Web Technologies — OCR A-Level Computer Science
Web Technologies explained
Web Technologies covers 4 specification points, including (a) HTML, CSS and JavaScript.
Read the full explanation
See appendix 5d. and (b) Search engine indexing.. Open a point below for its explanation and revision guidance.
(a) HTML, CSS and JavaScript. See appendix 5d.
This statement names three web technologies: HTML, CSS and JavaScript. HTML defines the structure and content of a page, such as headings, paragraphs and links. CSS controls presentation, such as colour, layout and font size, and is usually kept separate from the HTML. JavaScript runs in the browser to add behaviour, such as checking a form before submission. The statement also points to appendix 5d of the specification, which is not reproduced here, so consult it for any further detail rather than assuming its content. In a multiple-choice question, match each option to the role of one technology: structure, styling or behaviour.
(b) Search engine indexing.
Search engine indexing is the process of building a searchable database of web pages before any query is made. Crawlers follow hyperlinks to collect pages, and the indexer then records the words on each page. The usual structure is an inverted index, which maps each keyword to the pages containing it; for example, 'revision' might point to pages A, C and F. A search is answered by looking up keywords rather than scanning the whole web. In an MCQ, identify indexing as creating and storing this lookup structure, not as displaying results or ordering them.
(c) PageRank algorithm.
PageRank is an algorithm that ranks web pages by estimated importance, using the link structure of the web rather than only page content. A page gains rank when other pages link to it, and a link from a highly ranked page counts for more. Scores are calculated iteratively, with each page sharing its score across its outgoing links until values stabilise. A damping factor, often set to 0.85, models a user who sometimes jumps to a random page. In an MCQ, recognise PageRank as a link-based importance measure, not as the process that crawls pages or builds the index.
(d) Server and client side processing.
Server-side processing happens on the web server: scripts such as PHP or Python run there, often read or write a database, and send the finished result, typically HTML, back to the browser. Client-side processing happens in the user's browser, usually through JavaScript, which can validate form input or update a page without a new server request. Method: trace one action, such as submitting a login form, and decide which steps happen in the browser and which on the server. Client-side checks improve responsiveness but can be bypassed, so security-critical checks belong on the server.
Your focus
- Identify the role of HTML, CSS and JavaScript in a web page.
- Match a described feature of a web page to the correct technology.
- Locate and apply the detail in appendix 5d of the specification when answering questions on it.
Show all 12 objectives
- Identify indexing as the creation of a searchable structure before queries are made.
- Explain how crawlers and an indexer prepare pages for keyword lookup.
- Distinguish indexing from ranking and crawling when answering MCQs.
- Identify PageRank as a link-based importance algorithm.
- Describe how scores are shared across outgoing links in an iterative calculation.
- Distinguish PageRank from crawling and indexing in MCQ options.
- Identifies which tasks in a web application run on the server and which run in the browser.
- Explains why client-side validation improves responsiveness but cannot replace server-side checks.
- Describes a worked example that traces one user action through both processing locations.
Web Technologies exam tips
Marking Points
- Identifies HTML as the markup language that defines the structure and content of a web page.
- Identifies CSS as the styling language that controls presentation, such as layout, colour and font size.
- Identifies JavaScript as the scripting language that adds behaviour and interactivity in the browser.
- Matches each option to structure, styling or behaviour so that the correct technology is selected.
- Recognises that the statement points to appendix 5d and checks that appendix for any detail before answering on it.
- Identifies indexing as the building of a searchable structure before queries are made.
- Recognises that crawlers collect pages and that the indexer records their content.
- Links the inverted index to keyword lookup, mapping each keyword to the pages that contain it.
- Distinguishes indexing from ranking and from the display of search results.
- Identifies PageRank as an algorithm that ranks pages by estimated importance.
- States that a page's rank depends on links from other pages, and that links from highly ranked pages count for more.
- Recognises the iterative calculation in which each page's score is shared across its outgoing links until values stabilise.
- Distinguishes PageRank from crawling and from index construction.
- Identifies server-side processing as work carried out on the web server before a response is returned.
- Gives an example of server-side work, such as a script that queries a database and builds a page.
- Identifies client-side processing as work carried out in the user's browser, typically by JavaScript.
- Gives an example of client-side work, such as validating form input or updating content without a page reload.
- Explains the trade-off that client-side checks are fast but can be bypassed by the user.
Examiner Tips
- 💡Map each option to structure, styling or behaviour before reading the distractors closely.
- 💡Test options with a concrete example, such as a heading for HTML, a background colour for CSS or a form check for JavaScript.
- 💡Check appendix 5d of the specification for further detail rather than relying on memory.
- 💡Ask whether each option describes preparing a lookup structure before any search, which is the defining feature of indexing.
- 💡Eliminate options that describe crawling, displaying results or ranking, because these are separate steps in a search engine.
- 💡Remember that an inverted index is the typical structure, and check whether an option describes keyword-to-page mapping.
- 💡Look for options that mention links and iterative calculation, which are central to PageRank.
- 💡Eliminate options that describe content-only ranking or crawling, because PageRank uses link structure.
- 💡Check whether an option says importance is shared across outgoing links rather than giving every link the same value.
- 💡Name the machine that runs the code in every answer, whether the server or the browser.
- 💡Give one concrete example for each side, such as a database query for the server or form validation for the client.
- 💡When an option says a check is secure only on the client, reject it and consider whether the server still validates the input.
Common Mistakes
- Describes JavaScript as the language that sets out page structure; correct it by assigning structure to HTML.
- Describes CSS as the language that adds interactivity; correct it by assigning styling to CSS and interactivity to JavaScript.
- Treats the three technologies as interchangeable; correct it by matching each one to its distinct role.
- Invents the content of appendix 5d; correct it by consulting the specification appendix for any detail that is assessed.
- Treats indexing as crawling; crawlers only fetch pages, while indexing stores their content in a lookup structure.
- Assumes the index is searched in full during each query; the index is built beforehand so that keyword lookup is fast.
- Describes the index as a list of web pages; an inverted index maps keywords to the pages that contain them.
- Claims PageRank depends mainly on keyword counts; it depends mainly on the links pointing to a page.
- Assumes every incoming link carries equal weight; links from highly ranked pages count for more.
- Confuses PageRank with the indexing process; PageRank orders pages that have already been found and stored.
- Describes JavaScript as always server-side; correct this by stating that JavaScript running in the browser is client-side.
- Confuses the web server with the user's device; correct this by naming which machine executes the code.
- Treats client-side validation as sufficient for security; correct this by stating that the server must still check data it receives.