  User modeling, which learns to represent users into a low-dimensional
representation space based on their past behaviors, got a surge of interest
from the industry for providing personalized services to users. Previous
efforts in user modeling mainly focus on learning a task-specific user
representation that is designed for a single task. However, since learning
task-specific user representations for every task is infeasible, recent studies
introduce the concept of universal user representation, which is a more
generalized representation of a user that is relevant to a variety of tasks.
Despite their effectiveness, existing approaches for learning universal user
representations are impractical in real-world applications due to the data
requirement, catastrophic forgetting and the limited learning capability for
continually added tasks. In this paper, we propose a novel continual user
representation learning method, called TERACON, whose learning capability is
not limited as the number of learned tasks increases while capturing the
relationship between the tasks. The main idea is to introduce an embedding for
each task, i.e., task embedding, which is utilized to generate task-specific
soft masks that not only allow the entire model parameters to be updated until
the end of training sequence, but also facilitate the relationship between the
tasks to be captured. Moreover, we introduce a novel knowledge retention module
with pseudo-labeling strategy that successfully alleviates the long-standing
problem of continual learning, i.e., catastrophic forgetting. Extensive
experiments on public and proprietary real-world datasets demonstrate the
superiority and practicality of TERACON. Our code is available at
https://github.com/Sein-Kim/TERACON.
