GenBroker Tag Syntax

Use the GenBroker's Advanced tab's Tag Syntax sub-tab to configure tag extension syntax and XML DA syntax. (For help accessing GenBroker, refer to the GenBroker Overview topic.) You use this tab to redefine separators for OPC item names. The Tag Syntax sub-tab is shown in the figure below.

The GenBroker Tag Syntax Form

XML DA syntax has the following properties:

• URL/Item Separator. An XML DA OPC server is defined by its URL; for example:

http://opcfoundation.org/XmlDaSampleServer/Da30Service.asmx

An item on the server is defined by its name; for example:

Dynamic/Analog Types/Double.

When GENESIS64 applications refer to an item on an XML DA OPC server, they use one string which consists of the server’s URL and the item name, separated with the separator specified here; the default separator is #, and results in the following address:

http://opcfoundation.org/XmlDaSampleServer/Da30Service.asmx# Dynamic/Analog Types/Double.

• Item Path Separator. A client application can specify an optional item path, separated by the characters specified here. By default, the separator is :: (a double full colon symbol).

Tag extensions are used by ICONICS applications to request a specific value from the OPC Server. Use the Tag Extension Syntax section to identify the separators used in the syntax. Typically, you never change these values; however, if an OPC item ID or tag ID uses any of the characters listed on this tab as a separator, you must specify a different separator that is not in use elsewhere and which is reserved for use only as the separator.

Fields on the Tag Syntax tab (see above) include the following:

• Access path separator. The default is ::.

• Property separator. The default is -->.

• Attribute separator. The default is #.

• Scan rate separator. The default is @.

• Array begin and end symbols. The default are [ and ].

• Array index separator. The default is , (a comma).

• Req’d type separator. The default is | (the pipe character). Each tag has its native data type, known as the canonical data type. By default, OPC servers return values of this canonical data type if the client does not explicitly request another type. Some applications (such as, GraphWorX64) allow for specifying the requested data type. Other applications may use this feature, and make the requested data type part of the tag name (using the extended tag syntax). The requested data type may be added on the very end of the tag name and separated by the separator specified here. Example: tag:ICONICS.Simulator\SimulatePLC.Sine|R4

Standard Tag Syntax

The standard syntax for a tag in GENESIS64 client applications is:

[\\<node>\]<server>\<itemid>

where:

• <node> is a name or IP address of a node in the network. When omitted, the local node is used.

• <server> is a class ID (CLSID) or ProgID of an OPC DA Server.

• <itemid> is an OPC ItemID; this may contain any characters.

Example: \\PC1\ICONICS.Simulator\SimulatePLC.Sine

However, the client application may need to request additional information from the OPC server. To request additional information, the application request must follow the guides for tag extension syntax.

Tag extensions let client applications request additional or specific information from the OPC server. The syntax for tag extensions is described here. Tag extension syntax begins with tag: before the tag name, followed by any additional options; the options that are used must make use of the separators defined on the GenBroker’s Tag Syntax sub-tab (located on the Advanced tab). Note that you can combine options in a tag but the options that you use must conform to the sequence shown below in the syntax.

Syntax for Tag Extensions

Here is the syntax for tag extensions which makes use of the default separators:

@tag:[\\<node>\]<server>\<itemid>[::< accpath>][- -><prop>][< idx>][#< attr>][@<rate>]

where the variables used above include:

• <node>, <server> and <itemid> are as described above for the standard syntax.

• < accpath> is an optional access path string. This can be used (according to the OPC Specification) to give the server a hint of how to get the OPC item specified by its <itemid>. By default, the access path is preceded by :: (two colons), but you can change this by typing a different prefix in the Access Path Separator field on the GenBroker’s Tag Syntax tab.

• <prop> is a property ID or name as defined in the OPC 2.0 Specification. When specified, GenBroker uses the server’s IOPCItemProperties:: LookupItemIDs() function to get the property value. Note that not all OPC 2.0 compliant servers support this function, so the usage is limited. By default, the property ID or name is preceded by --> (two hyphens and a right arrow), but you can change this by typing a different prefix in the Property Separator field on the GenBroker’s Tag Syntax sub-tab (located on the Advanced tab).

Property IDs and names supported by GenBroker in tag extensions are listed in the table below. Their meanings are defined in the OPC Specification 2.0. The property names and IDs are interchangeable. Refer to these property names and IDs when reviewing the examples that follow.

Property Names and IDs

• <idx> is an index or indexes for an array. If the specified OPC item is of an array type, this allows for accessing one of its elements. The element is read-only. By default, multiple indexes are separated by , (a comma), but you can change the default value by typing a different separator in the Array Index Separator field on the GenBroker’s Tag Syntax tab. Also, by default the index (or indexes) is enclosed in brackets [ ]; you can change this by typing different values in the Array Begin Symbol and Array End Symbol fields on the Tag Syntax tab (located on the Advanced tab).

• <attr> specifies an attribute that should be returned instead of the item value. In OPC, values always come with a quality value and timestamp. The attributes defined here are derived from these values. The supported attributes are listed below. Unlike properties (see <prop> above), this option works with any OPC server, even OPC 1.0. The attributes are read-only. By default, an attribute is preceded by # (the number sign), but you can change this by typing a different prefix in the Attribute Separator field on the GenBroker’s Tag Syntax sub-tab (located on the Advanced tab).

When any of the following attributes is used in a tag extension, GenBroker returns the value of the attribute rather than the value of the specified item. Possible attributes are listed here. Refer to these attributes when reviewing the examples that follow.

Tag Extension Attributes

• <rate> specifies a scan rate for the given item. Usually the scan rate is defined for a group of items; for example, in GraphWorX64 it is defined for the whole display. But this tag extension option overrides the display scan rate, and instead specifies the scan rate for one particular item. The scan rate is in milliseconds. By default, the scan rate is preceded by @ (the ‘at’ sign), but you can change this by typing a different prefix in the Scan Rate Separator field on the GenBroker’s Tag Syntax sub-tab (located on the Advanced tab).

See Also:

GenBroker

Channels

Redundancy Node Pair Tab