INESC-ID

About: INESC-ID is a nonprofit organization based out in Lisbon, Portugal. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 932 authors who have published 2618 publications receiving 37658 citations.

SCert: Speculative certification in replicated software transactional memories

Abstract: Being much simpler to compose and verify than classical lock based synchronization schemes, Software Transactional Memories (STMs) have emerged as an attractive paradigm for supporting concurrent access to in-memory storage systems. This paper is focused on the issue of how to replicate STMs to enhance both their performance and dependability. This is an extremely challenging problem, since the communication/processing ratio in STMs is typically several orders of magnitude higher than in conventional database systems, thus amplifying the relative cost of replication.We present SCert (Speculative Certification), a novel replication protocol for STMs that exploits early knowledge about message ordering in the underlying atomic broadcast layer to propagate, in a speculative fashion, the updates of transactions before there is an agreement on the final serialization order. This speculative approach brings the two following key benefits. On one hand, it lowers the chances that transactions access stale snapshots, thus minimizing the probability of later incurring in an abort. On the other hand, it provides early conflict detection, thus reducing the amount of wasted computation and/or waiting time from transactions doomed to abort. An experimental study of SCert, based on a fully fledged distributed STM prototype and heterogeneous benchmarks, has shown performance gains of up to 4.5x when compared with previous certification based schemes.

Interoperable Intelligent Tutoring Systems as Open Educational Resources

Abstract: Because of interoperability issues, intelligent tutoring systems are difficult to deploy in current educational platforms without additional work. This limitation is significant because tutoring systems require considerable time and resources for their implementation. In addition, because these tutors have a high educational value, it is desirable that they could be shared, used by many stakeholders, and easily loaded onto different platforms. This paper describes a new approach to implementing open-source and interoperable intelligent tutors through standardization. In contrast to other methods, our technique does not require using nonstandardized peripheral systems or databases, which would restrict the interoperability of learning objects. Thus, our approach has the advantage of yielding tutors that are fully conformant to e-learning standards and that are free of external resource dependencies. According to our method, "atomic" tutoring systems are grouped to create "molecular" tree structures that cover course modules. In addition, given the interoperability of our technique, tutors can also be combined to create courses that have distinct granularities, topics, and target students. The key to our method is the focus on assuring what defines a tutor in terms of behavior and functionalities (inner loops and outer loops). Our proof of concept was developed using SCORM standards. This paper presents the implementation details of our technique, including the theoretical concepts, technical specifications, and practical examples.

Efficient resource allocation for multicast transmissions in Satellite-LTE networks

Abstract: This paper deals with the management of multicast transmissions in Satellite-Long Term Evolution (S-LTE) networks. With the purpose of offering high session quality by exploiting the multi-user diversity, we propose a framework for multicast subgroup formation in satellite networks. In particular, the idea at the basis of the proposed solution is to split the multicast satellite users in subgroups, according to the experienced channel conditions. Such an approach allows to convey multicast content without requiring additional data coding and guarantees high throughput and user fairness. The comparison among the results achieved through the designed framework and those present in literature demonstrates the effectiveness of the proposed approach for providing efficient multicast transmissions via satellite.