You can access the detailed Data Model in > Setup > Object Manager > Schema Builder.
Here is a high-level overview of the data model:
The TE Item is the primary transaction entity, storing all time and expense information for a week or day. It references accounts, opportunities, resources, projects, activity types, etc.
The Project is the primary data collection object and control, but is optional. The Project Line is the actual delivery and provides plan and actual information for real-time reporting. The Project Phase is an optional summary level.
The Resource links to a Salesforce user (internal) and contact (community user). The access to projects/lines can be restricted for a resource via Project (Line) Allocations.
Other data model areas are
- Time Off
- Payroll