ccl_asl is a small Python module for dealing with ASL (Apple System Log)/ASLDB files.
The module comprises a class library for accessing the records in your code (the AslDb class implements __iter__, __len__, __getitem__) and also a command-line interface for dumping the contents of logs to TSV files (other formats would be trivial to add).
The repository also contains a couple of examples of the module in use to parse battery usage from an iOS device, and a login, boot, shutdown, etc. timeline from OSX.
A blog explaining the file structure can be found here: http://www.cclgroupltd.com/parsing-apple-system-log-files-osx-ios/