Unit 7: Pattern detection and visualization

Activity 1: General introduction

Read this to understand the concepts of NLP, POS tags and parse trees

Natural language processing pipeline

A natural language processing (NLP) system is usually called an NLP pipeline. This because it usually involves several stages (steps or layers) of processing. The pipeline is one directional. There is an input (natural language) and an output (processed text). Simply put, NLP is applying artificial intelligence to human languages.

Source: Morioh

Part-of-speech (POS) tagging

POS tagging is the act of labelling words with a particular part of speech. The common parts of speech are noun, verb, adverb and adjective. However, most POS taggers use a much large set of tags. The most popular POS tagset has 36 tags. NLP pipelines that aim to map syntax or disambiguate meanings often use this layer. The Penn treebank tagset is shown in the table below.

CC Coordinating conjunction	CD Cardinal number	DT Determiner
EX Existential there	FW Foreign word	IN Preposition or subordinating conjunction
JJ Adjective	JJR Adjective, comparative	JJS Adjective, superlative
LS List item marker	MD Modal	NN Noun, singular or mass
NNS Noun, plural	NNP Proper noun, singular	NNPS Proper noun, plural
PDT Predeterminer	POS Possessive ending	PRP Personal pronoun
PRP$ Possessive pronoun	RB Adverb	RBRAdverb, comparative
RBS Adverb, superlative	RP Particle	SYM Symbol
TO to	UH Interjection	VB Verb, base form
VBD Verb, past tense	VBG Verb, gerund or present participle	VBN Verb, past participle
VBP Verb, non-3rd person singular present	VBZ Verb, 3rd person singular present	WDT Wh-determiner
WP Wh-pronoun	WP$ Possessive wh-pronoun	WRB Wh-adverb

If you are keen on learning this tagset. Try out this timed game.

Dependency parsing and parse trees

NLP pipelines can be used for many tasks. Dependency parsing is one task that is often used as one step or layer. Dependency parsing uses the part-of-speech tags assigned to words in a previous layer and creates a parse tree. The parse tree identifies a sentence and splits up the sentence sequentially. This shows the relationship between the words. During this process, trees of parent and child words are created. Parse trees are used in many NLP tasks. However, it needs to be remembered that any errors in the POS tags will affect the accuracy of the parse tree. The example below shows how a simple sentence can be broken down and the relationship between individual words mapped out on to a parse tree.

Source: Wikicommons

Activity 2: NLP Compromise

Watch and listen to this animated explanation of the JavaScript library NLP Compromise (17 min 52 sec). This library is recommended if you code in JavaScript. If you work in Python, you can omit this activity and focus on NLTK.