FEP - Format Use by an Archive - PDS - PDS

1. Archive Identification

Planetary Data System (PDS) - Archive for Planetary Science Community

2. Format (Format System) Identification

The current version of PDS standards are identified as PDS Standards Version 3. PDS labels are encoded in the Object Description Language (ODL) and required to have the statement PDS_VERSION_ID = PDS3. PDS labels contain meta-data that describe both the data structure, format, and the context within which the data was collected. The format description is included in the label. So for example, a simple raster image could be described in an ODL label using keywords that represent image attributes such as LINES, LINE_SAMPLES, and SAMPLE_BITS as well as target and instrument attributes such as TARGET_NAME and FILTER_NUMBER. The PDS recommends the use of simple data structures such as raster images and ASCII tables. The PDS allows the use of certain data formats such as FITS, where declarative descriptions of the format is sufficient to determine means for accessing the data.

The PDS standards architecture includes two primitive data objects that are used to derive all other data objects such as IMAGE, TIME_SERIES, and SPECTRUM. These latter data objects are used to describe each data product within an archived data set.

The PDS standards architecture also includes a planetary data model that describes the entities within the planetary science community. These entities include spacecraft, missions, instruments, targets, personnel and archive entities such as data sets and volumes. This model is documented in the Planetary Science Data Dictionary and the PDS Standards Reference. Pertinent sections of this model are represented using ODL labels in a PDS archive volume using catalog files. In addition, each product label includes selected keywords from the model that help in describing the context under which the data was collected. For example, a typical image label might contain DATA_SET_ID, TARGET_NAME, and INSTRUMENT_ID.

3. Format Selection Rationale

PDS ODL labels were and continued to be used for the preservation storage. PDS ODL templates were and continue to be used to capture and ingest information from data providers into archive.

4. Roles of Format

PDS ODL labels/templates are used to collect the information being submitted for inclusion in the archive. This includes information about the format of the data, structure of the data, state of the collecting instrument, and in general descriptions of all the entities helpful for understanding the context under which this data was collected.

This collected information becomes an integral part of the archive. The PDS assumes that the science data is useless without its associated meta-data.

The collected formation is loaded into catalogs and inventories and used to manage the data within the archive.

The collected information is disseminated with the data from the archive.

The PDS standards architecture and the use of PDS ODL labels and templates to describe data products and volumes has been very successful. The flexibility of the model, especially in consideration of the disparate nature of planetary science data, has been one of its great strengths.

5. Data Structures Supported

images, multi-dimensional tables, time series, spectra, cubes, telemetry, variable structures

The PDS uses two primitive objects, array and collection to derive all data objects such as IMAGE and TIME_SERIES. A foreign format (e.g. FITS) may be included in the PDS archive as long as the format can be described using a PDS object.

6. Support

The PDS Central Node is responsible for maintaining the PDS standards and as such has a process for the handling questions, change requests, and problems. The PDS maintains its standards documentation and makes them available via the Web.

7. Software

The PDS provides its data dictionary in a tool usable format. (ODL)

The PDS provides two label libraries that provide an API for parsing ODL labels and retrieving, writing, and updating the label components.

The PDS provides the Object Access Library (OAL) for retrieving, writing, and updating the data.

The PDS provides NASAView, a GUI data display application.

The PDS provides other software in its Tool Suite for other purposes including validation.

8. Desired Functions

It would help to have all the tools integrated into one consistant package with good documentation for each tool component. Having a more automated capability for using the tools (being able to easily set up batch processing for product validation) would also be beneficial. Integrating workflow techniques into the archive production and validation process would also make the process more efficient.

Integrating support for PDS formatted files into tools such as IDL or into NCSA or new NASA developed tools would be very beneficial.

As a collection, archive, distribution, and interchange format, the PDS ODL label format has performed well.

9. Other Comments

The advent of XML as an open, international interchange format has provided an opportunity to consider the use of technology provided by a much broader community. The apparent compatibility between XML and ODL would allow a broader interchange of PDS products and meta-data and the use of XML technology, while maintaining ODL as the PDS archive language.

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