  The recommendation systems aim to improve the user engagement by recommending
appropriate personalized content to users, exploiting information about their
preferences. We propose the enabler, a hybrid recommendation system which
employs various machine-learning (ML) algorithms for learning an efficient
combination of several recommendation algorithms and selects the best blending
for a given input.Specifically, it integrates three layers, namely, the trainer
which trains the underlying recommenders, the blender which determines the most
efficient combination of the recommenders, and the tester for assessing the
performance of the system. The enabler incorporates a variety of recommendation
algorithms that span from collaborative filtering and content-based techniques
to ones based on neural networks. It uses the nested cross validation for
automatically selecting the best ML algorithm along with its hyper-parameter
values for the given input, according to a specific metric. The enabler can be
easily extended to include other recommenders and blenders. The enabler has
been extensively evaluated in the context of video-streaming. It outperforms
various other algorithms, when tested on the Movielens 1M benchmark
dataset.encouraging results. Moreover For example, it achieves an RMSE of
0.8206, compared to the state-of-the-art performance of the AutoRec and SVD,
0.827 and 0.845, respectively. A pilot web-based recommendation system was
developed and tested in the production environment of a large telecom operator
in Greece. Volunteer customers of the video-streaming service provided by the
telecom operator employed the system in the context of an out-in-the-wild field
study with a post-analysis of the enabler, using the collected ratings of the
pilot, demonstrated that it significantly outperforms several popular
recommendation algorithms.
