Exam Board:
OCR A-Level
3.4 - Web Technologies
Specification:
Computer Science H446
Watch on YouTube:
HTML
CSS
JavaScript
Search Engines & PageRank
Server-Side & Client-Side Processing
This topic looks at the languages that web pages are comprised of (HTML, CSS and JavaScript) as well as search engines and network processing (client-side and server-side).
HTML
HTML (HyperText Markup Language) is the standard language used to create and structure web pages. It uses tags enclosed in angle brackets to define elements on a page.
A web page begins with <html>, which contains a <head> section for metadata, links and the <title> shown in the browser tab, and a <body> section for the visible content.
Headings like <h1> and <h2>, paragraphs <p>, lists <ul>, <ol> and <li>, and images <img src="..." alt="..."> are common elements.
Links are created using <a href="...">, while forms <form> with inputs like <input type="text"> or <input type="submit"> allow user interaction.
Other tags include <div> to group content and <script> to allow JavaScript to be embedded for interactivity.
CSS
CSS (Cascading Style Sheets) is used to control the appearance and layout of web pages written in HTML. It allows developers to style elements by changing properties such as color, font-family, and font-size to improve readability and design.
CSS can also adjust an element’s background-color, height and width to control its size and spacing. Borders can be customised using border-style, border-width and border-color.
By separating content (HTML) from presentation (CSS), web pages become easier to maintain and more consistent in appearance.
JavaScript
JavaScript is a programming language used to make web pages interactive and dynamic, allowing them to respond to user actions without needing to reload.
JavaScript can be used to validate form input, create animations and update page content in real time.​​
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JavaScript can output data in several ways, such as:
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Using alert() to display a pop-up message.
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Writing directly to the web page with document.write().
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Updating specific page elements with document.getElementById().innerHTML.
Search Engines & PageRank
Search engines work by using web crawlers (also called spiders or bots) to automatically scan and collect information from web pages across the internet.
The data gathered is then stored in a massive index, which acts like a digital library of all known web pages and their contents. When a user performs a search, the search engine uses algorithms, such as the PageRank algorithm, to rank pages based on relevance and importance, often considering the number and quality of links to a page.
The results are then displayed in order of how useful and authoritative the search engine believes each page is for the user’s query.
Server-Side & Client-Side Processing
Client-side processing occurs on the user’s device, typically using languages like JavaScript. It reduces the load on the server and provides faster, more responsive interactions for the user. However, it can be less secure, as code and data are visible and can be modified by the user.
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Server-side processing takes place on the web server, often using languages like PHP or Python. It is more secure and allows access to databases and sensitive operations. The disadvantage is that it can increase server load and make responses slower, especially with many users.
Questo's Key Terms
HTML: <html>, <link>, <head>, <title>, <body>, <h1>, <h2>, <h3>, <img>, src, alt, height, width, <a>, href, <div>, <form>, <input>, type, text, submit, <p>, <li>, <ol>, <ul>, <script>
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CSS: background-color, border-color, border-style, border-width, color, font-family, font-size, height, width, class, identifier
JavaScript: JavaScript, alert, write, getElementById
Search Engines: crawler, index, PageRank algorithm
Processing: server-side processing, client-server processing
Did You Know?
Sir Tim Berners-Lee, a British computer scientist, invented the World Wide Web (WWW), as well as HTML, the URL system and HTTP. The first-ever website, published in December 1990, is still live.
