Faceted Search

Faceted search, also called faceted navigation or faceted browsing, is a technique for accessing information organized according to a faceted classification system, allowing users to explore a collection of information by applying multiple filters. A faceted classification system classifies each information element along multiple explicit dimensions, enabling the classifications to be accessed and ordered in multiple ways rather than in a single, pre-determined, taxonomic order.

Facets correspond to properties of the information elements. They are often derived by analysis of the text of an item using entity extraction techniques or from pre-existing fields in a database such as author, descriptor, language, and format. Thus, existing web-pages, product descriptions or online collections of articles can be augmented with navigational facets.

Faceted search has become the de facto standard for e-commerce and product-related web sites. Other content-heavy sites also use faceted search. It has become very popular and users are getting used to it and even expect it.

Faceted search lets users refine or navigate a collection of information by using a number of discrete attributes – the so-called facets. A facet represents a specific perspective on content that is typically clearly bounded and mutually exclusive. The values within a facet can be a flat list that allows only one choice (e.g. a list of possible shoe sizes) or a hierarchical list that allow you to drill-down through multiple levels (e.g. product types, Computers > Laptops). The combination of all facets and values are often called a faceted taxonomy. These faceted values can be added directly to content as metadata or extracted automatically using text mining software.

For example, a recipe site using faceted search can allow users to decide how they’d like to navigate to a specific recipe, offering multiple entry points and successive refinements.

As users combine facet values, the search engine is really launching a new search based on the selected values, which allows the users to see how many documents are left in the set corresponding to each remaining facet choice. So while users think they are navigating a site, they are really doing the dreaded advanced search.

There are best practices in establishing facets. They are:

do not create too many facets - presenting users with 20 different facets will overwhelm them; users will generally not scroll too far down beyond the initial screen to locate your more obscure facets;

base facets on key use cases and known user access patterns - idenfity key ways users search and navigate your site. Analysing search logs, evaluating competitor sites, and user research and testing are great ways to figure out what key access points users are looking for. Interviewing as few as 10 users will often give you great insight into what the facet structure should be;

order facets and values based on importance - not all facets are equally important. Some access points are more important than others depending on what users are doing and where they are in the site. Present most popular facets on the top. When determining order for navigation, again think about your users and why they are coming to your site.

leverage the tool to show and hide facets and values - while the free or low-cost faceted search tools don’t all offer these configuration options, more sophisticated faceted search solutions allow you to create rules to progressively disclose facets.

Think of a site offering online greeting cards. While the visual theme of the card – teddy bears, a sunset, golf – might eventually be important to a user, it probably isn’t the first place they will start their search. They will likely start with occasion (birthday, Christmas), or recipient (father, friend), and then become interested in themes further down the line. Accordingly, we might hide the “themes” facet until a user has selected an occasion or recipient. You can selectively present facets based on your understanding of your users and their typical search patterns (as mentioned in the previous “do”).

Also take advantage of the search engine’s clutter-reducing features, such as the “more...” link. This allows you to present only the most popular items and hide the rest until the user specifically requests to see them. You can also do this at the facet level, collapsing lesser-used facets to present just the category name and let users who are interested expand that facet.

facet display should be dependent on the area of the site. If you are in the first few layers of your site, you should show fewer facets with more values exposed, whereas if you are deeper into product information you should show more facets, some with values exposed and others hidden.

create your taxonomy with faceted search in mind - a good taxonomy goes a long way in making a successful faceted search interface.

There are some important guidelines to follow in taxonomy design. Facets need to be well defined, mutually exclusive and have clear labels. For example, having one facet called “Training” and another “Events” is confusing: where do you put a seminar? Is it training or an event? If you have to wonder, your users will too. The taxonomy depth (how many levels deep does it go) and breadth (how many facets wide is it) are other important considerations. Faceted search works better with a broad taxonomy that is relatively shallow, as this lets users combine more perspectives rather than get stuck in an eternal drill down, which causes fatigue. The facet configuration and display rules will help you create the optimal progressive presentation of these facets so as to not overwhelm users with the breadth.

If you are torn between two places in the taxonomy for a term, consider putting it in both places. This is called polyhierarchy, and it is a good way to ensure findability from multiple perspectives. Polyhierarchy is best served within a facet rather than across multiple facets. Since facets should be mutually exclusive, you shouldn’t have much need to repeat terms across facets, which can be more confusing than helpful.

The most important thing however, is to be prepared to break any of these rules in the name of usability. Building a faceted taxonomy involves understanding your users’ search behavior.

As the trend towards increased social computing continues, Web 2.0 concepts are entering the realm of faceted search. We are starting to see social tags being used in faceted search and browse interfaces. Buzzillions.com, a product-review site, is using social tag-based facets in its navigation, allowing users to refine results based on tags grouped as "Pros" or "Cons". This site uses a nice blend of free social tagging and control to ensure good user experience; when you type in a tag to add to a product review, type-ahead verifies existing tags and prompts you to select one from the existing list of matches to maximize consistency.

Ultimately, navigation and search is one of the main interactions users have with your site, so getting it right is not just a matter of good design, it impacts the bottom line. Faceted search is a very popular and powerful solution when done well; it allows users to deconstruct a large set of results into bite-size pieces and navigate based on what’s important to them. But faceted search by itself is not necessarily going to make your users lives easier. You need to understand your users’ mental models (how they seek information), test your assumptions about how they will interpret your terms and categories and spend time refining your approach.

Faceted search can just add more complexity and frustrate your users if not considered from the user perspective and carefully thought through with sound usability principles in mind. Faceted search is raising the bar in terms of findability and how well you execute will determine whether your site meets the new standard.