EXCHANGING METADATA
PBS DLL XSD: XML Schema Definition

 

Download the PBS DLL XSD

The XML Schema Definition for the PBS Digital Learning Library Metadata Schema is available for download and use within your media management systems and data tranformation services.

In a nutshell, the PBS DLL XSD formally structures the metadata elements, using XSD conventions, and is used as the framework against which metadata descriptions from one cataloging or asset management system can be compared to that used in the PBS Digital Learning Library system. The XSD itself is not the actual tool that translates metadata from a source into a target system, but is the reference document that makes those translations possible (employing what is called an XSLT: Extensible Stylesheet Language Transformation).

Two documents are provided. One is the actual XSD. The other is a companion document identifying PBS DLL metadata asset types and controlled vocabulary terms that are employed in the schema.

    1. Download PBS DLL XSD v1.2 (12-10-2009)
    2. Download the PBS DLL Asset Types & Controlled Vocabularies v1.2 (12-10-2009)

For an at-a-glance illustration of the PBS DLL Metadata elements, jump to the page in the Metadata User Guide called Overviews of All Element > Diagram View.


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Discussion about the XML Schema Definitions

 

Knowledge Representation

A metadata schema, as well as the actual descriptions of media items that use the schema, need to be presented in some logical, clearly expressed framework so that the information can be interpreted accurately.

Interchange Structure

More importantly, using well-formed methods and frameworks to express metadata schemas and descriptions allows different parties to share data; they are communicating using the same language, the same grammar, and the same structuring of data.

A language that is often used in files to express well-formed data is XML, Extensible Markup Language. Unless the party offering and the party accepting the well-formed data interpret, validate, and implement that data in the same way, information is likely to be mangled. Four necessary conditions have been identified for describing common data interpretation, validation, and implementation between systems that are sharing data:

    1. common metadata meanings (semantics),
    2. common grammar and rules for expressing data (syntax),
    3. commonly defined metadata dictionary element properties (attributes), and
    4. shared information architectures concentrating element hierarchical structures and interdependencies (data models)

Items 1 through 3 (semantics, syntax, and attributes) are usually referred to as a Metadata Dictionary. Item 4 is the expression of the Metadata Dictionary within a Data Model's Framework. A DTD (Document Type Definition) and an XML Schema are both used to define the grammar and validate the data being shared. Some have stated that DTDs and XML Schemas function as blueprints for describing the structure of the XML language in a document. These blueprints supply the...

  • Sequence in which elements appear in an XML document
  • Interrelationships between different elements (interdependencies, parent-child associations or nested relationships)
  • Types of data that are used to express elements and attributes (text string, number, date, timestamp, etc.)

DTDs have been around longer than XML Schemas, and are very widely used. However, they have some limitations in their capacities, such as employing non-XML syntax to compose a DTD, support for limited data types, inability to identify namespaces, and no support for extensibility or inheritance. XML Schemas, however, do not have these limitations and also allow users to craft their own custom data types.

Typically, more complex data structures, with multiple data types, require the use of an XML Schema over that of a DTD.

PBS DLL offers an XML Schema Definition (XSD) document to define the framework of the PBS DLL elements, their inter-relationships and interdependencies.

TWO SCENARIOS FOR DATA SHARING / INTEROPERABILITY

When sharing metadata (facilitating interoperability), data that is exported from an information system (one metadata island) is transformed into a PBS DLL compliant XML document, using the framework of the PBS DLL XSD. The receiving information system (another metadata island) imports the PBS DLL compliant XML document and transforms that data to match its own internal structures and metadata schemas.

The following discussion highlights two different scenarios in which data is being exchanged between information systems.

SCENARIO 1: NO DATA TRANSALTION NEEDED

"Organization A" uses an In-House tool to create and save descriptive records for its media assets. This tool can export the records in an XML format, compliant with the PBS DLL XSD.

"Organization B" uses the PBS DLL metadata dictionary to create and save descriptive records of its media assets. They can automatically import and export metadata records in an XML format, compliant with the PBS DLL XSD.

 

SCENARIO 2: DATA TRANSLATION REQUIRED

"Organization C" purchased an asset management tool to create and save descriptive records for its media assets. This tool cannot export the records in an XML format that is compliant with the PBS DLL XSD.

"Organization D" purchased a different asset management tool to create and save descriptive records of its media assets. This tool cannot import or export the records in an XML format that is compliant with either the PBS DLL XSD.

Because the respective organizations use tools that format metadata records in different ways, they cannot exchange records unless they transform their metadata records into a new third format that can be understood by the information systems in each organization.

The PBS DLL XSD can be the third party reference that is used to move data between the two incompatible systems.

"Organization C" uses a data transformation method (such as XSLT--Extensible Stylesheet Language Transformations; W3C or Wikipedia definition) to translate records from their in-house format into PBS DLL XSD-compliant data.

"Organization D" recognizes and then transforms the PBS DLL XSD-compliant data supplied by "Organization C" into records understood by their in-house data format.

 

XML SCHEMA PRIMERS

For information purposes, listed here are selected Primers, XML Schema Definitions and Specifications as provided by the W3C ...

 


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