Definition

A set of characteristics describing a Transfer Object Group. Typically there can be multiple Transfer Object Groups conforming to the same Transfer Object Group Type.

Source: Consultative Committee on Space Data Systems. Producer-Archive Interface Specification (PAIS) - A Tutorial. CCSDS 651.2-G-1.

Introduction

PAIS requires that each Transfer Object Type Descriptor has at least one Transfer Object Group Type. Each Transfer Object Group Type container may contain any number of additional Group Type containers and an unlimited number of Data Object Types.

These containers are convenient for modeling hierarchies such as directory structures.

Transfer Object Group Types

Digital Objects
Physical Objects

PAIS uses the concept of a descriptor to formalize the description of hierarchical levels found within a model of objects for transfer (MOT). Section 3.2 of PAIS specifies a transfer object type descriptor model that is further described in the Section 4.2.5 of the PAIS tutorial. The PAIS transfer object type descriptor model includes mandatory and optional data elements and is not specialized with user-defined attributes. The descriptor model can be applied to the top-level collection and child collections in a model of objects for transfer (MOT).

Using collection descriptors to design a Model of Objects for Transfer (MOT) helps the Archive validate and understand parts of the transfer.

PAIS transfer object group type element

In progress!

Element					Mandatory / optional	Description	Sample value
groupType (PAIS 3.2.2.5 and PAIS tutorial 4.2.6.1)
	groupTypeID (PAIS tutorial 4.2.6.2)				Mandatory	Identifier of a transfer object group type that shall be used to distinguish this group type from other group types. It shall be unique within a given Producer-Archive Project. Uniqueness shall be checked by the Archive. This identifier may be used by a relationship attribute to refer to this transfer object group type.
	groupTypeDescription (PAIS tutorial 4.2.6.2)				Optional	Explanatory text describing the meaning of this transfer object group type.
	groupTypeStructureName (PAIS tutorial 4.2.6.3)				Mandatory	Name for the type of transfer object group type, such as directory, set, sequence, undescribed, in the sense defined below, or other name not included in this list.
	groupTypeEncoded (PAIS tutorial 4.5.2.1)				Optional
		encodingName			Optional	Identifier of the Descriptor Model upon which this Collection Descriptor is used. The Descriptor Model ID shall be unique across the Producer-Archive Project and shall be provided by the Archive. Use "CCSD0015" whenever the PAIS Collection Descriptor is used.	CCSD0015
		encodingDescription			Optional	Identifier of the version of the Collection Descriptor Model. Use "V1.0" whenever the PAIS Collection Descriptor is used.	V1.0
	groupTypeOccurrence (PAIS tutorial 4.2.6.4)				Mandatory	number of instances (Transfer Object Groups) of this Transfer Object Group Type in each instance of its containing group or, if there is no containing group, in each containing Transfer Object Type instance. This may be expressed as one, or more, or as a range of values. This number may not be known at the time of descriptor creation. In the case of a unique value, the Minimal Occurrence and the Maximal Occurrence shall have the same value:
		minOccurrence			Mandatory	Extensive descriptive phrase used as the name of the collection. The collectionTitle can help the understanding of the scope and purpose of the collection.	Selection 2 of ISEE 1,2 Magnetic_Field Data and Metadata
		maxOccurance			Mandatory	Explanatory text describing the meaning of the collection.The collectionDescription can help the understanding of the scope and purpose of the collection.	Selected ISEE 1,2 Magnetic_Field Data and Metadata grouped by Spacecraft and then by Yearly Directories (1978 through 1980 only) for days 001-007 inclusive.
	relation (PAIS 3.3.3.4)
		parentCollection			Mandatory	The DescriptorID of the parent collection to which this Descriptor belongs. The top-level collection needs a parentCollection element whose value is "NONE."	NONE
		association			Optional	Attribute used to describe a relationship from this collection to the object type or collection having the identifier given by the Target ID attribute (targeted object type include Transfer Object Type, Transfer Object Group Type, and Data Object Type).
			targetID		Optional	Identifier of target object or collection of the Producer-Archive Project to which the relationship is established. A Collection can be associated with Collections, Transfer Object Types, Transfer Object Group Types, and Data Object Types.	ISEE_Mag_Data_TC2
			relationDescription		Optional	Description of the relationship or role played by this collection with respect to the target object type or collection.
				relationType	Optional	Name for the relation (e.g., Data Entity Dictionary [DED], Syntax, Context, Provenance, Reference, Fixity Information) played by this collection with respect to the target object type or collection.	Contains
				relationTextualDescription	Optional	Text description of the relation.	Collection contains data Transfer Objects of this type.

Related terms

Model of objects for transfer (MOT)

References

Producer-archive interface specification (PAIS) recommended by the Consultative Committee for Space Data Systems (CCSDS 651.1-B-1) and formalized as ISO 20104:2015. See: https://public.ccsds.org/Pubs/651x1b1.pdf.

Consultative Committee for Space Data Systems. Producer-Archive Interface Specification (PAIS) – A Tutorial. CCSDS 651.2-G-1 (September 2016). https://public.ccsds.org/Pubs/651x2g1.pdf

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