PBCore Elements Viewed
Within the underlying metadata dictionary of PBCore, no hierarchical relationships (root, branches, leaves) are necessarily implied. However, in applying the elements from the metadata dictionary within an asset management system, or more importantly, when sharing metadata descriptions from a data export as a properly formatted XML document (that follows the PBCore XML Schema Definition: XSD), hierarchical relationships and interdependices between PBCore elements emerge as roots, branches and leaves.
A more complete explanation is provided on the PBCore web page entitled Hierarchical Relationships and Interdependencies between Metadata Elements.
These roots, branches, and leaves are alternatively expressed in a data model as "Master Container," "Content Classes,' "Containers," "Sub-Containers," and "Elements." PBCore has 53 elements arranged in 15 containers and 3 sub-containers, all organized within four content classes.
PBCore DESCRIPTION DOCUMENT (aka the MASTER CONTAINER)
The Master Container assembles together all collections of PBCore knowledge items. For PBCore these knowledge items are metadata descriptions of media. The MasterContainer is expressed as a document that hierarchically structures all the knowledge items and metadata terms and values related to a single data record associated with a media item. In our XML Schema Definition, the MasterContainer is referred to as the "PBCoreDescriptionDocument."
CONTENT CLASS (aka PBCore Section)
In the hierarchy of objects in the PBCore Description Document/Master Container, 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)
ELEMENT CONTAINERS & SUB-CONTAINERS (aka Schema Tag and Schema Sub-Tag, alternatively "branches"):
Elements are objects in the PBCore schema hierarchy that define a metadata field and its values, attributes and properties. An element may be standalone. If several metadata fields are thematically related to each other, they can be bound together under an Element Container. Related elements are subsumed by a larger theme, and should be bound together when data is shared (particularly if an Element Container is a repeatable description with multiple instances of its related Elements). Examples of related Elements bound within a Container are *title* and its associated *titleType*, that are bound together by the Element Container *PBCoreTitle*. Within hierarchical structures, a Container may house Sub-Containers, which themselves bind together related Elements. In PBCore, there are Sub-Containers found within the Content Class PBCoreInstantiation.
ELEMENTS (aka "leaves"):
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.
If we illustrate PBCore by its four Content Classes, associated Containers, Sub-Containers, and Elements, PBCore v1.1 begins to look like the following diagram (click on the image to see a higher resolution version):
In contrast and for comparison's sake, here is a diagram of the original "flat" arrangement of the elements found in PBCore v1.0 (click on the image to see a higher resolution image):
Listed below are quick jumps to other organizational views of the PBCore elements.
PBCore Element Views
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