The Classification interface is used to classify RegistryObject instances. A RegistryObject may be classified along multiple dimensions by adding zero or more Classification instances to the RegistryObject. For example, an Organization may be classified by its industry, by the products it sells and by its geographical location. In this example the RegistryObject would have at least three Classification instances added to it. The RegistryObject interface provides several addClassification methods to allow a client to add Classification instances to a Registry Object.

Figure 1 shows how a Classification classifies a RegistryObject using a ClassificationScheme.

Figure 1. Using a ClassificationScheme to Classify an Object

Internal vs. External Taxonomies

A taxonomy may be represented within a Jakarta XML Registries provider in one of the following ways:

1. The taxonomy elements and their structural relationship with each other are available within the Jakarta XML Registries provider. This case is referred to as Internal Taxonomy since the structure of the taxonomy is available internal to the Jakarta XML Registries provider.
2. The taxonomy elements and their structural relationship with each other is represented somewhere external to the Jakarta XML Registries provider. This case is referred to as External Taxonomy since the structure of the taxonomy is not available to the Jakarta XML Registries provider.

Internal vs. External Classifications

The Classification interface allows the classification of RegistryObjects using a ClassificationScheme whether the ClassificationScheme represents an internal taxonomy or an external taxonomy. When a Classification instance uses a ClassificationScheme representing an internal taxonomy then it is referred to as an internal Classification. When a Classification instance uses a ClassificationScheme representing an external taxonomy then it is referred to as an external Classification.

Internal Classification

When a Classification instance is used to classify a RegistryObject using an internal taxonomy it is referred to as an internal Classification. A client must call the setConcept method on a Classification and define a reference to a Concept instance from the Classification instance in order for that Classification to use an internal taxonomy. It is not necessary for the client to call setClassificationScheme for internal Classifications since the classifying Concept already knows it root ClassificationScheme.

Example of Internal Classification

Figure 2 shows an example of internal classification using a Concept to represent a taxonomy element. The example classifies an Organization instance as a Book Publisher using the NAICS standard taxonomy available as an internal taxonomy. Note that the figure does not show all the Concepts between the Book Publishers node and the NAICS ClassificationScheme to save space. Had they been there they would have been linked together by the parent attribute of each Concept.
Figure 2. Example of Internal Classification

External Classification

When a Classification instance is used to classify a RegistryObject using an external taxonomy it is referred to as an external Classification. A client must call the setValue method on a Classification and define a unique value that logically represents a taxonomy element within the taxonomy whose structure is defined externally. It is necessary for the client call setClassificationScheme for external Classifications since there is no other way to infer the ClassificationScheme that represents the external taxonomy.

Example of External Classification

Figure 3 shows an example of external classification. The example uses the same scenario where a Classification classifies an Organization instance as a Book Publisher using the NAICS standard taxonomy. However, this time the structure of the NAICS taxonomy is not available internally to the Jakarta XML Registries provider and consequently there is no Concept instance. Instead, the name and value attributes of the Classification are used to pinpoint the Book Publisher's taxonomy element. Note that name is optional but value is required.
Figure 3. Example of External Classification

An Example of Multiple Classifications

The next example shows how a RegistryObject may be classified by multiple classification schemes. In this example, two internal ClassificationSchemes named Industry and Geography are used to classify several Organization RegistryObjects by their industry and Geography. In Figure 4, in order to save space and improve readability, the Classification instances are not explicitly shown but are implied as associations between the RegistryObjects (shaded leaf node) and the associated Concepts.
Figure 4. Example of Multiple Classifications