Web Scraping With Semalt Expert
Web scraping, also known as web harvesting, is a technique used to extract data from websites. Web harvesting software can access a web directly using HTTP or a web browser. While the process may be implemented manually by a software user, the technique generally entails an automated process implemented using a web crawler or bot.
Web scraping is a process when structured data is copied from the web into a local database for reviews and retrieval. It involves fetching a web page and extracting its content. The content of the page may be parsed, searched, restructured and its data copied into a local storage device.
Web pages are generally built out of text-based markup languages such as XHTML and HTML, both of which contain a bulk of useful data in the form of text. However, many of these websites have been designed for human end-users and not for automated use. This is the reason why scraping software was created.
There are many techniques that can be employed for effective web scraping. Some of them have been elaborated below:
1. Human Copy-and-paste
From time to time, even the best web scraping tools can't replace the accuracy and efficiency of a human's manual copy-and-paste. This is mostly applicable in situations when websites set up barriers to prevent machine automation.
2. Text Pattern Matching
This is a fairly simple but powerful approach used to extract data from web pages. It may be based on the UNIX grep command or just a regular expression facility of a given programming language, for instance, Python or Perl.
3. HTTP Programming
HTTP Programming can be used for both static and dynamic web pages. The data is extracted through posting HTTP requests to a remote web server while making use of socket programming.
4. HTML Parsing
Many websites tend to have an extensive collection of pages created dynamically from an underlying structure source such as a database. Here, data that belongs to a similar category is encoded into similar pages. In HTML parsing, a program generally detects such a template in a particular source of information, retrieves its contents and then translates it into an affiliate form, referred to as a wrapper.
5. DOM parsing
In this technique, a program embeds in a full-fledged web browser such as Mozilla Firefox or the Internet Explorer to retrieve dynamic content generated by the client-side script. These browsers may also parse web pages into a DOM tree depending on the programs that can extract parts of the pages.
6. Semantic Annotation Recognition
The pages you intend to scrape may embrace semantic markups and annotations or metadata, which may be used to locate specific data snippets. If these annotations are embedded in the pages, this technique may be viewed as a special case of DOM parsing. These annotations may also be organized into a syntactic layer, and then stored and managed separately from the web pages. It allows scrapers to retrieve data schema as well as commands from this layer before it scraps the pages.
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