Often a webmaster, marketer or SEO specialist needs to extract data from the pages of websites and display them in a convenient form for further processing. This can be parsing prices in an online store, getting the number of likes or extracting the content of reviews from resources of interest.
By default, most site technical audit programs collect only the contents of H1 and H2 headers, however, if, for example, you want to collect H5 headers, then they will already need to be extracted separately. And in order to avoid routine manual work on parsing and extracting data from the HTML code of pages, web scrapers are usually used.
Web scraping is an automated process of extracting data from the pages of the site of interest according to certain rules.
Possible applications of web scraping:
Tracking the prices of goods in online stores.
Extracting descriptions of goods and services, getting the number of products and images in the listing.
Extracting contact information (email addresses, phone numbers, etc.).
Collecting data for marketing research (likes, shares, ratings).
Extraction of specific data from the code of HTML pages (search for analytics systems, checking for micro-markup).
Monitoring of ads.
The main methods of web scraping are data parsing methods using XPath, CSS selectors, XQuery, RegExp and HTML templates.
XPath is a special query language for XML/XHTML document elements. To access the elements, XPath uses DOM navigation by describing the path to the desired element on the page. With its help, you can get the value of an element by its ordinal number in a document, extract its text content or internal code, check for the presence of a certain element on the page. Description of XPath >>
CSS selectors are used to search for an element of its part (attribute). CSS is syntactically similar to XPath, while in some cases CSS locators work faster and are described more clearly and concisely. The downside of CSS is that it only works in one direction – deep into the document. XPath also works both ways (for example, you can search for a parent element by a child). CSS and XPath Comparison Table >>
XQuery is based on the XPath language. XQuery simulates XML, which allows you to create nested expressions in a way that is not possible in XSLT. Description of XQuery >>
RegExp is a formal search language for extracting values from a set of text strings corresponding to the required conditions (regular expression). Description of RegExp >>
HTML templates is a language for extracting data from HTML documents, which is a combination of HTML markup to describe a search pattern for the desired fragment plus functions and operations for extracting and converting data. Description of HTML templates >>
Usually, parsing solves problems that are difficult to handle manually. This can be web scraping of product descriptions when creating a new online store, scraping in marketing research to monitor prices, or to monitor ads (for example, for the sale of apartments).