Send out the spider
How does a search engine know what is on the web? It sends out a spider program. Be the spider, then write its steps.
You are the spider program. You read a web page, then follow its links to find more pages.
What the words mean
- Spider program: a program that visits web pages and reads their words. It is also called a web crawler.
- Index: an organised list of web pages and the words on them.
- Rank: to put the results in order, with the most suitable first.
The three jobs
- The spider program follows links from page to page and reads each one.
- It sends what it finds to the index, where it is organised.
- When you search, the search engine finds your words in the index and ranks the pages.
For teachers
This tool goes with Unit 2, Lesson 6 (Using more complex search techniques, part 1) of the Year 4 Inspire Computing student book. Use the parts in order. Each one takes about ten minutes.
- Before the screen: give some pupils a card with a page name and a few words. Join the cards with wool, leaving one card with no wool to it. A "spider" walks along the wool and reads each card, and a scribe writes the words on index cards. Then ask why nobody found the card with no wool.
- A difference from the book: the lesson says the spider searches for the term you typed. In a real search engine the spider has already done its work, and your search reads the index. This tool shows that order, because it explains why an index exists. End-of-unit question 3 still expects the option about searching web pages for key words, so tell pupils that is the answer to give.
- Program the spider has one right order. Wrong orders are useful: ask what the spider did, and what to change. It also prepares for sequencing and repetition in Unit 4.
- Use the index shows an untrue page ranked first for "elephant". Use it to link back to reliability in Lessons 1 and 2. Real search engines rank in many more ways than this one does.
- Exit question: a new web page has no links going to it. Why might a search engine not find it?
- Nothing a pupil does here is saved or sent anywhere. All the pages are made up.
More to try
- Look at the index at the back of a book. How is it like a search engine's index?
- Draw a web of five pages. Which page would a spider not be able to find?
- Say the spider's steps to a partner without looking at the screen.