A cohesive crack model is proposed to describe strain localization for the materials where strain... more A cohesive crack model is proposed to describe strain localization for the materials where strain-hardening is not prevailing over strain-softening (geomaterials, concrete-like materials, ceramics, etc.). Such a model is able to predict the size effects of fracture mechanics, i.e., the transition from ductile to brittle structure behaviour by increasing the size scale and keeping the geometrical shape unchanged. Whereas for Mode I, only untieing of the finite element nodes is applied to simulate crack growth, for Mixed Mode interelement crack propagation a topological variation is required at each step. In the case of four point shear testing, the load vs. deflection diagrams reveal snap-back instability for large sizes. By increasing the specimen sizes, such instability tends to reproduce the classical LEFM instability, predicted by the Maximum Circumferential Stress Criterion. Experimentally, the fracture toughness parameter of concrete appears to be unique and represented by the Mode I fracture energy Gp or the stress-intensity factor Kic even for Mixed Mode problems.
EDBT 2000 is the seventh conference in a series dedicated to the advancement of database technolo... more EDBT 2000 is the seventh conference in a series dedicated to the advancement of database technology. This year's conference special theme, "Connect Millions of Users and Data Sources," underscores the importance of databases for the information age that is dawning with the new millennium. The importance derives not just from the observation that the information age essentially rests on the convergence of communications, computing, and storage. Equally important, many of the concepts and techniques underlying the success of database systems have independent meaning and impact for today's distributed information systems. The papers in the volume should also be seen in this light. The EDBT 2000 conference program includes 30 research papers selected by the program committee out of 187 submissions, covering advances in research, development, and applications of databases. The conference program also includes six industry and applications papers, a panel discussion, six tutorials, and several software demonstrations. The conference features three distinguished invited speakers: Ashish Gupta discusses database issues in electronic commerce, Stefano Ceri addresses the impact and challenges of XML on databases, and Andreas Reuter shares his views on new perspectives on database technology. The technical contributions presented at the EDBT 2000 conference are collected and preserved in this volume that we are pleased to present to you with the expectation that it will serve as a valuable research and reference tool in your professional life. The conference would not have been possible without the efforts of many dedicated people. In particular we would like to thank the organization committee, Jay Grieves for supporting the Microsoft Conference Management Toolkit, the program committee members, and the reviewers whose names are also listed in the proceedings.
This book constitutes the refereed proceedings of the 10th International Conference on Extending ... more This book constitutes the refereed proceedings of the 10th International Conference on Extending Database Technology, EDBT 2006, held in Munich, Germany, in March 2006. The 60 revised research papers presented together with eight industrial application papers, 20 software demos, and three invited contributions were carefully reviewed and selected from 352 submissions. The papers are organized in topical sections.
A distinctive property of relational database systems is the ability to perform data updates and ... more A distinctive property of relational database systems is the ability to perform data updates and queries in atomic blocks called transactions, with the well-known atomicity, consistency, isolation and durability (ACID) properties. To date, the ability of systems performing reasoning to maintain the ACID properties, even over data held within a relational database, has been largely ignored. This article studies an approach to reasoning over data from web ontology language (OWL) 2 RL ontologies held in a relational database, where the ACID properties of transactions are maintained. Taking an incremental approach to maintaining materialised views of the result of reasoning, the approach is demonstrated to support a query and reasoning performance comparable to or better than other OWL reasoning systems, yet adding the important benefit of supporting transactions.
The NP2 relational model has been widely accep ted as one' of the extensions of Codd's relational... more The NP2 relational model has been widely accep ted as one' of the extensions of Codd's relational model which better meet the requirements imposed by the so-called non-standard database applications. The manners in which the NF2 relational model has been used so far are called standard ways of using the model. In this paper some nOD-standard ways to use the NF2 relation model are presented. Their common characteristics are analyzed and the concept of "object motors" is introducecl for~'new generation of computer systems.
Social media data streams are an invaluable source for timely and up-to-date information about cu... more Social media data streams are an invaluable source for timely and up-to-date information about current events. As a consequence, several event detection techniques have been proposed in the literature in order to tap this information source. However, most of these proposals focus on the information extraction aspect of the problem and tend to ignore the streaming nature of the input. The work conducted in our research group therefore intends to address these stream-related challenges, such as detecting events incrementally, reporting them in (near) real-time, and coping with fluctuations and spikes in the social media data stream. In this article, we report on the results that we obtained so far and outline our research agenda for the remainder of this work.
The ODMG proposal has helped to focus the work on object-oriented databases (OODBs) onto a common... more The ODMG proposal has helped to focus the work on object-oriented databases (OODBs) onto a common object model and query language. Nevertheless there are several shortcomings of the current proposal stemming from the adaption of concepts of object-oriented programming and a lack of formalization. In this paper we present a formalization of the ODMG model and the OQL query language that is used in the CROQUE project as a basis for query optimization. An essential part is a complete, formally sound type system that allows us to reason about the types of intermediate query results and gives rise to fully orthogonal queries, including useful extensions of projections and set operations. Dala Mining and Reverse Engineering S. Spaccapielra & F. Maryanski (Eds.
This paper de nes a formal classi cation of multi-database languages into ve l e v els of databas... more This paper de nes a formal classi cation of multi-database languages into ve l e v els of database integration with increasing degree of global control and decreasing degree of local autonomy. First, the fundamental interoperability concepts and mechanisms are identi ed for each of these levels. Their consequences on local autonomy a s w ell as implementation drawbacks are discussed. Second, various multi-database languages are classi ed into these categories. In addition to our own language COOL*, other proposals are analyzed, including SQL*Net, Multibase, Superviews, VODAK, Pegasus, and O*SQL.
Twitter's popularity as a source of up-to-date news and information is constantly increasing. In ... more Twitter's popularity as a source of up-to-date news and information is constantly increasing. In response to this trend, numerous event detection techniques have been proposed to cope with the rate and volume of Twitter data streams. Although most of these works conduct some evaluation of the proposed technique, a comparative study is often omitted. In this paper, we present a survey and experimental analysis of state-of-the-art event detection techniques for Twitter data streams. In order to conduct this study, we define a series of measures to support the quantitative and qualitative comparison. We demonstrate the effectiveness of these measures by applying them to event detection techniques as well as to baseline approaches using real-world Twitter streaming data.
The joint EDBT/ICDT conference (International Conference on Extending Database Technology / Inter... more The joint EDBT/ICDT conference (International Conference on Extending Database Technology / International Conference on Database Theory) is a well established conference series on data management, with annual meetings in the second half of March that attract 250 to 300 delegates. Three weeks before EDBT/ICDT 2020 was planned to take place in Copenhagen, the rapidly developing Covid-19 pandemic led to the decision to cancel the face-to-face event. In the interest of the research community, it was decided to move the conference online while trying to preserve as much of the real-life experience as possible. As far as we know, we are one of the first conferences that moved to a fully synchronous online experience due to the COVID- 19 outbreak. By fully synchronous, we mean that participants jointly listened to presentations, had live Q&A, and attended other live events associated with the conference. In this report, we share our decisions, experiences, and lessons learned.
Proceedings of the 2016 International Conference on Management of Data, 2016
A key promise of SQL is that the optimizer will find the most efficient execution plan, regardles... more A key promise of SQL is that the optimizer will find the most efficient execution plan, regardless of how the query is formulated. In general, query optimizers of modern database systems are able to keep this promise, with the notable exception of nested queries. While several optimization techniques for nested queries have been proposed, their adoption in practice has been limited. In this paper, we argue that the NF 2 (non-first normal form) algebra, which was originally designed to process nested tables, is a better approach to nested query optimization as it fulfills two key requirements. First, the NF 2 algebra can represent all types of nested queries as well as both existing and novel optimization techniques based on its equivalences. Second, performance benefits can be achieved with little changes to existing transformation-based query optimizers as the NF 2 algebra is an extension of the relational algebra.
Proceedings of the 15th Symposium on Database Programming Languages, 2015
Originally developed as a query language for XML databases, XQuery has evolved into a complete fu... more Originally developed as a query language for XML databases, XQuery has evolved into a complete functional programming language. In order to unlock all optimization opportunities, XQuery processors therefore need to combine traditional query optimization with techniques used in optimizing compilers. In this paper, we discuss how the well-known technique of function inlining can be applied to XQuery. We present an implementation of function inlining based on the query processor of BaseX, an open-source XML database. Finally, a detailed quantitative evaluation demonstrates that the performance benefits obtained by blending compiler and query optimizer techniques surpass results from any one single technique.
The continuous growth of social networks and the active use of social media services result in ma... more The continuous growth of social networks and the active use of social media services result in massive amounts of user generated data. Our goal is to leverage social media users as "social sensors" in order to increase the situational awareness within and about urban areas. In addition to the well known challenges of event and topic detection and tracking, this task involves a spatial and temporal dimension. In this paper, we present a visualization that supports analysts in monitoring events/topics and emotions both in time and in space. The visualization uses a clock face metaphor to encode temporal and spatial relationships, a color map to reflect emotion, and tag clouds for events and topics. A hierarchy of these clock faces supports drilling down to finer levels of granularity as well as rolling up the vast and fast flow of information. In order to showcase these functionalities of our visualization, we discuss several case studies that use the live data stream of the Twitter microblogging service. Finally, we demonstrate the usefulness and usability of the visualization in a user study that we conducted.
Decision-making in the field of academic planning involves extensive analysis of large data volum... more Decision-making in the field of academic planning involves extensive analysis of large data volumes originating from multiple systems. Academic workload management is concerned with distributing teaching resources in order to adequately support the university's educational framework (faculties, degrees, courses, admission policies, teaching workload etc). We propose a methodology for assessing educational capacity and planning its distribution and utilization in universities. The approach has been implemented as a decision support system allowing simulation and evaluation of various proposals and scenarios. The system integrates the input data from relevant sources into an autonomous data warehouse, while the client front-end ensures adequate output presentation to users so as reveal significant details and dependencies. Applying the system as "on-the-fly" decision-support facility by the policy-makers has resulted in significant acceleration of planning procedures, raised the overall awareness with respect to the underlying methodology and, ultimately, enabled more efficient academic administration.
A cohesive crack model is proposed to describe strain localization for the materials where strain... more A cohesive crack model is proposed to describe strain localization for the materials where strain-hardening is not prevailing over strain-softening (geomaterials, concrete-like materials, ceramics, etc.). Such a model is able to predict the size effects of fracture mechanics, i.e., the transition from ductile to brittle structure behaviour by increasing the size scale and keeping the geometrical shape unchanged. Whereas for Mode I, only untieing of the finite element nodes is applied to simulate crack growth, for Mixed Mode interelement crack propagation a topological variation is required at each step. In the case of four point shear testing, the load vs. deflection diagrams reveal snap-back instability for large sizes. By increasing the specimen sizes, such instability tends to reproduce the classical LEFM instability, predicted by the Maximum Circumferential Stress Criterion. Experimentally, the fracture toughness parameter of concrete appears to be unique and represented by the Mode I fracture energy Gp or the stress-intensity factor Kic even for Mixed Mode problems.
EDBT 2000 is the seventh conference in a series dedicated to the advancement of database technolo... more EDBT 2000 is the seventh conference in a series dedicated to the advancement of database technology. This year's conference special theme, "Connect Millions of Users and Data Sources," underscores the importance of databases for the information age that is dawning with the new millennium. The importance derives not just from the observation that the information age essentially rests on the convergence of communications, computing, and storage. Equally important, many of the concepts and techniques underlying the success of database systems have independent meaning and impact for today's distributed information systems. The papers in the volume should also be seen in this light. The EDBT 2000 conference program includes 30 research papers selected by the program committee out of 187 submissions, covering advances in research, development, and applications of databases. The conference program also includes six industry and applications papers, a panel discussion, six tutorials, and several software demonstrations. The conference features three distinguished invited speakers: Ashish Gupta discusses database issues in electronic commerce, Stefano Ceri addresses the impact and challenges of XML on databases, and Andreas Reuter shares his views on new perspectives on database technology. The technical contributions presented at the EDBT 2000 conference are collected and preserved in this volume that we are pleased to present to you with the expectation that it will serve as a valuable research and reference tool in your professional life. The conference would not have been possible without the efforts of many dedicated people. In particular we would like to thank the organization committee, Jay Grieves for supporting the Microsoft Conference Management Toolkit, the program committee members, and the reviewers whose names are also listed in the proceedings.
This book constitutes the refereed proceedings of the 10th International Conference on Extending ... more This book constitutes the refereed proceedings of the 10th International Conference on Extending Database Technology, EDBT 2006, held in Munich, Germany, in March 2006. The 60 revised research papers presented together with eight industrial application papers, 20 software demos, and three invited contributions were carefully reviewed and selected from 352 submissions. The papers are organized in topical sections.
A distinctive property of relational database systems is the ability to perform data updates and ... more A distinctive property of relational database systems is the ability to perform data updates and queries in atomic blocks called transactions, with the well-known atomicity, consistency, isolation and durability (ACID) properties. To date, the ability of systems performing reasoning to maintain the ACID properties, even over data held within a relational database, has been largely ignored. This article studies an approach to reasoning over data from web ontology language (OWL) 2 RL ontologies held in a relational database, where the ACID properties of transactions are maintained. Taking an incremental approach to maintaining materialised views of the result of reasoning, the approach is demonstrated to support a query and reasoning performance comparable to or better than other OWL reasoning systems, yet adding the important benefit of supporting transactions.
The NP2 relational model has been widely accep ted as one' of the extensions of Codd's relational... more The NP2 relational model has been widely accep ted as one' of the extensions of Codd's relational model which better meet the requirements imposed by the so-called non-standard database applications. The manners in which the NF2 relational model has been used so far are called standard ways of using the model. In this paper some nOD-standard ways to use the NF2 relation model are presented. Their common characteristics are analyzed and the concept of "object motors" is introducecl for~'new generation of computer systems.
Social media data streams are an invaluable source for timely and up-to-date information about cu... more Social media data streams are an invaluable source for timely and up-to-date information about current events. As a consequence, several event detection techniques have been proposed in the literature in order to tap this information source. However, most of these proposals focus on the information extraction aspect of the problem and tend to ignore the streaming nature of the input. The work conducted in our research group therefore intends to address these stream-related challenges, such as detecting events incrementally, reporting them in (near) real-time, and coping with fluctuations and spikes in the social media data stream. In this article, we report on the results that we obtained so far and outline our research agenda for the remainder of this work.
The ODMG proposal has helped to focus the work on object-oriented databases (OODBs) onto a common... more The ODMG proposal has helped to focus the work on object-oriented databases (OODBs) onto a common object model and query language. Nevertheless there are several shortcomings of the current proposal stemming from the adaption of concepts of object-oriented programming and a lack of formalization. In this paper we present a formalization of the ODMG model and the OQL query language that is used in the CROQUE project as a basis for query optimization. An essential part is a complete, formally sound type system that allows us to reason about the types of intermediate query results and gives rise to fully orthogonal queries, including useful extensions of projections and set operations. Dala Mining and Reverse Engineering S. Spaccapielra & F. Maryanski (Eds.
This paper de nes a formal classi cation of multi-database languages into ve l e v els of databas... more This paper de nes a formal classi cation of multi-database languages into ve l e v els of database integration with increasing degree of global control and decreasing degree of local autonomy. First, the fundamental interoperability concepts and mechanisms are identi ed for each of these levels. Their consequences on local autonomy a s w ell as implementation drawbacks are discussed. Second, various multi-database languages are classi ed into these categories. In addition to our own language COOL*, other proposals are analyzed, including SQL*Net, Multibase, Superviews, VODAK, Pegasus, and O*SQL.
Twitter's popularity as a source of up-to-date news and information is constantly increasing. In ... more Twitter's popularity as a source of up-to-date news and information is constantly increasing. In response to this trend, numerous event detection techniques have been proposed to cope with the rate and volume of Twitter data streams. Although most of these works conduct some evaluation of the proposed technique, a comparative study is often omitted. In this paper, we present a survey and experimental analysis of state-of-the-art event detection techniques for Twitter data streams. In order to conduct this study, we define a series of measures to support the quantitative and qualitative comparison. We demonstrate the effectiveness of these measures by applying them to event detection techniques as well as to baseline approaches using real-world Twitter streaming data.
The joint EDBT/ICDT conference (International Conference on Extending Database Technology / Inter... more The joint EDBT/ICDT conference (International Conference on Extending Database Technology / International Conference on Database Theory) is a well established conference series on data management, with annual meetings in the second half of March that attract 250 to 300 delegates. Three weeks before EDBT/ICDT 2020 was planned to take place in Copenhagen, the rapidly developing Covid-19 pandemic led to the decision to cancel the face-to-face event. In the interest of the research community, it was decided to move the conference online while trying to preserve as much of the real-life experience as possible. As far as we know, we are one of the first conferences that moved to a fully synchronous online experience due to the COVID- 19 outbreak. By fully synchronous, we mean that participants jointly listened to presentations, had live Q&A, and attended other live events associated with the conference. In this report, we share our decisions, experiences, and lessons learned.
Proceedings of the 2016 International Conference on Management of Data, 2016
A key promise of SQL is that the optimizer will find the most efficient execution plan, regardles... more A key promise of SQL is that the optimizer will find the most efficient execution plan, regardless of how the query is formulated. In general, query optimizers of modern database systems are able to keep this promise, with the notable exception of nested queries. While several optimization techniques for nested queries have been proposed, their adoption in practice has been limited. In this paper, we argue that the NF 2 (non-first normal form) algebra, which was originally designed to process nested tables, is a better approach to nested query optimization as it fulfills two key requirements. First, the NF 2 algebra can represent all types of nested queries as well as both existing and novel optimization techniques based on its equivalences. Second, performance benefits can be achieved with little changes to existing transformation-based query optimizers as the NF 2 algebra is an extension of the relational algebra.
Proceedings of the 15th Symposium on Database Programming Languages, 2015
Originally developed as a query language for XML databases, XQuery has evolved into a complete fu... more Originally developed as a query language for XML databases, XQuery has evolved into a complete functional programming language. In order to unlock all optimization opportunities, XQuery processors therefore need to combine traditional query optimization with techniques used in optimizing compilers. In this paper, we discuss how the well-known technique of function inlining can be applied to XQuery. We present an implementation of function inlining based on the query processor of BaseX, an open-source XML database. Finally, a detailed quantitative evaluation demonstrates that the performance benefits obtained by blending compiler and query optimizer techniques surpass results from any one single technique.
The continuous growth of social networks and the active use of social media services result in ma... more The continuous growth of social networks and the active use of social media services result in massive amounts of user generated data. Our goal is to leverage social media users as "social sensors" in order to increase the situational awareness within and about urban areas. In addition to the well known challenges of event and topic detection and tracking, this task involves a spatial and temporal dimension. In this paper, we present a visualization that supports analysts in monitoring events/topics and emotions both in time and in space. The visualization uses a clock face metaphor to encode temporal and spatial relationships, a color map to reflect emotion, and tag clouds for events and topics. A hierarchy of these clock faces supports drilling down to finer levels of granularity as well as rolling up the vast and fast flow of information. In order to showcase these functionalities of our visualization, we discuss several case studies that use the live data stream of the Twitter microblogging service. Finally, we demonstrate the usefulness and usability of the visualization in a user study that we conducted.
Decision-making in the field of academic planning involves extensive analysis of large data volum... more Decision-making in the field of academic planning involves extensive analysis of large data volumes originating from multiple systems. Academic workload management is concerned with distributing teaching resources in order to adequately support the university's educational framework (faculties, degrees, courses, admission policies, teaching workload etc). We propose a methodology for assessing educational capacity and planning its distribution and utilization in universities. The approach has been implemented as a decision support system allowing simulation and evaluation of various proposals and scenarios. The system integrates the input data from relevant sources into an autonomous data warehouse, while the client front-end ensures adequate output presentation to users so as reveal significant details and dependencies. Applying the system as "on-the-fly" decision-support facility by the policy-makers has resulted in significant acceleration of planning procedures, raised the overall awareness with respect to the underlying methodology and, ultimately, enabled more efficient academic administration.
A key promise of SQL is that the optimizer will find the most efficient execution plan, regardles... more A key promise of SQL is that the optimizer will find the most efficient execution plan, regardless of how the query is formulated. In general, query optimizers of modern database systems are able to keep this promise, with the notable exception of nested queries. While several optimization techniques for nested queries have been proposed, their adoption in practice has been limited. In this paper, we argue that the NF2 (non-first normal form) algebra, which was originally designed to process nested tables, is a better approach to nested query optimization as it fulfills two key requirements. First, the NF2 algebra can represent all types of nested queries as well as both existing and novel optimization techniques based on its equivalences. Second, performance benefits can be achieved with little changes to existing transformation-based query optimizers as the NF2 algebra is an extension of the relational algebra.
The continuous growth of social networks and the active use of social media services result in ma... more The continuous growth of social networks and the active use of social media services result in massive amounts of user-generated data. More and more people worldwide report and distribute up-to-date information about almost any topic. Therefore, we argue that this kind of data is a good basis to observe ongoing situations in cities as well as related situations from outside about these cities in real-time.
This paper presents a visualization for monitoring the situation (current topics and emotions) in cities and about cities, which is reflected in the live message stream of the social microblogging service Twitter, by using continuously updating and with sentiment colored TagClouds.
In recent years, the growing popularity and active use of social media services on the web have r... more In recent years, the growing popularity and active use of social media services on the web have resulted in massive amounts of user-generated data. With these data available, there is also an increasing interest in analyzing it and to extract information from it. Since social media analysis is concerned with investigating current events around the world, there is a strong emphasis on identifying these evens as quickly as possible, ideally in real-time. In order to scale with the rapidly increasing volume of social media data, we propose to explore very simple event identification mechanisms, rather than applying the more complex approaches that have been proposed in the literature. In this paper, we present a first investigation along this motivation. We discuss a simple sliding window model, which uses shifts in the inverse document frequency (IDF) to capture trending terms as well as to track the evolution and the context around events. Further, we present an initial experimental evaluation of the results that we obtained by analyzing real-world data streams from Twitter.
In order to manage XML documents, native XML databases use specific encodings that map the hierar... more In order to manage XML documents, native XML databases use specific encodings that map the hierarchical structure of a document to a flat representation. Several encodings have been proposed that differ in terms of their support for certain query workloads. While some encodings are optimized for query processing, others focus on data manipulation. For example, the Pre/Dist/Size XML encoding has been designed to support queries over all XPath axes efficiently, but processing atomic updates in XML documents can be costly. In this paper, we present a technique, so-called structural bulk updates, that works in concert with the XQuery Update Facility to support efficient updates on the Pre/Dist/Size encoding. We demonstrate the benefits of our technique in a detailed performance evaluation based on the XMark benchmark.
Nowadays, there are plenty of sources generating massive amounts of text data streams in a contin... more Nowadays, there are plenty of sources generating massive amounts of text data streams in a continuous way. For example, the increasing popularity and the active use of social networks result in voluminous and fast-flowing text data streams containing a large amount of user-generated data about almost any topic around the world. However, the observation and tracking of the ongoing evolution of topics in these unevenly distributed text data streams is a challenging task for analysts, news reporters, or other users. This paper presents \dquote{Stor-e-Motion} a shape-based visualization to track the ongoing evolution of topics' frequency (i.e., importance), sentiment (i.e., emotion), and context (i.e., story) in user-defined topic channels over continuous flowing text data streams. The visualization supports the user in keeping the overview over vast amounts of streaming data and guides the perception of the user to unexpected and interesting points or periods in the text data stream. In this work, we mainly focus on the visualization of text streams from the social microblogging service Twitter, for which we present a series of case studies (e.g., the observation of cities, movies, or natural disasters) applied on real-world data streams collected from the public timeline. However, to further evaluate our visualization, we also present a baseline case study applied on the text stream of a fantasy book series.
Twitter's increasing popularity as a source of up to date news and information about current even... more Twitter's increasing popularity as a source of up to date news and information about current events has spawned a body of research on event detection techniques for social media data streams. Although all proposed approaches provide some evidence as to the quality of the detected events, none relate this task-based performance to their run-time performance in terms of processing speed or data throughput. In particular, neither a quantitative nor a comparative evaluation of these aspects has been performed to date. In this paper, we study the run-time and task-based performance of several state-of-the-art event detection techniques for Twitter. In order to reproducibly compare run-time performance, our approach is based on a general-purpose data stream management system, whereas task-based performance is automatically assessed based on a series of novel measures.
Twitter's popularity as a source of up-to-date news and information is constantly increasing. In ... more Twitter's popularity as a source of up-to-date news and information is constantly increasing. In response to this trend, numerous event detection techniques have been proposed to cope with the rate and volume of social media data streams. Although most of these works conduct some evaluation of the proposed technique, a comparative study is often omitted. In this paper, we present a series of measures that we designed to support the quantitative and qualitative comparison of event detection techniques. In order to demonstrate the effectiveness of these measures, we apply them to state-of-the-art event detection techniques as well as baseline approaches using real-world Twitter streaming data.
Originally developed as a query language for XML databases, XQuery has evolved into a complete fu... more Originally developed as a query language for XML databases, XQuery has evolved into a complete functional programming language. In order to unlock all optimization opportunities, XQuery processors therefore need to combine traditional query optimization with techniques used in optimizing compilers. In this paper, we discuss how the well-known technique of function inlining can be applied to XQuery. We present an implementation of function inlining based on the query processor of BaseX, an open-source XML database. Finally, a detailed quantitative evaluation demonstrates that the performance benefits obtained by blending compiler and query optimizer techniques surpass results from any one single technique.
The continuous growth of social networks and the active use of social media services result in ma... more The continuous growth of social networks and the active use of social media services result in massive amounts of user-generated data. Our goal is to leverage social media users as "social sensors" in order to increase the situational awareness within and about urban areas. In addition to the well-known challenges of event and topic detection and tracking, this task involves a spatial and temporal dimension. In this article, we present a visualization that supports analysts in monitoring events/topics and emotions both in time and in space. The visualization uses a clock-face metaphor to encode temporal and spatial relationships, a color map to reflect emotion, and tag clouds for events and topics. A hierarchy of these clock-faces supports drilling down to finer levels of granularity as well as rolling up the vast and fast flow of information. In order to showcase these functionalities of our visualization, we discuss several case studies that use the live data stream of the Twitter microblogging service. Finally, we demonstrate the usefulness and usability of the visualization in a user study that we conducted.
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Papers by Marc H. Scholl
This paper presents a visualization for monitoring the situation (current topics and emotions) in cities and about cities, which is reflected in the live message stream of the social microblogging service Twitter, by using continuously updating and with sentiment colored TagClouds.