Text this: What have we learnt from deductive object-oriented database research?

 _    _      ___     _____     _    _    _____    
| |  | ||   / _ \\  |  __ \\  | || | || |  __ \\  
| |/\| ||  / //\ \\ | |  \ || | || | || | |  \ || 
|  /\  || |  ___  ||| |__/ || | \\_/ || | |__/ || 
|_// \_|| |_||  |_|||_____//   \____//  |_____//  
`-`   `-` `-`   `-`  -----`     `---`    -----`