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Projeto de investigação
NOVA Laboratory for Computer Science and Informatics
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Publicações
Overlay Networks for Edge Management
Publication . Costa, Pedro Akos; Fouto, Pedro; Leitão, João; DI - Departamento de Informática; NOVALincs
Edge computing has emerged as a solution to address existing limitations of cloud computing for bandwidth-heavy and time-sensitive applications, by moving (some) computations from bandwidth saturated Cloud infrastructures closer to client devices, where data is effectively produced and consumed. However, existing materializations of the edge computing paradigm take limited advantage of computational and storage power that exists in the edge and between client devices and the cloud. Most of these leverage static hierarchical topologies (e.g., Fog Computing) to pre-process data before sending it to the Cloud, which limits the advantages that can be extracted from the edge computing paradigm. In the past, peer-to-peer systems have sought to tackle the challenges of increasing scalability and availability for very large systems, with a large number of solutions being proposed namely, distributed overlay networks for resource management. In this paper, we argue that the clever adaptation of peer-to-peer solutions can enable novel applications to fully exploit the potential of the edge. In particular, we study the viability of taking advantage of specialized overlay networks in edge environments to enable the management of a large number of computational resources. Contrary to previous proposals, that assume the environment to be composed of mostly homogeneous devices, our proposal embraces existing heterogeneity and exploits the location of computational resources to devise a (partially) self-organizing overlay network that can be exploited both to provide membership information to applications, but also do efficiently disseminate management information across edge devices. We have conducted an experimental evaluation using container-based emulation in an heterogeneous network composed by 100 devices, with results showing that our protocol is able to maximize the bandwidth usage of the system, allowing more data to flow throughout the network, while retaining high robustness to failures.
Data Storage and Dissemination in Pervasive Edge Computing Environments
Publication . Silva, João André Almeida e; Paulino, Hervé; Lourenço, João
Nowadays, smart mobile devices generate huge amounts of data in all sorts of gatherings.
Much of that data has localized and ephemeral interest, but can be of great use if shared
among co-located devices. However, mobile devices often experience poor connectivity,
leading to availability issues if application storage and logic are fully delegated to a
remote cloud infrastructure. In turn, the edge computing paradigm pushes computations
and storage beyond the data center, closer to end-user devices where data is generated
and consumed. Hence, enabling the execution of certain components of edge-enabled
systems directly and cooperatively on edge devices.
This thesis focuses on the design and evaluation of resilient and efficient data storage
and dissemination solutions for pervasive edge computing environments, operating with
or without access to the network infrastructure. In line with this dichotomy, our goal can
be divided into two specific scenarios. The first one is related to the absence of network
infrastructure and the provision of a transient data storage and dissemination system
for networks of co-located mobile devices. The second one relates with the existence of
network infrastructure access and the corresponding edge computing capabilities.
First, the thesis presents time-aware reactive storage (TARS), a reactive data storage
and dissemination model with intrinsic time-awareness, that exploits synergies between
the storage substrate and the publish/subscribe paradigm, and allows queries within a
specific time scope. Next, it describes in more detail: i) Thyme, a data storage and dis-
semination system for wireless edge environments, implementing TARS; ii) Parsley, a
flexible and resilient group-based distributed hash table with preemptive peer relocation
and a dynamic data sharding mechanism; and iii) Thyme GardenBed, a framework
for data storage and dissemination across multi-region edge networks, that makes use of
both device-to-device and edge interactions.
The developed solutions present low overheads, while providing adequate response
times for interactive usage and low energy consumption, proving to be practical in a
variety of situations. They also display good load balancing and fault tolerance properties.
Access Control in Weakly Consistent Systems
Publication . Costa, Tiago Miguel Ferreira da; Leitão, João
Eventually consistent models have become popular in the last years in data storage
systems for cloud environments, allowing to give users better availability and lower
latency. In this model, it is possible for replicas to be temporarily inconsistent, having
been proposed various solutions to deal with this inconsistency and ensure the final
convergence of data. However, defining and enforcing access control policies under this model is still an open challenge.
The implementation of access control policies for these systems raises it’s own challenges, given the information about the permissions is itself kept in a weakly consistent form. In this dissertation, a solution for this problem is proposed, that allows to prevent the non authorized access and modification of data.
The proposed solution allows concurrent modifications on the security policies, ensuring their convergence when they are used to verify and enforce access control the associated data. In this dissertation we present an evaluation of the proposed model, showing the solution respects the correct functioning over possible challenging situations, also discussing its application on scenarios that feature peer-to-peer communication between clients and additional replicas on the clients, with the goal of providing a lower latency and reduce the load on centralized components.
Robust Contract Evolution in a TypeSafe MicroService Architectures
Publication . Seco, João Costa; Ferreira, Paulo; Lourenço, Hugo; Ferreira, Carla; Ferrão, Lúcio; NOVALincs; AOSA Inc.
Microservice architectures allow for short deployment cycles and immediate effects, but offer no safety mechanisms for service contracts when they need to be changed. Maintaining the soundness of microservice architectures is an error-prone task that is only accessible to the most disciplined development teams. The strategy to evolve a producer service without disrupting its consumers is often to maintain multiple versions of the same interface and dealing with an explicitly managed handoff period and its inherent disadvantages. We present a microservice management system that statically verifies service interface signatures against their references and supports the seamless evolution of compatible interfaces. We define a compatibility relationon types that captures real evolution patterns and embodies known good practices on the evolution of interfaces. Namely, we allow for addition, removal, and renaming of data fields of a producer module without breaking or needing to upgrade consumer services. The evolution of interfaces is supported by runtime generated proxy components that dynamically adapt data exchanged between services to match with the statically checked service code. The model proposed in this paper is instantiated in a core programming language whose semantics is defined by a labelled transition system and a type system that prevents breaking changes from being deployed. Standard soundness results for the core language entail the existence of adapters, and hence ensure the absence of adaptation errors and the correctness of the management model. This adaptive approach allows for gradual deployment of modules, without halting the whole system and avoiding losing or misinterpreting data exchanged between system nodes. Experimental data shows that an average of 57% of deployments that would require adaptation and recompilation are safe under our approach.
Translation Alignment and Extraction Within a Lexica-Centered Iterative Workflow
Publication . Gomes, Luís Manuel dos Santos; Lopes, José
This thesis addresses two closely related problems. The first, translation alignment, consists of identifying bilingual document pairs that are translations of each other within
multilingual document collections (document alignment); identifying sentences, titles,
etc, that are translations of each other within bilingual document pairs (sentence alignment); and identifying corresponding word and phrase translations within bilingual
sentence pairs (phrase alignment). The second is extraction of bilingual pairs of equivalent word and multi-word expressions, which we call translation equivalents (TEs), from sentence- and phrase-aligned parallel corpora.
While these same problems have been investigated by other authors, their focus has
been on fully unsupervised methods based mostly or exclusively on parallel corpora.
Bilingual lexica, which are basically lists of TEs, have not been considered or given enough importance as resources in the treatment of these problems. Human validation of TEs, which consists of manually classifying TEs as correct or incorrect translations, has also not been considered in the context of alignment and extraction. Validation strengthens the importance of infrequent TEs (most of the entries of a validated lexicon) that otherwise would be statistically unimportant.
The main goal of this thesis is to revisit the alignment and extraction problems in the
context of a lexica-centered iterative workflow that includes human validation. Therefore, the methods proposed in this thesis were designed to take advantage of knowledge accumulated in human-validated bilingual lexica and translation tables obtained by unsupervised methods. Phrase-level alignment is a stepping stone for several applications, including the extraction of new TEs, the creation of statistical machine translation systems, and the creation of bilingual concordances. Therefore, for phrase-level alignment, the higher accuracy of human-validated bilingual lexica is crucial for achieving higher quality results in these downstream applications.
There are two main conceptual contributions. The first is the coverage maximization
approach to alignment, which makes direct use of the information contained in a lexicon, or in translation tables when this is small or does not exist. The second is the introduction of translation patterns which combine novel and old ideas and enables precise and productive extraction of TEs. As material contributions, the alignment and extraction methods proposed in this thesis have produced source materials for three lines of research, in the context of three PhD theses (two of them already defended), all sharing with me the supervision of my advisor. The topics of these lines of research are statistical machine translation, algorithms and data structures for indexing and querying phrase-aligned parallel corpora, and bilingual lexica classification and generation. Four publications have resulted directly from the work presented in this thesis and twelve from the collaborative lines of research.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/CEC/04516/2013