The schema is documented here:
If you are using P6 EPPM, you can use the Extended Schema as described here:
This will require less joins in your queries since the extended schema was built exactly for that use.
- Project Long Name
- Baseline Dates
- Activity Dates
The Project Long Name is stored in the table PROJWBS. You need to join from PROJECT to PROJWBS using the proj_id column, and then in the PROJWBS query you want the record that says "proj_node_flag" = "Y"
The Baseline Dates are stored in the PROJECT table itself. The ORIG_PROJ_ID field is set on baselines and it says to which project they are attached to;
The Activity Dates fields are in the TASK table itself, however, the "Start Date" and "Finish Date" fields you see in the client are virtual, and depend on the actual status of the activity. For example, for a completed activity, the date fields used will be the actual ones, and for a non-started, it will likely be the planned date fields.
But check the docs and mainly the extended schema.