257:, i.e., become empty, so that classification becomes impossible. One solution of this problem is proposed by Dubois and Quafafou that proposed the Rough Version Space, where rough sets based approximations are used to learn certain and possible hypothesis in the presence of inconsistent data.
250:" search method that accompanies the version space framework is not a popular learning algorithm, there are some practical implementations that have been developed (e.g., Sverdlik & Reynolds 1992, Hong & Tsang 1997, Dubois & Quafafou 2002).
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consistent hypotheses) can be represented by just its lower and upper bounds (maximally general and maximally specific hypothesis sets), and learning operations can be performed just on these representative sets.
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After learning, classification can be performed on unseen examples by testing the hypothesis learned by the algorithm. If the example is consistent with multiple hypotheses, a majority vote rule can be applied.
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data already observed: Thus, if a novel (never-before-seen) data point is observed, it should be assumed to be negative. (I.e., if data has not previously been ruled in, then it's ruled out.)
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data already observed: Thus, if a novel (never-before-seen) data point is observed, it should be assumed to be positive. (I.e., if data has not previously been ruled out, then it's ruled in.)
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The notion of version spaces was introduced by
Mitchell in the early 1980s as a framework for understanding the basic problem of supervised learning within the context of
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Version space for a "rectangle" hypothesis language in two dimensions. Green pluses are positive examples, and red circles are negative examples. GB is the maximally
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training example, and hence become inconsistent. These maximal hypotheses essentially constitute a (optimistic) claim that the true concept is defined just by the
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training example, and hence become inconsistent. These minimal hypotheses essentially constitute a (pessimistic) claim that the true concept is defined just by the
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A major drawback of version space learning is its inability to deal with noise: any pair of inconsistent examples can cause the version space to
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In settings where there is a generality-ordering on hypotheses, it is possible to represent the version space by two sets of hypotheses: (1) the
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Hong, Tzung-Pai; Shian-Shyong Tsang (1997). "A generalized version space learning algorithm for noisy and uncertain data".
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positive hypothesis boundary. The intermediate (thin) rectangles represent the hypotheses in the version space.
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Rough Sets and
Current Trends in Computing: Proceedings of the Third International Conference, RSCTC 2002
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Dubois, Vincent; Quafafou, Mohamed (2002). "Concept learning with approximation: Rough version spaces".
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Thus, during learning, the version space (which itself is a set – possibly infinite – containing
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are removed from the space. This iterative refining of the hypothesis space is called the
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Sverdlik, W.; Reynolds, R.G. (1992). "Dynamic version spaces in machine learning".
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consistent hypotheses, where "consistent" indicates agreement with observed data.
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algorithm, the hypothesis space maintained inside the algorithm, its
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The most specific hypotheses (i.e., the specific boundary
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The most general hypotheses (i.e., the general boundary
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as possible. These hypotheses, if reduced any further,
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positive hypothesis boundary, and SB is the maximally
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Mitchell, Tom M. (1982). "Generalization as search".
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IEEE Transactions on
Knowledge and Data Engineering
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322:(2nd ed.). Prentice Hall. pp. 683–686.
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