Arrays are integer-indexed collections of objects of arbitrary type. The starting index value is usually 0 with the notable exception of CFML whose arrays have an initial index value of 1. Because of these differences working with array indices can lead to non-portable data. Structures are string-indexed collections of object of arbitrary type. In many languages they are known as associative arrays.
Structures contain one or more variables.
Because some of the languages supported by WDDX are not case-sensitive, no two variable names can differ only by their case. Only simple data types can be stored in recordsets. For tabular data storage of complex data types, an array of structures should be used. Because some of the languages supported by WDDX are not case-sensitive, no two field names can differ only by their case. Null values- WDDX provides no notion of a null object.