Prefetching techniques for client server object-oriented database systems

The performance of many object-oriented database applications suffers from the page fetch latency which is determined by the expense of disk access. In this work we suggest several prefetching techniques to avoid, or at least to reduce, page fetch latency. In practice no prediction technique is perfect and no prefetching technique can entirely eliminate delay due to page fetch latency. Therefore we are interested in the trade-off between the level of accuracy required for obtaining good results in terms of elapsed time reduction and the processing overhead needed to achieve this level of accuracy. If prefetching accuracy is high then the total elapsed time of an application can be reduced significantly otherwise if the prefetching accuracy is low, many incorrect pages are prefetched and the extra load on the client, network, server and disks decreases the whole system performance. Access pattern of object-oriented databases are often complex and usually hard to predict accurately. The ..

Distributed multimedia systems

A distributed multimedia system (DMS) is an integrated communication, computing, and information system that enables the processing, management, delivery, and presentation of synchronized multimedia information with quality-of-service guarantees. Multimedia information may include discrete media data, such as text, data, and images, and continuous media data, such as video and audio. Such a system enhances human communications by exploiting both visual and aural senses and provides the ultimate flexibility in work and entertainment, allowing one to collaborate with remote participants, view movies on demand, access on-line digital libraries from the desktop, and so forth. In this paper, we present a technical survey of a DMS. We give an overview of distributed multimedia systems, examine the fundamental concept of digital media, identify the applications, and survey the important enabling technologies.published_or_final_versio

Annotierte interaktive nichtlineare Videos - Software Suite, Download- und Cache-Management

Modern Web technology makes the dream of fully interactive and enriched video come true. Nowadays it is possible to organize videos in a non-linear way playing in a sequence unknown in advance. Furthermore, additional information can be added to the video, ranging from short descriptions to animated images and further videos. This affords an easy and efficient to use authoring tool which is capable of the management of the single media objects, as well as a clear arrangement of the links between the parts. Tools of this kind can be found rarely and do mostly not provide the full range of needed functions. While providing an interactive experience to the viewer in the Web player, parallel plot sequences and additional information lead to an increased download volume. This may cause pauses during playback while elements have to be downloaded which are displayed with the video. A good quality of experience for these videos with small waiting times and a playback without interruptions is desired. This work presents the SIVA Suite to create the previously described annotated interactive non-linear videos. We propose a video model for interactivity, non-linearity, and annotations, which is implemented in an XML format, an authoring tool, and a player. Video is the main medium, whereby different scenes are linked to a scene graph. Time controlled additional content called annotations, like text, images, audio files, or videos, is added to the scenes. The user is able to navigate in the scene graph by selecting a button at a button panel. Furthermore, other navigational elements like a table of contents or a keyword search are provided. Besides the SIVA Suite, this thesis presents algorithms and strategies for download and cache management to provide a good quality of experience while watching the annotated interactive non-linear videos. Therefor, we implemented a standard-independent player framework. Integrated into a simulation environment, the framework allows to evaluate algorithms and strategies for the calculation of start-up times, and the selection of elements to pre-fetch into and delete from the cache. Their interaction during the playback of non-linear video contents can be analyzed. The algorithms and strategies can be used to minimize interruptions in the video flow after user interactions. Our extensive evaluation showed that our techniques result in faster start-up times and lesser interruptions in the video flow than those of other players. Knowledge of the structure of an interactive non-linear video can be used to minimize the start-up time at the beginning of a video while minimizing an increase in the overall download volume.Moderne Web-Technologien lassen den Traum von voll interaktiven und bereicherten Videos wahr werden. Heutzutage ist es möglich, Videos in nicht-linearer Art und Weise zu organisieren, welche dann in einer vorher unbekannten Reihenfolge abgespielt werden können. Weiterhin können den Videos Zusatzinformationen in Form von kurzen Beschreibungen über animierte Bilder bis hin zu weiteren Videos hinzugefügt werden. Dies erfordert ein einfach und effizient zu bedienendes Autorenwerkzeug, das in der Lage ist, sowohl einzelne Medien-Objekte zu verwalten, als auch die Verbindungen zwischen den einzelnen Teilen klar darzustellen. Tools dieser Art sind selten und bieten meist nicht den vollen benötigten Funktionsumfang. Während dem Betrachter dieses interaktive Erlebnis im Web Player zur Verfügung gestellt wird, führen parallele Handlungsstränge und zusätzliche Inhalte zu einem erhöhten Download-Volumen. Dies kann zu Pausen während der Wiedergabe führen, in denen Elemente vom Server geladen werden müssen, welche mit dem Video angezeigt werden sollen. Ein gutes Benutzungserlebnis für solche Videos kann durch geringe Wartezeiten und eine unterbrechungsfreie Wiedergabe erreicht werden. Diese Arbeit stellt die SIVA Suite vor, mit der die zuvor beschriebenen annotierten interaktiven nicht-linearen Videos erstellt werden können. Wir bilden Interaktivität, Nichtlinearität und Annotationen in einem Video-Model ab. Dieses wird in unserem XML-Format, Autorentool und Player umgesetzt. Als Leitmedium werden hierbei Videos verwendet, welche aufgeteilt in Szenen zu einer Graphstruktur zusammengefügt werden können. Zeitlich gesteuerte zusätzliche Inhalte, sogenannte Annotationen, wie Texte, Bilder, Audio-Dateien und Videos, werden den Szenen hinzugefügt. Der Betrachter kann im Szenengraph navigieren, indem er in einem bereitgestellten Button-Panel eine Nachfolgeszene auswählt. Andere Navigationselemente sind ein Inhaltsverzeichnis sowie eine Suchfunktion. Neben der SIVA Suite beschreibt diese Arbeit Algorithmen und Strategien für Download und Cache Management, um eine gute Nutzungserfahrung während der Betrachtung der annotierten interaktiven nicht-linearen Videos zu bieten. Ein Webstandard-unabhängiges Playerframework erlaubt es, das Zusammenspiel von Algorithmen und Strategien zu evaluieren, welche für die Berechnung der Start-Zeitpunkte für die Wiedergabe, sowie die Auswahl von vorauszuladenden sowie zu löschenden Elemente verwendet werden. Ziel ist es, Unterbrechungen zu minimieren, wenn der Ablauf des Videos durch Benutzerinteraktion beeinflusst wird. Unsere umfassende Evaluation zeigte, dass es möglich ist, kürzere Startup-Zeiten und weniger Unterbrechungen mit unseren Strategien zu erreichen, als bei der Verwendung der Strategien anderer Player. Die Kenntnis der Struktur des interaktiven nicht-linearen Videos kann dazu verwendet werden, die Startzeit am Anfang der Szenen zu minimieren, während das Download-Volumen nicht erhöht wird

Building Internet caching systems for streaming media delivery

The proxy has been widely and successfully used to cache the static Web objects fetched by a client so that the subsequent clients requesting the same Web objects can be served directly from the proxy instead of other sources faraway, thus reducing the server\u27s load, the network traffic and the client response time. However, with the dramatic increase of streaming media objects emerging on the Internet, the existing proxy cannot efficiently deliver them due to their large sizes and client real time requirements.;In this dissertation, we design, implement, and evaluate cost-effective and high performance proxy-based Internet caching systems for streaming media delivery. Addressing the conflicting performance objectives for streaming media delivery, we first propose an efficient segment-based streaming media proxy system model. This model has guided us to design a practical streaming proxy, called Hyper-Proxy, aiming at delivering the streaming media data to clients with minimum playback jitter and a small startup latency, while achieving high caching performance. Second, we have implemented Hyper-Proxy by leveraging the existing Internet infrastructure. Hyper-Proxy enables the streaming service on the common Web servers. The evaluation of Hyper-Proxy on the global Internet environment and the local network environment shows it can provide satisfying streaming performance to clients while maintaining a good cache performance. Finally, to further improve the streaming delivery efficiency, we propose a group of the Shared Running Buffers (SRB) based proxy caching techniques to effectively utilize proxy\u27s memory. SRB algorithms can significantly reduce the media server/proxy\u27s load and network traffic and relieve the bottlenecks of the disk bandwidth and the network bandwidth.;The contributions of this dissertation are threefold: (1) we have studied several critical performance trade-offs and provided insights into Internet media content caching and delivery. Our understanding further leads us to establish an effective streaming system optimization model; (2) we have designed and evaluated several efficient algorithms to support Internet streaming content delivery, including segment caching, segment prefetching, and memory locality exploitation for streaming; (3) having addressed several system challenges, we have successfully implemented a real streaming proxy system and deployed it in a large industrial enterprise

Techniques of data prefetching, replication, and consistency in the Internet

Internet has become a major infrastructure for information sharing in our daily life, and indispensable to critical and large applications in industry, government, business, and education. Internet bandwidth (or the network speed to transfer data) has been dramatically increased, however, the latency time (or the delay to physically access data) has been reduced in a much slower pace. The rich bandwidth and lagging latency can be effectively coped with in Internet systems by three data management techniques: caching, replication, and prefetching. The focus of this dissertation is to address the latency problem in Internet by utilizing the rich bandwidth and large storage capacity for efficiently prefetching data to significantly improve the Web content caching performance, by proposing and implementing scalable data consistency maintenance methods to handle Internet Web address caching in distributed name systems (DNS), and to handle massive data replications in peer-to-peer systems. While the DNS service is critical in Internet, peer-to-peer data sharing is being accepted as an important activity in Internet.;We have made three contributions in developing prefetching techniques. First, we have proposed an efficient data structure for maintaining Web access information, called popularity-based Prediction by Partial Matching (PB-PPM), where data are placed and replaced guided by popularity information of Web accesses, thus only important and useful information is stored. PB-PPM greatly reduces the required storage space, and improves the prediction accuracy. Second, a major weakness in existing Web servers is that prefetching activities are scheduled independently of dynamically changing server workloads. Without a proper control and coordination between the two kinds of activities, prefetching can negatively affect the Web services and degrade the Web access performance. to address this problem, we have developed a queuing model to characterize the interactions. Guided by the model, we have designed a coordination scheme that dynamically adjusts the prefetching aggressiveness in Web Servers. This scheme not only prevents the Web servers from being overloaded, but it can also minimize the average server response time. Finally, we have proposed a scheme that effectively coordinates the sharing of access information for both proxy and Web servers. With the support of this scheme, the accuracy of prefetching decisions is significantly improved.;Regarding data consistency support for Internet caching and data replications, we have conducted three significant studies. First, we have developed a consistency support technique to maintain the data consistency among the replicas in structured P2P networks. Based on Pastry, an existing and popular P2P system, we have implemented this scheme, and show that it can effectively maintain consistency while prevent hot-spot and node-failure problems. Second, we have designed and implemented a DNS cache update protocol, called DNScup, to provide strong consistency for domain/IP mappings. Finally, we have developed a dynamic lease scheme to timely update the replicas in Internet

Extensions to the SMIL multimedia language

The goal of this work has been to extend the Synchronized Multimedia Integration Language (SMIL) to study the capabilities and possibilities of declarative multimedia languages for the World Wide Web (Web). The work has involved design and implementation of several extensions to SMIL. A novel approach to include 3D audio in SMIL was designed and implemented. This involved extending the SMIL 2D spatial model with an extra dimension to support a 3D space. New audio elements and a listening point were positioned in the 3D space. The extension was designed to be modular so that it was possible to use it in conjunction with other XML languages, such as XHTML and Scalable Vector Graphics (SVG) language. Web forms are one of the key features in the Web, as they offer a way to send user data to a server. A similar feature is therefore desirable in SMIL, which currently lacks forms. The XForms language, due to its modular approach, was used to add this feature to SMIL. An evaluation of this integration was carried out as part of this work. Furthermore, the SMIL player was designed to play out dynamic SMIL documents, which can be modified at run-time and the result is immediately reflected in the presentation. Dynamic SMIL enables execution of scripts to modify the presentation. XML Events and ECMAScript were chosen to provide the scripting functionality. In addition, generic methods to extend SMIL were studied based on the previous extensions. These methods include ways to attach new input and output capabilities to SMIL. To experiment with the extensions, a Synchronized Multimedia Integration Language (SMIL) player was developed. The current final version can play out SMIL 2.0 Basic profile documents with a few additional SMIL modules, such as event timing, basic animations, and brush media modules. The player includes all above-mentioned extensions. The SMIL player has been designed to work within an XML browser called X-Smiles. X-Smiles is intended for various embedded devices, such as mobile phones, Personal Digital Assistants (PDA), and digital television set-top boxes. Currently, the browser supports XHTML, SMIL, and XForms, which are developed by the current research group. The browser also supports other XML languages developed by 3rd party open-source projects. The SMIL player can also be run as a standalone player without the browser. The standalone player is portable and has been run on a desktop PC, PDA, and digital television set-top box. The core of the SMIL player is platform-independent, only media renderers require platform-dependent implementation.reviewe

Supervision de contenus multimédia : adaptation de contenu, politiques optimales de préchargement et coordination causale de flux

La qualité des systèmes d'informations distribués dépend de la pertinence du contenu mis à disposition, de la réactivité du service ainsi que de la cohérence des informations présentées. Nos travaux visent à améliorer ces trois critères de performance et passent par la prise en compte des caractéristiques de l'utilisateur, des ressources disponibles ou plus généralement du contexte d'exécution. Par conséquent, cette thèse comporte trois volets. Le premier volet se place dans le cadre de l'adaptation de systèmes d’information déployés dans des contextes dynamiques et stochastiques. Nous présentons une approche où des agents d’adaptation appliquent des politiques de décision séquentielle dans l'incertain. Nous modélisons ces agents par des Processus Décisionnels de Markov (PDM) selon que le contexte soit observable ou seulement partiellement observable (PDM Partiellement Observables). Dans le cas d’un service mobile de consultation de films, nous montrons en particulier qu’une politique d'adaptation de ce service à des ressources limitées peut être nuancée selon l'intérêt de l'utilisateur, estimé grâce à l’évaluation des signaux de retour implicite. Dans le deuxième volet, nous nous intéressons à l'optimisation de la réactivité d'un système qui propose des contenus hypermédia. Nous nous appuyons sur des techniques de préchargement pour réduire les latences. Comme précédemment, un PDM modélise les habitudes des utilisateurs et les ressources disponibles. La force de ce modèle réside dans sa capacité à fournir des politiques optimales de préchargement. Les premières politiques que nous obtenons sont simples. Nous enrichissons alors le modèle pour dériver des politiques de préchargement plus complexes et plus agressives et montrons leurs performances par simulation. Afin de personnaliser nos stratégies optimales nous proposons finalement un modèle PDMPO dont les politiques s'adaptent aux profils des utilisateurs. Le troisième volet se place dans le contexte des applications multimédia interactives distribuées et concerne le contrôle de la cohérence des flux multimédia répartis. Dans un tel contexte, plusieurs mécanismes de synchronisation sont nécessaires et plusieurs ordres logiques (fifo, causal, total) s'avèrent utiles. Nous proposons une boîte à outils capable de gérer plusieurs protocoles d’ordre partiel et d'assurer une délivrance correcte de chaque message, en respectant tous les ordres qui lui ont été imposés. Nous décrivons ensuite l’intégration des tolérances humaines vis-à-vis des courtes incohérences causales dans notre boîte à outils. Nos simulations montrent que de meilleures performances sont obtenues par cette méthode comparativement à d’autres approches, comme la causalité classique ou la Δ-causalité. ABSTRACT : Distributed systems information quality depends on service responsiveness, data consistency and its relevance according to user interests. The thesis aims to improve these three performance criteria by taking into account user characteristics, available ressources or more generally execution context. Naturally, the document is organized in three main parts. The first part discusses adaptation policies for information systems that are subject to dynamic and stochastic contexts. In our approach adaptation agents apply sequential decisional policies under uncertainty. We focus on the modeling of such decisional processes depending on whether the context is fully or partially observable. We use Markov Decision Processes (MDP) and Partially Observable MDP (POMDP) for modeling a movie browsing service in a mobile environment. Our model derives adaptation policies for this service that take into account the limited (and observable) resources. These policies are further refined according to the (partially observable) users’ interest level estimated from implicit feedback. Our theoretical models are validated through numerous simulations. The second part deals with hypermedia content delivery aiming to reduce navigation latencies by means of prefetching. As previously, we build upon an MDP model able to derive optimal prefetching policies integrating both user behaviour and ressource availability. First, we extend this model and propose more complex and aggressive policies. Second, the extended model is enriched by taking into account user's profile and therefore provides finer prefetching policies. It is worth noting that this model issues personnalized policies without explicily manipulating user profiles. The proposed extensions and the associated policies are validated through comparison with the original model and some heuristic approches. Finally, the third part considers multimedia applications in distributed contexts. In these contexts, highly interactive collaborative applications need to offer each user a consistent view of the interactions represented by the streams exchanged between dispersed groups of users. At the coordination level, strong ordering protocols for capturing and delivering streams' interactions (e.g. CAUSAL, TOTAL order) may be too expensive due to the variability of network conditions. We build upon previous work on expressing streams causality and propose a flexible coordination middleware for integrating different delivery modes (e.g. FIFO, CAUSAL, TOTAL) into a single channel (with respect to each of these protocols). Moreover, the proposed abstract channel can handle the mix of any partial or total order protocols. Integrating perceptual tolerance in our middleware, provides us with a coordination toolkit that performs better than Δ-causality, usually considered the best solutio

Research and Technology Highlights 1995

The mission of the NASA Langley Research Center is to increase the knowledge and capability of the United States in a full range of aeronautics disciplines and in selected space disciplines. This mission is accomplished by performing innovative research relevant to national needs and Agency goals, transferring technology to users in a timely manner, and providing development support to other United States Government agencies, industry, other NASA Centers, the educational community, and the local community. This report contains highlights of the major accomplishments and applications that have been made by Langley researchers and by our university and industry colleagues during the past year. The highlights illustrate both the broad range of research and technology (R&T) activities carried out by NASA Langley Research Center and the contributions of this work toward maintaining United States leadership in aeronautics and space research. An electronic version of the report is available at URL http://techreports.larc.nasa.gov/RandT95. This color version allows viewing, retrieving, and printing of the highlights, searching and browsing through the sections, and access to an on-line directory of Langley researchers

Summary of Research 1994

The views expressed in this report are those of the authors and do not reflect the official policy or position of the Department of Defense or the U.S. Government.This report contains 359 summaries of research projects which were carried out under funding of the Naval Postgraduate School Research Program. A list of recent publications is also included which consists of conference presentations and publications, books, contributions to books, published journal papers, and technical reports. The research was conducted in the areas of Aeronautics and Astronautics, Computer Science, Electrical and Computer Engineering, Mathematics, Mechanical Engineering, Meteorology, National Security Affairs, Oceanography, Operations Research, Physics, and Systems Management. This also includes research by the Command, Control and Communications (C3) Academic Group, Electronic Warfare Academic Group, Space Systems Academic Group, and the Undersea Warfare Academic Group

Second Annual Workshop on Space Operations Automation and Robotics (SOAR 1988)

Papers presented at the Second Annual Workshop on Space Operation Automation and Robotics (SOAR '88), hosted by Wright State University at Dayton, Ohio, on July 20, 21, 22, and 23, 1988, are documented herein. During the 4 days, approximately 100 technical papers were presented by experts from NASA, the USAF, universities, and technical companies. Panel discussions on Human Factors, Artificial Intelligence, Robotics, and Space Systems were held but are not documented herein. Technical topics addressed included knowledge-based systems, human factors, and robotics