On the Internet, a search engine is a coordinated set of programs that includes:
An alternative to using a search engine is to explore a structured directory of topics. Yahoo, which also lets you use its search engine, is the most widely-used directory on the Web. A number of Web portal sites offer both the search engine and directory approaches to finding information.
They also allowed one to form Boolean searches (except Hotbot as of 7/1/96, which promises to install this feature later), i. e. they allowed the user to specify combinations of words. In Alta Vista and Lycos, one does this by adding a "+" or a "-" sign before each word, or in Alta Vista you can choose to use the very strict syntax Boolean "advanced search." This advanced search was by far the hardest to use, but also the one most completely in the user's control (except for OpenText). In most other engines, you just use the words AND, NOT, and OR to get Boolean logic.
By far the best service for carefully specifying a search was Open Text. This form has great menus, making a complex Boolean search fast and easy. Best of all, this service permits you to specify that you want to search only titles or URLs. But then there's Alta Vista's little known "keyword" search syntax, now as powerful as OpenText, but not as easy to use. You can constrain a search to phrases in anchors, pages from a specific host, image titles, links, text, document titles, or URLs using this feature with the syntax keyword:search-word. There is an additional set of keywords just for searching Usenet. (To my knowledge, Alta Vista's keywords were undocumented before 7/19/96, so tell your friends you heard it here first!)
These types of search engines use a "spider" or a "crawler" to search the Internet. The crawler digs through individual web pages, pulls out keywords and then adds the pages to the search engine's database. Google and Yahoo are examples of crawler search engines.
The advantage of crawlers are:
2.Directories
Directories are human powered search engines. A website is submitted to the directory and must be approved for inclusion by editorial staff. Open Directory Project and the Internet Public Library are examples of directories.
Advantages:
3.Hybrids
Hybrids are a mix of crawlers and directories. Sometimes, you have a choice when you search whether to search the Web or a directory. Other times, you may receive both human powered results and crawler results for the same search. In this case, the human results are usually listed first.
4.Meta
Meta search engines are ones that search several other search engines at once and combines the results into one list. While you get more results with meta search engines, the relevancy and quality of the results may sometimes suffer. Dogpile and Clusty are examples of meta search engines.
- A spider (also called a "crawler" or a "bot") that goes to every page or representative pages on every Web site that wants to be searchable and reads it, using hypertext links on each page to discover and read a site's other pages
- A program that creates a huge index (sometimes called a "catalog") from the pages that have been read
- A program that receives your search request, compares it to the entries in the index, and returns results to you
An alternative to using a search engine is to explore a structured directory of topics. Yahoo, which also lets you use its search engine, is the most widely-used directory on the Web. A number of Web portal sites offer both the search engine and directory approaches to finding information.
Search Engine Features
Web location services typically specialize in one of the following: their search tools (how you specify a search and how the results are presented), the size of their database, or their catalog service. Most engines deliver too many matches in a casual search, so the overriding factor in their usefulness is the quality of their search tools. Every search engine I used had a nice GUI interface that allowed one to type words into their form, such as "(burger not cheeseburger) or (pizza AND pepperoni)."They also allowed one to form Boolean searches (except Hotbot as of 7/1/96, which promises to install this feature later), i. e. they allowed the user to specify combinations of words. In Alta Vista and Lycos, one does this by adding a "+" or a "-" sign before each word, or in Alta Vista you can choose to use the very strict syntax Boolean "advanced search." This advanced search was by far the hardest to use, but also the one most completely in the user's control (except for OpenText). In most other engines, you just use the words AND, NOT, and OR to get Boolean logic.
By far the best service for carefully specifying a search was Open Text. This form has great menus, making a complex Boolean search fast and easy. Best of all, this service permits you to specify that you want to search only titles or URLs. But then there's Alta Vista's little known "keyword" search syntax, now as powerful as OpenText, but not as easy to use. You can constrain a search to phrases in anchors, pages from a specific host, image titles, links, text, document titles, or URLs using this feature with the syntax keyword:search-word. There is an additional set of keywords just for searching Usenet. (To my knowledge, Alta Vista's keywords were undocumented before 7/19/96, so tell your friends you heard it here first!)
Types of Search Engines
1.CrawlersThese types of search engines use a "spider" or a "crawler" to search the Internet. The crawler digs through individual web pages, pulls out keywords and then adds the pages to the search engine's database. Google and Yahoo are examples of crawler search engines.
The advantage of crawlers are:
- They contain a huge amount of pages.
- Ease of use.
- Familiarity. Most people who search the Internet are familiar with Google.
- Sometimes, it's just too much information.
- It is easy to
trick the crawler. Websites have hidden data that can be manipulated to
make the page appear like it's something it's not. So, that search
result for Descartes might actually take you to a porn site.
- Page rank can be manipulated. While search engine companies frown on the practice, there are ways to improve where your page appears on the list of results.
2.Directories
Directories are human powered search engines. A website is submitted to the directory and must be approved for inclusion by editorial staff. Open Directory Project and the Internet Public Library are examples of directories.
Advantages:
- Each page is reviewed for relevance and content before being included. This means no more surprise porn sites.
- Less results sometimes means finding what you need quicker.
- Unfamiliar design and format.
- Delay in creation of a website and it's inclusion in the directory.
- May have trouble with more obscure searches.
3.Hybrids
Hybrids are a mix of crawlers and directories. Sometimes, you have a choice when you search whether to search the Web or a directory. Other times, you may receive both human powered results and crawler results for the same search. In this case, the human results are usually listed first.
4.Meta
Meta search engines are ones that search several other search engines at once and combines the results into one list. While you get more results with meta search engines, the relevancy and quality of the results may sometimes suffer. Dogpile and Clusty are examples of meta search engines.
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