This summary captures all subjects of the web technology course, given at the Vrije Universiteit Amsterdam. At the time of writing, it was given for first year bachelor students AI at the VU. It captures mainly the three main parts of web technology, namely HTML, CSS, and JavaScript. However, it a...
Hoofdstuk 1
1.1 Web history
Internet and web
● The internet began as four networked computers in 1969.
○ In this stage the internet looked and acted similar as today but in a simpler
way.
○ Documents were only text.
● FTP (file transfer protocol)
○ An early way for transferring files over the internet.
○ This was used to connect to servers, look at listings of available document
and download documents.
● In the early 1990s, Tim Berners-Lee was working at a Swiss research institute named
CERN and developed a more convenient way for computers to communicate files
over the internet.
○ He named his creation the World Wide Web, or simply “the web”.
● The web involved three things:
1. Text files, known as HTML files, containing links to other text files.
2. A program, known as a browser, for viewing HTML files.
3. A set of rules, known as the HTTP protocol, for transferring HTML files among
computers.
● A web page is a document that is viewed in a web browser.
● A collection of related web pages are organized into a website.
● A web server is a program that serves web pages to web browsers.
● Information mesh
○ Another name for the web that was considered by the web's creator.
Introduction of HTML (HyperText markup language)
● HTML is the standard markup language for web documents.
● Hypertext is text that has links to other text.
○ And today also images, videos etc.
● Document markup is special markings in the document that provide additional
information about links, formatting and images.
● HTML also permits adding metadata like search keywords, author information and
language
,Web vs. internet
● Internet:
○ The interconnection of computers communicating using a set of rules.
● The web
○ Just one particular use of the internet.
● Besides transferring web pages from one computer to another, the internet also
transmits email, video and other types of data.
Browser wars and HTML standardization
● Web browser
○ A web browser is a program that downloads an HTML document from a web
server.
○ displays the document to the user with the appropriate formatting.
○ Allows the user to interact with the document.
■ Such as clicking hyperlinks to access other documents.
○ A web browser uses HTML to understand the structure and semantics, or
meaning of the document.
● Early in browser history, browser developers competed for users by trying to provide
the best web browsing experience.
○ Browser developers added enhancements allowing greater interactivity in
web documents.
○ These enhancements only worked within specific browsers, so many
documents could not be viewed properly on all browsers.
● The 1st was about market share (1995 - 2002) .
○ Browsers added new features constantly to attract more people.
○ Internet explorer won.
○ Also introduced many page/browser incompatibilities.
■ Became hard to develop websites that worked on all browsers.
● Second war about market share (2004 - 2013)
○ Also about market share.
○ Performance and standards compliance became more important than new
features.
○ Chrome won.
● The frequent web page and browser incompatibility headaches pushed the industry
to value standardization.
● W3C (World Wide Web Consortium)
○ Is the international standards organization that traditionally has controlled a
number of web standards, including HTML.
○ HTML5 was the latest HTML standard released by the W3C in 2014.
● In 2019, the W3C relinquished HTML standards publishing to the WHATWG.
○ WHATWG: produces the HTML living standard, a continually evolving
standard without version numbers that replaces HTML5.
● A web page that conforms to the HTML living standard will look and act the same
way in most modern web browsers.
, ● With standardization, browser developers now compete on browser speed, standards
compliance, and browser features rather than on the basis of proprietary extensions.
Separation of duties
● A significant change that occurred over time was a move to separate document
structure, document presentation (how the document is displayed in a browser), and
web page interaction with the user.
● Document markup was initially used to control both document structure and
appearance.
○ Some markup was originally used just to control appearance.
● Interlacing document structure with presentation and interaction complicates having
pages work well across different devices like printers and phones.
● A modern web page is composed out of:
1. HTML defines the structure and content of a web page.
2. CSS specifies the layout and visible appearance.
3. JavaScript describes the dynamic behaviors and actions of a web page.
1.2 IP addresses, domain names and URLs
IP addresses, domain names and DNS
● An IP address (internet protocol address) is a computer’s unique address on the
internet.
● Usually represented numerically like 198.51.100.7.
● A typical IP address is 32 bits, divided into four 8-bit groups, each group often written
as a decimal number.
● You could use IP addresses to go to certain websites.
○ But these numbers are hard to remember.
○ Also and IP address can change.
● Commonly domain names are used to reach websites.
○ A domain name is a name for an IP address.
○ The name is easier to remember and type.
○ It is not sensitive to capital letters.
● When a computer sends a packet using a domain name over the internet, the first
step is to contact a DNS server to convert the domain name to an IP address.
○ DNS is short for Domain Name system.
○ 13 main DNS servers (root servers) exist in the world.
○ A computer’s operating system or an ISP keeps a reference to the root
servers IP addresses.
○ So the first step of sending an internet packet to a domain name is thus to
lookup the IP address via a DNS server.
Registering a domain name
, ● Anyone may register an unused domain name with a domain name registrar.
● Once a domain name is registered, the owner’s name, address, and other
registration information is made publicly available from ICANN’s Whois service.
IP addresses and bites
● The original internet protocol, known as IPv4, has 32-bit addresses.
● 32 bits can represent 232 or about 4 billion unique addresses.
○ Originally this was believed to be more than ever needed, but it is no longer
enough.
○ A new version of the internet protocol called IPv6, uses 128-bit addresses,
capable of representing 2128 addresses.
○ IPv4 and IPv6 currently co-exist and likely will for a long time.
Domain name levels
● Domain names are hierarchical (arranged in order of rank).
● A domain name belongs to one of numerous top-level domains (TLD)
○ Such as .com, .net. org etc.
○ Also each country is assigned a unique two-letter country code TLD (ccTLD).
■ Like .nl or .uk.
○ ICANN, the organization that manages TLDs now allows companies and
organizations to create customized TLDs, like whatever they want.
● Immediately after a top-level domain comes a second-level domain, such as
wikipedia.org.
○ A second-level domain is commonly an organization’s name as in
Stanford.edu.
○ Or to indicates the purpose of a website.
● Third-level and further level domains refer to sub-computer systems local to an
organization.
○ As in cs.stanford.edu (cs is for Stanford’s computer science department).
○ A common third-or-deeper-level domain is www.
■ Usually referring to an organization’s web server.
■ Many organizations use www optionally.
● Google.com by default goes to www.google.com.
● The hostname is the complete domain name, which is the characters after the
scheme and before the path.
○ Like www.google.com.
URLs (uniform resource locator)
● A URL is the location of a web resource on the web.
● A complete/valid url is the full url with all other things.
○ A user doesn’t have to give all those things, these will be assumed.
● A web resource is any retrievable item, like an HTML file, image, video, etc.
● A URL is composed of several parts:
○ Scheme: Characters at the beginning of a URL followed by a colon ‘:’ or a
colon and double slashes ‘://’
■ Common URL schemes include http, https, mailto, and file.
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