What are the simplest database types which I can use with ADO?
You can use MS-Access MDB files. It can be used via Microsoft OLEDB Jet 4 engine (Which is build in into Windows since at least Win XP) and is perfect for local desktop DB applications, with the ability to create Tables, PKs, Indexes, Queries/Views, Transactions, Multi-User, replication, compact/repair and much more with almost perfect compatibility to MS SQL-Server SQL syntax (since MS-Access is the ancestor of MS SQL-Server).MS-Access product (i.e MS Office) dose not have to be installed on the client machine. No extra drivers or files to install, and completely integrable with existing MS-Office products.
Edit: MDB files could be also Protected/Encrypted.
You have several options for store your data in single database file.
All of them can be accesed via ADO using a ODBC or OLEDB driver. my personal recomendation is Firebird, because is free, fast, stable and had a Embedded version.
This is a pretty useful comparison of a number of embedded databases. Of the ones tested these ones support (odbc), (oledb) or (both) and use a (single) file for the database:
- Accuracer (odbc) (single)
- NexusDB (odbc) (single v4 and newer)
- Firebird (both) (single) - multiple odbc implementations and the commercial IBProvider supports three different ways to connect to the ADO components.
- TurboDB (odbc) (single v4 and newer)
Note: Most of these also supply ADO.Net Providers as well.
The other's in the comparison (Advantage, ElevateDB, DBISAM and Apollo) use a file per table/index scheme.