Lecture 15: Introduction to POS Tagging

[@pawanchoure1289]

One of the oldest techniques of tagging is rule-based POS tagging. Rule-based taggers use a dictionary or lexicon for getting possible tags for tagging each word. If the word has more than one possible tag, then rule-based taggers use hand-written rules to identify the correct tag.

[@pawanchoure1289]

Stochastic (Probabilistic) tagging: A stochastic approach includes frequency, probability or statistics. The simplest stochastic approach finds out the most frequently used tag for a specific word in the annotated training data and uses this information to tag that word in the unannotated text.

[@pawanchoure1289]

Part-of-speech (POS) tagging is a popular Natural Language Processing process that refers to categorizing words in a text (corpus) in correspondence with a particular part of speech, depending on the definition of the word and its context.

[@pawanchoure1289]

the following types of POS taggers: Rule-Based: A dictionary is constructed with possible tags for each word. Rules guide the tagger to disambiguate. Rules are either hand-crafted, learned or both. An example rule might say, "If an ambiguous/unknown word X is preceded by a determiner and followed by a noun, tag it as an adjective." Statistical: A text corpus is used to derive useful probabilities. Given a sequence of words, the most probable sequence of tags is selected. These are also called stochastic or probabilistic taggers. Among the common models are n-gram model, Hidden Markov Model (HMM) and Maximum Entropy Model (MEM). Memory-Based: A set of cases is stored in memory, each case containing a word, its context and suitable tag. A new sentence is tagged based on best match from cases stored in memory. It's a combination of rule-based and stochastic method. Transformation-Based: Rules are automatically induced from data. Thus, it's a combination of rule-based and stochastic methods. Tagging is done using broad rules and then improved or transformed by applying narrower rules. Neural Net: RNN and Bidirectional LSTM are two examples of neural network architectures for POS tagging

[@pawanchoure1289]

Lemmatization usually refers to doing things properly with the use of a vocabulary and morphological analysis of words, normally aiming to remove inflectional endings only and to return the base or dictionary form of a word, which is known as the lemma . Morphological parsing, in natural language processing, is the process of determining the morphemes from which a given word is constructed. It must be able to distinguish between orthographic rules and morphological rules.

[@pawanchoure1289]

Naïve Bayes has a naive assumption of conditional independence for every feature, which means that the algorithm expects the features to be independent which not always is the case. Logistic regression is a linear classification method that learns the probability of a sample belonging to a certain class.

[@pawanchoure1289]

Discriminative models draw boundaries in the data space, while generative models try to model how data is placed throughout the space. A generative model focuses on explaining how the data was generated, while a discriminative model focuses on predicting the labels of the data.

[@ananyapamde4514]

I think the POS he means when he says particle is actually participle. Took me some time to figure it out.

[@jinunayak]

Parts of Speech- POS

[@pawanchoure1289]

transformation-based learning tag(TBL) in NLP.

[@tanmaysinha987]

excellent class sir