The Target.com recommender system is obviously using collaborative filtering recommendation algorithms. However, it is not using the traditional way but similar to what other major online retail stores use like Amazon.com, Walmart.com, etc., which is item based collaborative filtering.
There are many advantages to use item based versus other ways such as user based because items will always be items. Items do not change as much people do. So, the relationship between items are more permanent and more direct comparison we can make when compare similarity between items because they do not change over times. Aslo, you can save a lot of computation resources by evaluating relationship between items instead of customers because you probably have few items than number of customers in your system. This way, the system can run recommendation more frequently, make them more current, more up to date and better and able to use more complicated algorithms because you have less relationships to compute. Furthermore, item based method is based on people actually spending money, so you always going to get better and more reliable results when your based recommendation on people actually bought as opposed to what they view and what they click on.
At Target.com after a customer search an item and select, will navigate to the product page. This is where the recommender system will run the job to recommend other related products to customers. The recommender system comprise of 4 recommendation sections. The top one is the “frequently bought together” and it shows only the top 3 rated items. If customers want to explore more related items, they can go to “More to Consider” section. Or if customers just want to see similar items, they can go to “Similar Items”. The recommender system also show what other customers also bought when buying that item.