Design patterns are acknowledged as powerful conceptual tools to improve design quality and to reduce the time and cost of design by effect of the reuse of “good” solutions. In many fields such as software engineering, web engineering, and interface design, patterns are widely used by practitioners and are also investigated from a research perspective. Still, the concept of design pattern has received marginal attention in the arena of user interfaces (UIs) for Recommender Systems (RSs). To our knowledge, a little is known about the use of patterns in this specific class of applications, in spite of their increasing popularity, and no RS specific interface pattern is available in existing pattern languages. We have performed a systematic analysis of 28 real-world RSs in a variety of sectors, in order to: (i) discover occurrences of existing general (i.e., domain independent) UI patterns; (ii) identify recurrent UI design solutions for RS specific features; (iii) elicit a set of new UI patterns for RS interfaces. The analysis of patterns occurrences highlights the degree at which “good” UI design solutions are adopted in RSs for the different sectors. The new patterns can be used by UI designers of RSs to improve the UX of their systems.

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Interaction Design Patterns in Recommender Systems
Paolo Cremonesi,
Politecnico di Milano, Italy
Mehdi Elahi,
Politecnico di Milano, Italy
Franca Garzotto,
Politecnico di Milano, Italy
Corresponding article: Cremonesi, Paolo; Elahi, Mehdi; Garzotto, Franca; ,Interaction Design Patterns in
Recommender Systems, 11th Biannual Conference on Italian SIGCHI Chapter, 66-73, 2015, ACM

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Outline
n Introduction:
n Recommender Systems
n Design Pattern
n Analysis
n Methodology
n Results
n Conclusion and Future Work

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Recommender Systems
tools that support users decision making by suggesting products
that can be interesting to them.
Examples of Recommender Systems:

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Design Pattern: Definition
“… describes a problem which occurs over and over again in our
environment and then describes the core of the solution to that
problem, in such a way that you can use this solution a million times
over, without ever doing it the same way twice”
C. Alexander. The timeless way of building, volume 1. Oxford
University Press, 1979.

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Design Pattern: Properties
Main properties that the design pattern hold:
n Solves a problem: Patterns capture solutions, not just abstract
principles or strategies.
n Be a proven concept: Patterns capture solutions with a track
record, not theories or speculation.
n Provide a not obvious solution
n Have a significant human component

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Design Pattern: Main Elements
usually consists of the following elements:
n Problem: Problems are related to the usage of the system
and are relevant to the user or any other stakeholder.
n Usage: situation(s) in which the problems occur and the
pattern applies.
n Solution: a proven design solution to the problem,
described in terms of design characteristics of the
interface and the interaction

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Design Pattern: Main Elements
usually consists of the following elements:
n Rational: why the pattern actually works - The rationale
for the solution (principles of UX quality can be used as
arguments)
n Examples: how the pattern has been successfully
applied in real life systems. This is often accompanied
by a screenshot and a short description.
n Related Patterns: Other patterns may be needed to
solve sub problems

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Analysis: Methodology
1. selecting 28 real-world RSs grouped by “application domain” or
“business sector”;
2. inspecting the selected RSs using a pre-defined set of user
scenarios;
3. identifying recurring design solutions;
4. matching these solutions against existing UI patterns available in
a well-established pattern library, or articulating the description of
these solutions in terms of new patterns.

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Analysis: Inspected RSs
Domain RS Title
Recomended
Items
Online Dating Meetic, Badoo, PerfectMatch User Profiles
Photo Sharing
Flickr, DeviantArt, Imgur,
Photobucket
Photos
Social Bookmarking
StumbleUpon, Pinterest,
WeHeartIt
Online content
Social Network
Facebook, LinkedIn, Twitter,
MySpace, Google+, FourSquare
User Profiles,
Posts, Offers,
POIs
Social News Reddit, 9GAG, Digg Online content
Tourism Services
Booking, AirBnB, TripAdvisor,
Holiday, Watchdog, Gogobot,
Volagratis, Trivago, Yelp
POIs
R. K. Nageswara. "Application domain and functional classification of recommender systems—a
survey." DESIDOC Journal of Library & Information Technology 28, no. 3 (2010): 17-35.

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Example of Scenarios
Tourism Recommender Systems:
n A young couple wants to spend their holiday in London. They
would prefer to make an online reservation of their
accommodation and they register to a website for online
booking of hotels and bed & breakfast. They enter some
information requested by the service and then receive a list of
recommendations ordered by price. They choose one of them
and make reservation.

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Results: Design Pattern Usage in
RSs
Cremonesi, Paolo; Elahi, Mehdi; Garzotto, Franca; ,Interaction Design Patterns in Recommender
Systems, 11th Biannual Conference on Italian SIGCHI Chapter, 66-73, 2015, ACM

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Results:Why?!
n the greater the usage of
design pattern the more
complex is the RS
n Because the
functionalities offered by
Tourism Services and
Online Dating systems,
as well as the interaction
models, are more
complex in comparison
to the other RSs.

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Results: Generic Design Patterns in
RSs
Cremonesi, Paolo; Elahi, Mehdi; Garzotto, Franca; ,Interaction Design Patterns in Recommender
Systems, 11th Biannual Conference on Italian SIGCHI Chapter, 66-73, 2015, ACM

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Results:Why?!
pagination
Input prompt

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Specific Design Patterns in RSs
Social Connection
Facebook
Rationale:
• people are interested in doing
things with their friends or with
others who have similar tastes or
interests
• It also provides a better estimation
about what could be the users’
interests or tastes.

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Specific Design Patterns in RSs
Added Comments
Deviantart
Rational:
• people might be more prone to give
opinion directly to other users using
natural language, instead of other
interaction tools, such as like/dislike
or star ratings.
• The items with a large number of
comments might be interesting for
the community, for example, to be
shown on the top of the activity stream

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Specific Design Patterns in RSs
Social Login
Tripadvisor
Rational:
• users may prefer to use their online
profiles to avoid repeatedly
entering their information other
websites
• users may want to allow the system
to improve the recommendation
quality, by letting the system to
mining their social interactions

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Specific Design Patterns in RSs
Similar Content
Facebook
Rationale:
• users perceive those objects that are close to
each other as forming a group.
• similar content may better be shown close to
the currently displayed content
• The user will likely perceive the elements as
part of a group

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Specific Design Patterns in RSs
Profile as Business Card
PerfectMatchbody
Rationale:
• Users may enjoy f inding
elements of UI that they may
associate to their previous
experiences (e.g. business card
format) that resembles a tangible
object.

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Conclusion
We have
n performed a comprehensive analysis and identified a
wide range of instances of existing “generic” UI
design patterns
n we have discovered a number of recurrent UI design
problems and solutions that are specific to RSs. (No
previous study has analyzed UI design patterns for RSs)
n paved the ground for future research bridging RSs and
Interface Design by means of design patterns which
may be beneficial for RS practitioners to improve the UX
quality of RSs

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Future Work
n to study the possible correlation between the design
patterns adopted in RSs and the type of items
recommended by them.
n For example, the UI design for music RSs would be
different from computer products RSs.
? Design
Pattern ?

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Future Work
n to study the possible correlation between the
design patterns adopted in RSs and the
recommendation algorithm.
n For example, the design patterns adopted in
Collaborative Filtering RSs can be different from
Knowledge-based RSs.
? Design
Pattern ?

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Thank you!
Corresponding article: Cremonesi, Paolo; Elahi, Mehdi; Garzotto, Franca; ,Interaction Design Patterns in
Recommender Systems, 11th Biannual Conference on Italian SIGCHI Chapter, 66-73, 2015, ACM