Personalization, user-adaptive and recommender systems I am currently undergoing research into the field of systems that adapt content and layout depending on how the user uses the application. I am however puzzled as to the following terms as they are not really described properly and there seems to be no content on the differences between them which has been widely accepted. I have been researching and have seem the following terms pop up.


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*Personalization Systems

*User-Adaptive Systems

*Recommender Systems


Anyone willing to have a go at these terms?
 A: Recommender systems are the most straightforward to define: They're systems that try to recommend items to users, or predict how they might rate an item. ("Item" interpreted loosely—a product, a piece of information, another social media account to follow, etc.)
Wiki defines adaptation as when a system "adapts its behaviour to individual users based on information acquired about its user(s) and its environment." You'll find similar definitions elsewhere. This 1999 tutorial argues for defining a user-adaptive system as anything that "adapts its behavior to the individual user $\mathscr{U}$ on the basis of nontrivial inferences from information about $\mathscr{U}$."
This syllabus from a course on user adaptive systems includes modeling user belief and user profiling, along with recommender systems. One adaptive research group summarizes its adaptive and personalization work: "We are exploring how software can adapt to an individual, through techniques such as adaptive hypermedia and user context modelling." 
As Microsoft Research's Adaptive Systems and Interaction group describes itself, "ASI is at the center of user modeling at Microsoft Research, focused on inferring the goals and needs of users from multiple sources of information about activity and interests."
Again per Wiki, "Personalization, also known as customization, consists of tailoring a service or a product to accommodate specific individuals, as opposed to general groups."
With all this in mind, I'd offer these definitions:


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*A product is personalized if created with a particular individual in mind.

*A user-adaptive system is one that continuously or recurrently personalizes its own behavior based on interaction with a user.

*A recommender system is one that recommends items to a user, and may or may not be adaptive.


Though, I'd note that they're deeply related, and drawing the line between personalization and user-adaptive may be subjective and tricky at times. A custom printed sales flyer sent by mail with items I might be interested in is clearly personalized, and clearly not adaptive. 
If the firm tracks my purchases and updates a model of my preferences, is the system that chooses the items adaptive? The answer to that seems to rely on—forgive the pun—more personalized definitions.
