Web Search Interview Questions and Answers for 10 years experience

1. What are the key differences between a crawler and a spider?

   • Answer: While the terms are often used interchangeably, a crawler is a more general term for a program that systematically browses the web. A spider is a type of crawler that focuses on extracting data and following links to discover new content. Crawlers can have broader objectives beyond indexing, like monitoring website changes or collecting specific data.

2. Explain the concept of PageRank.

   • Answer: PageRank is an algorithm used by Google Search to rank websites in search engine results. It works by assigning a numerical weighting to each webpage based on the quantity and quality of backlinks. Pages with many backlinks from high-quality sites receive a higher PageRank, indicating greater importance and relevance.

3. Describe the role of an inverted index in web search.

   • Answer: An inverted index is a data structure that maps words to the documents containing them. This allows search engines to quickly find documents containing specific keywords without having to scan every document in the index. It's crucial for fast search retrieval.

4. What are some common challenges in web crawling?

   • Answer: Challenges include politeness (avoiding overloading websites), dealing with dynamic content (JavaScript rendering), handling robots.txt, identifying and avoiding traps (e.g., infinite loops), managing scale (crawling billions of pages), and dealing with duplicate content.

5. Explain the difference between TF-IDF and BM25.

   • Answer: Both TF-IDF (Term Frequency-Inverse Document Frequency) and BM25 (Best Match 25) are ranking algorithms. TF-IDF focuses on the frequency of a term within a document and across the entire corpus. BM25 is a more sophisticated algorithm that considers document length and term frequency more effectively, leading to better ranking results, particularly for longer documents.

6. How does search engine caching work?

   • Answer: Search engines cache copies of web pages to improve search speed and reduce load on websites. When a user searches, the search engine can quickly serve the cached version if it's relatively up-to-date, rather than fetching the page from the live server. This improves latency and reduces server strain.

7. What are some techniques used to combat spam in search results?

   • Answer: Techniques include link analysis (detecting unnatural link patterns), content analysis (identifying low-quality or keyword-stuffed content), user feedback (analyzing user clicks and reports), and machine learning models trained to identify spammy content and links.

8. Explain the concept of latent semantic indexing (LSI).

   • Answer: LSI uses linear algebra (Singular Value Decomposition) to discover relationships between terms. It helps improve search accuracy by understanding the semantic meaning of words, even if they don't appear explicitly in a query. It helps match documents that are semantically similar but use different words.

9. What is the role of query understanding in search?

   • Answer: Query understanding is the process of interpreting a user's search query to understand its intent and meaning. This involves natural language processing (NLP) techniques to handle synonyms, ambiguities, and different phrasing styles, leading to more accurate search results.

10. How do search engines handle different languages?

    • Answer: Search engines use language detection to identify the language of a webpage and query. They then use language-specific resources such as dictionaries, thesauri, and language models to process and rank results appropriately. They might also have separate indices for different languages.

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