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SIP Model is an abstract model that has to be followed by any PAIS compliant SIP.

Source:Consultative Committee on Space Data Systems.  Producer-Archive Interface Specification (PAIS) - A Tutorial. Report Concerning Space Data System Standards, CCSDS 651.2-G-1. Green Book. Issue 1. Washington, D.C.: CCSDS, September 2016. [Equivalent to ISO 20104:2015]

Introduction

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PAIS provides an abstract SIP Specification (CCSD0017) known as the SIP Model. The SIP Model puts constraints on all possible SIPs within a given Producer-Archive Project.

Section 5 of PAIS explains:

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  • SIP ID (mandatory) - Identifier of the delivered SIP within the context of the given Producer-Archive Project. If there are multiple Producer Sources submitting SIPs within a single Producer-Archive Project, this SIP ID must be unique across all such Producer Sources. It is inserted during SIP construction. The form shall be agreed between Producer and Archive, but the identifier shall be generated by the Producer. The Archive shall check uniqueness.

  • Producer-Archive Project ID (mandatory) - Identifier of the Producer-Archive Project that distinguishes the project from all other Producer-Archive Projects undertaken by this Archive. This ID shall be provided by the Archive for use in the SIPs (see also first paragraph PAIS section 3).

  • SIP Content Type ID (mandatory) - Identifier of the specification that defines which Transfer Object Types (i.e., Descriptor IDs) are allowed within this SIP, as well as their occurrence within the SIP. It has been defined previously in this document (see PAIS section 4).

  • SIP Sequence Number (optional) - Number indicating the order in which the SIP has been sent. This number is unique within the combined context of the Producer-Archive Project and Producer Source ID. This becomes mandatory for all SIPs sent by a Producer Source if any of the Transfer Objects to be provided by the Producer Source have a Descriptor that does not specify a unique value for the number of Transfer Objects to be delivered. It shall be generated by the Producer.

  • Any (optional) - Mechanism that allows a SIP to have any additional attributes within the structure of the SIP corresponding to this container.

Transfer Objects to Delete Container (optional)

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There are two methods by which a Producer-Archive Project can achieve SIPs that conform to the PAIS SIP Model:

The XML schema for the PAIS SIP model is available in the Data Archive Ingest XML repository.

As noted in Section 6.2.4 of the PAIS Tutorial:

The PAIS specifies a standard packaging mechanism for the implementation of PAIS SIPs. It is based on use of the XFDU packaging standard. When this is followed, and the semantics of PAIS section 5 are followed, the resulting implementation is said to be ‘XFDU PAIS SIP Conformant’. However, it is acceptable to use other packaging mechanisms. In this case the resulting SIP implementation can be said to be ‘Abstract PAIS SIP Conformant’ provided it also adheres to the semantics of PAIS section 5.

Relationship between SIP Model and Bag-info.txt

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Use of the BagIt specification does not necessarily result in an a SIP that conforms to the abstract SIP specification defined in PAIS. Further enhancements are required.

The following table illustrates the relationship between metadata elements specified in Section 2.2.2 of the BagIt File Packaging Format and the SIP Model attributes specified in Section 5.2.4 of PAIS. In some cases, the relationship is implicit

Bag-info.txt field

Description

PAIS SIP model attribute

Notes

Source-Organization

Organization transferring the content.

Producer source ID


Organization-Address

Mailing address of the organization.

N/A


Contact-Name

Person at the source organization who is responsible for the content transfer.

N/A


Contact-Phone

International format telephone number of person or position responsible.

N/A


Contact-Email

Fully qualified email address of person or position responsible.

N/A


External-Description

A brief explanation of the contents and provenance.

N/A

This information maps to the "transfer object type description" attribute in a transfer object type descriptor

Bagging-Date

Date (YYYY-MM-DD) that the content was prepared for transfer. This metadata element SHOULD NOT be repeated.



External-Identifier

A sender-supplied identifier for the bag.



Bag-Size

The size or approximate size of the bag being transferred, followed by an abbreviation such as MB (megabytes), GB (gigabytes), or TB (terabytes): for example, 42600 MB, 42.6 GB, or .043 TB. Compared to Payload-Oxum (described next), Bag-Size is intended for human consumption. This metadata element SHOULD NOT be repeated.


This information maps to the transfer object type size attribute in a transfer object type descriptor

Payload-Oxum

The "octetstream sum" of the payload, which is intended for the purpose of quickly detecting incomplete bags before performing checksum validation. This is strictly an optimization, and implementations MUST perform the standard checksum validation process before proclaiming a bag to be valid. This element MUST NOT be present more than once and, if present, MUST be in the form "_OctetCount_._StreamCount_", where _OctetCount_ is the total number of octets (8-bit bytes) across all payload file content and _StreamCount_ is the total number of payload files. This metadata element MUST NOT be repeated.



Bag-Group-Identifier

A sender-supplied identifier for the set, if any, of bags to which it logically belongs. This identifier SHOULD be unique across the sender's content, and if it is recognizable as belonging to a globally unique scheme, the receiver SHOULD make an effort to honor the reference to it. This metadata element SHOULD NOT be repeated.



Bag-Count

Two numbers separated by "of", in particular, "N of T", where T is the total number of bags in a group of bags and N is the ordinal number within the group. If T is not known, specify it as "?" (question mark): for example, 1 of 2, 4 of 4, 3 of ?, 89 of 145. This metadata element SHOULD NOT be repeated. If this metadata element is present, it is RECOMMENDED to also include the Bag-Group-Identifier element.



Internal-Sender-Identifier

An alternate sender-specific identifier for the content and/or bag.



Internal-Sender-Description

A sender-local explanation of the contents and provenance.