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Development Funding for PBCore provided by the
Corporation for Public Broadcasting

PBCore is a Metadata & Cataloging Resource
for Public Broadcasters & Associated Communities

Background of the PBCore
Public Broadcasting Metadata Dictionary Project


Intrinsic to digital technology is the ability for each piece of content to carry with it some data describing that content in a useful way. This descriptive data is called metadata. To address the need to manage metadata within public broadcasting’s diverse community, version 1.1 of PBCore (the Public Broadcasting Metadata Dictionary) has been developed by a cross-organizational team of public radio and television producers and managers, archivists and information scientists.

PBCore is designed to provide—for television, radio and Web activities—a standard way of describing and using this data, allowing content to be more easily retrieved and shared among colleagues, software systems, institutions, community and production partners, private citizens, and educators. It can also be used as a guide for the onset of an archival or asset management process at an individual station or institution. Such a standard is pivotal to applying the real power of digital technology to meet the mission of public broadcasting.

We can now control every aspect of production and distribution to a degree never possible with analog technology. A common metadata protocol will make it easier to use content in new ways, on new platforms, by new constituents. PBCore will facilitate new production collaborations and the ability to parse traditional programs into short segments for Web distribution or as niche content for specific community, service and institutional needs. For these and other applications where granular manipulation and interoperability of content are required, PBCore will be essential.

Since the initial publication (April 2005) of the Public Broadcasting Metadata Dictionary (PBCore v1.0), many stations, organizations and information systems began to use its 48 elements to describe the intellectual content, property rights, and instantiations/formats of their media items.

During this period, the PBCore project has been finalizing its XML Schema Definition (XSD) (for a discussion of XSD see The PBCore XML Schema web page). This XSD is the main framework upon which all the PBCore elements, their relationships, vocabulary picklists, and data types are organized and defined. The purpose of building an accurate and meticulous XSD is to ensure that when PBCore compliant metadata descriptions are shared between data systems, the contributing system and the receiving system are both able to "machine read" and faultlessly interpret and display the descriptions.

In the process of creating the PBCore XSD, we determined that some enhancements to the underlying structure of PBCore were necessary. For the most part, these enhancements are related to binding together related metadata elements (such as Title and TitleType) into new element containers. In a hierarchical arrangement, each element container collects and houses associated "child" elements that are thematically related. Basically, what was a "flat" arrangement of the 48 PBCore elements is becoming a more structured "hierarchical" model of 53 elements arranged in 15 containers and 3 sub-containers, all organized under 4 content classes.

A more complete explanation is provided on the PBCore web page entitled Hierarchical Relationships and Interdependencies between Metadata Elements.

The hierarchy of roots, branches, and leaves is alternatively expressed in a data model as "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.

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:

  1. PBCoreIntellectualContent
    9 containers; 16 elements
    (metadata elements describing the actual intellectual content of a media asset or resource)
  2. PBCoreIntellectualProperty
    4 containers; 7 elements
    (metadata elements related to the creation, creators, usage, permissions, constraints, and use obligations associated with a media asset or resource)

  3. PBCoreInstantiation
    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)

  4. PBCoreExtensions
    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)

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

The underlying meaning and attributes of the PBCore elements are not changing. However, their inter-dependencies and structural arrangements are, along with some modifications to data entry options (see PBCore v1.1 Changes for more information).

We feel the impending improvements to PBCore will greatly enhance its usability by Public Broadcasting communities and certainly improve the precision involved in sharing metadata between various information systems.

The need for a shared descriptive language for public broadcasters was underscored in the results of the test implementations, as well as the March 2004 Request for Comments. Test participants affirmed the belief that their organizations and public broadcasting need PBCore to be widely available and in use by a majority of broadcasters. Ninety-six percent of the RFC respondents agreed "public broadcasting needs a core metadata dictionary," and that PBCore meets this need.

In addition, 44 percent of participants plan to implement a metadata project within a year, and 74 percent within two years. Respondents indicated the use of PBCore would provide public broadcasting with a necessary tool for increasing station and network efficiencies and inter-station resource sharing. And 80 percent agreed the use of PBCore could afford new service opportunities for their organization or those with whom they work.

Available free of charge to public broadcasting stations, distributors, vendors, and partners, version 1.0 of PBCore was launched in the first quarter of 2005 and version 1.1 was published in the first quarter of 2007. Please reference the links to Who May Use PBCore and PBCore Licensing for additional information about usage and implementation.

Funded by the Corporation for Public Broadcasting and administered by WGBH/Boston, a well-formed metadata dictionary directly addresses public broadcasting’s mission by making its award-winning content more easily accessible to teachers, scholars, lifelong learners, engaged citizens, and community partners.

Based on Dublin Core: The PBCore is built on the foundation of the Dublin Core (ISO 15836), an international standard for resource discovery (http://dublincore.org), and has been reviewed by the Dublin Core Metadata Initiative Usage Board.



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