Data Preparer’s Workbook

DPW Appendix C: Glossary

Table of Contents

Attribute (see Data Element)

Browse Data Set

A data set, typically of limited size and resolution, created to provide an understanding of the type and quality of data available in a related full resolution data set. It may also enable the quick selection of specific products or intervals for further processing or analysis. For an image data set, a browse data set could be a set of subsampled images of lower resolution. A browse data set for a time series sampled on 4 second intervals may consist of the data averaged at 48 second intervals. The form of browse data is generally unique for each type of data set and depends on the nature of the data and the criteria used for data selection within the related science discipline.

Catalog Data

Data that is obtained from data sets or data products, and which serves to describe, identify, associate, characterize, or highlight the data set. The values of the data elements in a catalog object are the catalog data, and are loaded into a PDS catalog to facilitate data searching and ordering.

Catalog Object

A set of required keywords with values used to provide data for a data product or data set that is suitable for loading into a PDS catalog. A catalog object template that is filled in with values becomes a catalog object. See Appendix B of the PDS Standard Reference for a complete set of PDS Catalog Object examples.

Catalog Object Template

An uncompleted catalog object; similar to a form. Once values are assigned to each of the data elements in the catalog object template, it becomes a catalog object.

Data Element (Attribute, Element, Keyword)

A data element is a characteristic of an object or group of objects provided in a PDS label. For example, in a label containing the line

TARGET_NAME = JUPITER

the data element is TARGET_NAME. Some data elements describe the physical or logical characteristics of the data (the number of ROWS in a table, for example). Others describe the content of the data (MINIMUM_WAVELENGTH of a spectrum, for example) or information to be used in interpreting the data (such as a UNIT of measure). The terms attribute, element, and keyword are often used interchangeably with data element.

Data Object

A data object is that portion of a data product that contains the actual data that is described in a data object definition within a PDS label. It is tangible, and can be physically accessed and manipulated. For example, if a PDS label contains the following lines,

^TABLE = "T142836.DAT"
...
OBJECT = TABLE
ROWS = 1028
...
END_OBJECT = TABLE

the data object for this table is in the file T142836.DAT. The actual data object is often classified as a primary data object or a secondary data object.

Data Object Description

A set of required and optional keywords which are used in a PDS label to define the structure and characteristics of a data object. Data object descriptions begin and end with the OBJECT = and END_OBJECT = lines. The PDS standard data object descriptions are defined in Appendix A of the PDS Standards Reference.

Data Product

A grouping of primary and secondary data objects and their associated PDS labels resulting from a scientific observation. A data product is a component of a data set.

Data Product Label

A set of data elements and values, data object definitions, and optional SFDUs, expressed in ODL that identifies, describes, and defines the structure and context of a data product.

Data Set

An accumulation of data products, secondary or ancillary data, software, and documentation, that completely document and support the use of those data products. A data set can be part of a data set collection.

Data Set Collection

A collection of data sets that are related by observation type, discipline, target, or time, and treated as a unit. Data set collections are archived and distributed together for a specific scientific objective.

Element (see Data Element)

Keyword (see Data Element)

Label (see Data Product Label)

Logical Record

A record independent of its physical environment, that exists from the standpoint of its content, function, and use rather than its physical attributes. It is defined in terms of the information it contains. Portions of the same logical record may be located in different physical records, or several logical records may be located in one physical record.

Medium

Any physical material capable of holding data (e.g., pages, film, magnetic tape, CD-ROM, etc.).

Meta Data

Selected or summary information about data. PDS catalog objects and data product labels are forms of meta data for summarizing important aspects of data sets and data products.

Object

An abstract or atomic entity that corresponds to something tangible in an archive environment, such as a grouping of data (data object) or a related grouping of information about that data(catalog object).

Object Description Language (ODL)

A specific language used to encode data product labels and catalog objects for the Planetary Data System and other NASA data systems. ODL was developed by PDS and is based upon the Flexible Image Transport (FITS) and Video Image Communication and Retrieval (VICAR) labelling systems used by both the astronomy and planetary image communities. (See the Object Description Language Specification and Usage chapter of the PDS Standards Reference).

Physical Record

A record whose characteristics depend on the manner or form in which it is stored, retrieved, or moved. A physical record may contain one or several logical records or a part of a logical record.

Pointer

A statement within a data product label or catalog object that identifies or references a starting point within the same file or an external file. Pointers are used to identify the start of a data object, the location of additional text for insertion, or the location of descriptive information for further reference.

Primary Data Object

The primary data resulting from a scientific observation in a data product. Examples of primary data objects are the actual data for a single IMAGE, or a TABLE containing one hour of data for an instrument. A secondary data object may be associated with the primary data object.

Secondary Data Object

A data object associated with a primary data object in a data product. A secondary data object may provide additional information or may be necessary for processing or correctly interpreting the primary data object. For example, an engineering table(secondary data object) is often associated with a time series (primary data object) of values from an instrument to provide important housekeeping information required to properly use the data.

SFDU

A SFDU (Standard Formatted Data Unit) is a data object that conforms to a specific set of CCSDS (the Consultative Committee for Space Data Systems) recommendations for structure, construction rules, and field specification definition. Details about the PDS usage of SFDUs can be found in the SFDU Usage chapter of the PDS Standards Reference.

Standard Value

A standard value is one of a set of possible values that can be assigned to a data element. These value sets are extendable for many data elements. Further information on the use and addition of standard values can be found in the Planetary Science Data Dictionary.

Template (see Catalog Object Template)

Volume

A volume is a unit of physical media such as a CD-ROM or CD-WO, an 8mm magnetic tape, or a 9-track magnetic tape. Data sets may reside on one or more volumes and multiple data sets may also be stored on a single volume. Volumes may be grouped into volume sets.

Volume Set

A grouping of one or more related volumes treated as a unit.