Table 1.

Transfer learning subsettings.

	Subsetting Name	Description	Label Information
1	Inductive TL	the target task is different, but related, from the source task	comes from the target domain
2	Transductive TL	the source and target tasks are the same, while the source and target domains are different	comes from the source domain
3	Unsupervised TL	the target is different from, but related to, the source task, and the focus is on solving unsupervised learning tasks in the target domain	is always unknown for both the source and the target domains