OPC UA provides the information if a value is an array in the Variable Attributes ValueRank and ArrayDimensions. Every data type can be exposed as array. Arrays can have multiple dimensions. The dimension is defined through the Attribute ValueRank. Arrays can have variable or fixed lengths. The length of each dimension is defined by the Attribute ArrayDimensions. The array index starts with zero.
IEC 61131-3 allows the declaration of array data types with one or multiple dimensions and an index range instead of a length.
OPC UA has no standard concept for defining special array data types or exposing index ranges.
Example for an array data type declaration in IEC 61131-3:
TYPE ANALOG_16_INPUT_DATA : ARRAY [1..16] OF INT ; END_TYPE
Example for use of an array in a Ctrl Variable instantiation in IEC 61131-3:
VAR MyArray : ARRAY [1..16] OF INT; END_VAR