A RelativePath is a structure that describes a sequence of References and Nodes to follow. This annex describes a text format for a RelativePath that can be used in documentation or in files used to store configuration information.
The components of a RelativePath text format are specified in Table A.1.
|
Symbol |
Meaning |
|
/ |
The forward slash character indicates that the Server is to follow any subtype of HierarchicalReferences. |
|
. |
The period (dot) character indicates that the Server is to follow any subtype of a Aggregates ReferenceType. |
|
<[#!ns:]ReferenceType> |
A string delimited by the ‘<’ and ‘>’ symbols specifies the BrowseName of a ReferenceType to follow. By default, any References of the subtypes the ReferenceType are followed as well. A ‘#’ placed in front of the BrowseName indicates that subtypes should not be followed. A ‘!’ in front of the BrowseName is used to indicate that the inverse Reference should be followed. The BrowseName may be qualified with a namespace index (indicated by a numeric prefix followed by a colon). This namespace index is used specify the namespace component of the BrowseName for the ReferenceType. If the namespace prefix is omitted then namespace index 0 is used. |
|
[ns:]BrowseName |
A string that follows a ‘/’, ‘.’ or ‘>’ symbol specifies the BrowseName of a target Node to return or follow. This BrowseName may be prefixed by its namespace index. If the namespace prefix is omitted then namespace index 0 is used. Omitting the final BrowseName from a path is equivalent to a wildcard operation that matches all Nodes which are the target of the Reference specified by the path. |
|
& |
The & sign character is the escape character. It is used to specify reserved characters that appear within a BrowseName. A reserved character is escaped by inserting the ‘&’ in front of it. Examples of BrowseNames with escaped characters are: Received browse path nameResolves to “&/Name_1” “/Name_1” “&.Name_2” “.Name_2” “&:Name_3” “:Name_3” “&&Name_4” “&Name_4” |
Table A.2 provides RelativePaths examples in text format.
Table A.2 – RelativePath Examples
|
Browse Path |
Description |
|
“/2:Block&.Output” |
Follows any forward hierarchical Reference with target BrowseName = “2:Block.Output”. |
|
“/3:Truck.0:NodeVersion” |
Follows any forward hierarchical Reference with target BrowseName = “3:Truck” and from there a forward Aggregates Reference to a target with BrowseName “0:NodeVersion”. |
|
“<1:ConnectedTo>1:Boiler/1:HeatSensor” |
Follows any forward Reference with a BrowseName = ‘1:ConnectedTo’ and finds targets with BrowseName = ‘1:Boiler’. From there follows any hierarchical Reference and find targets with BrowseName = ‘1:HeatSensor’. |
|
“<1:ConnectedTo>1:Boiler/” |
Follows any forward Reference with a BrowseName = ‘1:ConnectedTo’ and finds targets with BrowseName = ‘1:Boiler’. From there it finds all targets of hierarchical References. |
|
“<0:HasChild>2:Wheel” |
Follows any forward Reference with a BrowseName = ‘HasChild’ and qualified with the default OPC UA namespace. Then find targets with BrowseName = ‘Wheel’ qualified with namespace index ‘2’. |
|
“<!HasChild>Truck” |
Follows any inverse Reference with a BrowseName = ‘HasChild’. Then find targets with BrowseName = ‘Truck’. In both cases, the namespace component of the BrowseName is assumed to be 0. |
|
“<0:HasChild>” |
Finds all targets of forward References with a BrowseName = ‘HasChild’ and qualified with the default OPC UA namespace. |
The following BNF describes the syntax of the RelativePath text format.
<relative-path>::= <reference-type> <browse-name> [relative-path]
<reference-type>::= '/' | '.' | '<' ['#'] ['!'] <browse-name> '>'
<browse-name>::= [<namespace-index> ':'] <name>
<namespace-index>::= <digit> [<digit>]
<digit> ::= '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'
<name> ::= (<name-char> | '&' <reserved-char>) [<name>]
<reserved-char>::= '/' | '.' | '<' | '>' | ':' | '#' | '!' | '&'
<name-char> ::= All valid characters for a String (see OPC 10000-3) excluding reserved-chars.