How Search Engines Work and the Librarian Metaphor

SEO is much easier if you understand how search engines work and my favorite metaphor is to think of a search engine as a librarian.

How is a search engine like a librarian?

Search engines work in three stages: spidering, indexing and ranking (the ranking stage is often referred to as serving).  Let’s consider each stage in the following table.

	Search Engine	Librarian
Spidering	Search Engine spiders crawl the web looking for new content or people register to have their sites crawled.	Librarians search for new publications or publishers contact them to tell them about new books.
Indexing	Search Engines analyse and index website content.	Bibliographers review and classify books.
Ranking	Search engines rank content using things like the page title, content and backlinks.	Librarians rank reading lists using things like the book title, abstract and document citations.

Table 1: A table comparing the three stages of search engine operation with that of a Librarian.

How Are Search Engine and Librarian Ranking Algorithms Similar?

Consider the following scenario. You ask a librarian to help you find a book on “the history of gardening spades”. What would happen?

1. The librarian would get a list of books from a database
2. They would review the title, abstract and citations and print off a list of books
3. They would visit the shelf and skim the books for relevance

Let’s assume there are two books on the shelf:

Book A: The History of Gardening Tools
Book B: The History of Gardening Spades (exact match)

Book B is an exact match. On the face of it looks like Book B would be the most relevant. But what if book A had a really good chapter on “the history of gardening spades”.  What if a quick skim of Book A showed us the following.

	Book A	Book B	Most Relevant
Title	The History of Gardening Tools	The History of Gardening Spades	Book B (exact match)
Relevant Pages	126	67	Book A
Relevant Diagrams	Lots	Not Many	Book A
Author Reputation	High	Unknown	Book A

Table 2: A table comparing the salient features of each book relating to the information we require.

From Table 2 we can see that Book A might be the better contender, but what if I told you that it was written in 1926 and that Book B was released last year. Which would you choose then?

There is no right or wrong answer to this question and search engines are presented with thousands of dilemmas like these every millisecond. In search engine terms, these are called Ranking Factors and the recipe that we use to make our decision is called the Algorithm.

For example, one librarian might completely discount Book A while another might say that it has stood the test of time and is therefore a strong contender.

This is analogous to the differences that we see in the results generated by different search engines such as Google and Bing. Both have different algorithms and return different results.

How can The Librarian Metaphor Help your SEO Efforts?

If you think of your website as a book and the search engine as a librarian, then Search Engine Optimisation will be intuitive. Just make sure that your book has the best and most relevant content and that you maintain a good reputation and the search engine will keep sending people to your spot on the shelf.