6.3 AliasNameCategoryType ObjectType Definition

6.3.1 Definition

AliasNameCategoryType instances are used to organize the AliasNameType instances that a Server defines. They can also include instances of AliasNameCategoryType to allow hierarchical groupings of AliasNames. It includes a mandatory Method for finding instances of AliasNameType in the AliasName hierarchy, starting at this instance of AliasNameCategoryType. For example, if the Method call is made on the Aliases AliasNameCategoryType instance (see 9.2), it would apply the AliasNameSearchPattern to all AliasNames that are defined under TagVariables, Topics and any other AliasNameCategoryType instance in the hierarchy.

Well-known AliasNameCategories are defined in this document. Other documents may also define well-known AliasNameCategories. A well-known AliasNameCategory has a static NodeId allowing it to be aggregated. For details on aggregation of AliasName and AliasNameCategories see Annex B.

The AliasNameCategoryType is a subtype of FolderType and is formally defined in Table 2.

The list of AliasNames that an Object contains could be dynamic. For example, AliasNames could be added in an aggregating Server as underlying Servers become available or could be removed if a Server is no longer available.

<Alias> represents any number of instances of AliasNameType. Each instance shall have at least one AliasFor Reference to a Node. Multiple <Alias> instances can point to the same Node.

<SubAliasNameCategories> allows the nesting or structuring of AliasNames into hierarchical groupings.

An <Alias> can appear in more than one place in the hierarchy of AliasNameCategories.

LastChange is the most recent time for any of the following activities:

The last time an AliasName was added to or deleted from the AliasNameCategory,

The last time an AliasNameCategory was added or deleted,

The last time the referenced Nodes of an AliasName in the AliasNameCategory changed.

For AliasNameCategoryType instances that are nested, the value of LastChange shall always be the latest VersionTime of all Organized AliasNames and AliasNameCategories.

The LastChange shall be persisted. A Client that detects a LastChange that is older than what it has cached, shall clear all cached AliasNameCategories and related AliasNames.

6.3.2 FindAlias Method

The FindAlias Method allows a Client to obtain the list of Nodes that match the provided AliasName search string. The signature of this Method is specified below, the arguments are defined in Table 3.

Signature

	FindAlias(
	  [in]  String				AliasNameSearchPattern,
	  [in]  NodeId				ReferenceTypeFilter,
	  [out] AliasNameDataType[]	AliasNodeList
	);

Method result codes are defined in Table 4

The Method is formally defined in Table 5.

It is important to note that there could be more than one entry for every AliasName. Multiple Servers could provide a Node that represents an equivalent object (such as a temperature sensor). An aggregating Server could also provide the Node. This Method will return the AliasNames in order of preference. That is the Server will return what it recommends as the best match first followed by the next best match etc. The criteria for ordering are Server specific. The criteria could be based on the ServerStatus of the Server that contains the referenced Node, it could be load balancing of Servers, it could be for off-loading of small device Servers, or it could be some other algorithm.

Clients should use the first usable entry in the list.

6.3.3 FindAliasVerbose Method

The FindAliasVerbose Method extends the FindAlias Method, by providing additional information in the returned data, all other aspects of the Method are identical to FindAlias. The signature of this Method is specified below; the arguments are defined in Table 6.

Signature

	FindAliasVerbose(
	  [in]  String					AliasNameSearchPattern,
	  [in]  NodeId					ReferenceTypeFilter,
	  [out] AliasNameVerboseDataType[]	AliasNodeList
	);

Method result codes are defined in Table 7.

The Method is formally defined inTable 8.

The FindAliasVerbose Method provides additional information in the AliasNameVerboseDataType, including AliasNameCategory information and ServerUri Information, see 7.3 for details.

6.3.4 AddAliasesToCategory Method

The AddAliasesToCategory Method allows a Client to add an AliasName to the AliasNameCategory. The signature of this Method is specified below, the arguments are defined in Table 9.

Signature

	AddAliasesToCategory( 
	  [in] String[]		AliasNames,	
	  [in] ExpandedNodeId[]	TargetNodes,
	  [in] String[]		TargetServers,
	  [in] NodeId			TargetReferenceType,
	  [out] StatusCode[]	ErrorCodes
	);

The generated AliasName Nodes are assigned a Server specific NodeId.

If the same AliasName is to reference multiple TargetNodes then the AliasName shall be listed in the AliasNames array multiple times, one for each TargetNode.

It is not required for an AliasName Server to check the existence of external Nodes (i.e. Nodes that are not on the Server hosting the AliasName). If a Server does check for external Nodes, it shall not fail the addition if the Server or Node on the external Server is not available, it shall return Uncertain_ReferenceOutOfServer. If the Server does not check for the external Node’s existence, it shall return Uncertain_ReferenceOutOfServer.

If an entry in the parallel arrays duplicates an existing AliasName entry (exact same AliasName, TargetNode and TargetServer) or it appears more than once in the array it shall be ignored and no error shall be generated.

The list of StatusCodes that could be returned in ErrorCodes is defined in Table 10.

Method result codes are defined in Table 11.

The Method is formally defined in Table 12.

6.3.5 DeleteAliasesFromCategory Method

The DeleteAliasesFromCategory Method allows a Client to remove AliasNames from the AliasNameCategory. The signature of this Method is specified below; the arguments are defined in Table 13.

This Method shall only delete AliasName instances that are defined on the Server exposing this Method. I.e. an aggregating Server that has pulled AliasName instances from an aggregated Server cannot delete AliasName instances that are from the aggregated Server.

Signature

	DeleteAliasesFromCategory  
	(
	  [in] String[]		AliasNames,
	  [in] ExpandedNodeId []	TargetNodes,
	  [out] StatusCode[]	ErrorCodes
	);

The length of each of the arrays shall be the same.

If the TargetNodes array entry is null or empty, all AliasNames with the provided name are deleted from the AliasNameCategory. If all targets for an AliasNames array entry cannot be deleted, then none of the targets are deleted.

The list of StatusCodes that could be returned in ErrorCodes is defined in Table 14

Method result codes are defined in Table 15

The Method is formally defined in Table 16.