Internet DRAFT - draft-wilper-semantic-content-pkgs
draft-wilper-semantic-content-pkgs
Network Working Group
Internet-Draft C. Wilper
Intended status: Experimental DuraSpace
Expires: October 15, 2012 April 13, 2012
Semantic Content Packages (SCP)
draft-wilper-semantic-content-pkgs-00
Abstract
This document specifies Semantic Content Packages, an experimental
data structure and associated format for storing and transmitting a
named set of RDF statements with a set of content streams. Packages
can be arranged as a set of files in a directory hierarchy or
serialized into a single stream for transmission and archival
storage. For the latter, a new ZIP-based media type,
application/scp, is defined.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 15, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 3
2. The SCP Data Structure . . . . . . . . . . . . . . . . . . . . 4
3. The SCP Vocabulary . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Bytestream . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. ContentLocation . . . . . . . . . . . . . . . . . . . . . . 4
3.2.1. ResolvableURI . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. PackagePath . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Package . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. PackageType . . . . . . . . . . . . . . . . . . . . . . . . 5
4. The SCP Format . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Directory Structure . . . . . . . . . . . . . . . . . . . 5
4.2. ZIP-based Serialization . . . . . . . . . . . . . . . . . 6
4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3.1. A Minimal Package . . . . . . . . . . . . . . . . . . 6
4.3.2. A Typed Package with an Image and Statements . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7.1. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. SCP-OWL-Ontology.ttl . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
1.1. Motivation
In data management, the primitives used to describe structured and
semi-structured data are usually determined by the kind of storage
technology at hand. For example, data stored in a relational
database is modeled using the well-known entity-relationship
paradigm, but data stored in a key-value store is modeled using a
different set of primitives.
Over time, high-value data will necessarily be migrated from one
storage technology to another. This is often complicated by the need
to translate the data model to the target storage technology while
retaining the original semantics.
The Resource Description Framework (RDF) provides a core data model
capable of expressing detailed descriptions about any kind of
resource in a way that is independent of any storage technology or
protocol. With this simple, but powerful capability, RDF can form
the basis of a more durable kind of content modeling paradigm.
Semantic Content Packages build upon the core RDF model by providing
a way to logically and physically bundle a set of statements with a
set of content streams, and to include a unique identifier within
each bundle.
1.2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. The SCP Data Structure
A Semantic Content Package is a logical container consisting of:
o A set of finite-length octet stream values, also known as
content, each with a distinct location within the package, a
path.
o An id which is a Uniform Resource Identifier (URI). Every
package MUST contain a content stream at path '.scpi/id' whose
value is an ASCII-encoded URI identifying the package.
o A set of Resource Description Framework (RDF) triples, also
known as statements. The path '.scpi/graph.ttl' is reserved
for an RDF Turtle [W3C.SUBM-turtle-20110328] serialization of
the statements, if any.
3. The SCP Vocabulary
SCP defines a minimal RDF vocabulary in order to:
1. Provide a uniform, but OPTIONAL way to refer to content within
a package. This allows assertions to be made about the content
using other, more appropriate vocabularies such as Dublin Core,
SKOS, PREMIS-OWL, and OAI-ORE [TBD: spec refs under Informative
References]
2. Allow packages to declare the compound data models, if any, to
which they conform.
All terms in this vocabulary are defined as Web Ontology Language
(OWL) classes or properties, and are described below. See Appendix A
for the official, machine-readable ontology.
3.1. Bytestream
A Bytestream is defined as a specific sequence of octets that exists
conceptually regardless of where the content might be found. The
"location" property refers to a ContentLocation. A Bytestream may
refer to any number of ContentLocations.
3.2. ContentLocation
A ContentLocation indicates where the content of Bytestream is
expected to be found. Two subclasses are defined by this
specification:
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3.2.1. ResolvableURI
A ResolvableURI is a kind of ContentLocation with a URI that can be
deferenced.
3.2.2. PackagePath
A PackagePath is a kind of ContentLocation that points to a path
within a Package. The "path" property refers to a Plain Literal
value, such as "path/to/file.txt", and the "inPackage" property
refers to the Package.
3.3. Package
A Package is a container for content and statements. The "type"
property refers to a PackageType.
3.4. PackageType
A PackageType is a particular kind of package. Some sort of data
model is usually associated with a PackageType, but the means by
which package types are described or represented is not expected to
be uniform, nor is a method suggested by this specification.
4. The SCP Format
Packages that adhere to the SCP data model MAY be stored in a variety
of ways. This specification defines two.
4.1. Directory Structure
The SCP model is designed to fit naturally into a filesystem
directory structure. Each content stream is available from some root
directory path, and the 'path' of that content stream in the package
is the relative path from the root directory of the package.
For example, if the root directory of a package is /tmp/mypackage,
there MUST be a directory whose full path is '/tmp/mypackage/.scpi'
with at least one file in it named 'id', whose content is the id of
the package.
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4.2. ZIP-based Serialization
A new ZIP-based Internet Media Type, application/scp (extension .scp)
is defined by this specification as a way to serialize packages.
The ZIP file is structured such that unzipping it will instantiate
the package in a directory structure as described in the section
above. It follows that it MUST contain an item named '.scpi/id'
whose content is the id of the package.
4.3. Examples
The following examples illustrate packages in a directory structure.
4.3.1. A Minimal Package
In order to represent a package, a directory is only required to have
one file in a particular place to declare id, as shown below:
example-package-1/
|
-- .scpi/
|
| id
| (http://example.org/pkg1)
-
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4.3.2. A Typed Package with an Image and Statements
This example shows a package containing a single image bundled with
several statements, including:
o An assertion of the "type" of package.
o An assertion from the Dublin Core vocabulary that the format of
the image is "image/jpeg".
o An assertion that the image Bytestream is expected to be
available in three known locations, one being a path within the
package itself.
example-package-2/
|
| image.jpg
| (binary data)
|
-- .scpi/
|
| id
| (http://example.org/pkg2)
|
| graph.ttl (
| @prefix dc: <http://purl.org/dc/elements/1.1/> .
| @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
| @prefix scp: <http://scpproject.org/ontology#> .
|
| <http://example.org/pkg2> rdf:type scp:Package ;
| scp:type <http://example.org/pkgtype-1> .
| _img rdf:type scp:Bytestream ;
| dc:format "image/jpeg" ;
| scp:location _path ,
| <http://example.org/pkg2/img1.jpg> ,
| <http://example.com/images/foo.jpg> .
| _path rdf:type scp:PackagePath ;
| scp:path "image1.jpg" ;
| scp:inPackage <http://example.org/pkg2> .
| )
-
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5. IANA Considerations
A new media type shall be registered for this format.
Type name:
application
Subtype name:
scp
Required parameters:
none
Optional parameters:
none
6. Security Considerations
The security considerations for this specification are the union of
those that apply to processing Turtle RDF and ZIP files.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[W3C.SUBM-turtle-20110328]
Beckett, T. and Berners-Lee, T., "Turtle - Terse RDF
Triple Language", W3C Team Submission
SUBM-turtle-20110328, March 2011,
<http://www.w3.org/TeamSubmission/2011/SUBM-turtle-
20110328/>
Latest version available at
<http://www.w3.org/TeamSubmission/turtle/>.
[TBD: Refs to RDF, OWL, ZIP, etc.]
7.1. Informative References
[TBD: Refs to DC, SKOS, OAI-ORE, PREMIS-OWL, etc.]
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Appendix A. SCP-OWL-Ontology.ttl
# Namespaces
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix scp: <http://scpproject.org/ontology#> .
# Classes
scp:Bytestream rdf:type owl:Class .
scp:ContentLocation rdf:type owl:Class .
scp:ResolvableURI rdfs:subClassOf scp:ContentLocation .
scp:PackagePath rdfs:subClassOf scp:ContentLocation .
scp:Package rdf:type owl:Class .
scp:PackageType rdf:type owl:Class .
# Properties
scp:location rdf:type owl:ObjectProperty ;
rdfs:domain scp:Bytestream ;
rdfs:range scp:ContentLocation .
scp:path rdf:type owl:DatatypeProperty ,
owl:FunctionalProperty ;
rdfs:domain scp:PackagePath ;
rdfs:range rdf:PlainLiteral .
scp:inPackage rdf:type owl:ObjectProperty ,
owl:FunctionalProperty ;
rdfs:domain scp:PackagePath ;
rdfs:range scp:Package .
scp:type rdf:type owl:ObjectProperty ;
rdfs:domain scp:Package ;
rdfs:range scp:PackageType .
Authors' Addresses
Chris Wilper
West Henrietta, NY
USA
Email: cwilper@gmail.com
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