A property list is a representation of a hierarchy of objects that can be stored in the file system and reconstituted later. Property lists give applications a lightweight and portable way to store small amounts of data. They are hierarchies of data made from specific types of objects—they are, in effect, an object graph. Property lists are easy to create programmatically and are even easier to serialize into a representation that is persistent. Applications can later read the static representation back into memory and recreate the original hierarchy of objects. Both Cocoa Foundation and Core Foundation have APIs related to property list serialization and deserialization.
Property lists consist only of certain types of data: dictionaries, arrays, strings, numbers (integer and float), dates, binary data, and Boolean values. Dictionaries and arrays are special types because they are collections; they can contain one or multiple data types, including other dictionaries and arrays. This hierarchical nesting of objects creates a graph of objects. The abstract data types have corresponding Foundation classes, Core Foundation types, and XML elements for collection objects and value objects.