Athena Vakali

Insight and perspectives for content delivery networks

Striking a balance between the costs for Web content providers and the quality of service for Web customers.

Content delivery networks: status and trends

CDNs improve network performance and offer fast and reliable applications and services by distributing content to cache servers located close to users. The Webs growth has transformed communications and business services such that speed, accuracy, and availability of network-delivered content has become absolutely critical - both on their own terms and in terms of measuring Web performance. Proxy servers partially address the need for rapid content delivery by providing multiple clients with a shared cache location. In this context, if a requested object exists in a cache (and the cached version has not expired), clients get a cached copy, which typically reduces delivery time. CDNs act as trusted overlay networks that offer high-performance delivery of common Web objects, static data, and rich multimedia content by distributing content load among servers that are close to the clients. CDN benefits include reduced origin server load, reduced latency for end users, and increased throughput. CDNs can also improve Web scalability and disperse flash-crowd events. Here we offer an overview of the CDN architecture and popular CDN service providers.

Community detection in Social Media

The proposed survey discusses the topic of community detection in the context of Social Media. Community detection constitutes a significant tool for the analysis of complex networks by enabling the study of mesoscopic structures that are often associated with organizational and functional characteristics of the underlying networks. Community detection has proven to be valuable in a series of domains, e.g. biology, social sciences, bibliometrics. However, despite the unprecedented scale, complexity and the dynamic nature of the networks derived from Social Media data, there has only been limited discussion of community detection in this context. More specifically, there is hardly any discussion on the performance characteristics of community detection methods as well as the exploitation of their results in the context of real-world web mining and information retrieval scenarios. To this end, this survey first frames the concept of community and the problem of community detection in the context of Social Media, and provides a compact classification of existing algorithms based on their methodological principles. The survey places special emphasis on the performance of existing methods in terms of computational complexity and memory requirements. It presents both a theoretical and an experimental comparative discussion of several popular methods. In addition, it discusses the possibility for incremental application of the methods and proposes five strategies for scaling community detection to real-world networks of huge scales. Finally, the survey deals with the interpretation and exploitation of community detection results in the context of intelligent web applications and services.

Content Delivery Networks

Content Delivery Networks enables the readers to understand the basics, to identify the underlying technology, to summarize their knowledge on concepts, ideas, principles and various paradigms which span on broad CDNs areas. Therefore, aspects of CDNs in terms of basics, design process, practice, techniques, performances, platforms, applications, and experimental results have been presented in a proper order. Fundamental methods, initiatives, significant research results, as well as references for further study have also been provided. Comparison of different design and development approaches are described at the appropriate places so that new researchers as well as advanced practitioners can use the CDNs evaluation as a research roadmap. All the contributions have been reviewed, edited, processed, and placed in the appropriate order to maintain consistency so that any reader irrespective of their level of knowledge and technological skills in CDNs would get the most out of it. The book is organized into three parts, namely, Part I: CDN Fundamentals; Part II: CDN Modeling and Performance; and Part III: Advanced CDN Platforms and Applications. The organization ensures the smooth flow of material as successive chapters build on prior ones.

Current Trends in Database Technology - EDBT 2004 Workshops

Session I: March 18, 2004, Heraklion, Crete, Greece.- Querying Sliding Windows Over Online Data Streams.- MIRA: Multilingual Information Processing on Relational Architecture.- Index-Based Keyword Search in Mediator Systems.- Concept-Based Search on Semi-structured Data Exploiting Mined Semantic Relations.- Distributed and Scalable Similarity Searching in Metric Spaces.- Pattern Based Management: Data Models and Architectural Aspects.- Managing Dynamic Repositories for Digital Content Components.- Semantic Web Recommender Systems.- Session II: March 29, 2004, Boston, MA, USA.- Trust Negotiation Systems.- Continuous Query Processing in Spatio-Temporal Databases.- Load Distribution for Distributed Stream Processing.- XML Query Processing and Optimization.- An Access Structure for Similarity Search in Metric Spaces.- Incremental Read-Aheads.- RAM: A Multidimensional Array DBMS.- Handling Inconsistencies in Data Warehouses.- Data Sharing and Querying for Peer-to-Peer Data Management Systems.- Relevance Feedback in XML Retrieval.- Database Technologies for Handling XML-Information on theWeb (DataX).- XML Challenges for the Database Community: Past, Present, and Future.- L-Tree: A Dynamic Labeling Structure for Ordered XML Data.- Implementation of XPath Axes in the Multi-dimensional Approach to Indexing XML Data.- Dynamic Range Labeling for XML Trees.- FliX: A Flexible Framework for Indexing Complex XML Document Collections.- A Statistical Approach for XML Query Size Estimation.- Summarizing XML Data by Means of Association Rules.- Prune XML Before You Search It: XML Transformations for Query Optimization.- Keeping Pace with Evolving XML-Based Specifications.- Knowledge Management Framework for the Collaborative Distribution of Information.- XML-Based Revocation and Delegation in a Distributed Environment.- Using a Transcode and Prefetch Method for Playing XML Contents Containing Multiple Multimedia Data on Mobile Terminals.- Whats Next in XML and Databases?.- Modeling Contextual Information Using Active Data Structures.- Context- and Situation-Awareness in Information Logistics.- An Indexing Scheme for Update Notification in Large Mobile Information Systems.- A Mobile Agents Based Architecture for the Distributed Processing of Continuous Location Queries in a Wireless Environment: Performance Evaluation.- Improving Usability of Location-Based Services with User-Centric Data Querying.- MITOS: A Smart Spaces System for Pervasive Computing.- Service Allocation in Selfish Mobile Ad hoc Networks Using Vickrey Auction.- Engineering Incentive Schemes for Ad hoc Networks.- The Case for Mobile OLAP.- Peer-to-Peer Computing and Databases (P2P&DB).- On Constructing Small Worlds in Unstructured Peer-to-Peer Systems.- SPROUT: P2P Routing with Social Networks.- A Simulation Framework for Schema-Based Query Routing in P2P-Networks.- A Distributed Algorithm for Robust Data Sharing and Updates in P2P Database Networks.- XPeer : A Self-Organizing XML P2P Database System.- Bit Zipper Rendezvous Optimal Data Placement for General P2P Queries.- Query Answering in Peer-to-Peer Data Exchange Systems.- Semantic Query Routing and Processing in P2P Database Systems: The ICS-FORTH SQPeer Middleware.- Query Processing in Super-Peer Networks with Languages Based on Information Retrieval: The P2P-DIET Approach.- A Query-Adaptive Partial Distributed Hash Table for Peer-to-Peer Systems.- P2PR-Tree: An R-Tree-Based Spatial Index for Peer-to-Peer Environments.- Clustering Information Over theWeb (ClustWeb).- Web Data Protection: Principles and Research Issues.- Clustering Structured Web Sources: A Schema-Based, Model-Differentiation Approach.- Clustering XML Documents Using Structural Summaries.- A Scalable Randomized Method to Compute Link-Based Similarity Rank on the Web Graph.- A Framework for Cluster Management.- Di?eminator: A Profile-Based Selective Dissemination System for XML Documents.- Query Recommendation Using Query Logs in Search Engines.- An Overview of Web Data Clustering Practices.

Intrusion detection in RBAC-administered databases

A considerable effort has been recently devoted to the development of database management systems (DBMS) which guarantee high assurance security and privacy. An important component of any strong security solution is represented by intrusion detection (ID) systems, able to detect anomalous behavior by applications and users. To date, however, there have been very few ID mechanisms specifically tailored to database systems. In this paper, we propose such a mechanism. The approach we propose to ID is based on mining database traces stored in log files. The result of the mining process is used to form user profiles that can model normal behavior and identify intruders. An additional feature of our approach is that we couple our mechanism with role based access control (RBAC). Under a RBAC system permissions are associated with roles, usually grouping several users, rather than with single users. Our ID system is able to determine role intruders, that is, individuals that while holding a specific role, have a behavior different from the normal behavior of the role. An important advantage of providing an ID mechanism specifically tailored to databases is that it can also be used to protect against insider threats. Furthermore, the use of roles makes our approach usable even for databases with large user population. Our preliminary experimental evaluation on both real and synthetic database traces show that our methods work well in practical situations

Cluster-Based Landmark and Event Detection for Tagged Photo Collections

An image analysis scheme can automate the detection of landmarks and events in large image collections, significantly improving the content-consumption experience.

Co-Clustering Tags and Social Data Sources

Under social tagging systems, a typical Web 2.0 application, users label digital data sources by using freely chosen textual descriptions (tags). Poor retrieval in the aforementioned systems remains a major problem mostly due to questionable tag validity and tag ambiguity. Earlier clustering techniques have shown limited improvements, since they were based mostly on tag co-occurrences. In this paper, a co-clustering approach is employed, that exploits joint groups of related tags and social data sources, in which both social and semantic aspects of tags are considered simultaneously. Experimental results demonstrate the efficiency and the beneficial outcome of the proposed approach in correlating relevant tags and resources.

Urban planning and smart cities: interrelations and reciprocities

Smart cities are emerging fast and they introduce new practices and services which highly impact policy making and planning, while they co-exist with urban facilities. It is now needed to understand the smart citys contribution in the overall urban planning and vice versa, to recognize urban planning offerings to a smart city context. This chapter highlights and measures smart city and urban planning interrelation and identifies the meeting points among them. Urban planning dimensions are drawn from the European Regional Cohesion Policy and they are associated with smart citys architecture layers.

LDAP: framework, practices, and trends

Directory services facilitate access to information organized under a variety of frameworks and applications. The lightweight directory access protocol is a promising technology that provides access to directory information using a data structure similar to that of the X.500 protocol. IBM Tivoli, Novell, Sun, Oracle, Microsoft, and many other vendors feature LDAP-based implementations. The technologys increasing popularity is due both to its flexibility and its compatibility with existing applications.