Annex A BNF definitions (Informative)
A.1 Overview over BNF
The BNF (Backus-Naur form) used in this annex uses `<´ and `>´ to mark symbols, `[´ and `]´ to identify optional paths and `|´ to identify alternatives. If the ‘(‘ and ‘)’ symbols are used, it indicates sets.
A.2 BNF of RelativePath
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 name Resolves 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.
| 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.A.3 BNF of NumericRange
The following BNF describes the syntax of the NumericRange parameter type.
<numeric-range> ::= <dimension> | <dimension> ',' <numeric-range>
<dimension> ::= <index> | <index> ':' <dimension>
<index> ::= <digit> | <digit> <index>
<digit> ::= '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'