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VOResource V0.8.1: an Overview of a Resource Data Model

Ray Plante (NCSA/UIUC)
9 September 2003

Abstract

VOResource is under going a major structural overhaul to address several issues regarding the basic metadata model. The latest iteration, version 0.8.1, is expected to influenze the next version of the "Resource Metadata" document (v0.9). The Resource data model is now split between a core schema, VOResource, and several extension schemas. This overview provides links to the various schema files, as well as a link to an example instance. The major changes are described.

1. Files to Review
2. Overview of Changes: Major Changes; Minor Changes
3. Data Model Structure
4. Current Issues

1. Files to Review

This new version of the Resource data model is split between a core schema, VOResource, and several extension schemas, defined in seperarte schemas. The schemas are:

VOResource-v0.8.1.xsd: core resource metadata
VOOrg-v0.1.xsd: extensions for describing organizations and projects.
VODataService-v0.1.xsd: extensions for describing data collections and services
VOPerson-v0.1: extensions for describing people.

An example describing several resources associated with the NCSA Astronomy Digital Image Library (ADIL):

adil-v0.8.1.xml

2. Overview of Changes

Major Changes

This new version of the resource metadata schema attempts to address the following concerns with the previous version of VOResource and "The Resource Metadata" document upon which it was based:

There were some terms that were part of the generic Resource metadata that did not apply to all resources across the board. For example, Curation metadata never applies to a Person, and Coverage should not apply to an Organization.
In general, Version 0.8.1 attempts do a better job at grouping elements within the inheritance hierarchy so that terms are applied only to resources where they make sense. In particular, it introduces a ManagedResource base class for resources such as Organisation, DataCollection, and Service that can be curated. It also introduces a new resource class, SkyService--inheriting from Service--to highlight services that have coverage.
The proper interpretation of Dublin Core can be confusing when applied to certain types of resources. For example, one does not usually think of an Organisation as having a Publisher; however, we can say that one organisation is responsible for managing another organization.
The updated schema breaks from the convention of strictly re-using Dublin Core names. Instead, when a clearer term is used, the mapping to the corresponding Dublin Core term is defined. (Currently, this is marked with a custom appinfo tag, <vm:dcterm>.)
In previous versions, it was unclear why certain terms were attributes of a resource's Curation and other, its Content. Furthermore, it was unclear what was considered the "content" of a resource like Organisation.
To clarify this distinction, the term Subject replaces Content, refering to the focus of a resource; the sub-elements describe various aspects of that focus. The term previously refered to as Subject is now called Topic.

Minor Changes

Element lists--that is, elements that may be repeated with different values--are rendered in the style recommended by Plante (with no container element). This style is a subject of debate, so this may change in subsequent versions.
References to other resources are done in a consistant way, providing a name or title and an optional IVOA identifier (e.g. see Manager, Contributor, Facility, ServiceRef, etc.).
In general, all complex types are globally defined (rather than anonymously defined).

3. Data Model Structure

The Generic Resource

The generic Resource tags are limited to 6 elements.
Arrow denotes an "is-A" relationship, e.g. "a Person is a Resource."

Person

ManagedResource

adds Curation and Subject to core desciption.
Organisation, Project, and DataCollection are ManagedResources, but a Person is not.