Martin Colebourne

Autosuggest mechanisms vary in terms of several key behaviours:

• Whether they offer search suggestions, actual results, or search enhancement functionality.
• Whether one of the items in the drop down is selected automatically.
• Whether they use auto-complete and what behaviour it has.
• Whether they typically lead to a search results page, or directly to an end destination.
• These alternatives can be combined in many ways, but analysis suggests that auto-suggests typically fall into three groups.

The rest of this article describes those groups and why they occur. Understanding these common cases will help you to design for your particular case, although you will still have to get creative if your circumstances are unusual!

TYPE 1: SEARCH SUGGESTIONS

• In the first type of autosuggest, the drop down offer search suggestions – essentially completions and extensions of the current string.
• None of the items in the drop down is selected by default – the user has to either arrow down to select one, or click on one with the mouse.
• Auto-complete fills the first suggestion into the search box, but it is a weak form of auto-complete: the user has to use the right arrow to ‘accept’ the suggestion, and then hit Enter to run the search (hitting Enter will just send the string as it has been typed).
• In all cases, the autosuggest leads to a full results page.

This type of autosuggest is typically paired with a search results page that is shown every time. The benefits of search suggestions are to allow the user to type fewer characters, by completing the string for them; to help resolve uncertain spellings; and more importantly, to encourage the user to enter a more specific search term (and one that is known to work), thus increasing the power of their query. This is especially useful if the universe to be searched is very large – as it is with a web search.

Examples include Google.com, Yahoo.com, Bing.com, ebay.com.

TYPE 2: SEARCH RESULTS

• In the second type of autosuggest, the drop down offers actual results.
• One item in the drop down is selected by default. This means that it is not possible to send the string that has been typed – only to accept one of the items from the drop down. As a result, the drop down usually contains a ‘Show all matches’ or ‘Search All’ option to allow the user to bypass the suggestions.
• Autosuggests of this type might use auto-complete, but this is a ‘strong’ form of auto-complete – the completed characters indicate what will happen when hitting Enter – there is no way of interacting with the auto-completed characters. (In essence auto-complete is simply an additional way of visualising the selected item in the drop down.
• Since the drop down shows actual results, selecting one leads directly to a destination. This means that the user doesn’t see a results page in most cases.

This type of autosuggest is useful where the universe of results is relatively small and where there isn’t an obvious location to display a search results page (e.g. it would be necessary to instantiate a new window in order to show results), since it offers the possibility to avoid search results and go directly to the end destination.

Another consideration is that search suggestions are not useful in all circumstances: if the universe of results is relatively small (thousands of items, rather than millions); the content of each searchable item is small (i.e. they are poorly tagged, or contain little text); or the lexicon of words within the items is relatively restricted (e.g. a list of people’s names); or some combination of these, then search suggestions will offer little benefit. This is because there is either less need to encourage the user to enter a more detailed search string, or because the limited content of each searchable item makes it difficult to offer useful suggestions.

Examples of autosuggests showing results include: Wikipedia, Google Finance, Yahoo Finance.

TYPE 3: SEARCH ENHANCEMENT TOOLS

A third type of autosuggest takes a different approach, with more complex functionality.

• The drop down offers ‘search enhancement’ features, in the form of options to scope the search, or to target words within the search string.
• Since these are suggested enhancements to the search term, there is not usually an item selected by default – ignoring the suggestions simply send the string as typed.
• Auto-complete is not usually used.
• This type of autosuggest is directly associated with a search results page – particularly a context where the results page can be seen as the actual destination (e.g. in a file browser), or at least a significant destination in its own right, rather than just a route to a end result.

This type of autosuggest is useful where there is a need to search a relatively structured set of data like a list of files – the enhancement tools can allow the user to target each word at a particular field. Alternatively, the drop down can present options with scope the search – this is useful where there are multiple independent result sets.

Examples of search enhancement autosuggests include Finder (OSX) and Flickr.com.

TYPE 4: COMPOSITE

The fourth type of autosuggest bridges multiple result sets, combining suggestions and results in multiple sections. Less commonly, results and suggestions may be mixed together in a single list.

• A composite autosuggest may offer any combination or suggestions, results and search enhancements.
• In most cases, the top item in the drop down is selected by default – this is useful as it helps to define what will happen when the user hits Enter, which may not be clear given that the search mechanism is bridging multiple result types.
• If auto-complete is offered, it is likely to be of the strong type described under type 2.
• A composite autosuggest will lead to a results page where necessary. However, in many cases, they are weighted towards going directly to a destination.

Composite autosuggests are useful in situations where a single search box is being used to bridge multiple results sets, particularly where those result sets have different properties – e.g. a web search, along with local favourites and history. A composite autosuggest can combine elements of all three other types, as in the example above, where the top section shows search suggestions, the middle section shows results and the bottom section allows for search scoping.

Less commonly, an autosuggest may offer composite functionality, but mingle the types in a single list, rather than displaying them in separate sections. This is the approach taken by Chrome.

Examples of composite autosuggests include Safari, Internet Explorer, Chrome and Spotlight (OSX).