Yesterday’s Thoughts

October 14, 2007

How Search Can Go Wrong

A few weeks ago, I had a bad experience using search at an e-commerce site. It cost me a little money and it cost the merchant a little good will. It was neither enough money nor enough good will to be serious, but that was just luck. If this had happened with a higher cost purchase the costs could have easily been higher. Since that time I have had several different similar experiences, so I thought I’d write about it to save you some cost or good will.

Most frequently when I am searching, if I enter multiple terms I am implicitly requesting results for items that match all of the terms. This is the way that results from Google and Yahoo work. If you search for Repair Manual the results are pages that contain both the term repair and the term manual.1

I’ve bolded and in the last sentence because that is the operative term. The results returned by Google and Yahoo are the logical conjunction (and) of the separate results for the individual terms. If I search for Repair and Manual, Google helpfully informs me, “The ‘AND’ operator is unnecessary — we include all search terms by default.”

The other commonly encountered method of combining results is disjunction. This search returns all pages that contain either repair or manual. There are obviously many more results in this case. For repair and manual Google returns not quite 2.5 M results, while for repair or manual Google returns more than 40 M results.

The problem that I encountered, was that many web sites silently ignore the de facto standard set by search engines and attempt disjuctive, or, searches. Instead of returning pages that contain repair and manual they return pages that contain repair or manual. I’m not exactly sure why so many e-commerce sites seem to do this, but it may have to do with available tools. I know that disjuctive search is the default for the Apache Lucerne search engine library, although Ferret, the Ruby search engine gem which was inspired by Lucerne, switches the default to conjunctive search.

Can you see where this is going?

I was attempting to repair a dishwasher that had stopped cleaning the dishes on the top rack. Some small piece of plastic – perhaps the inner liner of a yogurt container – had gotten loose in the dishwasher, been sucked into the pump and macerated. Small pieces of plastic had been blown through the entire circulatory system. I had cleaned much of it out, but it still wasn’t working and I wanted a closer look, but I wasn’t sure how to take some parts off without breaking them. All I needed was a Repair Manual for my washer.

A little Googling around led me to an appliance repair site. I located my make and model of dishwasher and searched for repair manual. When there was only one result returned, I wasn’t surprised. I only expected one.

Without any closer examination I added it to my cart along with the other part that I knew I needed.

Unfortunately, when the part arrived, it was accompanied not by a detailed Repair Manual but by the ludicrous User Manual that I already had.

I was a little annoyed with myself for not being more careful and a little annoyed at the merchant for giving me a misleading answer to my question, but the cost was minimal (perhaps I would have been more careful if it had been higher).

As I noted above, this experience has recurred several times since, minus the steps of adding an incorrect item to my shopping cart and buying it. I think merchants are making a mistake in ignoring the search engine standard and courting a possible liability.

Customers are dissatisfied by these unexpected results and if they make a purchase based on them, they are going to want their money back.


  1. Both search engines do some other processing, so the returned pages might contain “manuals” instead of “manual” or even “fix-it” instead of “repair.”

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