The GlobalDiscoveryServer Information Model used for discovery is shown in Figure 11. Most of the interactions between the GlobalDiscoveryServer and Application administrator or the Client will be via Methods defined on the Directory folder.

Figure 11 – The Address Space for the GDS

This Object is the root of the GlobalDiscoveryServer AddressSpace and it is the target of an Organizes reference from the Objects folder defined in OPC 10000-5. It organizes the information that can be accessed into subfolders. The implementation of a GDS can customize and organize the folders in any manner it desires. For example folders may exist for information models, or for optional services or for various locations in an administrative domain. It is defined in Table 2.

Table 2 – Directory Object Definition

Attribute	Value
BrowseName	Directory
Namespace	GDS (see 3.3)
TypeDefinition	DirectoryType defined in 6.3.3.
References	NodeClass	BrowseName	DataType	TypeDefinition	Modelling Rule

DirectoryType is the ObjectType for the root of the GlobalDiscoveryServer AddressSpace. It organizes the information that can be accessed into subfolders It also provides methods that allow applications to register or find applications. It is defined in Table 3.

Table 3 – DirectoryType Definition

Attribute	Value
BrowseName	DirectoryType
Namespace	GDS (see 3.3)
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	Modelling Rule
Subtype of the FolderType defined in OPC 10000-5.
HasComponent	Object	Applications	-	FolderType	Mandatory
HasComponent	Method	FindApplications	Defined in 6.3.4.		Mandatory
HasComponent	Method	RegisterApplication	Defined in 6.3.6.		Mandatory
HasComponent	Method	UpdateApplication	Defined in 6.3.7.		Mandatory
HasComponent	Method	UnregisterApplication	Defined in 6.3.8.		Mandatory
HasComponent	Method	GetApplication	Defined in 6.3.9.		Mandatory
HasComponent	Method	QueryApplications	Defined in 6.3.10.		Mandatory
HasComponent	Method	QueryServers	Defined in 6.3.11.		Mandatory

The Applications folder may contain Objects representing the Applications known to the GDS. These Objects may be organized into subfolders as determined by the GDS. Some characteristics for organizing applications are the networks, the physical location, or the supported profiles. The QueryServers Method can be used to search for OPC UA Applications based on various criteria.

A GDS is not required to expose its Applications as browsable Objects in its AddressSpace, however, each Application shall have a unique NodeId which can be passed to Methods used to administer the GDS.

The FindApplications Method returns the Applications associated with an ApplicationUri. It can be called by any Client application.

The RegisterApplication Method is used to add a new Application to the GDS. It requires administrative privileges.

The UpdateApplication Method is used to update an existing Application in the GDS. It requires administrative privileges.

The UnregisterApplication Method is used to remove an Application from the GDS. It requires administrative privileges.

The QueryApplications Method is used to find Client or Server applications that meet the criteria provided. This Method replaces the QueryServers Method.

The QueryServers Method is used to find Servers that meet the criteria specified. It can be called by any Client application. This Method has been replaced by the QueryApplications Method

FindApplications is used to find the ApplicationId for an OPC UA Application known to the GDS. In normal situations the list of records returned will not have more than one entry, however, system configuration errors can create situations where the GDS has multiple entries for a single ApplicationUri. If this happens a human will likely have to look at records to determine which record is the true match for the ApplicationUri.

If the returned array is null or zero length then the GDS does not have an entry for the ApplicationUri.

Signature

FindApplications(

[in] String applicationUri

[out] ApplicationRecordDataType[] applications

);

Argument	Description
applicationUri	The ApplicationUri that identifies the Application of interest.
applications	A list of application records that match the ApplicationUri. The ApplicationRecordDataType is defined in 6.3.5.

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_UserAccessDenied	The current user does not have the rights required.

Table 4 specifies the AddressSpace representation for the FindApplications Method.

Table 4 – FindApplications Method AddressSpace Definition

Attribute	Value
BrowseName	FindApplications
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory
HasProperty	Variable	OutputArguments	Argument[]	PropertyType	Mandatory

This type defines a DataType which represents a record in the GDS.

Table 5 – ApplicationRecordDataType Structure

Name	Type	Description
ApplicationRecordDataType	Structure	Subtype of the Structure DataType defined in OPC 10000-5.
applicationId	NodeId	The unique identifier assigned by the GDS to the record. This NodeId may be passed to other Methods.
applicationUri	String	The URI for the Application associated with the record.
applicationType	ApplicationType	The type of application. This type is defined in OPC 10000-4.
applicationNames	LocalizedText[]	One or more localized names for the application. The first element is the default ApplicationName for the application when a non-localized name is needed.
productUri	String	A globally unique URI for the product associated with the application. This URI is assigned by the vendor of the application.
discoveryUrls	String[]	The list of discovery URLs for an application. The first element is the default if a Client needs to choose one URL. The first HTTPS URL specifies the domain used as the Common Name of HTTPS Certificates. If the ApplicationType is Client then all of the URLs shall have the ‘inv+’ prefix which indicates they support reverse connect.
serverCapabilities	String[]	The list of server capability identifiers for the application. The allowed values are defined in Annex D.

Its representation in the AddressSpace is defined in Table 5a.

Table 5a – ApplicationRecordDataType Definition

Attribute		Value
BrowseName		ApplicationRecordDataType
Namespace		GDS (see 3.3)
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of the Structure DataType defined in OPC 10000-5.

RegisterApplication is used to register a new Application Instance with a GlobalDiscoveryServer.

This Method shall only be invoked by authorized users.

Servers that support transparent redundancy shall register as a single application and pass the DiscoveryUrls for all available instances and/or network paths.

RegisterApplication will create duplicate records if the ApplicationUri already exists since misconfiguration of applications can result in different applications having the same ApplicationUri. Before calling this Method the Client shall call FindApplications to check if a record for the application it is using already exists. If records are found which appear to belong to different applications (e.g. the DiscoveryUrls are different) then the Client shall report a warning before continuing.

If registration was successful and auditing is supported, the GDS shall generate the ApplicationRegistrationChangedAuditEventType (see 6.3.12).

Signature

RegisterApplication(

[in] ApplicationRecordDataType application

[out] NodeId applicationId

);

Argument	Description
application	The application that is to be registered with the GlobalDiscoveryServer.
applicationId	A unique identifier for the registered Application. This identifier is persistent and is used in other Methods used to administer applications.

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_InvalidArgument	The application or one of the fields of the application record is not valid. The text associated with the error shall indicate the exact problem.
Bad_UserAccessDenied	The current user does not have the rights required.

Table 6 specifies the AddressSpace representation for the RegisterApplication Method.

Table 6 – RegisterApplication Method AddressSpace Definition

Attribute	Value
BrowseName	RegisterApplication
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory
HasProperty	Variable	OutputArguments	Argument[]	PropertyType	Mandatory

UpdateApplication is used to update an existing Application in a GlobalDiscoveryServer.

This Method shall only be invoked by authorized users.

If the update was successful and auditing is supported, the GDS shall generate the ApplicationRegistrationChangedAuditEventType (see 6.3.12).

Signature

UpdateApplication(

[in] ApplicationRecordDataType application

);

Argument	Description
application	The application that is to be updated in the GDS database.

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_NotFound	The applicationId is not known to the GDS.
Bad_InvalidArgument	The application or one of the fields of the application record is not valid. The text associated with the error shall indicate the exact problem.
Bad_UserAccessDenied	The current user does not have the rights required.

Table 7 specifies the AddressSpace representation for the UpdateApplication Method.

Table 7 – UpdateApplication Method AddressSpace Definition

Attribute	Value
BrowseName	UpdateApplication
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory

UnregisterApplication is used to remove an Application from a GlobalDiscoveryServer.

This Method shall only be invoked by authorized users.

A Server Application that is unregistered may be automatically added again if the GDS is configured to populate itself by calling FindServersOnNetwork and the Server Application is still registering with its local LDS.

If un-registration was successful and auditing is supported, the GDS shall generate the ApplicationRegistrationChangedAuditEventType (see 6.3.12).

Signature

UnregisterApplication(

[in] NodeId applicationId

);

Argument	Description
applicationId	The identifier assigned by the GDS to the Application.

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_NotFound	The ApplicationId is not known to the GDS.
Bad_UserAccessDenied	The current user does not have the rights required.

Table 8 specifies the AddressSpace representation for the UnregisterApplication Method.

Table 8 – UnregisterApplication Method AddressSpace Definition

Attribute	Value
BrowseName	UnregisterApplication
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory

GetApplication is used to find an OPC UA Application known to the GDS.

Signature

GetApplication(

[in] NodeId applicationId

[out] ApplicationRecordDataType application

);

Argument	Description
applicationId	The ApplicationId that identifies the Application of interest.
application	The application record that matches the ApplicationId. The ApplicationRecordDataType is defined in6.3.5

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_NotFound	The no record found for the specified ApplicationId.
Bad_UserAccessDenied	The current user does not have the rights required.

Table 9 specifies the AddressSpace representation for the GetApplication Method.

Table 9 – GetApplication Method AddressSpace Definition

Attribute	Value
BrowseName	GetApplication
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory
HasProperty	Variable	OutputArguments	Argument[]	PropertyType	Mandatory

QueryApplications is used to find Client or Server applications that meet the specified filters. The only Clients returns are those that support the reverse connection capability described in OPC 10000-6.

QueryApplications returns ApplicationDescriptions instead of the ServerOnNetwork Structures returned by QueryServers. This is more useful to some Clients because it matches the return type of FindServers.

Any Client is able to call this Method, however, the set of results returned may be restricted based on the Client’s user credentials.

The applications returned shall pass all of the filters provided (i.e. the filters are combined in an AND operation). The capabilities parameter is an array and an application will pass this filter if it supports all of the specified capabilities.

Each time the GDS creates or updates an application record it shall assign a monotonically increasing identifier to the record. This allows Clients to request records in batches by specifying the identifier for the last record received in the last call to QueryApplications. To support this the GDS shall return records in order starting from the lowest record identifier. The GDS shall also return the last time the counter was reset. If a Client detects that this time is more recent than the last time the Client called the Method it shall call the Method again with a startingRecordId of 0.

Signature

QueryApplications(

[in] UInt32 startingRecordId

[in] UInt32 maxRecordsToReturn

[in] String applicationName

[in] String applicationUri

[in] UInt32 applicationType

[in] String productUri

[in] String[] capabilities

[out] DateTime lastCounterResetTime

[out] UInt32 nextRecordId

[out] ApplicationDescription[] applications

);

Argument	Description
INPUTS
startingRecordId	Only records with an identifier greater than this number will be returned. Specify 0 to start with the first record in the database.
maxRecordsToReturn	The maximum number of records to return in the response. 0 indicates that there is no limit.
applicationName	The ApplicationName of the applications to return. Supports the syntax used by the LIKE FilterOperator described in OPC 10000-4. Not used if an empty string is specified. The filter is only applied to the default ApplicationName.
applicationUri	The ApplicationUri of the applications to return. Supports the syntax used by the LIKE FilterOperator described in OPC 10000-4. Not used if an empty string is specified.
applicationType	A mask indicating what types of applications are returned. The mask values are: 0x1 – Servers; 0x2 – Clients; : If the mask is 0 then all applications are returned.
productUri	The ProductUri of the applications to return. Supports the syntax used by the LIKE FilterOperator described in OPC 10000-4. Not used if an empty string is specified.
capabilities	The capabilities supported by the applications returned. The applications returned shall support all of the capabilities specified. If no capabilities are provided this filter is not used.
OUTPUTS
lastCounterResetTime	The last time the counters were reset.
nextRecordId	The identifier of the next record. It is passed as the startingRecordId in subsequent calls to QueryApplications to fetch the next batch of records. It is 0 if there are no more records to return.
applications	A list of Applications which meet the criteria. The ApplicationDescription structure is defined in OPC 10000-4.

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_UserAccessDenied	The current user does not have the rights required.

Table 11 specifies the AddressSpace representation for the QueryApplications Method.

Table 10 – QueryApplications Method AddressSpace Definition

Attribute	Value
BrowseName	QueryApplications
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory
HasProperty	Variable	OutputArguments	Argument[]	PropertyType	Mandatory

QueryServers is used to find Server applications that meet the specified filters.

Any Client is able to call this Method, however, the set of results returned may be restricted based on the Client’s user credentials.

The applications returned shall pass all of the filters provided (i.e. the filters are combined in an AND operation). The serverCapabilities parameter is an array and an application will pass this filter if it supports all of the specified capabilities.

Each time the GDS creates or updates an application record it shall assign a monotonically increasing identifier to the record. This allows Clients to request records in batches by specifying the identifier for the last record received in the last call to QueryServers. To support this the GDS shall return records in order starting from the lowest record identifier. The GDS shall also return the last time the counter was reset. If a Client detects that this time is more recent than the last time the Client called the Method it shall call the Method again with a startingRecordId of 0.

Signature

QueryServers(

[in] UInt32 startingRecordId

[in] UInt32 maxRecordsToReturn

[in] String applicationName

[in] String applicationUri

[in] String productUri

[in] String[] serverCapabilities

[out] DateTime lastCounterResetTime

[out] ServerOnNetwork[] servers

);

Argument	Description
INPUTS
startingRecordId	Only records with an identifier greater than this number will be returned. Specify 0 to start with the first record in the database.
maxRecordsToReturn	The maximum number of records to return in the response. 0 indicates that there is no limit.
applicationName	The ApplicationName of the Applications to return. Supports the syntax used by the LIKE FilterOperator described in OPC 10000-4. Not used if an empty string is specified. The filter is only applied to the default ApplicationName.
applicationUri	The ApplicationUri of the Servers to return. Supports the syntax used by the LIKE FilterOperator described in OPC 10000-4. Not used if an empty string is specified.
productUri	The ProductUri of the Servers to return. Supports the syntax used by the LIKE FilterOperator described in OPC 10000-4. Not used if an empty string is specified.
serverCapabilities	The applications returned shall support all of the server capabilities specified. If no server capabilities are provided this filter is not used.
OUTPUTS
lastCounterResetTime	The last time the counters were reset.
servers	A list of Servers which meet the criteria. The ServerOnNetwork structure is defined in OPC 10000-4.

Method Result Codes (defined in Call Service)

Result Code	Description
Bad_UserAccessDenied	The current user does not have the rights required.

Table 11 specifies the AddressSpace representation for the QueryServers Method.

Table 11 – QueryServers Method AddressSpace Definition

Attribute	Value
BrowseName	QueryServers
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	InputArguments	Argument[]	PropertyType	Mandatory
HasProperty	Variable	OutputArguments	Argument[]	PropertyType	Mandatory

This event is raised when the RegisterApplication, UpdateApplication or UnregisterApplication Methods are called.

Its representation in the AddressSpace is formally defined in Table 12.

Table 12 – ApplicationRegistrationChangedAuditEventType Definition

Attribute		Value
BrowseName		ApplicationRegistrationChangedAuditEventType
Namespace		GDS (see 3.3)
IsAbstract		True
References	NodeClass		BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the AuditUpdateMethodEventType defined in OPC 10000-5.

This EventType inherits all Properties of the AuditUpdateMethodEventType. Their semantics are defined in OPC 10000-5.