  In recent years, the rise of deep learning and automation requirements in the
software industry has elevated Intelligent Software Engineering to new heights.
The number of approaches and applications in code understanding is growing,
with deep learning techniques being used in many of them to better capture the
information in code data. In this survey, we present a comprehensive overview
of the structures formed from code data. We categorize the models for
understanding code in recent years into two groups: sequence-based and
graph-based models, further make a summary and comparison of them. We also
introduce metrics, datasets and the downstream tasks. Finally, we make some
suggestions for future research in structural code understanding field.
