In this concept this atomic addressable item is called a node. Each node is a collection of attributes (value-holders) that have values accessible locally in context of the node. To enable browsing, i.e. to represent information about the internal structure of the nodes graph, nodes are interconnected by references (address-holders of coupled nodes).
NodeClass
. In other words, the node is an instance of the selected NodeClass
. Available NodeClass
types are predefined, i.e. the Address Space Meta-Model provides a strictly defined and non-extensible set of NodeClass
types. Each one is assigned a dedicated function to represent well-defined information at run-time. NodeClass
is a formal description of the node defining the allowed attributes and references. Each node must be an instance of the selected NodeClass
.NodeClass
types (Figure 1):View
: defines a subset of nodes in the Address Space.ObjectType
: provides definition for objects.Object
: is used to represent systems, system components, real-world objects and software objects.ReferenceType
: is used to define the meaning of the nodes relationship.DataType
: is used to define simple and complex data types of the Variable values.VariableType
: is used to provide type definition for variables.Variable
: is used as real-time process data holders, i.e. it provides a value.Method
: is a lightweight function, whose scope is bounded by an owning object.NodeClass
.NodeClass
represents a subset of the nodes in the Address Space. The entire Address Space is the default view. Each node in a view may contain only a subset of its references, as defined by the creator of the view. The View instance acts as the root for the nodes in the represented view.ObjectType
provides definition for objects. Object
instance are used to represent systems, system components, real-world objects and software objects.ReferenceType
are visible in the Address Space. In contrast, a reference instance of this type is an inherent part of a node and no NodeClass
is used to represent reference instances. In other words, any node is a collection of references, so there is no need to instantiate an additional object as reference with the role of a nodes couple.Variable
node is used to be a holder of the process data – it has a Value
attribute. To be used as the real-time process state representation, the value of the Value
attribute must be bound to a real data source, e.g. a sensor or actuator. The Method
node represents functions that can be called by the clients connected to the server. In this case the real-time process bindings are responsible for conveying the parameters current values, invoking the represented function and returning the execution result. Both classes are the main building blocks that allow the server to couple the exposed address space` with the current state and behavior of the underlying process.DataType
is used to define simple and structured data types. Data types are used to describe the bits pattern of the Value
attribute of Variable
and their VariableType
nodes. Therefore each Variable
and VariableType
refers to an instance of the DataType
NodeClass
.