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What are focused web crawlers?
A focused web crawler is a hypertext system that investigates, acquires, indexes, and supports pages on a definite set of subjects that define a relatively narrow segment of the web. It requires a very small investment in the hardware and web resources and yet manages respectable coverage at a quick rate, simply because there is relatively small to do.
The focused web crawler is conducted by a classifier that learns to identify relevance from examples embedded in a topic taxonomy, and a distiller which recognizes topical vantage points on the internet.
Focused web crawlers use vertical search engines to crawl web pages specific to a target topic. Each fetched page is classified into predefined target topic(s). If the page is predicted to be on-topic, then its links are extracted and are appended into the URL queue.
Otherwise, the crawling process does not proceed from this page. This kind of focused web crawler is known as a "full-page" focused web crawler because it classifies the full page content. In another term, the context of all the connections on the page is the full page content itself.
This kind of web crawler creates indexing more effectively directly helping us in achieving the basic requirement of quicker and more relevant retrieval of data from the huge repository of the World Wide Web. There are several search engines have started using this method to provide users a more rich experience while creating web content directly increasing their hit counts.
The crawler manager is a significant element of the system following the Hypertext Analyzer. The component downloads the files from the global web. The URLs in the URL repository are recovered and created to the buffer in the Crawler Manager.
The URL buffer is a priority queue. It depends on the size of the URL buffer, the crawler manager dynamically creates an instance for the crawlers, which will download the files. For more effectiveness, the crawler manager can generate a crawler pool. The manager is also answerable for limiting the speed of the crawlers and balancing the load between them. This is completed by inspecting the crawlers.
The crawler is a multi-thread Java code, which is adequate for downloading the web pages from the internet and saving the files in the document repository. Every crawler has its queue, which influences the file of URLs to be crawled. The crawler recovered the URL from the queue.
The different crawlers would have shared a request to the same server. If so, sending the request to a similar server will outcome in overloading the server. The server is active in completing the request that has to appear from the crawlers that have shared the request and looking forward to the response.
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