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Publications

2009

3D Object Reconstruction from Uncalibrated Images Using an Off-the-Shelf Camera

Authors
Azevedo, TCS; Manuel, J; Tavares, RS; Vaz, MAP;

Publication
ADVANCES IN COMPUTATIONAL VISION AND MEDICAL IMAGE PROCESSING: METHODS AND APPLICATIONS

Abstract
Three-dimensional (3D) objects reconstruction using just bi-dimensional (2D) images has been a major research topic in Computer Vision. However, it is still a hard problem to address, when automation, speed and precision are required and/or the objects have complex shapes or image properties. In this paper, we compare two Active Computer Vision methods frequently used for the 3D reconstruction of objects from image sequences, acquired with a single off-the-shelf CCD camera: Structure From Motion (SFM) and Generalized Voxel Coloring (GVC). SFM recovers the 3D shape of an object based on the relative motion involved, while VC is a volumetric method that uses photo-consistency measures to build the required 3D model. Both methods considered do not impose any kind of restrictions on the relative motion involved.

2009

Mapping between Alloy specifications and database implementations

Authors
Cunha, A; Pacheco, H;

Publication
SEFM 2009: SEVENTH INTERNATIONAL CONFERENCE ON SOFTWARE ENGINEERING AND FORMAL METHODS

Abstract
The emergence of lightweight formal methods tools such as Alloy improves the software design process, by encouraging developers to model and verify their systems before engaging in hideous implementation details. However, an abstract Alloy specification is far from an actual implementation, and manually refining the former into the latter is unfortunately a non-trivial task. This paper identifies a subset of the Alloy language that is equivalent to a relational database schema with the most conventional integrity constraints, namely functional and inclusion dependencies. This semantic correspondence enables both the automatic translation of Alloy specifications into relational database schemas and the reengineering of legacy databases into Alloy. The paper also discusses how to derive an object-oriented application layer to serve as interface to the underlying database.

2009

Using SysML in Systems Design

Authors
Costa, T; Sampaio, A; Alves, G;

Publication
2009 INTERNATIONAL CONFERENCE ON INFORMATION MANAGEMENT, INNOVATION MANAGEMENT AND INDUSTRIAL ENGINEERING, VOL 4, PROCEEDINGS

Abstract
System of systems involves several secondary systems working together with its creation gathering the knowledge of several distinct disciplines and teams, each one with their own background and methods, leading to a difficult communication between them. SysML, a language originated from UML, enables that communication, without background interference, with the use of a rich notation for systems design. This paper analyzes its use through the experience gained in the design of a chemical system with SysML.

2009

Adaptive Bayesian network classifiers

Authors
Castillo, G; Gama, J;

Publication
INTELLIGENT DATA ANALYSIS

Abstract
This paper is concerned with adaptive learning algorithms for Bayesian network classifiers in a prequential (on-line) learning scenario. In this scenario, new data is available over time. An efficient supervised learning algorithm must be able to improve its predictive accuracy by incorporating the incoming data, while optimizing the cost of updating. However, if the process is not strictly stationary, the target concept could change over time. Hence, the predictive model should be adapted quickly to these changes. The main contribution of this work is a proposal of an unified, adaptive prequential framework for supervised learning called AdPreqFr4SL, which attempts to handle the cost-performance trade-off and deal with concept drift. Starting with the simple Naive Bayes, we scale up the complexity by gradually increasing the maximum number of allowable attribute dependencies, and then by searching for new dependences in the extended search space. Since updating the structure is a costly task, we use new data to primarily adapt the parameters. We adapt the structure only when is actually necessary. The method for handling concept drift is based on the Shewhart P-Chart. We experimentally prove the advantages of using the AdPreqFr4SL in comparison with its non-adaptive versions.

2009

Computational complexity with experiments as oracles. II. Upper bounds

Authors
Beggs, E; Costa, JF; Loff, B; Tucker, JV;

Publication
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES

Abstract
Earlier, to explore the idea of combining physical experiments with algorithms, we introduced a new form of analogue digital (AD) Turing machine. We examined in detail a case study where an experimental procedure, based on Newtonian kinematics, is used as an oracle with classes of Turing machines. The physical cost of oracle calls was counted and three forms of AD queries were studied, in which physical parameters can be set exactly and approximately. Here, in this sequel, we complete the classi. cation of the computational power of these AD Turing machines and determine precisely what they can compute, using non- uniform complexity classes and probabilities.

2009

Worst-Case Running Times for Average-Case Algorithms

Authors
Antunes, L; Fortnow, L;

Publication
PROCEEDINGS OF THE 24TH ANNUAL IEEE CONFERENCE ON COMPUTATIONAL COMPLEXITY

Abstract
Under a standard hardness assumption we exactly characterize the worst-case running time of languages that are in average polynomial-time over all polynomial-time samplable distributions. More precisely we show that if exponential time is not infinitely often in subexponential space, then the following are equivalent for any algorithm A: For all P-samplable distributions mu, A runs in time polynomial on mu-average. For all polynomial p, the running time for A is bounded by 2(O(Kp(x)-K(x)+log(|x|))) for all inputs x. where K(x) is the Kolmogorov complexity (size of smallest program generating x) and K-p(x) is the size of the smallest program generating x within time p(|x|). To prove this result we show that, under the hardness assumption, the polynomial-time Kolmogorov distribution, m(p)(x) = 2(-Kp(x)), is universal among the P-samplable distributions.

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