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68-523: A Web crawler , sometimes called a spider or spiderbot and often shortened to crawler , is an Internet bot that systematically browses the World Wide Web and that is typically operated by search engines for the purpose of Web indexing ( web spidering ). Web search engines and some other websites use Web crawling or spidering software to update their web content or indices of other sites' web content. Web crawlers copy pages for processing by

136-591: A robots.txt file can request bots to index only parts of a website, or nothing at all. The number of Internet pages is extremely large; even the largest crawlers fall short of making a complete index. For this reason, search engines struggled to give relevant search results in the early years of the World Wide Web, before 2000. Today, relevant results are given almost instantly. Crawlers can validate hyperlinks and HTML code. They can also be used for web scraping and data-driven programming . A web crawler

204-505: A 100,000-pages synthetic graph with a power-law distribution of in-links. However, there was no comparison with other strategies nor experiments in the real Web. Boldi et al. used simulation on subsets of the Web of 40 million pages from the .it domain and 100 million pages from the WebBase crawl, testing breadth-first against depth-first, random ordering and an omniscient strategy. The comparison

272-473: A chatbot that can take orders via Facebook Messenger . Chatbots allow companies to allocate their employees' time to other tasks. One example of the malicious use of bots is the coordination and operation of an automated attack on networked computers, such as a denial-of-service attack by a botnet . Internet bots or web bots can also be used to commit click fraud and more recently have appeared around MMORPG games as computer game bots . Another category

340-458: A consistent manner. There are several types of normalization that may be performed including conversion of URLs to lowercase, removal of "." and ".." segments, and adding trailing slashes to the non-empty path component. Some crawlers intend to download/upload as many resources as possible from a particular web site. So path-ascending crawler was introduced that would ascend to every path in each URL that it intends to crawl. For example, when given

408-415: A crawler is, because this is the first one they have seen." A parallel crawler is a crawler that runs multiple processes in parallel. The goal is to maximize the download rate while minimizing the overhead from parallelization and to avoid repeated downloads of the same page. To avoid downloading the same page more than once, the crawling system requires a policy for assigning the new URLs discovered during

476-447: A crawler may examine the URL and only request a resource if the URL ends with certain characters such as .html, .htm, .asp, .aspx, .php, .jsp, .jspx or a slash. This strategy may cause numerous HTML Web resources to be unintentionally skipped. Some crawlers may also avoid requesting any resources that have a "?" in them (are dynamically produced) in order to avoid spider traps that may cause

544-604: A focused crawling depends mostly on the richness of links in the specific topic being searched, and a focused crawling usually relies on a general Web search engine for providing starting points. An example of the focused crawlers are academic crawlers, which crawls free-access academic related documents, such as the citeseerxbot , which is the crawler of CiteSeer search engine. Other academic search engines are Google Scholar and Microsoft Academic Search etc. Because most academic papers are published in PDF formats, such kind of crawler

612-407: A given page to the query before actually downloading the page. A possible predictor is the anchor text of links; this was the approach taken by Pinkerton in the first web crawler of the early days of the Web. Diligenti et al. propose using the complete content of the pages already visited to infer the similarity between the driving query and the pages that have not been visited yet. The performance of

680-410: A given query. Web crawlers that attempt to download pages that are similar to each other are called focused crawler or topical crawlers . The concepts of topical and focused crawling were first introduced by Filippo Menczer and by Soumen Chakrabarti et al. The main problem in focused crawling is that in the context of a Web crawler, we would like to be able to predict the similarity of the text of

748-631: A human could easily do but a bot would not.  This could be something like recognizing distorted letters or numbers, or picking out specific parts of an image, such as traffic lights on a busy street. CAPTCHAs are a great form of protection due to their ability to be completed quickly, low effort, and easy implementation. There are also dedicated companies that specialize in protection against bots, including ones like DataDome, Akamai, BrandSSL and Imperva.  These companies offer defense systems to their clients to protect them against DDoS attacks, infrastructure attacks, and overall cybersecurity.  While

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816-520: A human user. The history of social botting can be traced back to Alan Turing in the 1950s and his vision of designing sets of instructional code approved by the Turing test . In the 1960s Joseph Weizenbaum created ELIZA , a natural language processing computer program considered an early indicator of artificial intelligence algorithms. ELIZA inspired computer programmers to design tasked programs that can match behavior patterns to their sets of instruction. As

884-473: A number of challenges in system design, I/O and network efficiency, and robustness and manageability. Internet bot Efforts by web servers to restrict bots vary. Some servers have a robots.txt file that contains the rules governing bot behavior on that server. Any bot that does not follow the rules could, in theory, be denied access to or removed from the affected website. If the posted text file has no associated program/software/app, then adhering to

952-409: A previously-crawled-Web graph using this new method. Using these seeds, a new crawl can be very effective. A crawler may only want to seek out HTML pages and avoid all other MIME types . In order to request only HTML resources, a crawler may make an HTTP HEAD request to determine a Web resource's MIME type before requesting the entire resource with a GET request. To avoid making numerous HEAD requests,

1020-410: A random or a fixed order. Cho and Garcia-Molina proved the surprising result that, in terms of average freshness, the uniform policy outperforms the proportional policy in both a simulated Web and a real Web crawl. Intuitively, the reasoning is that, as web crawlers have a limit to how many pages they can crawl in a given time frame, (1) they will allocate too many new crawls to rapidly changing pages at

1088-403: A reliable source, such as an existing department or group at work. This way, malicious bots don't have the opportunity to infiltrate the study. Another form of protection against bots is a CAPTCHA test as mentioned in a previous section, which stands for "Completely Automated Public Turing Test".  This test is often used to quickly distinguish a real user from a bot by posing a challenge that

1156-420: A response. Such bots can often handle reporting weather, zip code information, sports scores, currency or other unit conversions, etc. Others are used for entertainment, such as SmarterChild on AOL Instant Messenger and MSN Messenger . Additional roles of an IRC bot may be to listen on a conversation channel, and to comment on certain phrases uttered by the participants (based on pattern matching ). This

1224-420: A result, natural language processing has become an influencing factor to the development of artificial intelligence and social bots. And as information and thought see a progressive mass spreading on social media websites, innovative technological advancements are made following the same pattern. Reports of political interferences in recent elections, including the 2016 US and 2017 UK general elections, have set

1292-407: A search engine, which indexes the downloaded pages so that users can search more efficiently. Crawlers consume resources on visited systems and often visit sites unprompted. Issues of schedule, load, and "politeness" come into play when large collections of pages are accessed. Mechanisms exist for public sites not wishing to be crawled to make this known to the crawling agent. For example, including

1360-400: A seed URL of http://llama.org/hamster/monkey/page.html, it will attempt to crawl /hamster/monkey/, /hamster/, and /. Cothey found that a path-ascending crawler was very effective in finding isolated resources, or resources for which no inbound link would have been found in regular crawling. The importance of a page for a crawler can also be expressed as a function of the similarity of a page to

1428-511: A server can have a hard time keeping up with requests from multiple crawlers. As noted by Koster, the use of Web crawlers is useful for a number of tasks, but comes with a price for the general community. The costs of using Web crawlers include: A partial solution to these problems is the robots exclusion protocol , also known as the robots.txt protocol that is a standard for administrators to indicate which parts of their Web servers should not be accessed by crawlers. This standard does not include

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1496-542: A single domain. Cho also wrote his PhD dissertation at Stanford on web crawling. Najork and Wiener performed an actual crawl on 328 million pages, using breadth-first ordering. They found that a breadth-first crawl captures pages with high Pagerank early in the crawl (but they did not compare this strategy against other strategies). The explanation given by the authors for this result is that "the most important pages have many links to them from numerous hosts, and those links will be found early, regardless of on which host or page

1564-425: A small selection will actually return unique content. For example, a simple online photo gallery may offer three options to users, as specified through HTTP GET parameters in the URL. If there exist four ways to sort images, three choices of thumbnail size, two file formats, and an option to disable user-provided content, then the same set of content can be accessed with 48 different URLs, all of which may be linked on

1632-469: A social bot. Many people believe that bots are vastly less intelligent than humans, so they are not worthy of our respect. Min-Sun Kim proposed five concerns or issues that may arise when communicating with a social robot, and they are avoiding the damage of peoples' feelings, minimizing impositions, disapproval from others, clarity issues, and how effective their messages may come across. People who oppose social robots argue that they also take away from

1700-425: A suggestion for the interval of visits to the same server, even though this interval is the most effective way of avoiding server overload. Recently commercial search engines like Google , Ask Jeeves , MSN and Yahoo! Search are able to use an extra "Crawl-delay:" parameter in the robots.txt file to indicate the number of seconds to delay between requests. The first proposed interval between successive pageloads

1768-468: Is also known as a spider , an ant , an automatic indexer , or (in the FOAF software context) a Web scutter . A Web crawler starts with a list of URLs to visit. Those first URLs are called the seeds . As the crawler visits these URLs, by communicating with web servers that respond to those URLs, it identifies all the hyperlinks in the retrieved web pages and adds them to the list of URLs to visit, called

1836-417: Is challenging and can add a significant overhead to the crawling process, so this is performed as a post crawling process using machine learning or regular expression algorithms. These academic documents are usually obtained from home pages of faculties and students or from publication page of research institutes. Because academic documents make up only a small fraction of all web pages, a good seed selection

1904-509: Is important in boosting the efficiencies of these web crawlers. Other academic crawlers may download plain text and HTML files, that contains metadata of academic papers, such as titles, papers, and abstracts. This increases the overall number of papers, but a significant fraction may not provide free PDF downloads. Another type of focused crawlers is semantic focused crawler, which makes use of domain ontologies to represent topical maps and link Web pages with relevant ontological concepts for

1972-463: Is neither the uniform policy nor the proportional policy. The optimal method for keeping average freshness high includes ignoring the pages that change too often, and the optimal for keeping average age low is to use access frequencies that monotonically (and sub-linearly) increase with the rate of change of each page. In both cases, the optimal is closer to the uniform policy than to the proportional policy: as Coffman et al. note, "in order to minimize

2040-409: Is particularly interested in crawling PDF, PostScript files, Microsoft Word including their zipped formats. Because of this, general open-source crawlers, such as Heritrix , must be customized to filter out other MIME types , or a middleware is used to extract these documents out and import them to the focused crawl database and repository. Identifying whether these documents are academic or not

2108-503: Is represented by spambots , internet bots that attempt to spam large amounts of content on the Internet, usually adding advertising links. More than 94.2% of websites have experienced a bot attack. There are malicious bots (and botnets ) of the following types: in 2012, journalist Percy von Lipinski reported that he discovered millions of bots or botted or pinged views at CNN iReport . CNN iReport quietly removed millions of views from

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2176-487: Is sometimes used as a help service for new users or to censor profanity . Social bots are sets of algorithms that take on the duties of repetitive sets of instructions in order to establish a service or connection among social networking users. Among the various designs of networking bots, the most common are chat bots , algorithms designed to converse with a human user, and social bots, algorithms designed to mimic human behaviors to converse with patterns similar to those of

2244-422: Is the case of vertical search engines restricted to a single top-level domain , or search engines restricted to a fixed Web site). Designing a good selection policy has an added difficulty: it must work with partial information, as the complete set of Web pages is not known during crawling. Junghoo Cho et al. made the first study on policies for crawling scheduling. Their data set was a 180,000-pages crawl from

2312-497: Is to be maintained." A crawler must carefully choose at each step which pages to visit next. The behavior of a Web crawler is the outcome of a combination of policies: Given the current size of the Web, even large search engines cover only a portion of the publicly available part. A 2009 study showed even large-scale search engines index no more than 40–70% of the indexable Web; a previous study by Steve Lawrence and Lee Giles showed that no search engine indexed more than 16% of

2380-448: Is worth noticing that even when being very polite, and taking all the safeguards to avoid overloading Web servers, some complaints from Web server administrators are received. Sergey Brin and Larry Page noted in 1998, "... running a crawler which connects to more than half a million servers ... generates a fair amount of e-mail and phone calls. Because of the vast number of people coming on line, there are always those who do not know what

2448-456: The stanford.edu domain, in which a crawling simulation was done with different strategies. The ordering metrics tested were breadth-first , backlink count and partial PageRank calculations. One of the conclusions was that if the crawler wants to download pages with high Pagerank early during the crawling process, then the partial Pagerank strategy is the better, followed by breadth-first and backlink-count. However, these results are for just

2516-405: The crawl frontier . URLs from the frontier are recursively visited according to a set of policies. If the crawler is performing archiving of websites (or web archiving ), it copies and saves the information as it goes. The archives are usually stored in such a way they can be viewed, read and navigated as if they were on the live web, but are preserved as 'snapshots'. The archive is known as

2584-553: The Apple App Store and Google Play , to manipulate positions or increase positive ratings/reviews. A rapidly growing, benign form of internet bot is the chatbot . From 2016, when Facebook Messenger allowed developers to place chatbots on their platform, there has been an exponential growth of their use on that app alone. 30,000 bots were created for Messenger in the first six months, rising to 100,000 by September 2017. Avi Ben Ezra, CTO of SnatchBot, told Forbes that evidence from

2652-417: The repository and is designed to store and manage the collection of web pages . The repository only stores HTML pages and these pages are stored as distinct files. A repository is similar to any other system that stores data, like a modern-day database. The only difference is that a repository does not need all the functionality offered by a database system. The repository stores the most recent version of

2720-540: The OPIC strategy and a strategy that uses the length of the per-site queues are better than breadth-first crawling, and that it is also very effective to use a previous crawl, when it is available, to guide the current one. Daneshpajouh et al. designed a community based algorithm for discovering good seeds. Their method crawls web pages with high PageRank from different communities in less iteration in comparison with crawl starting from random seeds. One can extract good seed from

2788-425: The Web are worth the same"), something that is not a realistic scenario, so further information about the Web page quality should be included to achieve a better crawling policy. Crawlers can retrieve data much quicker and in greater depth than human searchers, so they can have a crippling impact on the performance of a site. If a single crawler is performing multiple requests per second and/or downloading large files,

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2856-449: The Web crawler is the server and the Web sites are the queues. Page modifications are the arrival of the customers, and switch-over times are the interval between page accesses to a single Web site. Under this model, mean waiting time for a customer in the polling system is equivalent to the average age for the Web crawler. The objective of the crawler is to keep the average freshness of pages in its collection as high as possible, or to keep

2924-464: The Web in 1999. As a crawler always downloads just a fraction of the Web pages , it is highly desirable for the downloaded fraction to contain the most relevant pages and not just a random sample of the Web. This requires a metric of importance for prioritizing Web pages. The importance of a page is a function of its intrinsic quality, its popularity in terms of links or visits, and even of its URL (the latter

2992-485: The account of iReporter Chris Morrow. It is not known if the ad revenue received by CNN from the fake views was ever returned to the advertisers. The most widely used anti-bot technique is CAPTCHA . Examples of providers include Recaptcha , Minteye, Solve Media and NuCaptcha. However, captchas are not foolproof in preventing bots, as they can often be circumvented by computer character recognition, security holes, and outsourcing captcha solving to cheap laborers. In

3060-408: The average age of pages as low as possible. These objectives are not equivalent: in the first case, the crawler is just concerned with how many pages are outdated, while in the second case, the crawler is concerned with how old the local copies of pages are. Two simple re-visiting policies were studied by Cho and Garcia-Molina: In both cases, the repeated crawling order of pages can be done either in

3128-411: The case of Twitter, most of these bots are programmed with search filter capabilities that target keywords and phrases favoring political agendas and then retweet them. While the attention of bots is programmed to spread unverified information throughout the social media platforms, it is a challenge that programmers face in the wake of a hostile political climate. The Bot Effect is what Ferrera reported as

3196-411: The case of academic surveys, protection against auto test taking bots is essential for maintaining accuracy and consistency in the results of the survey. Without proper precautions against these bots, the results of a survey can become skewed or inaccurate. Researchers indicate that the best way to keep bots out of surveys is to not allow them to enter to begin with. The survey should have participants from

3264-470: The crawl originates." Abiteboul designed a crawling strategy based on an algorithm called OPIC (On-line Page Importance Computation). In OPIC, each page is given an initial sum of "cash" that is distributed equally among the pages it points to. It is similar to a PageRank computation, but it is faster and is only done in one step. An OPIC-driven crawler downloads first the pages in the crawling frontier with higher amounts of "cash". Experiments were carried in

3332-399: The crawler to download an infinite number of URLs from a Web site. This strategy is unreliable if the site uses URL rewriting to simplify its URLs. Crawlers usually perform some type of URL normalization in order to avoid crawling the same resource more than once. The term URL normalization , also called URL canonicalization , refers to the process of modifying and standardizing a URL in

3400-497: The crawling process, as the same URL can be found by two different crawling processes. A crawler must not only have a good crawling strategy, as noted in the previous sections, but it should also have a highly optimized architecture. Shkapenyuk and Suel noted that: While it is fairly easy to build a slow crawler that downloads a few pages per second for a short period of time, building a high-performance system that can download hundreds of millions of pages over several weeks presents

3468-580: The default. The MercatorWeb crawler follows an adaptive politeness policy: if it took t seconds to download a document from a given server, the crawler waits for 10 t seconds before downloading the next page. Dill et al. use 1 second. For those using Web crawlers for research purposes, a more detailed cost-benefit analysis is needed and ethical considerations should be taken into account when deciding where to crawl and how fast to crawl. Anecdotal evidence from access logs shows that access intervals from known crawlers vary between 20 seconds and 3–4 minutes. It

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3536-600: The expected obsolescence time, the accesses to any particular page should be kept as evenly spaced as possible". Explicit formulas for the re-visit policy are not attainable in general, but they are obtained numerically, as they depend on the distribution of page changes. Cho and Garcia-Molina show that the exponential distribution is a good fit for describing page changes, while Ipeirotis et al. show how to use statistical tools to discover parameters that affect this distribution. The re-visiting policies considered here regard all pages as homogeneous in terms of quality ("all pages on

3604-440: The expense of less frequently updating pages, and (2) the freshness of rapidly changing pages lasts for shorter period than that of less frequently changing pages. In other words, a proportional policy allocates more resources to crawling frequently updating pages, but experiences less overall freshness time from them. To improve freshness, the crawler should penalize the elements that change too often. The optimal re-visiting policy

3672-495: The genuine creations of human relationships. Opposition to social bots also note that the use of social bots add a new, unnecessary layer to privacy protection. Many users call for stricter legislation in relation to social bots to ensure private information remains preserved. The discussion of what to do with social bots and how far they should go remains ongoing. In recent years, political discussion platforms and politics on social media have become highly unstable and volatile. With

3740-624: The introduction of social bots on the political discussion scene, many users worry about their effect on the discussion and election outcomes. The biggest offender on the social media side is X (previously Twitter), where heated political discussions are raised both by bots and real users. The result is a misuse of political discussion on these platforms and a general mistrust among users for what they see. Search engines Search engines , including web search engines , selection-based search engines, metasearch engines , desktop search tools, and web portals and vertical market websites have

3808-438: The local copy is. The age of a page p in the repository, at time t is defined as: Coffman et al. worked with a definition of the objective of a Web crawler that is equivalent to freshness, but use a different wording: they propose that a crawler must minimize the fraction of time pages remain outdated. They also noted that the problem of Web crawling can be modeled as a multiple-queue, single-server polling system, on which

3876-555: The notion of bots being more prevalent because of the ethics that is challenged between the bot's design and the bot's designer. Emilio Ferrara , a computer scientist from the University of Southern California reporting on Communications of the ACM, said the lack of resources available to implement fact-checking and information verification results in the large volumes of false reports and claims made about these bots on social media platforms. In

3944-511: The pricing rates of these companies can often be expensive, the services offered can be crucial both for large corporations and small businesses. There are two main concerns with bots: clarity and face-to-face support. The cultural background of human beings affects the way they communicate with social bots. Others recognize that online bots have the ability to "masquerade" as humans online and have become highly aware of their presence. Due to this, some users are becoming unsure when interacting with

4012-634: The rules is entirely voluntary. There would be no way to enforce the rules or to ensure that a bot's creator or implementer reads or acknowledges the robots.txt file. Some bots are "good", e.g. search engine spiders , while others are used to launch malicious attacks on political campaigns, for example. Some bots communicate with users of Internet-based services, via instant messaging (IM), Internet Relay Chat (IRC), or other web interfaces such as Facebook bots and Twitter bots . These chatbots may allow people to ask questions in plain English and then formulate

4080-416: The search engine's point of view, there is a cost associated with not detecting an event, and thus having an outdated copy of a resource. The most-used cost functions are freshness and age. Freshness : This is a binary measure that indicates whether the local copy is accurate or not. The freshness of a page p in the repository at time t is defined as: Age : This is a measure that indicates how outdated

4148-520: The selection and categorization purposes. In addition, ontologies can be automatically updated in the crawling process. Dong et al. introduced such an ontology-learning-based crawler using a support-vector machine to update the content of ontological concepts when crawling Web pages. The Web has a very dynamic nature, and crawling a fraction of the Web can take weeks or months. By the time a Web crawler has finished its crawl, many events could have happened, including creations, updates, and deletions. From

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4216-439: The site. This mathematical combination creates a problem for crawlers, as they must sort through endless combinations of relatively minor scripted changes in order to retrieve unique content. As Edwards et al. noted, "Given that the bandwidth for conducting crawls is neither infinite nor free, it is becoming essential to crawl the Web in not only a scalable, but efficient way, if some reasonable measure of quality or freshness

4284-408: The socialization of bots and human users creating a vulnerability to the leaking of personal information and polarizing influences outside the ethics of the bot's code, and was confirmed by Guillory Kramer in his study where he observed the behavior of emotionally volatile users and the impact the bots have on them, altering their perception of reality. There has been a great deal of controversy about

4352-545: The use of bots in an automated trading function. Auction website eBay took legal action in an attempt to suppress a third-party company from using bots to look for bargains on its site; this approach backfired on eBay and attracted the attention of further bots. The United Kingdom-based bet exchange , Betfair , saw such a large amount of traffic coming from bots that it launched a WebService API aimed at bot programmers, through which it can actively manage bot interactions. Bot farms are known to be used in online app stores, like

4420-498: The use of their chatbot building platform pointed to a near future saving of millions of hours of human labor as 'live chat' on websites was replaced with bots. Companies use internet bots to increase online engagement and streamline communication. Companies often use bots to cut down on cost; instead of employing people to communicate with consumers, companies have developed new ways to be efficient. These chatbots are used to answer customers' questions: for example, Domino's developed

4488-526: The web page retrieved by the crawler. The large volume implies the crawler can only download a limited number of the Web pages within a given time, so it needs to prioritize its downloads. The high rate of change can imply the pages might have already been updated or even deleted. The number of possible URLs crawled being generated by server-side software has also made it difficult for web crawlers to avoid retrieving duplicate content . Endless combinations of HTTP GET (URL-based) parameters exist, of which only

4556-459: Was 60 seconds. However, if pages were downloaded at this rate from a website with more than 100,000 pages over a perfect connection with zero latency and infinite bandwidth, it would take more than 2 months to download only that entire Web site; also, only a fraction of the resources from that Web server would be used. Cho uses 10 seconds as an interval for accesses, and the WIRE crawler uses 15 seconds as

4624-427: Was based on how well PageRank computed on a partial crawl approximates the true PageRank value. Some visits that accumulate PageRank very quickly (most notably, breadth-first and the omniscient visit) provide very poor progressive approximations. Baeza-Yates et al. used simulation on two subsets of the Web of 3 million pages from the .gr and .cl domain, testing several crawling strategies. They showed that both

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