The AEM Tagging Framework

Tagging allows content to be categorized and organized. Tags can be classified by a namespace and a taxonomy. For detailed information about using tags:

• See Using Tags for information about tagging content as a content author.
• See Administering Tags for an administrator?s perspective about creating and managing tags, and to which content tags have been applied.

This article focuses on the underlying framework which supports tagging in AEM and how to use it as a developer.

Introduction

To tag content and use the AEM Tagging infrastructure :

• The tag must exist as a node of type cq:Tag under the taxonomy root node.
• The tagged content node’s NodeType must include the cq:Taggable mixin.
• The TagID is added to the content node’s cq:tags property and resolves to a node of type cq:Tag.

cq:Tag Node Type

The declaration of a tag is captured in the repository in a node of type cq:Tag.

• A tag can be a simple word (for example, sky) or represent a hierarchical taxonomy (for example, fruit/apple, meaning both the generic fruit and the more specific apple).
• Tags are identified by a unique TagID.
• A tag has optional meta information such as a title, localized titles, and a description. The title should be displayed in user interfaces instead of the TagID, when present.

The tagging framework also restricts authors and site visitors to use only specific, predefined tags.

Tag Characteristics

• The node type is cq:Tag.
• The node name is a component of the TagID.
• The TagID always includes a namespace.
• The jcr:title property (the Title to display in the UI) is optional.
• The jcr:description property is optional.
• When containing child nodes, is referred to as a container tag.
• The tag is stored in the repository below a base path called the taxonomy root node.

TagID

A TagID identifies a path which resolves to a tag node in the repository.

Typically, the TagID is a shorthand TagID starting with the namespace or it can be an absolute TagID starting from the taxonomy root node.

When content is tagged, if it does not yet exist, the cq:tags property is added to the content node and the TagID is added to the property’s String array value.

The TagID consists of a namespace followed by the local TagID. Container tags have subtags that represent a hierarchical order in the taxonomy. Subtags can be used to reference tags same as any local TagID. For example, tagging content with fruit is allowed, even if it is a container tag with subtags, such as fruit/apple and fruit/banana.

Taxonomy Root Node

The taxonomy root node is the base path for all tags in the repository. The taxonomy root node must not be a node of type cq:Tag.

In AEM, the base path is /content/cq:tags and the root node is of type cq:Folder.

Tag Namespace

Namespaces let you group things. The most typical use-case is to have a namespace per site (for example, public versus internal) or per larger application (for example, Sites or Assets), but namespaces can be used for various other needs. Namespaces are used in the user interface to show only the subset of tags (that is, tags of a certain namespace) that is applicable to the current content.

The tag’s namespace is the first level in the taxonomy subtree, which is the node immediately below the taxonomy root node. A namespace is a node of type cq:Tag whose parent is not a cq:Tag node type.

All tags have a namespace. If no namespace is specified, the tag is assigned to the default namespace, which is TagID default, that is, /content/cq:tags/default. The Title defaults to Standard Tagsin such cases.

Container Tags

A container tag is a node of type cq:Tag containing any number and type of child nodes, which makes it possible to enhance the tag model with custom metadata.

Furthermore, container tags (or super-tags) in a taxonomy serve as the subsummation of all subtags. For example, content tagged with fruit/apple is considered tagged with fruit, too. That is, searching for content tagged with fruit would also find the content tagged with fruit/apple.

Resolving TagIDs

If the tag ID contains a colon (:), the colon separates the namespace from the tag or subtaxonomy, which are then separated with normal slashes (/). If the tag ID does not have a colon, the default namespace is implied.

The standard and only location of tags is below /content/cq:tags.

Tags referencing non-existing paths or paths that do not point to a cq:Tag node are considered invalid and are ignored.

The following table shows some sample TagIDs, their elements, and how the TagID resolves to an absolute path in the repository:

Localization of Tag Title

When the tag includes the optional title string jcr:title, it is possible to localize the title for display by adding the property jcr:title.<locale>.

For more details, see the following:

• Tags in Different Languages describe the use of the APIs as a developer
• Managing Tags in Different Languages, which describe use of the Tagging console as an administrator

Access Control

Tags exist as nodes in the repository under the taxonomy root node. Allowing or denying authors and site visitors to create tags in a given namespace can be achieved by setting appropriate ACLs in the repository.

Denying read permissions for certain tags or namespaces controls the ability to apply tags to specific content.

A typical practice includes:

• Allowing the tag-administrators group/role write access to all namespaces (add/modify under /content/cq:tags). This group comes with AEM out-of-the-box.
• Allowing users/authors read access to all the namespaces that should be readable to them (mostly all).
• Allowing users/authors write access to those namespaces where tags should be freely definable by users/authors (add_node under /content/cq:tags/some_namespace)

Taggable Content : cq:Taggable Mixin

For application developers to attach tagging to a content type, the node’s registration (CND) must include the cq:Taggable mixin or the cq:OwnerTaggable mixin.

The cq:OwnerTaggable mixin, which inherits from cq:Taggable, is intended to indicate that the content can be classified by the owner/author. In AEM, it is only an attribute of the cq:PageContent node. The cq:OwnerTaggable mixin is not required by the tagging framework.

Node Type Notation (CND)

Node Type definitions exist in the repository as CND files. The CND notation is defined as part of the JCR documentation.

The essential definitions for the Node Types included in AEM are as follows:

[cq:Tag] > mix:title, nt:base
    orderable
    - * (undefined) multiple
    - * (undefined)
    + * (nt:base) = cq:Tag version

[cq:Taggable]
    mixin
    - cq:tags (string) multiple

[cq:OwnerTaggable] > cq:Taggable
    mixin

cq:tags Property

The cq:tags property is a String array used to store one or more TagIDs when they are applied to content by authors or site visitors. The property only has meaning when added to a node which is defined with the cq:Taggable mixin.

Moving and Merging Tags

The following is a description of the effects in the repository when moving or merging tags using the Tagging console.

When tag A is moved or merged into tag B under /content/cq:tags:

• Tag A is not deleted and receives a cq:movedTo property.

  • cq:movedTo points to tag B.

  • This property means that tag A has been moved or merged into tag B.

  • Moving tag B updates this property accordingly.

  • Tag A is therefore hidden and is only kept in the repository so it can resolve tag IDs in content nodes pointing to tag A.

  • The tag garbage collector removes tags like tag A once no more content nodes point to them.

  • A special value for the cq:movedTo property is nirvana, which is applied when the tag is deleted but cannot be removed from the repository because there are subtags with a cq:movedTo that must be kept.

    NOTE

    The cq:movedTo property is only added to the moved or merged tag if either of these conditions are met:

    1. The tag is used in content (meaning that it has a reference). OR
    2. The tag has children that have already been moved.
    * Tag B is created (if there is a move) and receives a `cq:backlinks` property.

  • cq:backlinks keeps the references in the other direction. That is, it keeps a list of all the tags that have been moved to or merged with tag B.

  • This functionality is mostly required to keep cq:movedTo properties up to date when tag B is moved/merged/deleted as well or when tag B is activated, in which case all its backlinks tags must be activated as well.

    NOTE

    The cq:backlinks property is only added to the moved or merged tag if either of these conditions are met:

    1. The tag is used in content (meaning that it has a reference), or
    2. The tag has children that have already been moved.

Reading a cq:tags property of a content node involves the following resolution:

1. If there is no match under /content/cq:tags, no tag is returned.
2. If the tag has a cq:movedTo property set, the referenced tag ID is followed.
   • This step is repeated as long as the followed tag has a cq:movedTo property.
3. If the followed tag does not have a cq:movedTo property, the tag is read.

To publish the change when a tag has been moved or merged, the cq:Tag node and all its backlinks must be replicated. This replication is automatically done when the tag is activated in the tag administration console.

Later updates to the page’s cq:tags property automatically clean up the old references. The clean up is triggered because resolving a moved tag through the API returns the destination tag, thus providing the destination tag ID.