Here is the overall big picture of the relationships between the various IBPP objects. Don't mis-read this graph: it is not a class derivation tree. The arrows show you the runtime dependencies of objects.

The blue rounded shapes are the IBPP 'Interfaces'. You call their corresponding Factories to get instances of these objects. Except for Database and for Service, each Factory call requires one or multiple references to other existing object instances. These dependencies are shown by the arrows. For instance, to instantiate an Events object, you need a Database object. Similarly, to get a Statement object, you need a Database and a Transaction.

The Transaction object has a double arrow to the Database. To instantiate a Transaction you indeed need a Database. But you can later simultaneously attach your Transaction to multiple Database objects: a transaction context can span multiple database attachments.

The yellow rectangles are ordinary C++ classes. They are just datatypes defined by IBPP. Their dotted connections simply show you which interfaces they are related to. Indeed, Date, Time, Timestamp and DBKey are datatypes useful to exchange some non C++ basic values with SQL statements. User is a datatype related to the users management methods of the Service interface.

Blob and Array are somewhat a special case. They are interfaces, and you instantiate them using their Factories, which both require a Database and a Transaction for their context. Though, when instantiated they are used in relation with Statement to access special SQL values (blobs and arrays). This is why they are shown on the graph with a dotted line to Statement.