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4.4. Metadata Extensions
In some cases, organizations may find that the core set of metadata elements defined by LOM is not adequate enough to describe SCORM Content Model Components. The organization may have a set of metadata extensions that are required to be used in describing these components. There are currently two types of extensions mechanism permitted within the LOM:
XML element extensions. The first mechanism allows for the extension of the LOM data model elements. It is permissible to add additional elements to metadata instances. For example, if an organization has additional information regarding intellectual property rights and conditions or use for their SCORM Content Model Components, it is feasible for the organization to add elements to the Rights Category. There are currently several ongoing research and development activities dealing with digital rights management. It is feasible that a set of elements describing a more robust and rich sets of rights will be
developed. This could ideally be used in describing SCORM Content Model Components by extending the Rights category.
Vocabulary extensions. Some of the IEEE elements have a defined list of vocabulary values. However, this is just a recommendation and the metadata instances are not required to use those vocabularies. If an organization has the need to use a different set of vocabularies, then the organization has several alternatives. If the organization wants to enforce validation of the vocabularies, then ADL recommends the use of the custom schema validation approach (refer to Section 4.4.2: Vocabulary Extension for more information on building XML Schema Definition files for validation purposes). The strict schema validation approach cannot be used since it will only validate strict LOM vocabulary pairs.
Several words of caution when using extensions.
1. When creating extension elements, it is not permitted to define elements that contain the same semantics of the currently defined IEEE LOM elements.
2. Metadata that relies on the recommended values will have the highest degree of semantic interoperability (i.e., the likelihood that such metadata will be understood by other end users or systems is the highest). To keep a high degree of semantic interoperability, ADL recommends that if extensions are needed to meet the needs of a vertical community (e.g., health care industry), then the vertical communities should work to a consensus on building a set of interoperable extensions.
The LOM distinguishes between two types of conformance to the IEEE standard. If a LOM metadata instance does not contain any extensions, then the IEEE standard refers to this as a strictly conforming LOM metadata instance. If a LOM metadata instance contains extended data elements, then the IEEE standard refers to this as a conforming LOM metadata instance. SCORM supports both types of conformance and recommends LOM metadata instances to be strictly conforming (based on the cautions described above).