Computer programs usually operate on tables of information. In most cases these tables are not simply amorphous masses of numerical values;they involve important structural relationships between the data elements.  

In its simplest form, a table might be a linear list of elements, when its relevant structural properties might include the answers to such questions as: Which element is first in the list? Which is last? Which elements precede and follow a given one? How many elements are in the list? A lot can be said about structure even in this apparently simple case. 

In more complicated situations, the table might be a two-dimensional array (a matrix or grid, having both a row and a column structure), or it might be an n-dimensional array for higher values of n; it might be a tree structure, representing hierarchical or branching relationships; or it might be a complex multilinked structure with a great many interconnections, such as we may find in a human brain.

In order to use a computer properly, we need to understand the structural relationships present within data, as well as the basic techniques for representing and manipulating such structure within a computer.