Definition

Either a collection descriptor or a transfer object type descriptor used in models of objects for transfer (MOTs) created as part of Producer-Archive Projects.

Collection descriptor: a set of attributes that describes a view of a single collection of data and that identifies the parent collection of which it is a part.
Transfer object type descriptor: a set of attributes that describes a transfer object type and that identifies the parent collection of which it is a part.

PAIS provides detailed specifications for descriptors and allows repositories to establish their own descriptor models with user-defined attributes and/or alterations to the standard specifications. Figure 2-2 in PAIS illustrates that descriptors are an essential part of the specification for SIP Content Types:

Image source

An example of the entities and their relationships involved in creating the formal specifications. Consultative Committee on Space Data Sytems. Producer-Archive Interface Specification recommended standard (CCSDS 651.1-B-1), Figure 2-2. https://public.ccsds.org/Pubs/651x1b1.pdf

Collection descriptors

Note: the PAIS Collection Descriptor XML Schema Definition is available as part of the Data Archive Ingest XML Registry maintained by the CCSDS.

PAIS recommends that repositories establish descriptor models that define the mandatory and optional attributes needed to describe collections and transfer object types used in models of objects for transfer (MOTs) created as part of Producer-Archive Projects. This section summarizes the specifications for descriptor models provided in PAIS. For a case study on specialized descriptor models, see the Descriptor models page in the University Archives wiki.

A collection descriptor is a set of attributes that serves two primary functions:

describe a single collection of data
identify a single parent collection

PAIS collections can include any number of child collections and/or transfer object types, and/or data object types. Any collection can be referenced as a parent by zero or more other collections and any number of transfer object types.

Image source

Collection Descriptor. Consultative Committee for Space Data Systems. Producer-Archive Interface Specification (PAIS) – A Tutorial, Figure 3-3. CCSDS 651.2-G-1 (September 2016). https://public.ccsds.org/Pubs/651x2g1.pdf

In other words, the PAIS collection descriptor specification can be understood as a technical implementation of the traditional theoretical concepts of respect des fonds and archival arrangement.

Collection descriptors specified in PAIS can be also considered an instantiation of the abstract concept of collection descriptions described in Section 4.2.2.8 of CCSDS 650.0-M-2 (OAIS). OAIS calls for a collection description that is roughly analogous to the top-level collection descriptor in a MOT (i.e., archival description at the fonds or collection level). OAIS also calls for associated "member descriptions" that are roughly analogous to child collection descriptors (i.e., archival description at the level of sous-fonds, series, sub-series, accession, etc.)

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Collection Description. Consultative Committee on Space Data Sytems. Open Archival Information System (OAIS) recommended practice, Figure 2-2. CCSDS 650.0-M-2.

Transfer object type descriptors

Note: the PAIS Transfer Object Type Descriptor XML Schema Definition is available as part of the Data Archive Ingest XML Registry maintained by the CCSDS.

A transfer object type descriptor is a set of attributes with two primary functions:

describe a transfer object type
identify the parent collection of which it is a part

Transfer object types must include at least one group type with any number of sub-group types and data object types.

Image source

Transfer Object Type Descriptor. Consultative Committee for Space Data Systems. Producer-Archive Interface Specification (PAIS) – A Tutorial, Figure 3-2. CCSDS 651.2-G-1 (September 2016). https://public.ccsds.org/Pubs/651x2g1.pdf

Transfer object type as the "link" between a MOT and SIPs

The major difference between collection descriptors and transfer object type descriptors is that transfer objects types are also used to model SIPs. Each SIP must conform to a pre-defined SIP content type that authorizes one or more transfer object type.

As noted on page 3-5 of the PAIS tutorial:

The transfer objects are instances of transfer object types of the Producer-Archive Project’s MOT. A transfer object in a SIP needs to be of a transfer object type authorized by the SIP content type referenced by the SIP Global Information. Similarly, the number of transfer objects of an authorized type need to be within the range defined in the SIP content type.

The following diagram illustrates how transfer object type descriptors from a MOT are incorporated into a SIP:

Image source

SIP Model. Consultative Committee for Space Data Systems. Producer-Archive Interface Specification (PAIS) – A Tutorial, Figure 3-5. CCSDS 651.2-G-1 (September 2016). https://public.ccsds.org/Pubs/651x2g1.pdf

Related terms

Model of objects for transfer (MOT)

Producer-Archive Project

SIP content type

Examples of ways repositories can meet requirements for descriptors

Coming soon.

Related technical standards

ISO standard	CCSDS recommendation	Description
ISO 14721:2012 (OAIS)	CCSDS 650.0-M-2, Section 4.2.2.8	The Collection Description is a subtype of the Package Description that has added structures to better handle the complex Content Information of an AIC. The Collection Description, which is modeled in figure 4-24, contains the information classes that are contained in the Unit Description. There are two types of Associated Description in a Collection Description: There is one Overview Description that describes the collection as a whole (i.e., the top-level collection in a model of objects for transfer (MOT). There are zero or more Member Descriptions that separately describe each member of the collection (i.e., child collections in a model of objects for transfer (MOT)
ISO 20652:2006 (PAIMAS)	CCSDS 651.0-M-1, Section 3.1.2.1 (Preliminary phase, actions P3 through P-8)	This is the primary starting point and it is important at this stage to clearly define and delimit the information which constitutes the primary object of the Producer-Archive Project. If there are still some open options, this is the time to make these explicit. The preliminary phase cannot be completed until this has been accomplished.
ISO 20652:2006 (PAIMAS)	CCSDS 651.0-M-1, Section 3.2.2.1 (Formal definition phase, actions F-3 through F-12)	This subsection discusses the precise definition of the information to be transferred from the Producer to the Archive. This definition is a formal model of objects to be delivered.
ISO 20652:2006 (PAIMAS)	CCSDS, 651.0-M-1, Action F-7	Choose the tools: Producer and Archive define the tools to be installed by the Producer or acquired by the Archive (to aid with data production, production of descriptors, document production, etc.).
ISO 20652:2006 (PAIMAS)	CCSDS, 651.0-M-1, Action F-8	Write a description of the Information Objects: A description of the elements previously negotiated by the Archive or the Producer must create an unambiguous record of the decisions and agreements. The record should be available to both the Producer and the Archive. This description will be part of the final Submission Agreement. This description refers to the Data Dictionary and the formal model (defined in subsections 3.2.2.1.3 and 3.2.2.1.4).
ISO 20104:2015 (PAIS)	CCSDS 651.1-B-1

References

Consultative Committee on Space Data Systems. Open Archival Information System (OAIS) recommended practice, Section 4.2.2.8. CCSDS 650.0-M-2.

Consultative Committee on Space Data Sytems. Producer-Archive Interface Specification recommended standard, Section 2.2. CCSDS 651.1-B-1.

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