英语翻译If you do not find the required information using the ti

英语翻译
If you do not find the required information using the tips from the previous section,then you need to consult an online service to find the piece of information you were looking for.Three different types of services have been established over the years:crawlers,directories and meta search engines.
The first crawler was created back in 1993.It was called the World Wide Worm.It crawled from one site to the next and indexed all pages by saving the content of the web pages into a huge database.Crawlers or spiders visit a web page,read it,and then follow links to other pages within the site and even follow links to other sites.Web crawlers return to each site on a regular basis,such as every month or two,to look for changes.Everything a crawler finds goes into a database,which people are able to query.
The advantage of the web crawlers is that they have an extensive database with almost the complete Internet indexed in it.The disadvantage is that you get thousands of web pages as a response for almost any request.
Web directories work a little differently.First of all they contain a structured tree of information.All information entered into this tree is either entered by the webmaster who wants to announce his new web page or by the directory maintainer who looks at the web pages submitted.The directories where webmasters can submit both the URL (Uniform Resource Locator) and the description normally contain more misleading information.
Getting into most web directories is a combination of luck and quality.Although anyone is able to submit a web page,there is no guarantee that a certain page will be included.Some directories charge for submission,which is basically a rip-off.
Some crawlers maintain an associated directory.If your site is in the directory,the ranking of your web site normally will be higher,as it is already pre-classified.Many directories work with crawlers together,in order to deliver results,when nothing can be found in the directory.
Meta search engines do not have a database with URLs and descriptions.Instead they have a database of search engines.If you enter your keywords into a meta search engine it will send out requests to all the directories and crawlers it has stored in its database.The meta search engines with a more sophisticated application in the background are able to detect double URLs which come back from the various search engines and present only a single URL to the customer.

如果找不到所需的信息,使用上一节中的提示,你需要咨询一个在线的服务,以查找您正在寻找的信息的.多年来建立了三个不同类型的服务：搜索引擎抓取、 目录和元.
早在 1993 年成立了第一次爬网程序.它被称为世界通用蠕虫.它从一个站点到下一个爬网,并通过将 web 页的内容保存到一个庞大的数据库索引的所有页面.抓取或蜘蛛访问 web 页、 读,然后链接到其他站点内的页面,甚至请到其他网站的链接.网络抓取工具定期如每个月或两个查找更改返回到每个站点.一个爬网程序发现一切都到哪个人能够查询的数据库.
网络抓取工具的优点是他们几乎完整的网络索引在它有庞大的数据库.缺点是获取作为响应的数千个 web 页面以几乎任何请求.
web 目录工作有点不同.首先,它们包含信息的结构的的树.或者输入由网站管理员想要宣布他新的 web 页或目录维护者看网页提交到这棵树输入的所有信息都.在网站管理员可以提交 URL （统一资源定位器） 和说明通常的目录包含更多具误导性的信息.
进入大多数 web 目录是运气和质量的组合.虽然任何足以提交一个 web 页,但有某些页面将包含不能保证.某些目录充电,基本上是一个食的提交.
一些的爬网程序维护一个相关联的目录.在目录中如果您的网站排名的您的 web 站点通常会更高,已是 pre-classified.多个目录使用的爬网程序一起,为了提供的结果,当什么可以在目录中找到.
元搜索引擎并没有一个数据库的 url 和描述.相反,他们有一个数据库的搜索引擎.如果您它会发出请求的所有目录和抓取它已在它的数据库中存储的元搜索引擎中输入您的关键字.一个更复杂的应用程序在后台与元搜索引擎能够检测双 url 从各种搜索引擎回来,向客户只能是一个单一的 URL.