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Instance-based anytime algorithm to data stream classification

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Cristiano Inácio Lemes
Total Authors: 1
Document type: Master's Dissertation
Press: São Carlos.
Institution: Universidade de São Paulo (USP). Instituto de Ciências Matemáticas e de Computação (ICMC/SB)
Defense date:
Examining board members:
Gustavo Enrique de Almeida Prado Alves Batista; André Carlos Ponce de Leon Ferreira de Carvalho; Pedro Pereira Rodrigues
Advisor: Gustavo Enrique de Almeida Prado Alves Batista

Data stream learning is a very important research field that has received much attention from the scientific community. In many real-world applications, data is generated as potentially infinite temporal sequences. The main characteristic of stream processing is to provide answers observing stringent restrictions of time and memory. For example, a data stream classifier must provide an answer for each event before the next one arrives. If this does not occur, some events from the data stream may be left unclassified. Many streams generate events with highly variable output rate, i.e. the time interval between two consecutive events may vary greatly. For a learning system to be successful, two properties must be satisfied: (i) it must be able to provide a classification for a new example in a short time and (ii) it must be able to adapt the classification model to treat concept change, since the data may not follow a stationary distribution. Batch machine learning algorithms do not satisfy those properties because they assume that the distribution is stationary and they are not prepared to operate with severe memory and processing constraints. To satisfy these requirements, these algorithms must be adapted to the data stream context. One possible adaptation is to turn the algorithm into an anytime classifier. Anytime algorithms may be interrupted and still provide an approximated answer (classification) at any time. Another adaptation is to turn the algorithm into an incremental classifier so that its model may be updated with new examples from the data stream. In this work, it is performed an evaluation of two approaches for data stream learning. The first one is based on a state-of-the-art k-nearest neighbor anytime classifier. A new tiebreak approach is proposed to be used with this algorithm. Experiments show consistently better results in the performance of this algorithm in many benchmark data sets. The second proposed approach is to adapt the anytime algorithm for concept change. This approach was called Incremental Anytime Algorithm, and it was designed with two versions. One version is based on the Space Saving algorithm and the other is based in a Sliding Window. Experiments show that both versions are significantly better than baseline approaches. (AU)