OPC UA allows information to be represented as complex Variables (Variable with nested sub-variable) and/or as complex DataTypes, where a DataType has a structure or other special meaning associated with it. Each of the nested Variables can have a value that represents a simple base DataType such as an Integer or can represent a custom DataType such as a Currency or a structure.

The format of a value is represented by Attributes of Variables. This standard maps all value formats defined in ISA-95 into those attributes.

Arrays of values are represented by DataType, ValueRank, ArrayDimensions, and MaxArrayLength attribute of a VariableType. (See OPC 10000-3). The following examples illustrate the usage of these Attributes:

  1. A set of values for a single dimension array of integers with 6 values

EBNF: [ 1 , 2 , 3 , 4 , 5 , 6]

OPC UA: DataType =Int32(any), ValueRank =OneDimension(1), ArrayDimensions =6, MaxArrayLength=6.

  1. A set of values for a two dimension array of size 2x3

EBNF: [ [1 , 2] , [3 , 4] ,[5 , 6]]

OPC UA: DataType=Int32(any), ValueRank= 2, ArrayDimensions=[2,3], MaxArrayLength=6

  1. A set of values for a four dimension array of size 2x3x4x5

EBNF: omitted for simplicity

OPC UA: DataType=Int32(any), ValueRank= 4, ArrayDimensions=[2,3,4,5], MaxArrayLength=120

Ranges of values are represented by Range DataType defined in OPC 10000-8. If the Range is an array, then ValueRank, ArrayDimensions, and MaxArrayLength attributes are utilized to indicate an array.

  1. A simple range of values

EBNF: {0..100}

OPC UA : DataType =Range, ValueRank = Scalar (−1)

  1. A non-continuous range of values

EBNF: {0 .. 100 , 200 .. 300 , 500 , 600 .. 650}

OPC UA : DataType =Range, ValueRank = OneDimension (1), ArrayDimensions =4

A set of allowed values is defined in EnumStrings and the EnumValues Standard Property of Enumeration DataType.

  1. A series of values that defines colours.

EBNF: <Red, Green, Yellow, Blue>

OPC UA : Array of LocalizedText that is a list of the enumeration strings is set to EnumStrings

Structured data element is defined in custom DataType derived from Structure DataType or is represented by nested VariableType that has Variables as children.

  1. A structured data element represented as flattened Property Name

Struct Simple {

Integer Position;

Float LastValue;

Boolean Exists;

String Comment;}

ISA-95: Simple.Position, Simple.LastValue, Simple.Exists, Simple.Comment

OPC UA: ABC DataType (custom DataType) derived from Structure DataType is defined, with the given structure.

  1. A structured data element represented by creating an ISA95Property with no data value with nested child ISA95Properties and identification of element.

Struct Simple {

public int Position;

public double LastValue;

public bool Exists;

public string Comment;}

ISA-95: Property [ID=”Simple”]

Property [ID=”Simple”]\ Property [ID=”Position”]

Property [ID=”Simple”]\ Property [ID=”LastValue”]

Property [ID=”Simple”]\ Property [ID=”Exists”]

Property [ID=”Simple”]\ Property [ID=”Comment”]

OPC UA: All ISA95Properties are represented as Variables and Simple property points to Position, LastValue, Exists, and Comment properties by HasComponent or subtypes of HasComponent ReferenceType. (See clause

  1. A combination of a) and b) where a structured data element represented by creating a ISA95 Property with a data value that is a structured data element and with nested child properties and identification of element (see Figure 14). This is the preferred method for modelling complex information. [Note: the figure flow the template defined in OPC 10000-3 with some extensions defined in Annex F]


Figure 14 - Complex Data Mapping