Information Retrieval — Exam Power Notes
Quick Revision Guide
1. Information Retrieval
Information Retrieval (IR) is the process of finding relevant information from large collections of documents, especially text.
2. IR System
A typical IR system collects documents, preprocesses text, builds an index, processes queries, ranks results, and presents
relevant information.
3. Key Concepts
Document = information unit. Query = user's request. Index = structure for efficient lookup. Relevance = closeness to the
user's information need. Ranking = ordering results by estimated relevance.
4. Text Preprocessing
Common steps include tokenization, normalization, stop-word handling, and stemming or lemmatization.
5. Inverted Index
An inverted index maps terms to the documents containing them. It is a core structure for fast text retrieval.
6. Boolean Retrieval
Boolean search uses operators such as AND, OR, and NOT to combine terms and select matching documents.
7. TF-IDF
TF-IDF gives higher importance to terms that occur frequently in a document but are relatively uncommon across the
collection.
8. Precision and Recall
Precision = proportion of retrieved results that are relevant. Recall = proportion of all relevant items that were retrieved.
9. Ranking
Retrieval systems rank documents using signals such as term statistics, similarity measures, and learned ranking methods.
10. Applications
IR is used in web search, digital libraries, enterprise search, document management, question answering, and information
discovery.
11. Challenges
Common challenges include ambiguous queries, synonyms, spelling variations, huge collections, duplicate content,
changing information, and determining relevance.
12. Short Q&A;
Q: What is an inverted index? A: A term-to-document lookup structure. Q: What is precision? A: The fraction of retrieved
results that are relevant. Q: What is recall? A: The fraction of relevant items successfully retrieved.
13. MCQs
1) Which structure maps terms to documents? A) Inverted index B) Queue C) Stack D) Router — Answer: A. 2) Which
operator requires both terms? A) OR B) AND C) NOT D) XOR — Answer: B. 3) TF-IDF estimates term importance —
Answer: True.
Quick Revision Guide
1. Information Retrieval
Information Retrieval (IR) is the process of finding relevant information from large collections of documents, especially text.
2. IR System
A typical IR system collects documents, preprocesses text, builds an index, processes queries, ranks results, and presents
relevant information.
3. Key Concepts
Document = information unit. Query = user's request. Index = structure for efficient lookup. Relevance = closeness to the
user's information need. Ranking = ordering results by estimated relevance.
4. Text Preprocessing
Common steps include tokenization, normalization, stop-word handling, and stemming or lemmatization.
5. Inverted Index
An inverted index maps terms to the documents containing them. It is a core structure for fast text retrieval.
6. Boolean Retrieval
Boolean search uses operators such as AND, OR, and NOT to combine terms and select matching documents.
7. TF-IDF
TF-IDF gives higher importance to terms that occur frequently in a document but are relatively uncommon across the
collection.
8. Precision and Recall
Precision = proportion of retrieved results that are relevant. Recall = proportion of all relevant items that were retrieved.
9. Ranking
Retrieval systems rank documents using signals such as term statistics, similarity measures, and learned ranking methods.
10. Applications
IR is used in web search, digital libraries, enterprise search, document management, question answering, and information
discovery.
11. Challenges
Common challenges include ambiguous queries, synonyms, spelling variations, huge collections, duplicate content,
changing information, and determining relevance.
12. Short Q&A;
Q: What is an inverted index? A: A term-to-document lookup structure. Q: What is precision? A: The fraction of retrieved
results that are relevant. Q: What is recall? A: The fraction of relevant items successfully retrieved.
13. MCQs
1) Which structure maps terms to documents? A) Inverted index B) Queue C) Stack D) Router — Answer: A. 2) Which
operator requires both terms? A) OR B) AND C) NOT D) XOR — Answer: B. 3) TF-IDF estimates term importance —
Answer: True.
