BagIt Profiles Specification

Status of this specification

Current version: 1.3.0 (2019-11-13).

Original draft created by members of the Access 2012 Hackfest group: Meghan Currie, Krista Godfrey, Mark Jordan, Nick Ruest, William Wueppelmann, and Dan Chudnov.

Feedback / discussion

Please comment on this draft specification in the Digital Curation Google Group, https://groups.google.com/forum/?fromgroups#!forum/digital-curation .

Purpose and background

The purpose of the BagIt Profiles Specification is to allow creators and consumers of Bags to agree on optional components of the Bags they are exchanging. Details of the profile are instantiated in a JSON file that both the producing and consuming applications interpret using the conventions described below. The profile file sits at an HTTP URI (e.g., http://example.com/bagitprofiles/profile-bar-v0.1.json), and can therefore be read by any number of applications creating or consuming Bags:

                        BagIt Profile JSON file
                                    /       \
                                   v         v
                    Bag creating app 1  -->  Bag consuming app
                    Bag creating app 2

This proposed Specification builds on the sample profile included in the Library of Congress Bagger tool. However, that profile was local to LC and not intended to be implemented widely. The proposed Specification is intended to be an optional extension to the cannonical BagIt spec, and in no way modifies that specification. Like the BagIt spec, this Profile spec is agnostic to the payload stored in a Bag's data directory.

Use cases for BagIt profiles include distributed mass production of Bags, repository or application-specific content ingestion via Bags (e.g. SWORD, Archivematica), and Preservation-as-a-Service.

Workflow

The intended workflow for using a BagIt profile is:

1. The creator of the Bags ensures that Bags it produces meet all of the constraints expressed in the agreed-upon and published BagIt profile file. The creator declares the BagIt-Profile-Identifier in the bag-info.txt file of the Bags.

2. The consumer of the Bags identifies the profile(s) from the BagIt-Profile-Identifier field in their bag-info.txt. The consumer then retrieves the profile file from its URI and validates incoming Bags against it; specifically, it must complete the Bag if fetch.txt is present, validate the complete Bag against the profile, and then validate the Bag against the cannonical BagIt spec.

Each of these steps may be performed by a separate tool or microservice; in fact, implementers may integrate validation functionality in tools that perform other Bag-processing functions. For example, the completion of a holey Bag might be performed by a more general Bag-processing tool and need not be delegated to a separate validation tool.

Some profile constraints are fatal: for example, failure to validate 'Accept-Serialization' or 'Accept-BagIt-Version' implies that the rest of the bag is unverifiable and processing should stop. Therefore, the task that checks these two constraints should be performed as early as possible in the workflow. Processing may continue after non-fatal errors in order to generate a comprehensive error report.

Implementation details

Bags complying to a BagIt profile MUST contain the tag BagIt-Profile-Identifier in their bag-info.txt, which value is the URI of the JSON file containing the profile it conform to. This tag MAY be repeated if the bag conforms to multiple profiles. The URI that identifies the profile SHOULD be versioned, e.g. http://example.com/bagitprofiles/profile-bar-v0.1.json. Resolving the URI with Accept: application/json SHOULD provide a BagIt Profile as JSON according to this specification.

The following fields make up a BagIt profile. Each field is a top-level JSON key, as illustrated in the examples that follow. LIST in the field definitions indicates that the key can have one or more values, serialized as a JSON array. Itemized values separated by a | indicate allowed options for that field.

1. BagIt-Profile-Info:

A list of tags that describes the profile itself. The following tags are required in this section: Source-Organization, External-Description, Version, and BagIt-Profile-Identifier. Starting with version v1.2.0, BagIt-Profile-Version is also required.

The Source-Organization and External-Description tags are taken from the reserved tags defined in the BagIt spec.

The value of Version contains the version of the profile; the value of BagIt-Profile-Identifier is the URI where the profile file is available, and will have the same value as the BagIt-Profile-Identifier tag in bag-info.txt (see below).

The value of BagIt-Profile-Version contains the version of this specification the profile.conforms to. Since the tag was introduced after version v1.1.0, any profile not explicitly defining BagIt-Profile-Version should be treated as conforming to version [1.1.0] of this specification.

Inclusion of Contact-Name, Contact-Phone and Contact-Email, as defined in the BagIt spec, is not required but is encouraged.

2. Bag-Info:

   Specifies which tags are required, etc. in bag-info.txt. Each tag definition takes four optional parameters: 1) "required" is true or false (default false) and indicates whether or not this tag is required. 2) "values" is a list of acceptable values. If empty, any value is accepted. 3) "repeatable" is true or false (default true) and indicates whether or not this tag can be repeated in bag-info.txt. 4) "description" is a string providing notes or description related to this tag.

   Implementers may define in the Bag-Info section of their profile whatever tags their application requires, i.e., tags defined here are not limited to the 'reserved metadata element names' identified in the BagIt spec.

   The tag BagIt-Profile-Identifier is always required, but SHOULD NOT be listed under Bag-Info in the profile.

3. Manifests-Required: LIST

   Each manifest type in LIST is required. The list contains the type of manifest (not the complete filename), e.g. ["sha1", "md5"].

4. Manifests-Allowed: LIST

   (Added in v1.3.0)

   If specified, only the manifest types in LIST are permitted. The list contains the type of manifest (not the complete filename), e.g. ["sha1", "md5"].

   When specified along with Manifests-Required, Manifests-Allowed must include at least all of the manifest types listed in Manifests-Required.

   If not specified, all manifest types are permitted.

5. Allow-Fetch.txt: true|false

   A fetch.txt file is allowed within the bag. Default: true

6. Serialization: forbidden|required|optional

   Allow, forbid or require serialization of Bags. Default is optional.

7. Accept-Serialization: LIST

   A list of MIME types acceptable as serialized formats. E.g. "application/zip". If serialization has a value of required or optional, at least one value is needed. If serialization is forbidden, this has no meaning.

8. Accept-BagIt-Version: LIST

   A list of BagIt version numbers that will be accepted. At least one version number is required. All version numbers MUST be UTF-8 encoded strings.

9. Tag-Manifests-Required: LIST

Each tag manifest type in LIST is required. The list contains the type of manifest (not the complete filename), e.g. ["sha1", "md5"].

10. Tag-Manifests-Allowed: LIST

    (Added in v1.3.0)

    If specified, only the tag manifest types in LIST are permitted. The list contains the type of manifest (not the complete filename), e.g. ["sha1", "md5"].

    When specified along with Tag-Manifests-Required, Tag-Manifests-Allowed must include at least all of the tag manifest types listed in Tag-Manifests-Required.

    If not specified, all tag manifest types are permitted.

11. Tag-Files-Required: LIST

A list of a tag files that must be included in a conformant Bag. Entries are full path names relative to the Bag base directory. As per the BagIt Spec, these tag files need not be listed in tag manifest files. Tag-Files-Required SHOULD NOT include bag-info.txt (which is always required), nor any required manifest files, which instead are required by Manifests-Required and Tag-Manifests-Required.

Every file in Tag-Files-Required must also be present in Tag-Files-Allowed.

12. Tag-Files-Allowed: LIST

(Added in v1.2.0)

A list of tag files that may be included in a conformant Bag. Entries are either full path names relative to the bag base directory or path name patterns in which asterisks can represent zero or more characters (c.f. glob(7)).

If Tag-Files-Allowed is not provided, its value is assumed to be ['*'], i.e. all tag files are allowed.

As per the BagIt Spec, these tag files need not be listed in tag manifest files. Tag-Files-Required SHOULD NOT include bag-info.txt (which is always required), nor any required manifest files, which instead are required by Manifests-Required and Tag-Manifests-Required.

At least all the tag files listed in Tag-Files-Required must be in included in Tag-Files-Allowed.

Examples

bagProfileFoo.json

{
   "BagIt-Profile-Info":{
      "BagIt-Profile-Identifier":"http://www.library.yale.edu/mssa/bagitprofiles/disk_images.json",
      "Source-Organization":"Yale University",
      "Contact-Name":"Mark Matienzo",
      "External-Description":"BagIt profile for packaging disk images",
      "Version":"0.3"
   },
   "Bag-Info":{
      "Bagging-Date":{
         "required":true
      },
      "Source-Organization":{
         "required":true,
         "values":[
            "Simon Fraser University",
            "York University"
         ]
      },
      "Contact-Phone":{
         "required":true
      }
   },
   "Manifests-Required":[
      "md5"
   ],
   "Allow-Fetch.txt":false,
   "Serialization":"required",
   "Accept-Serialization":[
      "application/zip",
      "application/tar"
   ],
   "Accept-BagIt-Version":[
      "0.96",
      "0.97"
   ]
}

bagProfileBar.json

{
   "BagIt-Profile-Info":{
      "BagIt-Profile-Identifier":"http://canadiana.org/standards/bagit/tdr_ingest.json",
      "Source-Organization":"Candiana.org",
      "Contact-Name":"William Wueppelmann",
      "Contact-Email":"[email protected]",
      "External-Description":"BagIt profile for ingesting content into the C.O. TDR loading dock.",
      "Version":"1.2"
   },
   "Bag-Info":{
      "Source-Organization":{
         "required":true,
         "values":[
            "Simon Fraser University",
            "York University"
         ]
      },
      "Organization-Address":{
         "required":true,
         "values":[
            "8888 University Drive Burnaby, B.C. V5A 1S6 Canada",
            "4700 Keele Street Toronto, Ontario M3J 1P3 Canada"
         ]
      },
      "Contact-Name":{
         "required":true,
         "values":[
            "Mark Jordan",
            "Nick Ruest"
         ]
      },
      "Contact-Phone":{
         "required":false
      },
      "Contact-Email":{
         "required":true
      },
      "External-Description":{
         "required":true
      },
      "External-Identifier":{
         "required":false
      },
      "Bag-Size":{
         "required":true
      },
      "Bag-Group-Identifier":{
         "required":false
      },
      "Bag-Count":{
         "required":true
      },
      "Internal-Sender-Identifier":{
         "required":false
      },
      "Internal-Sender-Description":{
         "required":false
      },
      "Bagging-Date":{
         "required":true
      },
      "Payload-Oxum":{
         "required":true
      }
   },
   "Manifests-Required":[
      "md5"
   ],
   "Allow-Fetch.txt":false,
   "Serialization":"optional",
   "Accept-Serialization":[
      "application/zip"
   ],
   "Tag-Manifests-Required":[
     "md5"
   ],
   "Tag-Files-Allowed":[
     "DPN/*"
   ],
   "Tag-Files-Required":[
     "DPN/dpnFirstNode.txt",
     "DPN/dpnRegistry"
   ],
   "Accept-BagIt-Version":[
      "0.96"
   ]
}

@todo

• Add license (CC0/Public Domain?).
• Request feedback from BagIt implementer community, initially in the Digital Curation Google Group.
• Write code to confirm proof-of-concept use cases.
• Formalize specification. (Version 1.0 2013-05-19)
• Write standard libraries to assist in profile validation. (Python done)
• Establish a public registry of BagIt profiles for common uses, such as ingestion of content into repository platforms.

License