OpcUA.VariableNode (Opex62541 v0.1.2) View Source

VariableNode

Variables store values in a value together with metadata for introspection. Most notably, the attributes data type, value_rank and array dimensions constrain the possible values the variable can take on.

Variables come in two flavours: properties and datavariables. Properties are related to a parent with a hasProperty reference and may not have child nodes themselves. Datavariables may contain properties (hasProperty) and also datavariables (hasComponents).

All variables are instances of some variabletypenode in return constraining the possible data type, value rank and array dimensions attributes.

Data Type

The (scalar) data type of the variable is constrained to be of a specific type or one of its children in the type hierarchy. The data type is given as a NodeId pointing to a DataTypeNode in the type hierarchy. See the Section DataTypeNode for more details.

If the data type attribute points to UInt32, then the value attribute must be of that exact type since UInt32 does not have children in the type hierarchy. If the data type attribute points Number, then the type of the value attribute may still be UInt32, but also Float or Byte.

Consistency between the data type attribute in the variable and its VariableTypeNode is ensured.

Value Rank

This attribute indicates whether the value attribute of the variable is an array and how many dimensions the array has. It may have the following values:

  • n >= 1: the value is an array with the specified number of dimensions
  • n = 0: the value is an array with one or more dimensions
  • n = -1: the value is a scalar
  • n = -2: the value can be a scalar or an array with any number of dimensions
  • n = -3: the value can be a scalar or a one dimensional array

Consistency between the value rank attribute in the variable and its variabletypenode is ensured.

TODO: Array Dimensions

If the value rank permits the value to be a (multi-dimensional) array, the exact length in each dimensions can be further constrained with this attribute.

  • For positive lengths, the variable value is guaranteed to be of the same length in this dimension.
  • The dimension length zero is a wildcard and the actual value may have any length in this dimension.

Consistency between the array dimensions attribute in the variable and its variabletypenode is ensured.

Indicates whether a variable contains data inline or whether it points to an external data source.

Link to this section Summary

Link to this section Functions

Specs

new(term(), list()) :: %OpcUA.VariableNode{
  access_level: term(),
  args: term(),
  array: term(),
  array_dimensions: term(),
  browse_name: term(),
  data_type: term(),
  description: term(),
  display_name: term(),
  historizing: term(),
  minimum_sampling_interval: term(),
  value: term(),
  value_rank: term(),
  write_mask: term()
}