2nd Amsterdam RecSys Meetup – Postponed

We’re currently working together with Sanoma planning the next RecSys meetup. The event will take place on October 28th at Sanoma in Hoofddorp. The building is next to the Hoofddorp train station and easy accessible by car.

More information about talks and other details will be available in the coming weeks.


The event has been postponed, we will be posting a new date shortly


1st RecSys:NL Meetup – Wrap up

The first RecSys:NL Meetup has taken place! The event was hosted by CWI with a line-up of three great talks by Lukas Vermeer of, Jimmy Lin of University of Maryland, and Niels Basjes of

This first meetup was an experiment checking how big the interest for a meetup like this would. We’re very happy to say that the interest and attendance by far supassed our expectations. There was a crowd of well above 30 people in the audience and the general interest in topics related to recommender system seemed high. Hopefully meetup was only the first of many recurring events.


The following talks were given at the event:

Recommendations at

Lukas Vermeer spoke about recommendations at one of the world’s largest booking websites, what type of recommendations, experiments and data provide recommendations for travelers. Even though there were some fine-grained details that Lukas could not reveal, the talk gave a lot of insight into what the team behind the recommendations at booking are facing in order to provide the best experience for their users.

There are no slides available for this talk.

WTF at Twitter

Jimmy Lin spoke about the Who(m) To Follow (WTF) service at Twitter which he was involved in developing during his extended sabbatical at Twitter (2010-2012). As the name suggests, the service recommends twitter’s users other users to follow.

There are no slides available for this talk.

 Big data at

Niels Basjes spoke in great detail about’s MapReduce-based recommendation systems. In the talk Niels described the development of the service from idea to production system and what challenges were involved.

Pictures from the event


1st RecSys Amsterdam Meetup – Agenda

The first RecSys Meetup in Amsterdam will be hosted by CWI on August 19th at 18:00.

We will start at around 18:00 at CWI where there’ll be three talks, refreshments and snacks. After the talks we head over to Cafe Restaurant Polder to mingle and have some drinks.

Please note that participants need to sign up for tickets at our Eventbrite page

We’re very excited to announce the following talks:

Talk 1: Recommendations at All RecSys Are Not Created Equal – Lukas Vermeer @lukasvermeer is the world’s leading online hotel and accommodation reservations company, and guarantees the best prices for any type of property – from small independents to five-star luxury. Guests can access the website anytime, anywhere from their desktop, mobile phone or tablet device, even without an account. The website is available in 41 languages, offers over 330,000 hotels and other accommodation properties in 180 countries.

The scale and diversity of the product and customer base poses quite a challenge to our recommender systems applications. Additionally, there are obstacles such as sparsity, scarcity, anonymity and the effects of time and price that are more relevant in industries where product prices are generally significantly greater than that of a rental movie or a book.

In this talk, we will look at some of the different applications of recommender systems as they appear on the site, dive into specific challenges we face when designing recommendation systems for the hospitality industry and discuss the necessity of mixing types of recommender systems with business logic to find the right balance.

Speaker Bio:

Lukas Vermeer is a Data Scientist at

Talk 2: WTF: The Who to Follow Service at Twitter – Jimmy Lin @lintool

WTF (“Who to Follow”) is Twitter’s user recommendation service, which is responsible for creating millions of connections daily between users based on shared interests, common connections, and other related factors. This paper provides an architectural overview and shares lessons we learned in building and running the service over the past few years. Particularly noteworthy was our design decision to process the entire Twitter graph in memory on a single server, which significantly reduced architectural complexity and allowed us to develop and deploy the service in only a few months. At the core of
our architecture is Cassovary, an open-source in-memory graph processing engine we built from scratch for WTF. Besides powering Twitter’s user recommendations, Cassovary is also used for search, discovery, promoted products, and other services as well. We describe and evaluate a few graph recommendation algorithms implemented in Cassovary, including a novel approach based on a combination of random walks and SALSA. Looking into the future, we revisit the design of our architecture and comment on its limitations, which are presently being addressed in a second-generation system under development.

Speaker Bio:

Jimmy Lin is an associate professor in the iSchool at the University of Maryland, affiliated with the Department of Computer Science and the Institute for Advanced Computer Studies. Recently, Lin just completed an extended sabbatical at Twitter, where from 2010-2012 he worked on services designed to surface relevant content for users and the distributed infrastructure that supports mining relevance signals from massive amounts of data.

Talk 3: Scalable search suggestions with Hadoop/MapReduce (provisional) -  Niels Basjes @nielsbasjes

In this talk, we will look at scalability of search suggestions (item-to -item recommendations of the most probable search term) in an online shopping scenario using Hadoop/MapReduce.

Speaker Bio:

Niels Basjes has been working for since May 2008. Before that he was working as a Web analytics architect for Moniforce, and as an ICT architect/researcher at the National Aerospace Laboratory in Amsterdam. Since the second half of the 1990s he has been working on processing problems that require scalability. He has applied these concepts in the past 15 years in aircraft/runway planning, IT operations and in the field of web analytics to build reports for some of the biggest websites in the Netherlands. Also at the primary focus of Niels Basjes are scalability problems and he is responsible for a shift in thinking about data and the business value it contains. Niels studied Computer Science at the TU Delft, and has Business administration degree at Nyenrode University.

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1st Recommender Meetup Amsterdam

The first Recommender Meetup Amsterdam will be held on Monday August 19th at CWI in Amsterdam Science Park.

We will be posting more information about this event at a later point in time.


RecSys:NL has a home

Finally the Dutch recommender systems community has a home. This space will be used to communicate meetups and other events related to recommender systems in the Netherlands.