3.2 Data Abstraction

Enduring Understanding

To find specific solutions to generalizable problems, programmers represent and organize data in multiple ways.

Learning Objective

Represent a list or string using a variable. 

Essential Knowledge

A list is an ordered sequence of elements. For example,

[value1, value2, value3, ...]

describes a list where value1 is the first element, value2 is the second element, value3 is the third element, and so on.

An element is an individual value in a list that is assigned a unique index.

An index is a common method for referencing the elements in a list or string using natural numbers.

A string is an ordered sequence of characters.

Learning Objective

For data abstraction:

a. Develop data abstraction using lists to store multiple elements.

b. Explain how the use of data abstraction manages complexity in program code. 

Essential Knowledge

Data abstraction provides a separation between the abstract properties of a data type and the concrete details of its representation.

Data abstractions manage complexity in programs by giving a collection of data a name without referencing the specific details of the representation.

Data abstractions can be created using lists.

Developing a data abstraction to implement in a program can result in a program that is easier to develop and maintain.

Data abstractions often contain different types of elements.

The use of lists allows multiple related items to be treated as a single value. Lists are referred to by different names, such as array, depending on the programming language.

Exclusion Statement: The use of linked lists is outside of the scope of this course and the AP Exam.

The exam reference sheet provides the notation

[value1, value2, value3, ...]

Text:

aList <-- [value1, value2, value3, ...]

Block:

creates a new list that contains the values value1, value2, value3, and ... at indices 1, 2, 3, and ... respectively and assigns it to aList.

Text:

aList <-- []

Block:

creates a new empty list and assigns it to aList.

Text:

aList <-- bList

Block:

assigns a copy of the list bList to the list aList. For example, if bList contains [20, 40, 60], then aList will also contain [20, 40, 60] after the assignment.

The exam reference sheet describes a list structure whose index values are 1 through the number of elements in the list, inclusive. For all list operations, if a list index is less than 1 or greater than the length of the list, an error message is produced and the program will terminate.