Elements are objects that define a metadata field and its values, semantics, attributes, and properties (for a list of the attributes defined for PBCore elements, see our web page PBCore Element Attributes). An Element is the actual "thing" that carries the descriptive metadata about a media item, such as a title, a date, keywords, rights information, mime types, media types, etc. The metadata elements are what a cataloger interacts with (creating descriptions) within a cataloging tool or asset management system.
An element may be standalone. If several metadata fields are thematically related to each other, then they are governed by a larger theme, and shoud be bound together when data is shared. When bound, these related elements become part of what is called an Element Container.
An advantage to using the Element Container approach is that, unlike the basically flat arrangement of elements found in Dublin Core (http://www.dublincore.org), PBCore is able to bind together the data found in related elements and keep them that way. For example, a *title* and its associated *titleType* can be catalogued and bound together as one instance of the container *pbcoreTitle*. The container *pbcoreTitle* can be repeated within a single metadata record, with another *title* and *titleType*. For example, a working title or an alternative title can be specified, but still be part of one data record, instead of making multiple data records, each with redundant metadata (descriptions, keywords, coverage, etc.). Similarly a particular format (and its associated specifications) for a media item can be described within the container *pbcoreInstantiation*, and repeated multiple times for different formats/instantiations, all within a single metadata record.
Content Classes are created as "conceptual wrappers" that cluster together a list or structure of thematically-related Elements (metadata fields and their attributes and properties). PBCore maintains four Content Classes as the conceptual wrappers for its various metadata elements:
9 containers; 16 elements
(metadata elements describing the actual intellectual content of a media asset or resource)
4 containers; 7 elements
(metadata elements related to the creation, creators, usage, permissions, constraints, and use obligations associated with a media asset or resource)
1 container, 3 sub-containers; 28 elements
(metadata elements that identify the nature of the media asset as it exists in some form or format in the physical world or digitally)
1 container; 2 elements
(additional descriptions that have been crafted by organizations outside of the PBCore Project. These extensions fulfill the metadata requirements for these outside groups as they identify and describe their own types of media with specialized, custom terminologies unique to their needs and community requirements)
The Content Classes enhance the ability to understand the hierarchical structure of a data dictionary and its associated data models. This hierarchical structure is easily viewed by observing a Graphical Illustration of the PBCore Elements, their interdependencies within Element Containers, housed within Content Classes. Click on the thumbnail image below to open a high resolution diagram of PBCore v1.1, showing its structure.
- 4 Content Classes
- 15 Element Containers
- 3 Sub-Containers
- 53 Elements
To see a table of the elements organized by Content Classes, link to our web page PBCore Elements Viewed by Content Classes.
For an expanded discussion, link to our web page on Hierarchical Relationships and Element Interdependencies.
To read about other components in hierarchies, link to our web page on Element Containers.