1 Introduction
The goal of the IVOA is to publish a number of standards for services which can interoperate to create a Virtual Observatory. Central to the coordination of these services is the concept of a registry ([RegInt]) where resources can be described and thus discovered by elements in the grid. The standard Resource Metadata for the Virtual Observatory
[Hanisch et al. 2004] (hereafter referred to as
RM) defines metadata terms for describing resources.
A specific XML encoding of these resources is described in the IVOA standard VOResource: an XML Encoding Schema for Resource Metadata [Plante et al. 2006] (hereafter refered to as the VR). In this document there are several elements that have a standardID
attribute that should have a value of a resource identifier as defined in [ID] . There is no formal validation requirement in the schema that the identifier actually point to a resource entry in the registry. This schema allows such standards to be registered so that there can be an unambigous, machine-readable entry made in a registry for each approved IVOA standard. This would allow automatic resource validation applications to be written that can check validity constraints beyond that of simple XML validity. In addition the schema provides a standard way to economically register sets of such identifiers that could be then used for resource identifier enumerations in other schema.
It is envisaged that instances conforming to this schema will normally only be published in the central "registry of registries", but they are not restricted only to that registry.
This document specifically describes an extension of the metadata concepts and an XML encoding called VOStandard. The VOStandard schema provides XML encoding that extends the VR so that can be used to describe applications (see section below for discussion of what constitues an application).
Details of the VOStandard Schema
In accordance with the guidelines laid down by [VR], there has been no attempt to create enumerated lists for cases where there list could not be closed (e.g. the set of operating system names will grow as new operating systems are developed). This means that the values of certain elements in a document instance will not be checked by even a validating XML parser, and validation that the element contents are allowed will have to be done by a separate process. This section will list the allowed values for those enumerations where appropriate and instance documents MUST use these exact strings to represent the same concept.
Use of the VOStandard Schema
It should be noted that in many cases there is no need to introduce a dependency on this schema in other registry schemas e.g. the VOResouce schema does not include the VOStandard schema - it simply defines a type vr:ResourceIdentifier
that limits a string to have the correct resource identifider syntax. XML entities registered using the VOResouce schema SHOULD refer to entities registered with the VOStandard schema when creating a standardID attribute, although there is no compulsion in the XML schema language to do so. The major IVOA standards will already have an appripriate standard describing resource registered, however it should always be possible for an 'experimental' standard to be registered.
Details of the elements for defining Standards
TBC
Defining enumerations of Identifiers
The second major structure in the VOStandard schema is the ResourceEnumList type, which is designed to allow sets or enumerations of resource identifiers to be registered. The typical use of this facility is to avoid having to create formal xml string enumerations in schema definitions. Using enumerations in schema for lists that cannot be closed at the time of initial release is undesirable because it implies that new versions of schema would need to be released when the enumeration changes, with consequent disruption to deployed services. However, not having a machine readable definition of the enumerations is also undesirable as it means that any validation application would also have to updated as the list expanded - registering the enumerations provides a good mixture of flexibility and rigour.
The structure that is used to achieve this aim is simply defined as a list of names with an accompanying description. The intention is that the name attribute in the BaseKey
is used as the "fragment" part of the resource identifier URI i.e. the part after the # in the URI string. e.g.
ivo://authority/resource#name
This form of defining enumerations has several advantages over defining each member of the enumeration as a separate resource
- The enumerations are naturally grouped under a single registry resource, and so can be retrieved with one registry query and need no further metadata to assert the association.
- The "Dublin core" metadata that is associated with a resource need only be entered once for the whole enumeration, rather than for each member of the enumeration - this saves both curation effort and space in the registry.
An example of BaseKey usage
A good example of where an enumeration is not closed is that of the names of programming languages.
<p:Resource xsi:type="vstd:ResourceEnumList" created="2001-12-31T12:00:00"
updated="2001-12-31T12:00:00" status="active">
<title>application languages</title>
<identifier>ivo://net.ivoa.application/languages</identifier>
<curation>
<publisher>IVOA</publisher>
<creator>
<name>IVOA</name>
<logo>http://www.ivoa.net/icons/ivoa_logo_small.jpg</logo>
</creator>
<date role="representative">2006-07-17</date>
<version>1.0</version>
<contact>
<name>IVOA Grid Registry WG</name>
<email>registry@ivoa.net</email>
</contact>
</curation>
<content>
<subject>standard language identifiers</subject>
<description>These language identifiers are to be used in the value of the va:ProgrammingLanguage type</description>
<referenceURL>http://www.ivoa.net/twiki/bin/view/IVOA/IvoaResReg</referenceURL>
</content>
<key name="C">
<description>The C programming language</description>
</key>
<key name="CPP">
<description>The C++ programming language</description>
</key>
<key name="CSharp">
<description>The C# programming language</description>
</key>
<key name="FORTRAN">
<description>The FORTRAN programming language</description>
</key>
<key name="Java">
<description>The Java programming language</description>
</key>
<key name="Perl">
<description>The Perl programming language</description>
</key>
<key name="Python">
<description>The Python programming language</description>
</key>
</p:Resource>
Note
When these enumerations are presented to a user in a GUI it is expected that the only the "fragment" part that distinguishes the various members of the enumeration will be used as a choice value, as the full IVO ID is not usually particularly "user-friendly".
Extending the BaseKey
The structure can be extened to provide additional metadata that is associated with the resource identifier. The diagram below shows how this structure is extended in the VOSpaceResource schema to add information about particular protocols.
Appendix A: The complete VOStandard Schema
Note that this schema can be found on-line at http://www.ivoa.net/xml/VOStandard/v0.2 (i.e. the target namespace can also be used as a URL for the schema not yet uploaded for this draft) This location should represent the definitive source, the schema is only copied below for completeness of this document.
Appendix B: Standards instance
This is an example of the ivoa standards that can be defined with the VOStandard Schema. This example should not be taken as the definitive definition for any standards mentioned - an IVOA registry should always be consulted, where the standards will be registered under the authority identifier net.ivoa.standards
Appendix C: Change History
This is the first version that has been made public - it is derived from wiki content.
References
- [RFC 2119]
- Bradner, S. 1997.
Key words for use in RFCs to Indicate Requirement
Levels, IETF RFC 2119,
http://www.ietf.org/rfc/rfc2119.txt
- [RM]
- Hanisch, Robert (ed.) 2004. Resource Metadata for the Virtual Observatory, Version 1.01, IVOA Recommendation,
http://www.ivoa.net/Documents/REC/ResMetadata/RM-20040426.htm
- [VR]
- Plante, Ray (ed.) 2006. VOResource: an XML Encoding Schema for Resource Metadata, IVOA Working Draft,
http://www.ivoa.net/Documents/latest/VOResource.html
- [CEA]
- Harrison, Paul. 2006. VOCEA: Schema , IVOA Working Draft,
http://www.ivoa.net/Documents/latest/VOCEA.html
- [xml]
- Bray, Tim, Paoli, Jean, Sperberg-McQueen, C. M., Maler, Eve,
Yergeau, Francois (editors) 2004,
Extensible Markup
Language (XML) 1.0 (Third Edition), W3C
Recommendation 04 February 2004,
http://www.w3.org/TR/REC-xml
- [schema]
- Fallside, David C., Walmsley, Priscilla (editors) 2004,
XML Schema
Part 0: Primer Second Edition, W3C Recommendation 28
October 2004,
http://www.w3.org/TR/xmlschema-0/
- [ISO8601]
- Wolf, Misha and Wicksteed, Charles 1997,
Date and
Time Format,
http://www.w3.org/TR/NOTE-datetime
. - [ID]
- Plante, R., Linde, T., Williams, R., Noddle, K. 2005,
IVOA Identifiers v1.1,
http://www.ivoa.net/Documents/REC/Identifiers/Identifiers-200505XX.html
.
Last modified: 25-Apr-2007 15:55