← QCE Digital Solutions Unit 1

Search engines as a digital solution

A digital solution that solves the problem of finding information by indexing web pages and ranking the results for a user's query.

Part of: QCE Digital Solutions Unit 1 — Understanding Digital Problems — Module 18

Understanding Search engines as a digital solution in QCE Digital Solutions Unit 1

What it does: The query is the input from the user, and the search engine matches it against the index. Ranking gives each page a score for the query and orders results from highest score to lowest. Crawlers visit pages and add them to an index. Searching the index is much faster than searching the live web. Ranking sorts results by signals such as relevance, so the most useful pages are near the top. The core problem is finding information in a huge amount of web content. Storing files is a different problem. Ranking can be influenced by advertising or other factors, so the top result is not always the most relevant or fair.

Common mistakes: Indexing adds the words found on each page to the index. Removing them would leave nothing to search. It should be ADD page words to index. Results are ranked by the relevance score worked out in the loop, not by title. It should be SORT matches BY score DESC.

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This module's key terms are also in a printable crossword (Modules 1–58) and word search (Modules 1–81).

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Learning
Duo
How does a search engine find pages so it can answer queries quickly?
It searches the whole live web from scratch each time you typeIt crawls web pages and stores them in an index
Matches
Search engine shows every page on the web in random order
↓
A search engine does not return pages randomly. It must rank results by relevance to the query so the user can find useful information.
Applying
Meanings
Term
search engine
Meaning
A digital solution that solves the problem of finding information by indexing web pages and ranking the results for a user's query.
Practice
BEGIN SearchEngine
Testing
Gaps
(page)
Check Answer
Spots
1FOR each page IN crawl_list
2 REMOVE words from index

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Quick Questions

1. How does a search engine find pages so it can answer queries quickly?
A. It crawls web pages and stores them in an index ✓
B. It searches the whole live web from scratch each time you type
Crawlers visit pages and add them to an index. Searching the index is much faster than searching the live web.
2. What does a search engine do with the results it finds for a query?
A. Shows them in a random order
B. Ranks them so the most relevant appear first ✓
Ranking sorts results by signals such as relevance, so the most useful pages are near the top.
3. Which one is the user's query?
A. The words typed in to describe what they want to find ✓
B. The list of pages the search engine stores
The query is the user's input. The stored list of pages is the index, which is a different part of the system.
4. Which describes the problem a search engine solves?
A. Storing a user's personal files securely
B. Finding useful information among billions of web pages ✓
The core problem is finding information in a huge amount of web content. Storing files is a different problem.
5. A student searches 'best phone' and the top results are paid adverts. What limit does this show?
A. Bias: ranking can favour some pages over more useful ones ✓
B. The index has crashed
Ranking can be influenced by advertising or other factors, so the top result is not always the most relevant or fair.

Match the Pairs

crawler → A program that follows links from page to page to discover and collect web pages for the search engine
index → A stored database of words and the pages they appear on, so results can be found quickly
The user's query is the words typed in to describe the information they want to find → query = "best study tips year 11"
Ranking sorts the matching pages so the most relevant results appear first → results.sort(key=score, reverse=True)
Search engine shows every page on the web in random order → A search engine does not return pages randomly. It must rank results by relevance to the query so the user can find useful information.
Top result = always the most accurate and unbiased page → A top-ranked page is not always accurate or unbiased. Ranking can be affected by bias, paid adverts and poor relevance, so users must check sources.

Key Term

search engine
A digital solution that solves the problem of finding information by indexing web pages and ranking the results for a user's query.

Fill in the Blanks

1. FOR EACH page IN web crawl(page) index(page)
Hint: Type the function name for visiting a page to collect its content.
2. FOR EACH word IN page.text ADD page TO index[word]
Hint: Type the loop variable that is used as the index key for each page.
3. query ← INPUT("Search: ") matches ← index[query]
Hint: Type the variable that holds the user's search words.
4. SORT matches BY score DESCENDING DISPLAY matches
Hint: Type the keyword for the sort order that puts the best-scoring results first.
5. IF page.relevance < 0.2 THEN REMOVE page FROM results
Hint: Type the comparison operator that finds pages with a low relevance score.

Spot the Error

Question 1
A FOR each page IN crawl_list
B REMOVE words from index
C ADD links to crawl_list
Line B — Indexing adds the words found on each page to the index. Removing them would leave nothing to search. It should be ADD page words to index.
Question 2
A FOR each page IN matches
B page.score ← relevance(page)
C END FOR
D SORT matches BY title DESC
Line D — Results are ranked by the relevance score worked out in the loop, not by title. It should be SORT matches BY score DESC.
Question 3
A OUTPUT 'Search for:'
B query ← INPUT()
C words ← LENGTH(query)
D results ← index.find(words)
Line C — LENGTH gives a number, not a list of words, so index.find cannot use it. The query should be split into words with SPLIT(query, ' ').
Question 4
A score ← 0
B score ← score - matching_words
C RETURN score
Line B — Each matching word should raise a page's relevance score, so it must be added. Subtracting would rank the best matches lowest.
Question 5
A FOR each result IN results
B IF result.relevant THEN
C HIDE result
D END IF
Line C — Relevant results should be shown to the user. Hiding them removes the useful pages. It should be DISPLAY result.

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