What is a search engine and how to classify it?

Search engine is an online tool, which collects and organizes information on the Internet so that users can find relevant content by inputting keywords. Search engines can make various classifications according to different classification standards. According to the data sources and indexing methods of search engines, they can be divided into the following categories: 1. Web-wide search engine: use automated programs (spiders) to traverse the Internet, collect web pages and build indexes, such as Google and Bing. 2. Vertical search engines: focus on specific fields or industries and provide more accurate search results, such as Baidu Library and sogou zhihu Search. 3. Meta-search engine: query the results of multiple search engines at the same time and summarize them, such as sogou and Shenma. 4. Local search engine: provide search services in specific geographical areas, such as Baidu map and Google map. In addition, according to the business model and function of search engines, they can also be divided into the following categories: 1. Basic search engines: mainly provide search services by displaying organic search results, such as Google and Baidu. 2. Paid search engine: In addition to organic search results, it also provides advertising promotion services, such as GoogleAds and baidu promotion. 3. Social search engine: integrating social media content and user-generated information, such as Twitter search and Weibo search.