An introduction to the evolution of databases and data models since the 1960s:

• Haadi, Muhammed. The Evolution of Database. All About Databases (2010)

This free online course on database design for historical research, written by a historian, is useful for thinking about designing structured data even if you don't plan to use relational databases:

• Merry, Mark. Designing Databases for Historical Research. (Institute of Historical Research)

A helpful introductory online workshop:

• Tooling up for the Digital Humanities: Databases