A Newer Algorithm than Just Breadth First Search and Depth First Search in Web Crawling

Tsubasa Kato
4 min readJul 1, 2024

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So, my AI friend Perplexity and I conversed in a topic about making a better algorithm than jsust breadth first search and depth first search.

Here are quotes from it, maybe it will spark a new idea for your next web crawling algorithm.

Question (Me): Given a list of URLs like [url1, url2, url3] and so on, how would you let the web crawler explore new sites without using regular algorithms such as breadth first search or depth first search? Can you give me hints on creating a new algorithm?
Answer from Perplexity:
Creating a new algorithm for web crawling that doesn’t rely on traditional methods like breadth-first search (BFS) or depth-first search (DFS) is an interesting challenge. Here are some hints and ideas for developing a novel approach:

Priority-based Exploration:
Instead of exploring URLs in a fixed order, assign priorities to URLs based on certain criteria. This could lead to a more dynamic and potentially more efficient crawling strategy.

Hints for implementation:

Develop a scoring system for URLs based on factors like:
Relevance to a specific topic
Domain authority
Freshness of content
Number of inbound links
Use a priority queue to manage the URLs, with higher-scored URLs explored first

Random Walk with Restarts:
Implement a random walk approach where the crawler randomly chooses the next URL to visit, with occasional “restarts” to the initial seed URLs.

Hints for implementation:

Randomly select the next URL from the current page’s outgoing links
Implement a “restart probability” to occasionally jump back to a seed URL
This approach can help discover diverse content and avoid getting stuck in specific website sections

Clustering-based Crawling:
Group URLs into clusters based on similarity, then explore these clusters strategically.

Hints for implementation:

Use techniques like K-means clustering or hierarchical clustering to group URLs
Criteria for clustering could include URL structure, content similarity, or topic relevance
Explore clusters in a round-robin fashion or based on cluster priority

Evolutionary Algorithm Approach:
Treat the crawling process as an optimization problem and use evolutionary algorithms to evolve the best crawling strategy.

Hints for implementation:

Define a “chromosome” that represents a crawling strategy (e.g., order of URL exploration)
Implement fitness functions based on crawling goals (e.g., content diversity, information gain)
Use genetic operations like crossover and mutation to evolve better strategies over time

Reinforcement Learning Crawler:
Develop a crawler that learns and improves its exploration strategy over time using reinforcement learning techniques.

Hints for implementation:

Define states (e.g., current URL, crawl history) and actions (e.g., which link to follow next)
Implement a reward system based on the quality or relevance of discovered content
Use algorithms like Q-learning or Deep Q-Networks to learn optimal crawling policies

Content-driven Exploration:
Instead of focusing solely on link structure, use the content of pages to guide the crawling process.

Hints for implementation:

Implement text analysis to identify key topics or entities on each page
Use this information to predict which links are likely to lead to relevant content
Prioritize exploration based on content relevance and diversity

These approaches offer alternatives to traditional BFS and DFS methods, potentially leading to more efficient or targeted web crawling. The choice of algorithm would depend on specific crawling goals, such as content discovery, topic focus, or website mapping. Remember to consider ethical crawling practices and respect robots.txt files when implementing any crawling algorithm.
Question (Me): What are some alternative algorithms to BFS and DFS for web crawling?

Answer from Perplexity:
Based on the search results, there are several alternative algorithms to Breadth-First Search (BFS) and Depth-First Search (DFS) for web crawling:

Best-First Search (BFS): This algorithm visits links on each page in order of their estimated importance or relevance. It uses a heuristic function to dynamically adjust the crawling order based on factors like relevance, quality, or freshness of pages

・Priority-based crawling: This approach assigns priorities to URLs based on certain criteria and uses a priority queue to manage them. URLs with higher scores are explored first
・Shark-Search: This is described as a more aggressive version of Fish-Search, though details are not provided in the given results
・Distributed crawling: This method involves multiple crawlers working in parallel and coordinating their efforts. It can overcome limitations of single-crawler algorithms in terms of scalability, performance, robustness, and politeness
・PageRank-based crawling: Pages are downloaded in descending order of their estimated PageRank (or a variant), based on the pages and links acquired so far by the crawler
・Indegree-based prioritization: The crawler prioritizes pages with the highest number of incoming hyperlinks from previously downloaded pages
・Combination strategies: Some research suggests combining different approaches, such as a combination of breadth-first ordering with prioritizing the largest sites first

・These alternative algorithms aim to address various challenges in web crawling, such as improving efficiency, targeting specific content, or adapting to the structure and characteristics of the web. The choice of algorithm depends on the specific goals, resources, and constraints of the crawling task.

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Tsubasa Kato
Tsubasa Kato

Written by Tsubasa Kato

Japanese Search Engineer. Likes Quantum Computers and handheld computers.

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