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

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