MLG 019 Natural Language Processing 2

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Notes and resources at ocdevel.com/mlg/19

Classical NLP Techniques:

• Origins and Phases in NLP History: Initially reliant on hardcoded linguistic rules, NLP's evolution significantly pivoted with the introduction of machine learning, particularly shallow learning algorithms, leading eventually to deep learning, which is the current standard.

• Importance of Classical Methods: Knowing traditional methods is still valuable, providing a historical context and foundation for understanding NLP tasks. Traditional methods can be advantageous with small datasets or limited compute power.

• Edit Distance and Stemming:

  • Levenshtein Distance: Used for spelling corrections by measuring the minimal edits needed to transform one string into another.
  • Stemming: Simplifying a word to its base form. The Porter Stemmer is a common algorithm used.

• Language Models:

  • Understand language legitimacy by calculating the joint probability of word sequences.
  • Use n-grams for constructing language models to increase accuracy at the expense of computational power.

• Naive Bayes for Classification:

  • Ideal for tasks like spam detection, document classification, and sentiment analysis.
  • Relies on a 'bag of words' model, simplifying documents down to word frequency counts and disregarding sequence dependence.

• Part of Speech Tagging and Named Entity Recognition:

  • Methods: Maximum entropy models, hidden Markov models.
  • Challenges: Feature engineering for parts of speech, complexity in named entity recognition.

• Generative vs. Discriminative Models:

  • Generative Models: Estimate the joint probability distribution; useful with less data.
  • Discriminative Models: Focus on decision boundaries between classes.

• Topic Modeling with LDA:

  • Latent Dirichlet Allocation (LDA) helps identify topics within large sets of documents by clustering words into topics, allowing for mixed membership of topics across documents.

• Search and Similarity Measures:

  • Utilize TF-IDF for transforming documents into vectors reflecting term importance inversely correlated with document frequency in the corpus.
  • Employ cosine similarity for measuring semantic similarity between document vectors.