3.1. Data
Dataset consists of 98 ship engines that could be categorized with five
types of engines. Therefore, our hierarchical model has a 1-5-98
structure; 1 engine archetype, 5 engine types, and 98 ship types. The
numbers of ships in the five categories are also different as in section
2.1.
Fig. 1 shows the age, type of engine, and ship of existing data. As can
be seen from the figure, the amount of data for each category is highly
unbalanced. Moreover, the similarity between data under the same
category could be inferred; for example, data with the same type of
engine display a similar age period.