It will be nice to create document based application.
http://developer.apple.com/library/mac/#documentation/DataManagement/Conceptual/DocBasedAppProgrammingGuideForOSX/Introduction/Introduction.html
The Cocoa document architecture provides your app with many built-in features, such as autosaving, asynchronous document reading and writing, file coordination, and multilevel undo support. In most cases, it is trivial to opt-in to these behaviors. If your app has particular requirements beyond the defaults, the document architecture provides many opportunities for extending and customizing your app’s capabilities through mechanisms such as delegation, subclassing and overriding existing methods with custom implementations, and integration of custom objects.
It will be nice to create document based application.
http://developer.apple.com/library/mac/#documentation/DataManagement/Conceptual/DocBasedAppProgrammingGuideForOSX/Introduction/Introduction.html
The Cocoa document architecture provides your app with many built-in features, such as autosaving, asynchronous document reading and writing, file coordination, and multilevel undo support. In most cases, it is trivial to opt-in to these behaviors. If your app has particular requirements beyond the defaults, the document architecture provides many opportunities for extending and customizing your app’s capabilities through mechanisms such as delegation, subclassing and overriding existing methods with custom implementations, and integration of custom objects.