I recall the IRC conversation Brad and Jean-Marc first had about this a couple months ago. Basically, Overflow keeps class definitions in C++, which are then inherited by the XML-based .n files. The .n files also describe node connectivity/linkage. Jean-Marc asked during the conversation if the .def files were class definitions or instances. Brad replied that they were both. Brad also mentioned that the advantages of .def and the use of the filesystem hierarchy were (1) better access to class definitions (XML is used rather than C++), (2) crash recovery (the DL is always writing to the filesystem), and (3) the manipulation of networks (requiring a great deal of node and link shuffling). It seemed to me that Jean-Marc agreed about the advantages of .def. The advantages to .n that I can see are (1) clear distinction between class definition and instance, and (2) the use of /less/ files (perhaps a network can always be described in a single XML file). Brad, if you want to switch to the use of .n files and Overflow's overall approach, can you explain (1) how class definitions will be stored and accessed, and if they'll be distinguished any better from class instances, (2) how crash recovery will take place (will .n always reflect the state of the networks?), and (3) if writing to .n all the time is any better or quicker than writing to .def's all the time. Cheers. Jeff -- J.W. Bizzaro jeff at bioinformatics.org Director, Bioinformatics.org: The Open Lab http://bioinformatics.org/~jeff "Let the machine do the dirty work." -- Kernighan and Ritchie --