ADT: Abstract Data Type

The description of a data type is distinct from its computer implementation

An abstract data type defines a data type in terms of a type and a set of operations on the type

  • details of implementation are hidden (encapsulation)
  • a data structure is the physical implementation of the ADT

Data at 3 different Levels

 

Application (or user) level: modeling real-life data in a specific context.

 

Logical (or ADT) level: abstract view of the domain and operations. ...WHAT

 

Implementation level: specific representation of the structure to hold the data items, and the coding for operations. .......HOW

 

Abstract Data Type

  • Implementation Independent
  • High-Level Description of the data and Operations that Manipulate them.
  • In OOP: e.g. UML class diagram

Data Structure

  • Implmentation of an ADT
  • specifically how we represent the data, and through algorihtms how we manipulate them.
  • In OOP: the actual coded class with variables and methods.

Understanding ADTs is understanding how to manage complexity through abstraction

Example: A library

  • Application (or user) level: Library of Congress, or Baltimore County Public Library.

  • Logical (or ADT) level: domain is a collection of books; operations include: check book out, check book in, pay fine, reserve a book.

  • Implementation level: representation of the structure to hold the “books”, and the coding for operations.

 

ADT Operator Categories

Constructors

creates a new instance of the ADT

Transformers/ Mutators

alters the state of one or more of the data values associated with the ADT

Observers

obtains information about the state of one or more data balues.

  • predicates - tests if a certain property is true
  • accessor/selector - returns a copy of an item
  • summary - returns info about the ADT as a whole.

Iterators

process all components in a data structure in some sequence.

 

 
© Lynne Grewe