5 Data encoding

5.1 General

5.1.2 Built-in Types

All OPC UA DataEncodings are based on rules that are defined for a standard set of built-in types. These built-in types are then used to construct structures, arrays and Messages. The built-in types are described in Table 1.

Table 1 – Built-in Data Types

ID	Name	Nullable	Default	Description
1	Boolean	No	false	A two-state logical value (true or false).
2	SByte	No	0	An integer value between −128 and 127 inclusive.
3	Byte	No	0	An integer value between 0 and 255 inclusive.
4	Int16	No	0	An integer value between −32 768 and 32 767 inclusive.
5	UInt16	No	0	An integer value between 0 and 65 535 inclusive.
6	Int32	No	0	An integer value between −2 147 483 648 and 2 147 483 647 inclusive.
7	UInt32	No	0	An integer value between 0 and 4 294 967 295 inclusive.
8	Int64	No	0	An integer value between −9 223 372 036 854 775 808 and 9 223 372 036 854 775 807 inclusive.
9	UInt64	No	0	An integer value between 0 and 18 446 744 073 709 551 615 inclusive.
10	Float	No	0	An IEEE single precision (32 bit) floating point value.
11	Double	No	0	An IEEE double precision (64 bit) floating point value.
12	String	Yes	null	A sequence of Unicode characters.
13	DateTime	Yes	DateTime.MinValue (see 5.1.4)	An instance in time.
14	Guid	Yes	All zeros	A 16-byte value that can be used as a globally unique identifier.
15	ByteString	Yes	null	A sequence of octets.
16	XmlElement	Yes	null	A sequence of Unicode characters that is an XML element.
17	NodeId	Yes	All fields set to default.	An identifier for a node in the address space of an OPC UA Server.
18	ExpandedNodeId	Yes	All fields set to default.	A NodeId that allows the namespace URI to be specified instead of an index.
19	StatusCode	No	Good	A numeric identifier for an error or condition that is associated with a value or an operation.
20	QualifiedName	Yes	All fields set to default.	A name qualified by a namespace.
21	LocalizedText	Yes	All fields set to default.	Human readable text with an optional locale identifier.
22	ExtensionObject	Yes	All fields set to default.	A structure that contains an application specific data type that may not be recognized by the receiver.
23	DataValue	Yes	All fields set to default.	A data value with an associated status code and timestamps.
24	Variant	Yes	Null	A union of all of the types specified above.
25	DiagnosticInfo	Yes	No fields specified.	A structure that contains detailed error and diagnostic information associated with a StatusCode.

Most of these data types are the same as the abstract types defined in OPC 10000-3 and OPC 10000-4. However, the ExtensionObject and Variant types are defined in this document. In addition, this document defines a representation for the Guid type defined in OPC 10000-3.

The Nullable column indicates whether a ‘null’ value exists for the DataType in all DataEncodings. A ‘null’ value is a value that is equavalent ‘no value specified’. A nullable type with a default value means the default value shall be interpreted equivalent to a null.

The Default column specifies the default value for the type if a default value is needed. The default value for all arrays is ‘null’.