is a specialized format for organizing and storing data. it is a scheme for organizing related pieces of information. examples are arrays, linked lists, queues, stacks, binary trees, etc.
collection of data items in memory of a running program that are organized in some fashion that allows items to be stored and retrieved by some fixed methods
a method of organizing data characterized by the access provided to the data.  databases are mapped to a number of different files maintained by the underlying o.s.