Web scraping (web harvesting or web data extraction) is a computer software technique of extracting information from websites. This is accomplished by either directly implementing the Hypertext Transfer Protocol (on which the Web is based), or embedding a web browser.
Web scraping is closely related to web indexing, which indexes information on the web using a bot or web crawler and is a universal technique adopted by most search engines. In contrast, web scraping focuses more on the transformation of unstructured data on the web, typically in HTML format, into structured data that can be stored and analyzed in a central local database or spreadsheet. Web scraping is also related to web automation, which simulates human browsing using computer software. Uses of web scraping include online price comparison, contact scraping, weather data monitoring, website change detection, research, web mashup and web data integration.
Web scraping is the process of automatically collecting information from the World Wide Web. It is a field with active developments sharing a common goal with the semantic web vision, an ambitious initiative that still requires breakthroughs in text processing, semantic understanding, artificial intelligence and human-computer interactions. Current web scraping solutions range from the ad-hoc, requiring human effort, to fully automated systems that are able to convert entire web sites into structured information, with limitations.
- Human copy-and-paste: Sometimes even the best web-scraping technology cannot replace a human’s manual examination and copy-and-paste, and sometimes this may be the only workable solution when the websites for scraping explicitly set up barriers to prevent machine automation.
- Text grepping and regular expression matching: A simple yet powerful approach to extract information from web pages can be based on the UNIX grep command or regular expression-matching facilities of programming languages (for instance Perl or Python).
- HTTP programming: Static and dynamic web pages can be retrieved by posting HTTP requests to the remote web server using socket programming.
- HTML parsers: Many websites have large collections of pages generated dynamically from an underlying structured source like a database. Data of the same category are typically encoded into similar pages by a common script or template. In data mining, a program that detects such templates in a particular information source, extracts its content and translates it into a relational form, is called a wrapper. Wrapper generation algorithms assume that input pages of a wrapper induction system conform to a common template and that they can be easily identified in terms of a URL common scheme. Moreover, some semi-structured data query languages, such as XQuery and the HTQL, can be used to parse HTML pages and to retrieve and transform page content.
- DOM parsing: By embedding a full-fledged web browser, such as the Internet Explorer or the Mozilla browser control, programs can retrieve the dynamic content generated by client-side scripts. These browser controls also parse web pages into a DOM tree, based on which programs can retrieve parts of the pages.
- Web-scraping software: There are many software tools available that can be used to customize web-scraping solutions. This software may attempt to automatically recognize the data structure of a page or provide a recording interface that removes the necessity to manually write web-scraping code, or some scripting functions that can be used to extract and transform content, and database interfaces that can store the scraped data in local databases.
- Vertical aggregation platforms: There are several companies that have developed vertical specific harvesting platforms. These platforms create and monitor a multitude of “bots” for specific verticals with no "man in the loop" (no direct human involvement), and no work related to a specific target site. The preparation involves establishing the knowledge base for the entire vertical and then the platform creates the bots automatically. The platform's robustness is measured by the quality of the information it retrieves (usually number of fields) and its scalability (how quick it can scale up to hundreds or thousands of sites). This scalability is mostly used to target the Long Tail of sites that common aggregators find complicated or too labor-intensive to harvest content from.
- Semantic annotation recognizing: The pages being scraped may embrace metadata or semantic markups and annotations, which can be used to locate specific data snippets. If the annotations are embedded in the pages, as Microformat does, this technique can be viewed as a special case of DOM parsing. In another case, the annotations, organized into a semantic layer, are stored and managed separately from the web pages, so the scrapers can retrieve data schema and instructions from this layer before scraping the pages.
- Computer vision web-page analyzers: There are efforts using machine learning and computer vision that attempt to identify and extract information from web pages by interpreting pages visually as a human being might.
||The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject. (October 2015)|
One of the first major tests of screen scraping involved American Airlines (AA), and a firm called FareChase. AA successfully obtained an injunction from a Texas trial court, stopping FareChase from selling software that enables users to compare online fares if the software also searches AA's website. The airline argued that FareChase's websearch software trespassed on AA's servers when it collected the publicly available data. FareChase filed an appeal in March 2003. By June, FareChase and AA agreed to settle and the appeal was dropped.
Southwest Airlines has also challenged screen-scraping practices, and has involved both FareChase and another firm, Outtask, in a legal claim. Southwest Airlines charged that the screen-scraping is Illegal since it is an example of "Computer Fraud and Abuse" and has led to "Damage and Loss" and "Unauthorized Access" of Southwest's site. It also constitutes "Interference with Business Relations", "Trespass", and "Harmful Access by Computer". They also claimed that screen-scraping constitutes what is legally known as "Misappropriation and Unjust Enrichment", as well as being a breach of the web site's user agreement. Outtask denied all these claims, claiming that the prevailing law in this case should be US Copyright law, and that under copyright, the pieces of information being scraped would not be subject to copyright protection. Although the cases were never resolved in the Supreme Court of the United States, FareChase was eventually shuttered by parent company Yahoo!, and Outtask was purchased by travel expense company Concur. In 2012, a startup called 3Taps scraped classified housing ads from Craigslist. Craigslist sent 3Taps a cease-and-desist letter and blocked their IP addresses and later sued, in Craigslist v. 3Taps. The court held that the cease-and-desist letter and IP blocking was sufficient for Craigslist to properly claim that 3Taps had violated the Computer Fraud and Abuse Act.
Although these are early scraping decisions, and the theories of liability are not uniform, it is difficult to ignore a pattern emerging that the courts are prepared to protect proprietary content on commercial sites from uses which are undesirable to the owners of such sites. However, the degree of protection for such content is not settled, and will depend on the type of access made by the scraper, the amount of information accessed and copied, the degree to which the access adversely affects the site owner’s system and the types and manner of prohibitions on such conduct.
Outside of the United States, in February 2006, the Danish Maritime and Commercial Court (Copenhagen) ruled that systematic crawling, indexing, and deep linking by portal site ofir.dk of real estate site Home.dk does not conflict with Danish law or the database directive of the European Union.
In Facebook, Inc. v. Power Ventures, Inc., a district court ruled in 2012 that Power Ventures could not scrape Facebook pages on behalf of a Facebook user. The case is on appeal, and the Electronic Frontier Foundation filed a brief in 2015 asking that it be overturned. In AP v Meltwater, a court in the US held Meltwater liable for scraping and republishing news information from the Associated Press, but a court in the United Kingdom held in favor of Meltwater.
In a February 2010 case complicated by matters of jurisdiction, Ireland's High Court delivered a verdict that illustrates the inchoate state of developing case law. In the case of Ryanair Ltd v Billigfluege.de GmbH, Ireland's High Court ruled Ryanair's "click-wrap" agreement to be legally binding. In contrast to the findings of the United States District Court Eastern District of Virginia and those of the Danish Maritime and Commercial Court, Mr. Justice Michael Hanna ruled that the hyperlink to Ryanair's terms and conditions was plainly visible, and that placing the onus on the user to agree to terms and conditions in order to gain access to online services is sufficient to comprise a contractual relationship.  The decision is under appeal in Ireland's Supreme Court.
- Apache Camel
- Automation Anywhere
- Data Toolbar
- OutWit Hub
- WSO2 Mashup Server
- Yahoo! Query Language (YQL)
Technical measures to stop bots
The administrator of a website can use various measures to stop or slow a bot. Some techniques include:
- Blocking an IP address either manually or based on criteria such as Geolocation and DNSRBL. This will also block all browsing from that address.
- Disabling any web service API that the website's system might expose.
- Bots sometimes declare who they are (using user agent strings) and can be blocked on that basis (using robots.txt); 'googlebot' is an example. Other bots make no distinction between themselves and a human using a browser.
- Bots can be blocked by excess traffic monitoring.
- Bots can sometimes be blocked with tools to verify that it is a real person accessing the site, like a CAPTCHA. Bots are sometimes coded to explicitly break specific CAPTCHA patterns or may employ third-party services that utilize human labor to read and respond in real-time to CAPTCHA challenges.
- Commercial anti-bot services: Companies offer anti-bot and anti-scraping services for websites. A few web application firewalls have limited bot detection capabilities as well.
- Locating bots with a honeypot or other method to identify the IP addresses of automated crawlers.
- Obfuscation using CSS sprites to display such data as phone numbers or email addresses, at the cost of accessibility to screen reader users.
- Because bots rely on consistency in the front-end code of a target website, adding small variations to the HTML/CSS surrounding important data and navigation elements would require more human involvement in the initial set up of a bot and if done effectively may render the target website too difficult to scrape due to the diminished ability to automate the scraping process.
- Song, Ruihua; Microsoft Research (Sep 14, 2007). "Joint Optimization of Wrapper Generation and Template Detection" (PDF). The 13th International Conference on Knowledge Discovery and Data Mining.
- Semantic annotation based web scraping
- Roush, Wade (2012-07-25). "Diffbot Is Using Computer Vision to Reinvent the Semantic Web". www.xconomy.com. Retrieved 2013-03-15.
- "Internet Law, Ch. 06: Trespass to Chattels". www.tomwbell.com. 2007-08-20. Retrieved 2007-08-20.
- "What are the "trespass to chattels" claims some companies or website owners have brought?". www.chillingeffects.org. 2007-08-20. Retrieved 2007-08-20.
- "Ticketmaster Corp. v. Tickets.com, Inc.". 2007-08-20. Retrieved 2007-08-20.
- "American Airlines v. FareChase" (PDF). 2007-08-20. Retrieved 2007-08-20.
- "American Airlines, FareChase Settle Suit.". The Free Library. 2003-06-13. Retrieved 2012-02-26.
- Imperva (2011). Detecting and Blocking Site Scraping Attacks. Imperva white paper..
- Adler, Kenneth A. (2003-07-29). "Controversy Surrounds 'Screen Scrapers': Software Helps Users Access Web Sites But Activity by Competitors Comes Under Scrutiny". Retrieved 2010-10-27.
- "QVC Inc. v. Resultly LLC, No. 14-06714 (E.D. Pa. filed Nov. 24, 2014)" (PDF). 2014-11-24. Retrieved 2015-11-05.
- "QVC Inc. v. Resultly LLC, No. 14-06714 (E.D. Pa. filed Nov. 24, 2014)". United States District Court for the Eastern District of Pennsylvania. Retrieved 5 November 2015.
- Neuburger, Jeffrey D (5 December 2014). "QVC Sues Shopping App for Web Scraping That Allegedly Triggered Site Outage". The National Law Review (Proskauer Rose LLP). Retrieved 5 November 2015.
- "Did Iqbal/Twombly Raise the Bar for Browsewrap Claims?" (PDF). 2010-09-17. Retrieved 2010-10-27.
- "UDSKRIFT AF SØ- & HANDELSRETTENS DOMBOG" (PDF). bvhd.dk. 2006-02-24. Retrieved 2007-05-30.
- "Can Scraping Non-Infringing Content Become Copyright Infringement... Because Of How Scrapers Work? | Techdirt". Techdirt. 2009-06-10. Retrieved 2016-05-24.
- "Facebook v. Power Ventures". Electronic Frontier Foundation. Retrieved 2016-05-24.
- "High Court of Ireland Decisions >> Ryanair Ltd -v- Billigfluege.de GMBH 2010 IEHC 47 (26 February 2010)". British and Irish Legal Information Institute. 2010-02-26. Retrieved 2012-04-19.
- National Office for the Information Economy (February 2004). "Spam Act 2003: An overview for business" (PDF). Australian Communications Authority. p. 6. Retrieved 2009-03-09.
- National Office for the Information Economy (February 2004). "Spam Act 2003: A practical guide for business" (PDF). Australian Communications Authority. p. 20. Retrieved 2009-03-09.