Here are my first thoughts:
What We Should Include:
I think that any material relating to databases should certainly explain their advantages - concurrent access, central storage, security, single source of truth. We should also include information about data types - text, number, date, and in particular the spatial data type - how to store points, lines and polygons in the database. Connecting the GIS to the database and viewing and editing the data is also fundamental.
|R-Tree Index (from: http://en.wikipedia.org/wiki/R-tree)|
What Should Be Left Out:
|E-R Diagram (from http://en.wikpedia.org/wiki/E-R_diagram)|
As you can see, overall I found myself erring on the side of 'include', most likely as I am an "expert" in the subject and for me all of it is important. I suspect that this dilemma will face us again and again as this project grows and more material is added. This also highlights the importance of the use-cases and talking to end-users when developing this type of material.
(With thanks to Kate Jones for the re-use of the title of one of her blog posts.)