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Introduction to Natural Language Processing
Porter Stemmer and its Rules
Q no
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Its main use is as part
of a term normalization process that is usually done when setting up Information Retrieval systems
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It is more efficient not to use a dictionary (don’t have to maintain it if things change)
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Porter Stemmers use simple algorithms to determine which affixes to strip in which order
and when to apply repair strategies
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*v* - the stem contains a vowel
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g
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*o - the stem ends cvc, where the second c is not W, X or Y (e
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-WIL, -HOP)

In a set of rules written below each other, only one is obeyed
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2 Corpora and Role of Corpora in NLP
Ans: A collection of written text or recorded Speech
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A corpus is a collection of text or speech material that has been brought together according to be
a certain set of predetermined criteria
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Performing these counts enables the researcher not only to search for and spot key words and
phrases, but also to examine their concordances (i
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the words that occur around them)
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o More annotated text often yield more effective patterns
o Different genres may have different properties
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Systems can “train” separately on different genres

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Systems can “train” on one diverse corpus

Other analytic techniques, such as collocation analysis, enable the researcher to identify and extract
terms within a corpus that are associated (or, in other words, that collocate) with any other
particular word
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Other commonly used techniques include:
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Part-of-speech annotation: grammatical labelling of the words in a corpus;

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Semantic tagging: automatic grouping of words into categories based on meaning;

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Named-entity recognition: the process of automatically locating, classifying and
annotating named elements, such as people, organizations or places, in running texts
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But to
date, relatively little work has sought to add a spatial dimension to corpus analysis despite the clear
coherence of the corpus-based approach with the ideas underlying the field of Geographical
Information Systems (GIS)

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