OpcLabs.EasyOpc.UA.Filtering Namespace

This namespace provides classes and interfaces that provide filtering capabilities in OPC Unified Architecture.

Classes

	Class	Description
	UAAttributeOperand	An operand consisting of an attribute of a node in a type, with optional relative path and alias.
	UAContentFilterElement	The filter criteria (an operator and its operands).
	UAContentFilterElementBuilder	The builder for content filter element.
	UAFilterElements	Provides an easy way to construct basic filter elements (literal, attribute, or a simple attribute), and elements with various operators.
	UAFilterOperand	Base class for different types of filter operands.
	UAFilterOperandCollection	A collection of content filter operands.
	UALiteralOperand	An operand consisting of a literal value.
	UASimpleAttributeOperand	An operand consisting of an attribute of a node in a type, with optional simple relative path, and no alias.
	UASimpleAttributeOperandCollection	A collection of simple attribute operands.

Enumerations

	Enumeration	Description
	UAFilterOperator	Filter operator to be evaluated.

Remarks

The UAEventFilter object (used for specifying the event filters) is probably the most complicated part of the OPC UA Alarms & Condition features. It has two main parts: Select clauses (contained in the SelectClauses property, of UAAttributeFieldCollection type), and a Where clause (contained in the WhereClause property, of UAContentFilterElement type). The Select clauses contain a collection of the attribute fields to return with each event in a notification. The Where clause contains the criteria limiting the notifications.

In order to make the creation of some event filters appear shorter in the code, a UAEventFilterBuilder class is provided. Instances of this builder can be implicitly converted to the event filter itself (hence you can create just the UAEventFilterBuilder objects, and use them at all places where the UAEventFilter object is expected). The builder contains a Where clause, and is a collection of Select clauses. You can therefore use the C# collection initializer to specify the Select clauses.

In COM (tools like VB6, Delphi etc.), creation of OPC UA Event Filters requires longer code. For related information, see http://kb.opclabs.com/Creating_an_OPC_UA_event_filter_in_COM .

Reference

OpcLabs.EasyOpcUA Assembly