I hope someone can point me in the direction of some docs, video or whatever, that covers the grand conceptual model embodied in OpenProject, and guidance on how to map it to actual work in representative scenarios.

I would hope such docs/videos would introduce all the types of objects (and their attributes) that OpenProject tracks, and would give us a clear picture (possibly a diagram!) of how they all related to each other. So, for example, it would probably center on the Project object, and detail the attributes of a Project, and objects that are subsidiary to Project, such as a collection of Work Packages, a wiki, Gantt charts and so on.  Evidently, there can be subprojects, though it's unclear to me the nature of the project-subproject relationship.  

At the moment, I see copious documentation of the UI that accesses the underlying data structure in one way or another. But trying to work out the underlying model by inference from the UI is a bit tedious and frustrating.

Part of what I'd like to understand from the underlying model (in conjunction with the UI), is how OpenProject's model best fits to the actual work we would like to track.  As just one coarse aspect, what size scope of actual work (duration, complexity, resources etc) best corresponds to an OpenProject Project, versus a Work Package. In trying to use the Trial subscription, it's not at all clear what opportunities or pitfalls there are if a particular piece of work is tracked as a Project, a Subproject, or a Work Package (with subsidiary Work Packages).

As an example, https://www.openproject.org/docs/getting-started/work-packages-introduction/  mentions different Work Package types... but this does not appear to be a built in feature, but rather something users (or admins?) are free to configure, by virtue, for example (I think), of defining a specific set of fields that a certain Work Package type tracks, and a custom set of statuses that such a WP can have, and so on.  It would be helpful to know at what level(s) such specifics are defined, as that would be the level that should encompass all WPs to which these specifics can apply.

I'm sure that the answer to this example can be found; that specific is not what I'm interested in.  I'm interested in where, in general, all these OpenProject model object-to-obect relationships, and object-attributes are spelled out, so we don't have to resort to inferring them from the UI.

As a related idea -- it would be very helpful to read some case studies that show good implementations of OpenProject at specific different business types.  Such as -- a software development company, or an electronic product engineering company, or a building construction company.  Not vacuous interviews with middle managers who championed OpenProject to their upper management and now everyone is happy.  I'm talking about giving us a description of how tasks or products or whatever at that company are mapped to specific OpenProject features (model objects), what workflow that mapping facilitates (or fails to facilitate), and so on.  If this exists already I'd love to see it.

Thanks for any input on any of the above!