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As any classification of materials in such systems are absent, it is necessary to resort to them only then, when you precisely know keywords concerning that it is necessary, - we shall tell, a surname of the man or it is enough some of rare terms from the appropriate area. If to set search on the a little widespread words, you will have not enough life to bypass all URL-addresses, received as a result of search, - for example, the index of system Alta Vista contains of 11 billions words taken from 30 millions of WWW-pages.
An automatic index of WWW-pages exists much: WebCrawler, Lycos, Excite, Inktomi, Open Text and others. Some of them (for example, Lycos) represent more or less successful synthesis of the subject catalogue and automatic index.
Alta Vista.
Its(her) address http://altavista.digital.com. This system has appeared in December 1995. She (it) one of largest on volume of indexes from all such retrieval systems both most powerful and floppy rules of construction of searches. Alta Vista understands two different languages of searches rather strongly distinguished from each other. On the first page Alta Vista you see the form for simple search (Simple Search), and the panel of heading at the top of page contains the button Advanced Search, having pressed which, you receive the form for complication of search.
Except for WWW-pages, Alta Vista conducts a separate index for clauses from more than 14000 conferences Usenet (including hierarchy of groups relcom. *).
Search Alta Vista: that Alta Vista worked on group of words, only when they cost(stand) beside, it is necessary to conclude this group in inverted commas. If it is necessary to exclude from result all documents containing a certain word, it is necessary to attribute this word with is familiar “minus”.
The word without any mark works in search precisely the same as also it with is familiar “plus”.
As against Yahoo, by default Alta Vista searches of entry of the whole words. The ordered terms should stand in the document separately, instead of to be a part of other chains of symbols. If you need to find of all entry of a word, even when it is included into structure of other words, use a symbol *. The asterisk can stand only at the end of a word, and prevent giving many (too much) of results, Alta Vista requires(demands), that the word which is coming to an end on *, should consist not less than of 3 letters. Moreover, a symbol * allows to find not any termination (ending) of a word, but only not exceeding length of five symbols and not containing of capital letters or figures.
Results of search Alta Vista, as well as Yahoo, gives out as the list of the links on the documents, but instead of the description of each document near to his(its) heading you will see simply first some lines of his(its) text. If will be found more than 10 documents, Alta Vista will break their list on pages till 10 links on everyone. Alta Vista sorts the links so that on the first place there were “most important” documents with your keywords at definition of a degree of importance taking into account the following factors:
Whether the keywords into heading of the documents enter;
Whether these words in the first several lines of the documents contain;
As far as are close to each other in the text the keywords are found out.
Info seek
Info seek, entered in of operation at the end of 19996 years, is somewhat reminiscent Alta Vista, however volume of the complete texts, surveyed by him,(it,) of the documents yet does not exceed 30 million. Web-pages. The address: http://www.infoseek.com. It is rather powerful system having high speed and idle time in circulation. Opportunities of drawing up of search almost same, as well as in Alta Vista, but not so rich. At almost complete preservation of values of marks "«plus", "«minus" and "«inverted commas", sensitivity to a difference header both lower case letters and opportunity to limit search to fragments Web- of pages, Info seek yet has no ability to define(determine) beside the worth terms (there is no operator NEAR), to limit search by date of updating a source and, main, to truncate terminations(ending) the key terms.
Реферат опубликован: 5/12/2009