Metadata is often called ‘data about data’.
Where data can be defined as a representation of facts, concepts or instructions, metadata can be defined as information about how data are defined, structured and represented. It can provide meaning and context to data by describing how data is captured and the business rules for collecting data. It can also assist in the interpretation of data.
For example, the data value 185 is largely meaningless without additional information. Is it a street number, a clinical measurement, a test result or the number of services provided?
Adding information about the unit of measure (e.g. centimetres), what the data relates to (e.g. a person) and what it is measuring (e.g. their height) makes for a more useful data value. Additional details of how the measurement was made (e.g. self-reported) could be added to further improve the utility of the data.
When a data value (e.g. 185) is transmitted or linked to a specific metadata item (e.g. Person—body height (self-reported), total centimetres NNN), the meaning is also made clear and can be understood by the recipient.
Metadata that have been endorsed for use across Australia are referred to as metadata standards.
Types of metadata in METeOR
There are two types of metadata used in METeOR - metadata items and navigational items.
Metadata items proceed through a series of registration states until they become endorsed as official metadata standards. There are eight predominant metadata items currently used in METeOR:
- Object class: a person, organisation, structure or event, e.g. Person or Family
- Property: a characteristic of an object class, e.g. Sex or Date of Birth
- Data element concept: union of an object class and property, e.g. Person-Sex
- Value domain: a set of permissible values, e.g. Sex code N
- Data element: union of a data element concept and value domain, e.g. Person-Sex, Code N
- Classification scheme: official terminological system e.g. International Classification of Diseases
- Data set specification: a group of data elements for collection, e.g. Admitted Patient Care National Minimum Data Set
- Glossary item: definition of a term that is not an object class e.g. Live birth
Navigational items are items that are added to METeOR by the Registrars to make the navigation and management of metadata items easier and more meaningful. This means that navigational items are not official data standards. There are two navigational items currently used in METeOR:
- Property group: a group of properties with similar characteristics e.g. Educational characteristics (Student type, Qualification status)
- Object class specialisation: a group of object class sub-types e.g. Person/group of persons (Adult, child)