Christian von der Weth | National University of Singapore (original) (raw)

Papers by Christian von der Weth

Computing Research Repository, 2011

NoSQL systems are more and more deployed as back-end infrastructure for large-scale distributed o... more NoSQL systems are more and more deployed as back-end infrastructure for large-scale distributed online platforms like Google, Amazon or Facebook. Their applicability results from the fact that most services of online platforms access the stored data objects via their primary key. However, NoSQL systems do not efficiently support services referring more than one data object, e.g. the term-based search for data objects. To address this issue we propose our architecture based on an inverted index on top of a NoSQL system. For queries comprising more than one term, distributed indices yield a limited performance in large distributed systems. We propose two extensions to cope with this challenge. Firstly, we store index entries not only for single term but also for a selected set of term combinations depending on their popularity derived from a query history. Secondly, we additionally cache popular keys on gateway nodes, which are a common concept in real-world systems, acting as interface for services when accessing data objects in the back end. Our results show that we can significantly reduces the bandwidth consumption for processing queries, with an acceptable, marginal increase in the load of the gateway nodes.

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2013 IEEE/WIC/ACM International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), 2013

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2013 IEEE/WIC/ACM International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), 2013

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2010 IEEE International Conference on Multimedia and Expo, 2010

User-generated content in the spirit of Web 2.0 is a promising means to improve the search for re... more User-generated content in the spirit of Web 2.0 is a promising means to improve the search for relevant information on the web, particularly multimedia content. The idea is that user col-laboratively search or browse for information, either directly by communicating or indirectly by adding meta information (e.g., tags) to web pages. However, current solutions are bound to specific web sites

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2011 IEEE/WIC/ACM International Conferences on Web Intelligence and Intelligent Agent Technology, 2011

... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderwe... more ... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderweth@ deri.org ... This work has been done while Christian von der Weth was working at the Nanyang ... a key k becomes unpopular, we suspend k, ie we delete k's inverted list and mark k as ...

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... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderwe... more ... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderweth@ deri.org ... This work has been done while Christian von der Weth was working at the Nanyang ... a key k becomes unpopular, we suspend k, ie we delete k's inverted list and mark k as ...

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IEEE Internet Computing, 2000

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21st International Conference on Data Engineering Workshops (ICDEW'05), 2005

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2010 IEEE 12th Conference on Commerce and Enterprise Computing, 2010

In service-oriented computing, software agents interact by requesting and providing services. Sin... more In service-oriented computing, software agents interact by requesting and providing services. Since providing a service incurs cost, uncooperative behavior dominates in the absence of an incentive mechanism. An economic model that describes interactions between individuals is the Helping Game. There, pairs of requester and provider are randomly matched. In various real-world applications in turn, several providers offer similar services, and

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Lecture Notes in Computer Science, 2006

Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior... more Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior-based trust models typically include a fixed evaluation scheme to derive the trustworthiness of an entity from knowledge about its behavior in previous interactions. This paper in turn proposes a framework for behavior-based trust models for open environments with the following distinctive characteristic. Based on a relational representation

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Lecture Notes in Social Networks, 2012

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2009 Seventh IEEE European Conference on Web Services, 2009

In service-oriented architectures, participants keep interacting by exchanging tasks, in order to... more In service-oriented architectures, participants keep interacting by exchanging tasks, in order to increase their benefit. Since carrying out a task incurs costs, and participants often interact with unknown partners, uncooperative behavior dominates in the absence of a mechanism. A well-known economic model describing this situation is the Helping Game. In previous helping experiments, participants decide 'by hand' before each interaction

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Advanced Information Networking and Applications, 2011

Finding relevant and reliable information on the web is a non-trivial task. While internet search... more Finding relevant and reliable information on the web is a non-trivial task. While internet search engines do find correct web pages with respect to a set of keywords, they often cannot ensure the relevance or reliability of their content. An emerging trend is to harness internet users in the spirit of Web 2.0, to discern and personalize relevant and reliable information. Users collaboratively search or browse for information, either directly by communicating or indirectly by adding meta information (e.g., tags) to web pages. While gaining much popularity, such approaches are bound to specific service providers, or the Web 2.0 sites providing the necessary features, and the knowledge so generated is also confined to, and subject to the whims and censorship of such providers. To overcome these limitations we introduce COBS, a browser-centric knowledge repository which enjoys the inherent openness (similar to Wikipedia) while aiming to provide end-users the freedom of personalization and privacy by adopting an eventually hybrid/p2p back-end. In this paper we first present the COBS front-end, a browser add-on that enables users to tag, rate or comment arbitrary web pages and to socialize with others in both a synchronous and asynchronous manner. We then discuss how a decentralized back-end can be realized. While Distributed Hash Tables (DHTs) are the most natural choice, and despite a decade of research on DHT designs, we encounter several, some small, while others more fundamental shortcomings that need to be surmounted in order to realize an efficient, scalable and reliable decentralized back-end for COBS. To that end, we outline various design alternatives and discuss qualitatively (and quantitatively, when possible) their (dis-)advantages. We believe that the objectives of COBS are ambitious, posing significant challenges for distributed systems, middleware and distributed data-analytics research, even while building on the existing momentum. Based on experiences fr om our ongoing work on COBS, we outline these systems research issues in this position paper.

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In service-oriented computing, software agents interact by requesting and providing services. Sin... more In service-oriented computing, software agents interact by requesting and providing services. Since providing a service incurs cost, uncooperative behavior dominates in the absence of an incentive mechanism. An economic model that describes interactions between individuals is the Helping Game. There, pairs of requester and provider are randomly matched. In various real-world applications in turn, several providers offer similar services, and requesters have a choice of providers. The rationale behind strategic provider selection is to choose the provider that is most likely to perform the task as desired. The results from existing studies of the Helping Game are not directly applicable to settings with provider selection. To analyze how strategic provider selection affects the efficiency of enterprise systems, we have designed and carried out an experimental study. Our results show that cooperative participants receive significantly more requests than uncooperative ones, making cooperation expensive. We conclude that system designers must incentivize requesters to balance their tasks between providers.

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European Conference on Web Services, 2009

In service-oriented architectures, participants keep interacting by exchanging tasks, in order to... more In service-oriented architectures, participants keep interacting by exchanging tasks, in order to increase their benefit. Since carrying out a task incurs costs, and participants often interact with unknown partners, uncooperative behavior dominates in the absence of a mechanism. A well-known economic model describing this situation is the Helping Game. In previous helping experiments, participants decide 'by hand' before each interaction

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OTM Workshops, 2006

Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior... more Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior-based trust models typically include a fixed evaluation scheme to derive the trustworthiness of an entity from knowledge about its behavior in previous interactions. This paper in turn proposes a framework for behavior-based trust models for open environments with the following distinctive characteristic. Based on a relational representation

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IEEE International Conference on e-Commerce Technology, 2007

... negative weights. – PageRank [23] assigns a vertex a high index value if many other vertices ... more ... negative weights. – PageRank [23] assigns a vertex a high index value if many other vertices with a high index value point to it: PRank(vi)=(1−d)+d· ∑ vj ∈In(vi) w(e(vj ,vi))·PRank(vj ) ∑ vk∈Out(vj ) w(e(vj ,vk)) The HITS algorithm ...

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Lecture Notes in Computer Science, 2006

Peer-to-Peer data structures (P2P data structures) let a la rge number of anonymous peers share t... more Peer-to-Peer data structures (P2P data structures) let a la rge number of anonymous peers share the data-management workload. A common assump- tion behind such systems is that peers behave cooperatively. But as with many distributed systems where participation is voluntary, and the participants are not clearly observable, unreliable behavior is the dominant st rategy. This calls for reputation systems that

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Advances in Social Network Analysis and Mining, 2010

In open environments, deciding if an individual is trustworthy, based on his past behavior, is fu... more In open environments, deciding if an individual is trustworthy, based on his past behavior, is fundamentally important. To accomplish this, centrality in a so-called feedback graph is often used as a trust measure. The nodes of this graph represent the individuals, and an edge represents feedback that evaluates a past interaction. In the open environments envisioned where individuals can specify

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Computing Research Repository, 2011

NoSQL systems are more and more deployed as back-end infrastructure for large-scale distributed o... more NoSQL systems are more and more deployed as back-end infrastructure for large-scale distributed online platforms like Google, Amazon or Facebook. Their applicability results from the fact that most services of online platforms access the stored data objects via their primary key. However, NoSQL systems do not efficiently support services referring more than one data object, e.g. the term-based search for data objects. To address this issue we propose our architecture based on an inverted index on top of a NoSQL system. For queries comprising more than one term, distributed indices yield a limited performance in large distributed systems. We propose two extensions to cope with this challenge. Firstly, we store index entries not only for single term but also for a selected set of term combinations depending on their popularity derived from a query history. Secondly, we additionally cache popular keys on gateway nodes, which are a common concept in real-world systems, acting as interface for services when accessing data objects in the back end. Our results show that we can significantly reduces the bandwidth consumption for processing queries, with an acceptable, marginal increase in the load of the gateway nodes.

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2013 IEEE/WIC/ACM International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), 2013

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2013 IEEE/WIC/ACM International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), 2013

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2010 IEEE International Conference on Multimedia and Expo, 2010

User-generated content in the spirit of Web 2.0 is a promising means to improve the search for re... more User-generated content in the spirit of Web 2.0 is a promising means to improve the search for relevant information on the web, particularly multimedia content. The idea is that user col-laboratively search or browse for information, either directly by communicating or indirectly by adding meta information (e.g., tags) to web pages. However, current solutions are bound to specific web sites

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2011 IEEE/WIC/ACM International Conferences on Web Intelligence and Intelligent Agent Technology, 2011

... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderwe... more ... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderweth@ deri.org ... This work has been done while Christian von der Weth was working at the Nanyang ... a key k becomes unpopular, we suspend k, ie we delete k's inverted list and mark k as ...

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... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderwe... more ... Christian von der Weth DERI, National University of Ireland, Galway Email: christian.vonderweth@ deri.org ... This work has been done while Christian von der Weth was working at the Nanyang ... a key k becomes unpopular, we suspend k, ie we delete k's inverted list and mark k as ...

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IEEE Internet Computing, 2000

Bookmarks Related papers MentionsView impact

21st International Conference on Data Engineering Workshops (ICDEW'05), 2005

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2010 IEEE 12th Conference on Commerce and Enterprise Computing, 2010

In service-oriented computing, software agents interact by requesting and providing services. Sin... more In service-oriented computing, software agents interact by requesting and providing services. Since providing a service incurs cost, uncooperative behavior dominates in the absence of an incentive mechanism. An economic model that describes interactions between individuals is the Helping Game. There, pairs of requester and provider are randomly matched. In various real-world applications in turn, several providers offer similar services, and

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Lecture Notes in Computer Science, 2006

Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior... more Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior-based trust models typically include a fixed evaluation scheme to derive the trustworthiness of an entity from knowledge about its behavior in previous interactions. This paper in turn proposes a framework for behavior-based trust models for open environments with the following distinctive characteristic. Based on a relational representation

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Lecture Notes in Social Networks, 2012

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2009 Seventh IEEE European Conference on Web Services, 2009

In service-oriented architectures, participants keep interacting by exchanging tasks, in order to... more In service-oriented architectures, participants keep interacting by exchanging tasks, in order to increase their benefit. Since carrying out a task incurs costs, and participants often interact with unknown partners, uncooperative behavior dominates in the absence of a mechanism. A well-known economic model describing this situation is the Helping Game. In previous helping experiments, participants decide 'by hand' before each interaction

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Advanced Information Networking and Applications, 2011

Finding relevant and reliable information on the web is a non-trivial task. While internet search... more Finding relevant and reliable information on the web is a non-trivial task. While internet search engines do find correct web pages with respect to a set of keywords, they often cannot ensure the relevance or reliability of their content. An emerging trend is to harness internet users in the spirit of Web 2.0, to discern and personalize relevant and reliable information. Users collaboratively search or browse for information, either directly by communicating or indirectly by adding meta information (e.g., tags) to web pages. While gaining much popularity, such approaches are bound to specific service providers, or the Web 2.0 sites providing the necessary features, and the knowledge so generated is also confined to, and subject to the whims and censorship of such providers. To overcome these limitations we introduce COBS, a browser-centric knowledge repository which enjoys the inherent openness (similar to Wikipedia) while aiming to provide end-users the freedom of personalization and privacy by adopting an eventually hybrid/p2p back-end. In this paper we first present the COBS front-end, a browser add-on that enables users to tag, rate or comment arbitrary web pages and to socialize with others in both a synchronous and asynchronous manner. We then discuss how a decentralized back-end can be realized. While Distributed Hash Tables (DHTs) are the most natural choice, and despite a decade of research on DHT designs, we encounter several, some small, while others more fundamental shortcomings that need to be surmounted in order to realize an efficient, scalable and reliable decentralized back-end for COBS. To that end, we outline various design alternatives and discuss qualitatively (and quantitatively, when possible) their (dis-)advantages. We believe that the objectives of COBS are ambitious, posing significant challenges for distributed systems, middleware and distributed data-analytics research, even while building on the existing momentum. Based on experiences fr om our ongoing work on COBS, we outline these systems research issues in this position paper.

Bookmarks Related papers MentionsView impact

In service-oriented computing, software agents interact by requesting and providing services. Sin... more In service-oriented computing, software agents interact by requesting and providing services. Since providing a service incurs cost, uncooperative behavior dominates in the absence of an incentive mechanism. An economic model that describes interactions between individuals is the Helping Game. There, pairs of requester and provider are randomly matched. In various real-world applications in turn, several providers offer similar services, and requesters have a choice of providers. The rationale behind strategic provider selection is to choose the provider that is most likely to perform the task as desired. The results from existing studies of the Helping Game are not directly applicable to settings with provider selection. To analyze how strategic provider selection affects the efficiency of enterprise systems, we have designed and carried out an experimental study. Our results show that cooperative participants receive significantly more requests than uncooperative ones, making cooperation expensive. We conclude that system designers must incentivize requesters to balance their tasks between providers.

Bookmarks Related papers MentionsView impact

European Conference on Web Services, 2009

In service-oriented architectures, participants keep interacting by exchanging tasks, in order to... more In service-oriented architectures, participants keep interacting by exchanging tasks, in order to increase their benefit. Since carrying out a task incurs costs, and participants often interact with unknown partners, uncooperative behavior dominates in the absence of a mechanism. A well-known economic model describing this situation is the Helping Game. In previous helping experiments, participants decide 'by hand' before each interaction

Bookmarks Related papers MentionsView impact

OTM Workshops, 2006

Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior... more Trust models have been touted to facilitate cooperation among unknown entities. Existing behavior-based trust models typically include a fixed evaluation scheme to derive the trustworthiness of an entity from knowledge about its behavior in previous interactions. This paper in turn proposes a framework for behavior-based trust models for open environments with the following distinctive characteristic. Based on a relational representation

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IEEE International Conference on e-Commerce Technology, 2007

... negative weights. – PageRank [23] assigns a vertex a high index value if many other vertices ... more ... negative weights. – PageRank [23] assigns a vertex a high index value if many other vertices with a high index value point to it: PRank(vi)=(1−d)+d· ∑ vj ∈In(vi) w(e(vj ,vi))·PRank(vj ) ∑ vk∈Out(vj ) w(e(vj ,vk)) The HITS algorithm ...

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Lecture Notes in Computer Science, 2006

Peer-to-Peer data structures (P2P data structures) let a la rge number of anonymous peers share t... more Peer-to-Peer data structures (P2P data structures) let a la rge number of anonymous peers share the data-management workload. A common assump- tion behind such systems is that peers behave cooperatively. But as with many distributed systems where participation is voluntary, and the participants are not clearly observable, unreliable behavior is the dominant st rategy. This calls for reputation systems that

Bookmarks Related papers MentionsView impact

Advances in Social Network Analysis and Mining, 2010

In open environments, deciding if an individual is trustworthy, based on his past behavior, is fu... more In open environments, deciding if an individual is trustworthy, based on his past behavior, is fundamentally important. To accomplish this, centrality in a so-called feedback graph is often used as a trust measure. The nodes of this graph represent the individuals, and an edge represents feedback that evaluates a past interaction. In the open environments envisioned where individuals can specify

Bookmarks Related papers MentionsView impact