A range of applications, from predicting the spread of human and electronic viruses to city planning and resource management in mobile communications, depend on our ability to foresee the whereabouts and mobility of individuals, raising a fundamental question: To what degree is human behavior predictable? Here we explore the limits of predictability in human dynamics by studying the mobility patterns of anonymized mobile phone users. By measuring the entropy of each individual's trajectory, we find a 93% potential predictability in user mobility across the whole user base. Despite the significant differences in the travel patterns, we find a remarkable lack of variability in predictability, which is largely independent of the distance users cover on a regular basis.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-007155.pdf

Limits of predictability in human mobility

Today's real-time systems (RTS) are characterized by managing large volumes of dispersed data making real-time distributed data processing a reality. Large business houses need to do distributed processing for many reasons, and they often must do it in order to stay competitive. So, efficient database management algorithms and protocols for accessing and manipulating data are required to satisfy timing constraints of supported applications. Therefore, new research in distributed real-time database systems (DRTDBS) is needed to investigate possible ways of applying database systems technology to real-time systems. This paper first discusses the performance issues that are important to DRTDBS, and then surveys the research that has been done so far on the issues like priority assignment policy, commit protocols and optimizing the use of memory in non-replicated/replicated environment pertaining to distributed real time transaction processing. In fact, this study provides a foundation for addressing performance issues important for the management of very large real time data and pointer to other publications in journals and conference proceedings for further investigation of unanswered research questions.

Distributed real time database systems: background and literature review

The TCP/IP stack plays an important role in terms of data transmission, traffic control and address assignment in the Internet of Vehicles (IoV), which has seen phenomenal growth in recent years. However, with the increasing technical requirements and daily demand in IoV, the drawbacks of traditional TCP/IP protocols, e.g., weak scalability in large networks, low efficiency in the dense environment and unreliable addressing in high mobility circumstance, become non-trivial especially in vehicular environments. Fortunately, the emerging Named Data Networking (NDN) technology provides a good choice to address the above issues in vehicular environments. Specifically, the introduced content store module in NDN which caches the sent/received contents, can greatly improve the networking performance by suppressing redundancy as well as enriching diversity. With aforementioned motivations, we thoroughly studied previous works on Vehicular Named Data Networking (VNDN) with emphasis on content caching, and then demonstrate the feasibility and necessity for employing NDN in vehicular environments with the help of content caching. Subsequently, we further strengthened the importance of cache selection and replacement strategies in VNDN framework, which is positioned to meet the challenges of data transmission efficiency and resource consumption by leveraging in-network vehicular caching. After that, we engaged in an in-depth survey on the existing cache selection and replacement schemes in VNDN, with their applicability compared. Next, further challenges during caching design were elaborately analyzed considering the specific characteristics of VNDN. Finally, we highlighted the potential research directions which may shine lights on the promising efforts to improve the performance of VNDN content caching.

Caching in Vehicular Named Data Networking: Architecture, Schemes and Future Directions

As robotic systems become more and more advanced the need to integrate existing deliberative functionalities such as chronicle recognition, motion planning, task planning, and execution monitoring ...

/pdf/dyknow-a-stream-based-knowledge-processing-middleware-4ah2nj6jj6.pdf

DyKnow : A Stream-Based Knowledge Processing Middleware Framework

A method of insuring the integrity of a plurality of updates brought in real-time to a production database concurrently used by one or more software applications is described. The production database includes a plurality of products participating to the definition of objects. The method first includes requesting the issuance of a unique filing number associated to a draft state version of the plurality of updates while keeping them invisible to the end-users of the production database. Then, a set of product items identified as a whole by the unique filing number are created or copied from the production database and gathered under the form of a meta-product on which the plurality of updates is applied. After updating, the meta-product is successively set into a customizable flow of one or more validation states in order to perform a cross-validation of the plurality of updates. After validation, the meta-product is set into a production state where the uniquely identified meta-product becomes immediately visible and useable by the end-users.

Method allowing validation in a production database of new entered data prior to their release

Although there are several factors contributing to the difficulty in meeting distributed real time transaction deadlines, data conflicts among transactions, especially in commitment phase, are the prime factor resulting in system performance degradation. Therefore, design of an efficient commit protocol is of great significance for distributed real time database systems (DRTDBS). Most of the existing commit protocols try to improve system performance by allowing a committing cohort to lend its data to an executing cohort, thus reducing data inaccessibility. These protocols block the borrower when it tries to send WORKDONE/PREPARED message [1, 6, 8, 9], thus increasing the transactions commit time. This paper first analyzes all kind of dependencies that may arise due to data access conflicts among executing-committing transactions when a committing cohort is allowed to lend its data to an executing cohort. It then proposes a static two-phase locking and high priority based, write-update type, ideal for fast and timeliness commit protocol i.e. SWIFT. In SWIFT, the execution phase of a cohort is divided into two parts, locking phase and processing phase and then, in place of WORKDONE message, WORKSTARTED message is sent just before the start of processing phase of the cohort. Further, the borrower is allowed to send WORKSTARTED message, if it is only commit dependent on other cohorts instead of being blocked as opposed to [1, 6, 8, 9]. This reduces the time needed for commit processing and is free from cascaded aborts. To ensure non-violation of ACID properties, checking of completion of processing and the removal of dependency of cohort are required before sending the YES-VOTE message. Simulation results show that SWIFT improves the system performance in comparison to earlier protocol. The performance of SWIFT is also analyzed for partial read-only optimization, which minimizes intersite message traffic, execute-commit conflicts and log writes consequently resulting in a better response time. The impact of permitting the cohorts of the same transaction to communicate with each other [5] on SWIFT has also been analyzed.

SWIFT--A new real time commit protocol

IDRC: A Distributed Real-Time Commit Protocol

Transaction scheduling protocols for controlling priority inversion: A review

Database performance is an important aspect of database usability. Distributed real time database systems (DRTDBS) must be designed on all levels of database architecture to support timely execution of requests. The primary performance objective in DRTDBS is to minimize the number of missed deadlines. Due to the demanding nature of this objective, traditional approaches are inadequate. However, the research in DRTDBS has been mostly devoted to extending traditional transaction processing techniques to solve the issues important for the design of DRTDBS. In this environment, new policies/protocols must be designed to efficiently handle the transactions execution. Our works involves design of new priority assignment policies and commit protocols and comparison of their performances with existing policies/protocols.

/pdf/some-performance-issues-in-distributed-real-time-database-3l5k7en4yg.pdf

Udai Shanker

Papers

Distributed real time database systems: background and literature review

SWIFT--A new real time commit protocol

IDRC: A Distributed Real-Time Commit Protocol

Transaction scheduling protocols for controlling priority inversion: A review

Some Performance Issues in Distributed Real Time Database Systems