What is changing?

XML (Extensible Markup Language)

PDS has adopted XML for PDS4. The Extensible Markup Language (XML) is an international standard that is widely used by many online data systems to document their data. It provides a standard syntax and structure for describing data for many different industries. A significant number of vendors and programming languages provide support for reading and writing XML files. XML integrates directly with web-based applications allowing for the metadata, described in XML, to be rendered in a number of different formats.

In previous versions of PDS, the Object Description Language (ODL) was used to capture metadata labels for archived data. ODL is a proprietary language developed and maintained by the PDS. The standards management along with tool and library support were resourced by the PDS. As a result, limited tool support exists. In addition, variations in the use of ODL and the implementation of data products led to differences in the implementation of the PDS standards which affects usability and interoperability.

For PDS4, the use of XML will allow PDS labeled metadata, captured in XML, to take advantage of the wealth of software and tools available for the development of online, web-based systems and to use its resources to improve accessibility and usability of the data. It also allows for the generation of standard templates that can be used to improve consistency across missions, nodes and international partners. The consistency in defining and enforcing common metadata across PDS4 data products will also help improve data search across the PDS.

PDS is ensuring that its adoption of XML will comply with best practices allowing for direct use by popular off the shelf XML tools. For more information about XML, please refer to Wikipedia.

PDS Standards and Information Model

PDS is developing PDS4 using a rigorous process for defining the standards. This process includes development of a self-consistent information model. All PDS metadata will be derived from this model. In addition, common templates and data dictionary terms will be consistent across missions and instrument teams.

Software System

The PDS is a geographically distributed federation of nodes which encompasses the entire system. In order to deliver and integrated system and improve overall access to PDS data, the PDS is re-architecting the system to deliver a modern, online data system. The online system will improve both the efficiency of ingestion and the distribution of the data.

The software system will provide software services which can be remotely accessed allowing users to search, access and transform data that are archived in distributed data repositories. All of the metadata will be described using the PDS4 XML data standard. The software tools and services delivered with PDS4 will take advantage of the XML structure to improve tool and service development to be compliant to a PDS-wide information model. In addition, PDS intends to release a core software library to help tool developers in delivering PDS4 compatible tools.

In addition to developing services and tools, the PDS will be ensuring that all PDS data is registered and available through an online set of registries. These registries will improve integration with PDS search services to allow better navigation across the system.

In addition to efforts in supporting integration of the PDS nodes, the PDS is working with the International Planetary Data Alliance to develop data sharing standards and to improve international access to PDS compatible archives.