BagIt-LDP

Table of Contents

1. Introduction
2. Media Type and LDP Considerations
3. Bagit Profile
4. Context And Typed Tags
5. Document Continuation
6. References

Introduction

The data structure resulting from a parsed BagIt tag file is a map of string labels to untyped string values in order. As such, the tag file is losslessly translatable to JSON-LD. This primary goal of this document is to outline a BagIt-Profile and parsing practice to leverage this JSON-LD compatibility to serialize and deserialize LDP resources as BagIt archives. The secondary goal is to produce object serializations that are sufficiently backwards-compatible to be used as plain BagIt archives in non-LDP contexts, e.g. AP Trust.

Rationale

1. The tagfile/json-ld translatability
2. The fact that <iana:describedby> is a predicate that indicates graph continuation
3. The fact that json-ld's @value attribute can point to a relative fileUri for binary content (so that a node could have a separate @id uri and @value uri).

If you have some ttl of your LDP object -- with relative URIs -- and you have a Described-By tag in your bag-info that points to the ttl, and you have a context tagfile that says:

{ "Described-By" : { "@id" : "iana:describedby", "@type" : "xsd:anyURI" } }

Then you basically have a graph serialization in the payload as well as including a context.

Media Type and LDP Considerations

Spec needs a media type that indicates a zipped BagIt archive: application/zip+bagit ?

• LDP clients that POST BagIt serializations MUST indicate the ldp:RDFSource or ldp:Container interaction model.
• LDP clients that require BagIt serializations on GET MUST indicate the requirement in Accept.
• LDP servers that support BagIt serializations on POST MUST advertise support in Accept-Post.
• LDP servers that support BagIt serializations on PUT MUST advertise support in Accept-Put.
• LDP servers that do not support BagIt serializations SHOULD respond with HTTP 415 to POST with a BagIt serialization.

Bagit Profile

Context And Typed Tags

Since tag names are case insensitive, the context information below should be considered to match all case variation of the tag names.

JSON-LD disallows aliasing @context; the "reserved context" alias below is effective rather than literal.

Default Context

Reserved Context

{
  "BagIt-Context" : "@context",
  "Bagging-Date" : {"@type":"xsd:date"},
  "BagIt-Profile-Identifier" : {"@type:"xsd:anyURI"},
  "BagIt-Payload-URI" : {"@type:"xsd:anyURI"},
  "bagit-payload" : "BagIt-Payload-URI"
}

Default Context

{
  "External-Identifier" : "@id",
  "Described-By" : {
    "@id" : "http://www.iana.org/assignments/link-relations/describedby",
    "@type" : "xsd:anyURI",
  }
}

Examples

bag-info.txt

context.txt

Contained resource URIs

• Resolution of relative file URIs to bag root
• Resolution of relative URIs to context, starting at External-Identifier
• bagit-payload URI and json-ld expansion
• Binary content indicated with owl:sameAs <fileUri>? "@value" : <fileUri>?
• Content serialized for proxied resources?

Document Continuation

A tag with @id of <http://www.iana.org/assignments/link-relations/describedby> SHOULD be a relative URI pointing to additional description of the resource currently in context. If this is serialized data (a file URI), the tag's context SHOULD indicate its MIME with @format.

Cached Resources and Binary Content in the Bag

Use of @value = file uri for cached published context, nonRdfSource content with URI id.

References

• BagIt 0.97
• BagIt Profiles
• JSON-LD
• LDP