Search engines are programs and these can be set up or programmed in different ways. The following features categorize a search engine and work largely independently of one another.
Differentiation according to the types of data
One of the characteristics that search engines use to categorize is the type of data that a search engine crawls. The data can be roughly divided into different document types. There are search engines for text content, images, videos and sound recordings such as music. Depending on the type of search engine, different result lists are generated.
With a text search engine, the user is shown short excerpts of the respective texts; these excerpts are referred to as snippets.
The results lists look different with image search engines. Here you can see a miniature view of many images that match the search term you entered.
In turn, the results of a video search engine differ from those of a text search engine or an image search engine. After entering a search term, the user is generated a list of results with suitable videos.
Categorization according to the data source of the recorded data
Another feature for categorizing search engines is the data source from which the search engines collect the data. A distinction must be made here:
Web search engines: These search engines collect data from the World Wide Web.
Vertical search engines: Vertical search engines collect documents on a specific topic such as health or law. Vertical search engines look at a selected area of the World Wide Web.
Usenet search engines: This type of search engine collects data and contributions from the Usenet discussion medium, which is distributed around the world. Usenet is the oldest network for exchanging messages and files.
Intranet search engines: The intranet search engines are limited to the collection of data from the computers of a company’s intranet. An intranet is a non-public computer network and is often used in organizations, companies or authorities and is available as an information, communication and application platform.
Enterprise search engines: Enterprise search engines are company-internal search engines that are optimally adapted to a company’s individual requirements. These search engines enable a central search via various data sources within a company, such as file servers, wikis, databases and the intranet.
Desktop search engines: Desktop search engines are programs that search the local database of a computer.
Categorization after implementation of the operation of a search engine
Another feature is the way of implementing the operation of a search engine. This characteristic relates to how the search engines obtain and evaluate data and then show the user relevant results.
Index search engines
The popular search engines nowadays are called index search engines.
Information is obtained from index search engines using so-called “crawlers”, “spiders” or “robots”. These programs analyze documents and try to extract the essential information or keywords. The documents are then saved in databases. Index search engines evaluate the indexed documents exclusively automatically.
This has the advantage that a very large amount of data can be indexed and the search process is quickly carried out.
The indexing of the data and the maintenance of the data stock is very complex since information sources have to be searched constantly to keep the search engine up to date.
Meta Search Engine
The difference between an index search engine and a metasearch engine is that metasearch engines do not have their own index, i.e. meta-search engines work without their own database.
If a user makes a search query with the help of a metasearch engine, this accesses the databases of various other search engines instead of its own index. The metasearch engine carries out a so-called metasearch. This metasearch happens when the metasearch engine forwards the search query to several search engines in parallel.
The results of the normal search engines are collected by the metasearch engine and displayed in a list of results. Duplicate entries from various search engines are automatically removed.
The disadvantage of these metasearch engines is that the search time is quite long due to the many simultaneous queries.
The meta-search engines are well suited for a search for rare and special terms if previous searches on individual services were unsuccessful.
Hybrid search engines
In addition to the index search engines and the meta-search engines, so-called hybrid search engines also exist.
Hybrid search engines have their own index, but this is very small so that these search engines also send queries to other search engines and then combine them in the result lists.
Hybrid search engines, which are also called real-time search engines, only start the indexing process after a query. In this way, the pages found are always up-to-date.
However, the quality of the results is poor due to the lack of a broad database, especially with less common search terms.