Recent Publications

Silva JMC, Carvalho P, Lima SR.  2015.  A modular sampling framework for flexible traffic analysis. 2015 23rd International Conference on Software, Telecommunications and Computer Networks (SoftCOM). :200-204. Abstract
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Pontes R, Matos M, Oliveira JN, Pereira JO.  2015.  Implementing a Linear Algebra Approach to Data Processing. Grand Timely Topics in Software Engineering - International Summer School {GTTSE} 2015, Braga, Portugal, August 23-29, 2015, Tutorial Lectures. 10223:215–222. Abstract
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Almeida PS, Moreno CB, Gonçalves R, Preguiça N, Fonte V.  2014.  Scalable and Accurate Causality Tracking for Eventually Consistent Stores. Distributed Applications and Interoperable Systems. 8460 Abstractdvvset-dais.pdf

In cloud computing environments, data storage systems often rely on optimistic replication to provide good performance and availability even in the presence of failures or network partitions. In this scenario, it is important to be able to accurately and efficiently identify updates executed concurrently. Current approaches to causality tracking in optimistic replication have problems with concurrent updates: they either (1) do not scale, as they require replicas to maintain information that grows linearly with the number of writes or unique clients; (2) lose information about causality, either by removing entries from client-id based version vectors or using server-id based version vectors, which cause false conflicts. We propose a new logical clock mechanism and a logical clock framework that together support a traditional key-value store API, while capturing causality in an accurate and scalable way, avoiding false conflicts. It maintains concise information per data replica, only linear on the number of replica servers, and allows data replicas to be compared and merged linear with the number of replica servers and versions.

Sousa M, Campos JC, Alves M, Harrison M.  2014.  Formal Verification of Safety-Critical User Interfaces: a space system case study. Formal Verification and Modeling in Human Machine Systems: Papers from the AAAI Spring Symposium. :62-67. Abstract7722-34384-1-pb.pdf

Safe operation of safety critical systems depends on appropriate interactions between the human operator and the computer system. Specification of such safety-critical systems is fundamental to enable exhaustive and automated analysis of operator system interaction. In this paper we present a structured, comprehensive and computer-aided approach to formally specify and verify user interfaces based on model checking techniques.

Pedro AM, Pereira D, Pinho LM, Pinto JS.  2014.  Towards a Runtime Verification Framework for the Ada Programming Language. Proceedings of the 19th International Conference on Reliable Software Technologies. Abstract2014_rstae_14.pdf

Runtime verification is an emerging discipline that investi- gates methods and tools to enable the verification of program properties during the execution of the application. The goal is to complement static analysis approaches, in particular when static verification leads to the ex- plosion of states. Non-functional properties, such as the ones present in real-time systems are an ideal target for this kind of verification method- ology, as are usually out of the range of the power and expressiveness of classic static analyses. In this paper, we present a framework that allows real-time programs written in Ada to be augmented with runtime ver- ification capabilities. Our framework provides the infrastructures which is needed to instrument the code with runtime monitors. These moni- tors are responsible for observing the system and reaching verdicts about whether its behavior is compliant with its non-functional properties. We also sketch a contract language to extend the one currently provided by Ada, with the long term goal of having an elegant way in which run- time monitors can be automatically synthesized and instrumented into the target systems. The usefulness of the proposed approach is demon- strated by showing its use for an application scenario.

Carvalho N, Sousa CS, Pinto JS, Tomb A.  2014.  Formal Verification of kLIBC with the WP Frama-C plug-in. Proceedings of the 6th NASA Formal Methods Symposium . Abstract2014_nfm_14_a.pdf

This paper presents our results in the formal verification of kLIBC, a minimalistic C library, using the Frama-C/WP tool. We report how we were able to completely verify a significant number of func- tions from and . We discuss difficulties encoun- tered and describe in detail a problem in the implementation of common functions, for which we suggest alternative implementations. Our work shows that it is presently already viable to verify low-level C code, with heavy usage of pointers. Although the properties proved tend to be shallower as the code becomes of a lower-level nature, it is our view that this is an important direction towards real-world software verifica- tion, which cannot be attained by focusing on deep properties of cleaner code, written specifically to be verified.

Pasquet M, Maia F, Rivière E, Schiavoni V.  2014.  Autonomous Multi-Dimensional Slicing for Large-Scale Distributed Systems. Proceedings of the 14th International Conference on Distributed Applications and Interoperable Systems - DAIS. Abstractautonomous-multi-dimensional.pdf

Slicing is a distributed systems primitive that allows to autonomously partition a large set of nodes based on node-local attributes. Slicing is decisive for automatically provisioning system resources for different services, based on their requirements or importance. One of the main limitations of existing slicing protocols is that only single dimension attributes are considered for partitioning. In practical settings, it is often necessary to consider best compromises for an ensemble of metrics.
In this paper we propose an extension of the slicing primitive that allows multi-attribute distributed systems slicing. Our protocol employs a gossip-based approach that does not require centralized knowledge and allows self-organization. It leverages the notion of domination between nodes, forming a partial order between multi-dimensional points, in a similar way to SkyLine queries for databases. We evaluate and demonstrate the interest of our approach using large-scale simulations.

Cunha A, Macedo N, Guimarães T.  2014.  Target oriented relational model finding. 7th International Conference on Fundamental Approaches to Software Engineering - FASE. 8411 AbstractPaper

Model finders are becoming useful in many software engineering problems. Kodkod is one of the most popular, due to its support for relational logic (a combination of first order logic with relational algebra operators and transitive closure), allowing a simpler specification of constraints, and support for partial instances, allowing the specification of a priori (exact, but potentially partial) knowledge about a problem's solution. However, in some software engineering problems, such as model repair or bidirectional model transformation, knowledge about the solution is not exact, but instead there is a known target that the solution should approximate. In this paper we extend Kodkod's partial instances to allow the specification of such targets, and show how its model finding procedure can be adapted to support them (using both PMax-SAT solvers or SAT solvers with cardinality constraints). Two case studies are also presented, including a careful performance evaluation to assess the effectiveness of the proposed extension.

Macedo N, Cunha A, Pacheco H.  2014.  Towards a framework for multi-directional model transformations. 3rd International Workshop on Bidirectional Transformations - BX. 1133 AbstractPaper

The Query/View/Transformation Relations (QVT-R) standard for bidirectional model transformation is notorious for its underspecified semantics. When restricted to transformations between pairs of models, most of the ambiguities and omissions have been addressed in recent work. Nevertheless, the application of the QVT-R language is not restricted to that scenario, and similar issues remain unexplored for the multidirectional case (maintaining consistency between more than two models), that has been overlooked so far.
In this paper we first discuss ambiguities and omissions in the QVT-R standard concerning the mutidirectional transformation scenario, and then propose a simple extension and formalization of the checking and enforcement semantics that clarifies some of them. We also discuss how such proposal could be implemented in our Echo bidirectional model transformation tool.
Ours is just a small step towards making QVT-R a viable language for bidirectional transformation in realistic applications, and a considerable amount of basic research is still needed to fully accomplish that goal.

Cunha J, Fernandes JP, Mendes J, Pereira R, Saraiva JA.  2014.  Design and Implementation of Queries for Model-Driven Spreadsheets. CEFP - Central European Functional Programming School. Abstractdsl13_query.pdf

This paper presents a domain-specific querying language for model-driven spreadsheets. We briefly show the design of the language and present in detail its implementation, from the denormalization of data and translation of our user-friendly query language to a more efficient query, to the execution of the query using Google. To validate our work, we executed an empirical study, comparing QuerySheet with an alternative spreadsheet querying tool, which produced positive results.

Cunha J, Fernandes JP, Saraiva JA.  2014.  Spreadsheet Engineering. CEFP - Central European Functional Programming School. Abstractdsl13_notes.pdf

These tutorial notes present a methodology for spreadsheet engineering. First, we present data mining and database techniques to reason about spreadsheet data. These techniques are used to compute relationships between spreadsheet elements (cells/columns/rows). These relations are then used to infer a model de ning the business logic of the spreadsheet. Such a model of a spreadsheet data is a visual domain speci c language that we embed in a well-known spreadsheet system. The embedded model is the building block to de ne techniques for modeldriven spreadsheet development, where advanced techniques are used to guarantee the model-instance synchronization. In this model-driven environment, any user data update as to follow the the model-instance conformance relation, thus, guiding spreadsheet users to introduce correct data. Data re nement techniques are used to synchronize models and instances after users update/evolve the model. These notes brie y describe our model-driven spreadsheet environment, the MDSheet environment, that implements the presented methodology. To evaluate both proposed techniques and the MDSheet tool, we have conducted, in laboratory sessions, an empirical study with the summer school participants. The results of this study are presented in these notes.

Macedo N, Pacheco H, Sousa NR, Cunha A.  2014.  Bidirectional Spreadsheet Formulas. VL/HCC - IEEE Symposium on Visual Languages and Human-Centric Computing. 6120 Abstractvlhcc14ss.pdf

Bidirectional transformations have potential applications in a vast number of computer science domains. Spreadsheets, on the other hand, are widely used for developing business applications, but their formulas are unidirectional, in the sense that their result can not be edited and propagated back to their input cells. In this paper, we interpret such formulas as a well-known class of bidirectional transformations that go by the name of lenses. Being aimed at users that are not proficient with programming languages, we devote particular attention to the seamless embedding of the proposed bidirectional mechanism with the typical workflow of spreadsheet environments, allowing users to have a fine control and understanding of the behavior of the derived backward transformations.

Maia F, Matos M, Vilaça R, Pereira JO, Oliveira R, Rivière E.  2014.  DATAFLASKS: epidemic store for massive scale systems. The 33rd IEEE Symposium on Reliable Distributed Systems (SRDS 2014) . Abstractmain.pdf

Very large scale distributed systems provide some of the most interesting research challenges while at the same time being increasingly required by nowadays applications. The escalation in the amount of connected devices and data being produced and exchanged, demands new data management systems. Although new data stores are continuously being proposed, they are not suitable for very large scale environments. The high levels of churn and constant dynamics found in very large scale systems demand robust, proactive and unstructured approaches to data management. In this paper we propose a novel data store solely based on epidemic (or gossip-based) protocols. It leverages the capacity of these protocols to provide data persistence guarantees even in highly dynamic, massive scale systems. We provide an open source prototype of the data store and correspondent evaluation.

Felber P, Pasin M, Rivière E, Schiavoni V, Sutra P, Coelho F, Matos M, Oliveira R, Vilaça R.  2014.  On the Support of Versioning in Distributed Key-Value Stores. 33rd IEEE International Symposium on Reliable Distributed Systems - SRDS. Abstractpaper.pdf

The ability to access and query data stored in multiple versions is an important asset for many applications, such as Web graph analysis, collaborative editing platforms, data forensics, or correlation mining. The storage and retrieval of versioned data requires a specific API and support from the storage layer. The choice of the data structures used to maintain versioned data has a fundamental impact on the performance of insertions and queries. The appropriate data structure also depends on the nature of the versioned data and the nature of the access patterns. In this paper we study the design and implementation space for providing versioning support on top of a distributed key-value store (KVS). We define an API for versioned data access supporting multiple writers and show that a plain KVS does not offer the necessary synchronization power for implementing this API. We leverage the support for listeners at the KVS level and propose a general construction for implementing arbitrary types of data structures for storing and querying versioned data. We explore the design space of versioned data storage ranging from a flat data structure to a distributed sharded index. The resulting system, \system, is implemented on top of an industrial-grade open-source KVS, Infinispan. Our evaluation, based on real-world Wikipedia access logs, studies the performance of each versioning mechanisms in terms of load balancing, latency and storage overhead in the context of different access scenarios.

Campos F, Matos M, Pereira JO, Rua D.  2014.  A peer-to-peer service architecture for the Smart Grid (short paper). 14th IEEE International Conference on Peer-to-Peer Computing - P2P. Abstract222.p2p2014_063.pdf

The Smart Grid vision needs to address hard challenges such as interoperability, reliability and scalability before it can become fulfilled. The need to provide full interoperability between current and future energy and non-energy systems and its disparate technologies along with the problem of seamless discovery, configuration, and communication of a large variety of networked devices ranging from the resource constrained sensing devices to the large machines inside a data center requires an agnostic Service Oriented Architecture. Moreover, the sheer scale of the Smart Grid and the criticality of the communication among its subsystems for proper management, demands a scalable and reliable communication framework able to work in an heterogeneous and dynamic environment. In this position paper, we propose a generic framework, based on Web Services for interoperability, and epidemic or gossip based communication protocols for reliability and scalability, that can serve a general management substrate where several Smart Grid problems can be solved. We illustrate the flexibility of the proposed framework by showing how it can be used in two specific scenarios.