Per Sort

 @proceedings{esawVII,
    doi = {10.1007/978-3-540-75524-1},
    editor = {Gregory M.P. O'Hare and Ricci, Alessandro and Michael J. O'Grady and Oğuz Dikenelli},
    isbn = {978-3-540-75522-7},
    publisher = {Springer},
    series = {Lecture Notes in Computer Science},
    subseries = {Lecture Notes in Artificial Intelligence},
    subtitle = {7th International Workshop, {ESAW} 2006, Dublin, Ireland, September 6-8, 2006 Revised Selected and Invited Papers},
    title = {Engineering Societies in the Agents World VII},
    url = {http://link.springer.com/10.1007/978-3-540-75524-1},
    volume = 4457,
    year = 2007
} 

 @proceedings{esawVI,
    doi = {10.1007/11759683},
    editor = {Dikenelli, Oğuz and Gleizes, Marie-Pierre and Ricci, Alessandro},
    isbn = {3-540-34451-9},
    publisher = {Springer},
    series = {Lecture Notes in Computer Science},
    subseries = {Lecture Notes in Artificial Intelligence},
    subtitle = {6th International Workshop, ESAW 2005, Kusadasi, Turkey, October 26--28, 2005, Revised Selected and Invited Papers},
    title = {Engineering Societies in the Agents World VI},
    url = {http://link.springer.com/10.1007/11759683},
    volume = 3963,
    year = 2006
}