize probability distributions with respect to this phenomenon. We then introduce the family of information-based IR models which naturally captures heuristic retrieval constraints when the underlying probability distribution is bursty and propose a new IR model within this family, based on the log-logistic distribution. The experiments we conduct on several collections illustrate the good behavior of the loglogistic IR model: It significantly outperforms the Jelinek-Mercer and Dirichlet prior language models on most collections we have used, with both short and long queries and for both the MAP and the precision at 10 documents. It also compares favorably to BM25 and has similar performance to classical DFR models such as InL2 and PL2. If Information Retrieval (IR) on the web is dominated by systems learning ranking functions from log data, standard ad hoc IR is largely dominated by probabilistic systems with few parameters to set, as Okapi, the language models or the Divergence from Randomness (DFR) models. These latter models are based on several probabilistic distributions and assumptions which help their deployment in practical situations. If these models are well founded from an information retrieval point of view (they satisfy the heuristic retrieval constraints given in [9] for example), the probability distributions they rely on yield in general a poor fit to empirical data. Thus, in the ''model word frequency distributions to retrieve documents'' approach, the first part (model word frequency distributions) is somehow neglected with respect to the second part (retrieve documents) in most models.. We present in this paper a new IR model, based on probability distributions fitting well empirical data, and satisfying heuristic retrieval constraints. To do so, we first explore the links between heuristic retrieval constraints and word frequency distributions. After proposing an analytical view of heuristic retrieval constraints which extends the work presented in [9] and yields simple tests to determine whether a retrieval function satisfies the constraints or not, we review empirical findings on word frequency distributions and the central role played by burstiness in this context. This is the subject of Sect. 2. In Sect. 3, we analyze DFR models thanks to the retrieval constraints we reformulated. In Sect. 4, we introduce the family of information-based IR models and develop, within this family, a new IR model based on the log-logistic distribution. In Sect. 5, we illustrate the good behavior of our model through a series of experiments which validate the good fit it provides to empirical data and the good performance it yields in IR when compared to language models and Divergence from Randomness models. We then discuss several aspects of our approach in Sect. 6, prior to conclude.. The notations we use throughout the paper are summarized in Table 1 . We can sum up the different points developed in this section as follows:. 1. IR models have to fulfill heuristic retrieval constraints stated in conditions 1-6, 2. Word frequency distributions should be bursty according to the above definitions, 3. Word frequency distributions used in standard IR models are usually not bursty.. The question which naturally follows from these findings is whether one can build an IR model based on bursty distributions and compliant with the heuristic retrieval constraints. The next section is devoted to the presentation of such a model. Before that, we analyze the Divergence from Randomness framework with respect to the retrieval constraints. We have in this paper first introduced an analytical characterization of heuristic retrieval constraints and reviewed several DFR models wrt this characterization. This review showed that the first normalization principle of DFR is necessary to make the model compliant with retrieval constraints. We have then introduced a new model based on the log-logistic distribution to derive a simplified DFR model, and have shown that this simplified model contained, as a special case, the standard language model with JelinekMercer smoothing. This relation is, to our knowledge, the first connection between the DFR and language modeling approaches to IR.. We have then reviewed empirical findings on word frequency distributions and the central role played by burstiness in this context. This has led us to propose a formal definition of burstiness which can be used to characterize probability distributions wrt this phenomenon. We have then introduced the family of information-based IR models which naturally captures heuristic retrieval constraints when the underlying probability distribution is bursty. In particular, theorem 4 guarantees that the concavity constraint is satisfied for bursty distributions, whereas the form of the family guarantees the other constraints when the length normalization function is increasing in x d w and decreasing in y d , which is the case for all the normalization functions we know of. We have then proposed a new IR model within this family, based on the log-logistic distribution.. The experiments we have conducted on three different collections illustrate the good behavior of the LGD model: this model significantly outperforms the Jelinek-Mercer and Dirichlet prior language models on most collections, with both short and long queries and for both the MAP and the precision at 10 documents. The LGD also yields results similar to DFR ones, while being simple. Future work will investigate an extension of information models for pseudo-relevance feedback and the use of other bursty distributions in the framework we have developed.

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


Semantic linkages in research information systems as a new data source for scientometric studies Abstract A growing number of research information systems use a semantic linkage technique to represent in explicit mode information about relationships between elements of its content. This practice is coming nowadays to a maturity when already existed data on semantically linked research objects and expressed by this scientific relationships can be recognized as a new data source for scientometric studies. Recent activities to provide scientists with tools for expressing in a form of semantic linkages their knowledge, hypotheses and opinions about relationships between available information objects also support this trend. The study presents one of such activities performed within the Socionet research information system with a special focus on (a) taxonomy of scientific relationships, which can exist between research objects, especially between research outputs; and A growing number of modern research information systems (RIS) are using a semantic linkage technique to visualize for its users some information about relationships between entities form its content. This practice is coming nowadays to a maturity when a pool of already existed semantic linkages provided information on what research objects are semantically linked and what kind of relationships were expressed by this can be recognized as a new data source for scientometric studies.. Basically the semantic linkage technique is used to explicitly express all kinds of relationships that exist between information objects representing in RIS content people, organizations, research results, scientific assertions, etc. At abstract level this technique is specified in RDF (http://www.w3.org/RDF/) and used as a base by different teams of developers like linking open data (LOD), 1 open annotation, 2 and many others. Specifically for RIS the semantic linkage technique is also developed by the CERIF task group (Jörg et al. 2012a, b) . Some of these applications have a convergence tendency, e.g. between CERIF and LOD by exposing CERIF-driven relational data as linked data (Jörg et al. 2012b) .. At conceptual level the RDF semantics specification 3 underlies for well-known nanopublication approach (Groth et al. 2010) , as well the CERIF semantic model is used in many projects; e.g. to build the semantic linkages open repository (Parinov 2012a) .. There are several public RIS where the semantic linkage technique is available for scientists, e.g. at NanoPub.org (Groth et al. 2010) , SiteULike.org (Shotton 2010a) , Socionet.ru (Parinov and Kogalovsky 2011; Parinov 2012a, b) and some others.. One of these RIS-Socionet.ru-is designed to improve standard semantic web techniques (Parinov 2012a, b) and to be compatible with the CERIF semantics specification (Jörg et al. 2012a) . Socionet serves the research community and gives scientists an ability to express and share with the community some additional research information by linking semantically pairs of information objects from content of available RIS.. For general purposes the similar idea is developed by Open Annotation Community Group as a common, RDF-based, specification for annotating digital resources. 4 Semantic linkages created at Socionet match well with the open annotation model and can be recognized as a specific case of the digital resources annotating. But the Socionet approach is more focused on developing of: (a) taxonomy of scientific relationships, which can exist between research objects, especially between research outputs; and (b) a semantic segment of a research e-infrastructure that includes a semantic interoperability support, a monitoring of changes in linkages and linked objects, notifications and a new model of communication for scientists, and at last-scientometric indicators built by processing of semantic linkages data.. Implementation of a semantic linkage technique in a form of a researcher's personal tool within the Socionet RIS demonstrates also strong similarities with collaborative tagging services which are very popular among users of many social networks like Twitter, Flickr, etc.. The collaborative tagging (also known as a folksonomy) is defined as a ''method of allowing anyone (users) to link keywords or tags to content, at pleasure'' (Dix et al. 2006) . The semantic linkage technique can be defined as a method of allowing anyone (e.g. scientists as users of RIS) to link any pair of available research objects from RIS content. A semantic meaning of the linkage expresses scientist's knowledge, hypothesis or an opinion about a scientific relationship between the linked objects. And scientists do it at pleasure, as their regular scientific creativity (Parinov 2012a, b) .. In contrast with typical collaborative tagging at Socionet the semantic linkage technique uses available taxonomy of scientific relationships that can exist between different types of research information objects (between person and organization profiles, projects, research outputs, etc.). Within the Socionet the taxonomy is represented as hierarchical structure of controlled semantic vocabularies.. Currently in the research community there are several initiatives provided proper ontologies and semantic vocabularies for scientific relationships classification. One of them is the semantic publishing and referencing (SPAR) ontologies (Shotton 2010b While a substance of scientific relationships between a person and an organization are well known and more or less have been classified, the taxonomy of relationships between research outputs is still under development. SPAR ontologies include very useful the Citation Typing Ontology (CiTO) (Shotton 2010c) and DoCo ontology (Shotton and Peroni 2011) , which allow us to build initial semantic vocabularies.. In addition some available studies give us empirically based corrections and improvements for initial classification of relationships between research outputs. It is a long-standing study of the rhetorical and argumentative characteristics of scientific discourse (Shum et al. 2010) and recent research on analysis of sentiments in the text surrounding references in scientific papers that conducted in a framework of the Maps of Science building (Small 2011) .. The study of scientific discourse provided us with some classification of typical motivations for making citations (Shum et al. 2010 ). Information about the same motivations can be also extracted from the citation context by using special software that discussed in Shum et al. (2010) .. The sentiments' extraction from the citation contexts about the cited research papers can be done by existed sentiment analysis tools which have been developed to build taxonomy over social networks data (Galassini et al. 2011 Since the taxonomy should also be ''live'', at Socionet we provide scientists with a tool to update and develop scientific relationship classifications (semantic vocabularies) in decentralized, but to some extent controlled way (Parinov 2012b) .. Semantic linkages created by scientists between research objects of RIS content can be organized either as a specialized information system, e.g. an open repository of semantic linkages (Parinov 2012a) or this data can be stored just within a publication's metadata (Nanopub, SiteULike). In any way the data of semantic linkages accumulated and stored in RIS can be processed to provide for the scientific community some additional useful information e.g. like the ''Semantic Halo'' (Dix et al. 2006 ) initially designed for traditional social networks.. By processing semantic linkages data collected in RIS one can build at least two types of new scientometric indicators: (1) statistical aggregators of research objects properties (e.g. download statistics, number of citations, etc.) according information what objects are linked; (2) statistical distributions for scientific relationship classes associated with research objects from RIS content.. Using these two types of indicators at least following new scientometric studies can be done:. • Quantitative studies of all accumulated semantic linkages including different sort of its structuring and aggregation, e.g. numbers of linkages (total and by scientific relationship classes) for specific objects (authors, organizations, etc.); aggregated numbers of linkages for all objects belonged to one author (total, by relationship classes, by values from semantic vocabularies, etc.); and many others; • Qualitative studies of relationships specified by scientists over all available research objects, including statistical distribution of expressed relationships for specific objects, graphs of linkages with semantic values assigned to each edge of the graph, and so on.. These new scientometric indicators can significantly improve a visualization of research outputs usage and impact. It gives the community useful additional information for better research assessment and evaluation of individual scientists and research organizations as well. Scientomentics studies based on proposed approach, if the collected data is statistically significant, can e.g. answer: (a) who used what research results as a basis for creating a new scientific knowledge (e.g. a ''use method from'' of a semantic linkage meaning that should have the highest positive assessment); (b) whose research results prove/repeat or are proved by other results that can be assessed as an indicator of credibility; (c) whose results are mentioned just as illustrations that should be assessed as a weak usage; (d) whose results are criticized or disapproved that means assessment of suspicious research results with currently not clear research impact; and so on.. In the ''Semantic linkages in research information systems'' section of this study we provide basic information about a semantic linkage technique and its possible application within RIS. We discuss requirements to proper implementation of this technique at RIS which should allow a collecting of new data for scientometric studies. We also present in this section our approach to provide scientists with the semantics which necessary for expressing of scientific relationships over available research objects. It includes examples of basic semantic vocabularies that setting up taxonomy used also when we build the data sets for scientometric studies.. In the ''An abstract computing model of a new data source'' section we propose an abstract model of the data source used to aggregate and process the semantic linkage data. We discuss possible scientometric indicators which can be built according this model.. In the ''Examples of scientometric indicators'' section we discuss ideas and provide some examples of scientometric indicators based on two data sets: (a) what objects are linked and (b) what scientific relationships (semantics) are expressed by the linkages. Most of these indicators have been generated at the moment by Socionet services and are available for users. Statistical significance of the indicators will be improved with a growth of users and amount of semantic linkages accumulated at Socionet.. In conclusion we summarize benefits of this new data source for scientometrics studies. A semantic linkage technique implemented in RIS opens for scientists a new dimension for scientific creativity. Monitoring and processing of created semantic linkages within RIS content establish a data source for new scientometric studies, which gives the research community different benefits and new opportunities.. Additionally to already existed scientometric indicators the proposed data source allows a deep inspection of impact/usage characteristics for a scientist and a research organization in both static and dynamic aspects.. Obtained in this way, assessments of research productivity and performance will be substantially more informative than the currently used citation indexes and characteristics of publication activity. Thus, using this new opportunities in procedures of professional certification and in research funding schemas will create more effective incentives and motivations for scientists.

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