Information Retrieval
This note mainly focuses on text information retrieval. It is mainly based on JHU's, ETHzurich's and Stanford's information retrieval course.

Overview

Data -> Search -> User
More detail:
  • Data: Getting documents and preprocessing documents
    • Crawler
    • Text preprocessing, Clustering, Information Extraction (Named Entity, Relation, Topic Models, etc.)
    • Forward Index, Inverted Index
  • Search: Querying content (Search engine) or filtering content (Recommendation system). Not different that much.
    • Querying: Boolean Retrieval, Vector Space Model, Probabilistic Model, Learning to Rank
    • Filtering: Content Filtering, Collaborative Filtering, Also use Querying methods
    • Ranking: Scoring, Link Analysis
  • User: Content presentation

Retrieval In General

  • The way user accessing data: Push mode (Recommendation system like news feed) -> filtering content and Pull model (Search engine) -> querying content.
  • Retrieval compared to Database: Database usually holds structured data, with well-defined query semantics.
  • Know that user information need is almost always larger than the given query.
  • Search core methods: Selection (binary decision) or Ranking (Continous scoring and thresholding). If we assume the utility of a document to a user is independent of any other document and the usesr browse the results sequentially, we could rank documents in descending order of the probability that a document is relevant to the query.
  • Search results evaluation: Precision and Recall.

General Text Preprocessing

  • Tokenization
  • Normalization: Map term variant to the same form.
  • Stemming: Extract root word.
  • Stop words: Omit common words

Main Topics