Social networking services (SNSs) such as Facebook and Twitter have experienced explosive growth during the few past years. Millions of users have created their profiles on these services because they experience great benefits in terms of friendship. SNSs can help people to maintain their friendships, organize their social lives, start new friendships, and meet others who share their hobbies and interests. However, all these benefits can be eclipsed by the privacy hazards that affect people in SNSs. People expose intimate information about their lives on SNSs, and this information affects the way others think about them. It is crucial that users be able to control how their information is distributed through the SNSs and decide who can access it. This article presents a list of privacy threats that can affect SNS users and what requirements privacy mechanisms should fulfill to prevent this threats. Then the article reviews current approaches and analyzes to what extent they cover the requirements.

In hard real-time systems, gain time is defined as the difference between the Worst Case Execution Time (WCET) of a hard task and its actual processor consumption at runtime. This paper presents the results of an empirical study about how the presence of a significant amount of gain time in a hard real-time system questions the advantages of using the most representative scheduling algorithms or policies for aperiodic or soft tasks in fixed-priority preemptive systems. The work presented here refines and complements many other studies in this research area in which such policies have been introduced and compared. This work has been performed by using the authors' testing framework for soft scheduling policies, which produces actual, synthetic, randomly generated applications, executes them in an instrumented Real-Time Operating System (RTOS), and finally processes this information to obtain several statistical outcomes. The results show that, in general, the presence of a significant amount of gain time reduces the performance benefit of the scheduling policies under study when compared to serving the soft tasks in background, which is considered the theoretical worst case. In some cases, this performance benefit is so small that the use of a specific scheduling policy for soft tasks is questionable.

Abstract Security is becoming a major concern in multiagent systems, since an agent's incorrect or inappropriate behaviour may cause non‐desired effects, such as money and data loss. Some multiagent platforms (MAP) are now providing baseline security features, such as authentication, authorization, integrity and confidentiality. However, they fail to support other features related to the sociability skills of agents such as agent groups. What is more, none of the listed MAPs provide a mechanism for preserving the privacy of the users (regarding their identities) that run their agents on such MAPs. In this paper, we present the security infrastructure (SI) of the Magentix MAP, which supports agent groups and preserves user identity privacy. The SI is based on identities that are assigned to all the different entities found in Magentix (users, agents and agent groups). We also provide an evaluation of the SI describing an example application built on top of Magentix and a performance evaluation of it. Copyright © 2010 John Wiley & Sons, Ltd.

Abstract In embedded systems, the typical host/target development scheme normally requires a tracing mechanism to be available in the target system in order to collect run‐time information of the application. This information is then used in the host system to debug, monitor, fine tune, etc., the application. Related to this, POSIX has recently incorporated the definition of standard tracing services into the complete POSIX 1003.1‐2001 standard. It is obvious that standard interfaces present several advantages for applications, specially regarding portability. However, the observed trend in real‐time operating systems (RTOSs) of progressively incorporating the POSIX interfaces have not reached the POSIX tracing services. As far as we know, this tracing interface has not been incorporated yet into any commercial RTOS, probably because it is quite recent and its tracing model is too complex and demanding for small, embedded real‐time systems. After carefully analyzing and then implementing and using the POSIX Trace standard in both RT‐Linux and MarteOS, this paper presents the redefinition of the POSIX tracing standard from the perspective of small real‐time systems and, in particular, systems conforming to the POSIX Minimal Realtime System Profile (MRSP). The new tracing model is calledLightweight POSIX tracing. The model has been carefully designed to maintain all the syntax, and almost all the semantics, of the original standard, but it allows for the definition of useful subsets of the original standard that can be implemented very efficiently. The experimental results show that a minimal tracing system which is appropriate for MRSP systems exhibits a significantly smaller memory footprint and lower overhead, compared to the implementation of the complete standard. Copyright © 2007 John Wiley & Sons, Ltd.