VODataService: a VOResource Schema Extension for Describing Collections and Services
Version 1.01

Status of this document

A list of current IVOA Recommendations and other technical documents can be found at http://www.ivoa.net/Documents/.

Acknowledgements

This document has been developed with support from the National Science Foundation's Information Technology Research Program under Cooperative Agreement AST0122449 with The Johns Hopkins University, from the UK Particle Physics and Astronomy Research Council (PPARC), and from the Eurpean Commission's Sixth Framework Program via the Optical Infrared Coordination Network (OPTICON).

The Virtual Observatory (VO) is general term for a collection of federated resources that can be used to conduct astronomical research, education, and outreach. The International Virtual Observatory Alliance (IVOA) is a global collaboration of separately funded projects to develop standards and infrastructure that enable VO applications.

XML document validation is a software process that checks that an XML document is not only well-formed XML but also conforms to the syntax rules defined by the applicable schema. Typically, when the schema is defined by one or more XML Schema [schema] documents (see next section), validation refers to checking for conformance to the syntax described in those Schema documents. This document describes additional syntax constraints that cannot be enforced solely by the rules of XML Schema; thus, in this document, use of the term validation includes the extra checks that goes beyond common Schema-aware parsers which ensure conformance with this document.

The eXtensible Markup Language, or XML, is document syntax for marking textual information with named tags and is defined by the World Wide Web Consortium (W3C) Recommendation, XML 1.0 [XML]. The set of XML tag names and the syntax rules for their use is referred to as the document schema. One way to formally define a schema for XML documents is using the W3C standard known as XML Schema [schema].

This document defines the VOResource schema using XML Schema. The full Schema document is listed in Appendix A. Parts of the schema appear within the main sections of this document; however, documentation nodes have been left out for the sake of brevity.

Reference to specific elements and types defined in the VOResource schema include the namespaces prefix, vr, as in vr:Resource (a type defined in the VOResource schema). Reference to specific elements and types defined in the VODataService extension schema include the namespaces prefix, vs, as in vs:DataCollection (a type defined in the VODataService schema). Use of the vs prefix in compliant instance documents is strongly recommended, particularly in the applications that involve IVOA Registries (see [RI], section 3.1.2). Elsewhere, the use is not required.

Contents

• Abstract
• Status of this document
• Acknowledgments
• Conformance-related definitions
• Syntax Notation Using XML Schema
• 1. Introduction
• 2. The VOResource Data Model
  • 2.1. The Schema Namespace and Location
  • 2.2. Summary of Metadata Concepts
• 3. The VODataService Metadata
  • 3.1. Resource Type Extensions
  • 3.2. Coverage
  • 3.3. Tabular Data
  • 3.4. Data Parameters
  • 3.5. Interface Type Extension: ParamHTTP
• Appendix A: the VODataService XML Schema
• Appendix B: Compatibility Issues with VODataService 1.0
• Appendix C: Change History
• References

1. Introduction

The VOResource standard [VOR] provides a means of encoding IVOA Resource Metadata [RM] in XML. VOResource uses XML Schema [schema] define most of the XML syntax rules (while a few of the syntax rules are outside the scope of Schema). VOResource also describes mechanisms for creating extensions to the core VOResource metadata. This allows for the standardization of new metadata for describing specialized kinds of resources in piecemeal way without deprecating the core schema or other extensions. This document defines one such extension referred to as VODataService.

The purpose of this extension is to define common XML Schema types--particularly new resource types--that are useful for describing data collections and services that access data. In particular, it allows one to describe the data's coverage: the parts of the sky the data is associated with and the time and frequency ranges that were observed or modeled to create the data. It also allows one to describe tables in detail. In particular, one can describe each of the columns of a table--providing, for example, its name, type, UCD, and textual description. When this metadata is part of a resource description in a registry [VOR], it becomes possible to discover tables that contains particular kinds of data.

It is intended that VODataService will be central to describing services that support standard IVOA data access layer protocols such as Simple Image Access [SIA] and Simple Cone Search [SCS]. While other VOResource extensions would define the protocol-specific metadata (encapsulated as a standard capability [VOR]), the general service resource description would share the common data concepts such as coverage and tabular data. Note, however, that a service described using the VODataService schema need not support any standard protocols. With the VODataService extension schema plus the core VOResource schema, it is possible to describe a custom service interface that accesses data.

As a legal extension of VOResource [VOR], the use of VODataService is subject to the rules and recommendations for XML [xml], XML Schema [schema], and VOResource itself.

The VODataService extension in general enables the description of two types of resources: data collections and services that access data. Here's an example of a VOResource document (abbreviated for the purposes of illustration) that describes a service from the NASA Extragalactic Database (NED) that provides measured redshifts for a given object.

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<?xml version="1.0" encoding="UTF-8"?>
<ri:Resource xmlns="" 
             xsi:type="vs:CatalogService" status="active" 
             updated="2008-04-29T14:51:54Z" created="2005-10-14T01:46:00Z"
             xmlns:ri="http://www.ivoa.net/xml/RegistryInterface/v1.0" 
             xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0" 
             xmlns:vs="http://www.ivoa.net/xml/VODataService/v1.1" 
             xmlns:stc="http://www.ivoa.net/xml/STC/stc-v1.30.xsd" 
             xmlns:xlink="http://www.w3.org/1999/xlink" 
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://www.ivoa.net/xml/VOResource/v1.0
                                 http://www.ivoa.net/xml/VOResource/v1.0
                                 http://www.ivoa.net/xml/VODataService/v1.1
                                 http://www.ivoa.net/xml/VODataService/v1.1
                                 http://www.ivoa.net/xml/STC/stc-v1.30.xsd
                                 http://www.ivoa.net/xml/STC/stc-v1.30.xsd">

  <title>The NASA/IPAC Extragalactic Database</title>
  <shortName>NED_redshift</shortName>
  <identifier>ivo://ned.ipac/Redshift_By_Object_Name</identifier>
  <curation>
    <publisher>The NASA/IPAC Extragalactic Database</publisher>
    <contact>
      <name>Olga Pevunova</name>
      <email>contact@datacenter.edu</email>
    </contact>
  </curation>
  <content>
    <subject>redshift</subject>
    <subject>galaxies</subject>
    <description>
      NED is built around a master list of extragalactic objects for
      which cross-identifications of names have been established,
      accurate positions and redshifts entered to the extent possible,
      and some basic data collected. This service will return recorded 
      redshifts for a given object.
    </description>
    <referenceURL>http://nedwww.ipac.caltech.edu/help/data_help.html#zdat</referenceURL>
    <type>BasicData</type>
    <contentLevel>Research</contentLevel>
  </content>

  <capability>
    <interface xsi:type="vs:ParamHTTP">
      <accessURL use="base">
         http://nedwww.ipac.caltech.edu/cgi-bin/nph-datasearch?search_type=Redshifts&
      </accessURL>
      <queryType>GET</queryType>
      <resultType>application/xml+votable</resultType>
      <param use="required">
        <name>objname</name>
        <description>Name of object</description>
        <dataType>string</dataType>
      </param>
      <param use="required">
        <name>of</name>
        <description>Output format parameter, must be "xml_main" for VOTable output.</description>
        <dataType>string</dataType>
      </param>
    </interface>
  </capability>

  <coverage>
    <stc:STCResourceProfile>
       <stc:AstroCoordSystem xlink:type="simple"
                             xlink:href="ivo://STClib/CoordSys#UTC-FK5-TOPO" 
                             id="UTC-FK5-TOPO"/> 
       <stc:AstroCoordArea coord_system_id="UTC-FK5-TOPO">
          <stc:AllSky/>
       </stc:AstroCoordArea>
    </stc:STCResourceProfile>
    
    <waveband>Radio</waveband>
    <waveband>Optical</waveband>
  </coverage>

  <tableset>
    <schema>
      <name>default</name>
      <table role="out">
        <qualifiedName>default</qualifiedName>
        <column>
          <name>No.</name>
          <description>
             A sequential data-point number applicable to this list only.
          </description>
          <ucd>meta.number</ucd>
          <dataType>int</dataType>
        </column>
        <column>
          <name>Name in Publication</name>
          <description>
             The object's name in NED's standard format, of the object to which the data apply.
          </description>
          <ucd>meta.id;name</ucd>
          <dataType>string</dataType>
        </column>
        <column>
          <name>Published Velocity</name>
          <description>
            The radial velocity , derived from derived from the shift of some spectral feature, in km/sec
          </description>
          <unit>km/sec</unit>
          <ucd>src.spect.dopplerVeloc</ucd>
          <dataType>int</dataType>
        </column>
      </table>
    <schema>
  </tableset>
</ri:Resource>

1. the extra namespaces associated with VODataService metadata; if STC coverage information is not included, then only the VODataService namespaced is needed.
2. the specific type of resource indicated by the value of the xsi:type attribute; in this case vs:CatalogService indicates that this is describing a service that accesses tabular data.
3. the location of the VOResource-related schema documents used by this description,
4. the core VOResource metadata,
5. an interface described by the VODataService interface type, vs:ParamHTTP; this type can indicate input arguments it supports.
6. a description of the coverage, including an STC description plus waveband keywords.
7. a description of the table that is returned by the service.

2.1. The Schema Namespace and Location

The namespace associated with VODataService extensions is "http://www.ivoa.net/xml/VODataService/v1.1". Just like the namespace URI for the VOResource schema, the VODataService namespace URI can be interpreted as a URL. Resolving it will return the XML Schema document (given in Appendix A) that defines the VODataService schema.

Authors of VOResource instance documents may choose to provide a location for the VOResource XML Schema document and its extensions using the xsi:schemaLocation attribute. While the choice of the location value is the choice of the author, this specification recommends using the VODataService namespace URI as its location URL (as illustrated in the example above), as in,

xsi:schemaLocation="http://www.ivoa.net/xml/VODataService/v1.1
                    http://www.ivoa.net/xml/VODataService/v1.1"

Note: The IVOA Registry Interface standard [RI] actually requires that the VOResource records it shares with other registries provide location URLs via xsi:schemaLocation for the VOResource schema and all legal extension schemas that are used in the records. This rule would apply to the VODataService schema.

The prefix, vs, is used by convention as the prefix defined for the VODataService schema; however, instance documents may use any prefix of the author's choosing. In applications where common use of prefixes is recommended (such as with the Registry Interface specification [RI]), use of the vs prefix is recommended. Note also that in this document, the vr prefix is used to label, as shorthand, a type or element name that is defined in the VOResource schema, as in vr:Resource.

Note: One reason one may not be able to use vs to represent the VODataService schema, version 1.1, is because it is already in defined to represent VODataService v1.0 and cannot be overridden. At this writing, there are no IVOA applications in which this is the case. Consult Appendix B for more details on compatibility issues.

As recommend by the VOResource standard [VOR], the VODataService schema sets elementFormDefault="unqualified". This means that it is not necessary to qualify element names defined in this schema with a namespace prefix (as there are no global elements defined). The only place it is usually needed is as a qualifier to a VODataService type name given as the value of an xsi:type attribute.

The VODataService extension defines four new types of resources. Two inherit directly from vr:Resource:

vs:DataCollection

This resource declares the existence of a collection of data, what it represents, and how to get it. The access to the data may be limited to access a human-readable web page (given by content/referenceURL); however, if the constituents of the collection are available statically via a URL (e.g. an FTP URL to a directory containing all the files), that URL can be provided. It can also provide pointers to other IVOA registered services that can be used to access the data.

vs:StandardSTC

This resource type declares one or more coordinate systems describe using STC [STC] such that each can be assigned a globally unique identifier (based on the IVOA identifier for the resource record itself). This identifier can then be referenced in any other STC description in lieu of a fully described coordinate system. Coordinate system described in this way become reusable standards once they are registered in an IVOA registry.

The other two resource types represent specialized services:

vs:DataService

Inheriting from vr:Service, this type is for services that access astronomical data. It adds the ability to describe the data's coverage of the sky, frequency, and time.

vs:CatalogService

Inheriting from vs:DataService, this type specifically refers to a service that accesses tabular data. In addition to the coverage information, this type adds the ability to describe the tables and their columns. This is intended for describing services that support the "simple" IVOA data access layer protocols such as Simple Image Access [SIA] and Simple Cone Search [SCS].

In general, coverage refers to the extent that data samples the measurement range of the sky (space), frequency, and time. The coverage metadata (encoded via the vs:Coverage type) has two parts to it. The first part allows a full STC profile description (via the imported STC element, <stc:STCResourceProfile>). The second part captures key coverage metadata defined in the IVOA Resource Metadata standard [RM]. The RM-derived coverage elements can be considered summarizing metadata for many of the details that may appear within the STC description, and enables simpler searching of high-level coverage information.

The detailed STC profile contained within the <stc:STCResourceProfile> element is capable of describing coverage not only in space, time, and frequency but also velocity and redshift. The profile contains up to three types of component descriptions ([STC], section 4.1): coordinate systems, coordinate values, and coordinate areas or ranges. The first component describes the coordinate systems that coordinate values, areas, and regions are referenced to. While any arbitrary system can be described in this first part, it is expected that most VODataService instances will provide a simple pointer to a predefined system in a registered vs:StandardSTC record (using the mechanism summarized in section 3.1.2 below). The coordinate values part will usually be used to describe the coordinate resolution, errors, or typical sizes. The coordinate areas part describes the actual coverage over any of the coordinates.

Table descriptions appear within a single <tableset> element. This element can in turn can contain one or more <schema> element in which each schema represents a set of logically related tables. It is not required that that the schema grouping match the underlying database's catalogs or schemas (as defined in [SQLGuide]), though it may. In some cases, such as when describing the table that is returned from an SIA service, the terms catalog and schema may have little relevance; in this case, the table can be considered part of a sole "default" schema.

For each table in a schema, one can describe each of the columns, providing such information as its name, type, UCD [UCD], units, and a textual description. Providing this information makes it possible to select a resource based on the kind data contained in its tables.

Finally, the VODataService defines specialized interface type (inheriting from vr:Interface) called vs:ParamHTTP. This interface is used to describe an interface that is invoked over HTTP as either a GET or a POST [HTTP] in which the arguments are encoded as name=value pairs. In addition to the access URL, it can include not only the mime-type of the returned response, it can also enumerate the input arguments that are supported by the service implementation. Much like table columns, one can indicate for each argument the name, the UCD, the data type, the units, whether it is required, and a textual description the argument. Note that this does not capture any interdependencies between arguments. For example, it cannot indicate if one argument only makes sense in the presence of another argument.

This section enumerates the types and elements defined in the VODataService extension schema and describes their meaning. Where a term matches a term in the RM, its meaning is given in terms of the RM definition.

A data collection, which is describable with the vs:DataCollection resource type, is a logical group of data which, in general, is composed of one or more accessible datasets. A collection can contain any combination of images, spectra, catalogs, time-series, or other data. (In contrast, we talk about a dataset as being a collection of digitally-encoded data that is normally accessible as a single unit, e.g. a file.)

The vs:DataCollection type adds seven additional metadata elements beyond the core VOResource metadata [VO].

<xs:complexType name="DataCollection">
   <xs:complexContent>
      <xs:extension base="vr:Resource">
         <xs:sequence>

           <xs:element name="facility" type="vr:ResourceName" 
                       minOccurs="0" maxOccurs="unbounded"/>
           <xs:element name="instrument" type="vr:ResourceName" 
                       minOccurs="0" maxOccurs="unbounded"/>
           <xs:element name="rights" type="vr:Rights" 
                       minOccurs="0" maxOccurs="unbounded"/>
           <xs:element name="format" type="vs:Format" 
                       minOccurs="0" maxOccurs="unbounded"/>
           <xs:element name="coverage" type="vs:Coverage" minOccurs="0"/>
           <xs:element name="tableset" type="vs:TableSet" minOccurs="0">
             <xs:unique name="DataCollection-schemaName">
                <xs:selector xpath="schema" />
                <xs:field xpath="name" />
             </xs:unique>
             <xs:unique name="DataCollection-tableName">
                <xs:selector xpath="schema/table" />
                <xs:field xpath="name" />
             </xs:unique>
           <xs:element>
           <xs:element name="accessURL" type="vr:AccessURL" minOccurs="0"/>

         </xs:sequence>
      </xs:extension>
   </xs:complexContent>
</xs:complexType>

The definition of <tableset> element places forces certain names within its description to be unique; these constraints are explained further in 3.3.1.

All of the child elements except <tableset> derive from RM terms. Four of the elements--<facility>, <instrument>, <rights>, and <accessURL>--are reuses of elements defined in the core VOResource schema, sharing the same syntax and similar semantics. In particular, the meanings of <facility> and <instrument> in the context of vs:DataCollection are different from that in vr:Organisation only in that in the former type, they refer to the origin of the data.

vs:DataCollection Extension Metadata Elements
Element	Definition
facility	RM Name: Facility Value type: string with optional ID attribute: vr:ResourceName Semantic Meaning: the observatory or facility used to collect the data contained or managed by this resource. Occurrences: optional; multiple occurrences allowed
instrument	RM Name: Instrument Value type: string with optional ID attribute: vr:ResourceName Semantic Meaning: the instrument used to collect the data contained or managed by this resource. Occurrences: optional; multiple occurrences allowed
rights	RM Name: Rights Value type: string, controlled vocabulary: xs:token Semantic Meaning: Information about rights held in and over the resource. Occurrences: optional; multiple occurrences allowed Allowed Values: public unrestricted, public access is allowed without authentication. secure authenticated, public access is allowed. proprietary only proprietary access is allowed with authentication.
format	RM Name: Format Value type: string with optional isMIMEType attribute, vs:Format Semantic Meaning: The physical or digital manifestation of the information supported by a resource. Occurrences: optional; multiple occurrences allowed Comments: MIME types should be used for network-retrievable, digital data. Non-MIME type values are used for media that cannot be retrieved over the network--e.g. CDROM, poster, slides, video cassette, etc.
coverage	RM Name: Coverage Value type: composite; vs:Coverage Semantic Meaning: Extent of the content of the resource over space, time, and frequency. Occurrences: optional
tableset	Value type: composite; vs:TableSet Semantic Meaning: A description of tables that are part of this collection. Occurrences: optional.
accessURL	RM Name: Service.AccessURL Value type: URL with optional use attribute: vr:AccessURL Semantic Meaning: The URL can be used to download the data contained in this data collection. Occurrences: required; multiple occurrences allowed.

See section 3.3 for a specification of the vs:TableSet type for describing tables.

The vs:StandardSTC resource type is used to register standard coordinate systems, positions, or regions using the Space-Time Coordinate (STC, [STC]) standard schema so that they can by uniquely referenced by name by other resource descriptions or applications. This resource type extends the core metadata with a single element, <stcDefinitions>, which contains the STC definitions.

<xs:complexType name="StandardSTC">
   <xs:complexContent>
      <xs:extension base="vr:Resource">
         <xs:sequence>
            <xs:element name="stcDefinitions"
                        type="stc:STCResourceProfile"
                        minOccurs="0" maxOccurs="unbounded"/>
         </xs:sequence>
      </xs:extension>
   </xs:complexContent>
</xs:complexType>

The curation metadata that is part of the core VODataService should generally refer to the publishing organization and persons that are responsible for defining the systems, updating the definitions as needed, and responding to user questions about the definitions. The content metadata, in particular the textual contents of the <description> element, should describe the purpose of the definition and where references to the defined systems, positions, or regions may be used.

vs:StandardSTC Extension Metadata Elements
Element	Definition
stcDefintions	Value type: composite; stc:stcDescriptionType Semantic Meaning: the definitions of systems, positions, and regions that are available for referencing. Occurrences: required; multiple occurrences allowed

The content of the <stcDefinitions> element is controlled by the STC schema. Because that schema uses the elementFormDefault="true" and most of the STC elements are defined to be global [schema], <stcDefinitions> child elements must be qualified as being in the STC namespace (http://www.ivoa.net/xml/STC/stc-v1.30.xsd), by either setting the default namespace (via the xmlns attribute) or via explicit qualification via a prefix (see example).

The vs:DataService resource type is for describing a service that provides access to astronomical data. This service adds to the core VOResource service metadata the ability to associate an observing facility and/or instrument with the data as well as describe the coordinate coverage of data via its child <coverage> element. Note that while these elements are all optional, resource of this type still implies access to astronomical data.

<xs:complexType name="DataService">
   <xs:complexContent>
      <xs:extension base="vr:Service">
         <xs:sequence>
           <xs:element name="facility" type="vr:ResourceName" 
                       minOccurs="0" maxOccurs="unbounded"/>
           <xs:element name="instrument" type="vr:ResourceName" 
                       minOccurs="0" maxOccurs="unbounded"/>
           <xs:element name="coverage" type="vs:Coverage" minOccurs="0"/>
         </xs:sequence>
      </xs:extension>
   </xs:complexContent>
</xs:complexType>

The use and meaning of the <facility> and <instrument> elements are the same as for vs:DataCollection.

vs:DataService Extension Metadata Elements
Element	Definition
facility	RM Name: Facility Value type: string with optional ID attribute: vr:ResourceName Semantic Meaning: the observatory or facility used to collect the data contained or managed by this resource. Occurrences: optional; multiple occurrences allowed
instrument	RM Name: Instrument Value type: string with optional ID attribute: vr:ResourceName Semantic Meaning: the instrument used to collect the data contained or managed by this resource. Occurrences: optional; multiple occurrences allowed
coverage	RM Name: Coverage Value type: composite; vs:Coverage Semantic Meaning: Extent of the content of the resource over space, time, and frequency. Occurrences: optional

The contents of the <coverage> element is detailed in section 3.2.

The vs:CatalogService resource type is for describing a service that interacts with astronomical data through one or more specified tables. Because it extends the vs:DataService type, a catalog service can have a coverage description as well. The tabular data may optionally be described via a <tableset> element.

<xs:complexType name="CatalogService">
      <xs:complexContent>
         <xs:extension base="vs:DataService">
            <xs:sequence>

               <xs:element name="tableset" type="vs:TableSet" minOccurs="0">
                  <xs:unique name="CatalogService-schemaName">
                     <xs:selector xpath="schema" />
                     <xs:field xpath="name" />
                  </xs:unique>
                  <xs:unique name="CatalogService-tableName">
                     <xs:selector xpath="schema/table" />
                     <xs:field xpath="name" />
                  </xs:unique>
                <xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

The definition of <tableset> element places forces certain names within its description to be unique; these constraints are explained further in 3.3.1.

vs:CatalogService Extension Metadata Elements
Element	Definition
tableset	Value type: composite; vs:TableSet Semantic Meaning: A description of the tables that are accessible through this service. Occurrences: optional

The vs:Coverage type describes how the data samples the sky, frequency, and time.

<xs:complexType name="Coverage">
      <xs:sequence>

         <xs:element ref="stc:STCResourceProfile" minOccurs="0"/>
         <xs:element name="footprint" type="vs:ServiceReference" 
                     minOccurs="0"/>
         <xs:element name="waveband" type="vs:Waveband" 
                     minOccurs="0" maxOccurs="unbounded"/>
         <xs:element name="regionOfRegard" type="xs:float"
                     minOccurs="0" maxOccurs="unbounded"/>

      </xs:sequence>            
   </xs:complexType>

A detailed, systematic description of coverage is provided via the child <stc:STCResourceProfile> element, taken from the STC schema, version 1.3, with the namespace, http://www.ivoa.net/xml/STC/stc-v1.30.xsd (hereafter referred using the stc: prefix). This element is defined in the STC schema as a global element; furthermore, the STC schema sets its global elementFormDefault="qualified". Consequently, the <stc:STCResourceProfile> element and all its child elements must be qualified as part of the STC namespace as required by XML Schema [schema]. In applications where common use of XML prefixes is required or encouraged (e.g. the IVOA Registry Interfaces [RI]), use of the stc: prefix to represent the STC namespace is encouraged.

The remaining elements provide some summary information about the coverage.

vs:Coverage Metadata Elements
Element	Definition
STCResourceProfile	Value type: composite: an stc:STCResourceProfile element from the STC schema. Semantic Meaning: The STC description of the location of the resource's data (or behavior on data) on the sky, in time, and in frequency space, including resolution. Occurrences: optional Comments: In general, this description should be approximate; a more precise description can be provided by the service referred to by the <footprint> element.
footprint	Value type: a URL with an optional IVOA identifier attribute: Semantic Meaning: a reference to a footprint service for retrieving precise and up-to-date description of coverage. Occurrences: optional Comments: the ivo-id attribute refers to a Service record having a footprint service capability. That is, the record will have a capability element describing the footprint service (see "Note on Footprint Service" below for further discussion). The resource referred to may be the current one.
waveband	RM Name: Coverage.Spectral Value type: string with controlled vocabulary: vs:Waveband Semantic Meaning: a named spectral region of the electro-magnetic spectrum that the resource's spectral coverage overlaps with. Occurrences: optional; multiple occurrences allowed Allowed Values: Radio any wavelength > 10 mm (or frequency < 30 GHz) Millimeter 0.1 mm <= wavelength <= 10 mm; 3000 GHz >= frequency >= 30 GHz. Infrared 1 micron <= wavelength <= 100 microns Optical 0.3 microns <= wavelength <= 1 micron; 300 nm <= wavelength <= 1000 nm; 3000 Angstroms <= wavelength <= 10000 Angstroms UV 0.1 micron <= wavelength <= 0.3 microns; 100 nm <= wavelength <= 3000 nm; 1000 Angstroms <= wavelength <= 30000 Angstroms EUV 100 Angstroms <= wavelength <= 1000 Angstroms; 12 eV <= energy <= 120 eV X-ray 0.1 Angstroms <= wavelength <= 100 Angstroms; 0.12 keV <= energy <= 120 keV Gamma-ray energy >= 120 keV
regionOfRegard	RM Name: Coverage.RegionOfRegard Value type: a floating point number: xs:float Semantic Meaning: a single numeric value representing the angle, given in decimal degrees, by which a positional query against this resource should be "blurred" in order to get an appropriate match. Occurrences: optional Comments: In the case of image repositories, this value might refer to a typical field-of-view size, or the primary beam size for radio aperture synthesis data. In the case of object catalogs, region of regard should normally be the largest of the typical size of the objects, the astrometric errors in the positions, or the resolution of the data.

Note on Footprint Service: The <footprint> element has been defined in anticipation of a future standard IVOA footprint service protocol that can be used to respond to detailed spatial overlap queries. Consequently, in the future, applications may be able to assume the protocol that footprint service URL supports. When an application is unable to make any assumptions, the IVOA Identifier given by the attribute should be resolved and the returned resource description should be searched for a recognized footprint service capability.

The vs:TableSet type can be used to describe a set of tables that are part of a single resource and can be consider functionally all located at a single site.

<xs:complexType name="TableSet">
   <xs:sequence>
      <xs:element name="schema" type="vs:TableSchema" 
                  minOccurs="1" maxOccurs="unbounded"/>
   </xs:sequence>

   <xs:anyAttribute namespace="##other" />
</xs:complexType>

vs:TableSet Metadata Elements
Element	Definition
schema	Value type: composite; vs:TableSchema Semantic Meaning: A named description of a set of logically related tables. Occurrences: required; multiple occurrences are allowed. Comments: See section 3.3.1 regarding unique names for schemas.

The vs:TableSchema type collects tables together that are logically related. For example, a single resource may provide access several major astronomical catalogs (e.g. SDSS, 2MASS, and FIRST) from one site, enabling high-performance cross-correlations between them. Each catalog can be described in a separate <schema> element, using the elements from the vs:TableSchema type.

<xs:complexType name="TableSchema">
   <xs:sequence>

      <xs:element name="name" type="xs:token" minOccurs="1" maxOccurs="1"/>
      <xs:element name="title" type="xs:token" minOccurs="0"/>
      <xs:element name="description" type="xs:token" 
                  minOccurs="0" maxOccurs="1"/>
      <xs:element name="utype" type="xs:token" minOccurs="0"/>
      <xs:element name="table" type="vs:Table" 
                  minOccurs="0" maxOccurs="unbounded"/>

   </xs:sequence>

   <xs:anyAttribute namespace="##other" />
</xs:complexType>

vs:TableSchema Metadata Elements
Element	Definition
name	Value type: string: xs:token Semantic Meaning: A name for the set of tables. Occurrences: required Comments: If there is no appropriate logical name associated with this set, the name should be explicitly set to "default". See section 3.3.1 regarding the uniqueness of this name.
title	Value type: string: xs:token Semantic Meaning: a descriptive, human-interpretable name for the table set. Occurrences: optional Comments: This is used for display purposes and is useful when there are multiple schemas in the context (e.g. within a tableset; otherwise, the resource title could be used instead). Note, however, that there is no requirement regarding uniqueness. If a title is not provided, the schema name can be used for display purposes.
description	Value type: string: xs:token Semantic Meaning: A free text description of the tableset that should explain in general how all of the tables are related. Occurrences: optional
utype	Value type: string: xs:token Semantic Meaning: an identifier for a concept in a data model that the data in this schema as a whole represent. Occurrences: optional Comments: The format defined in the VOTable standard, section 4.1 [VOTable] is strongly recommended; see "Note on UType Format below.
table	Value type: composite: vs:Table Semantic Meaning: A marked description of one of the tables that makes up the set. Occurrences: optional; multiple occurrences are allowed. Comments: See section 3.3.1 regarding unique names for schemas.

Note on UType Format: As of this writing, an IVOA standard for the format of utypes is still under development. As a result, the most definitive documentation of the format is in section 4.1 of the VOTable specification [VOTable], which is expected to be a more general form to be spelled out in the eventual utype standard. Use of that latter standard is recommended once it becomes available.

Each table in a schema is described in detail using the vs:Table type.

<xs:complexType name="Table">
   <xs:sequence>

      <xs:element name="name" type="xs:token" 
                  minOccurs="1" maxOccurs="1"/>
      <xs:element name="title" type="xs:token" minOccurs="0"/>
      <xs:element name="description" type="xs:token" minOccurs="0"/>
      <xs:element name="utype" type="xs:token" minOccurs="0"/>
      <xs:element name="column" type="vs:TableParam" 
                  minOccurs="0" maxOccurs="unbounded"/>

   </xs:sequence>

   <xs:attribute name="type" type="xs:string"/>
   <xs:anyAttribute namespace="##other" />
</xs:complexType>

vs:Table Metadata Elements
Element	Definition
name	Value type: string: xs:token Semantic Meaning: A fully qualified name for the table. This name should include all catalog or schema prefixes needed to sufficiently uniquely distinguish it in a query to the table. Occurrences: required Comments: In general, the format of the qualified name may depend on the on the context; however, when the table is intended to be queryable via ADQL, then the catalog and schema qualifiers are delimited from the table name with dots (.). If there is no appropriate logical name associated with this table, the name should be explicitly set to "default". See section 3.3.1 regarding the uniqueness of this name.
title	Value type: string: xs:token Semantic Meaning: a descriptive, human-interpretable name for the table set. Occurrences: optional Comments: This is used for display purposes. There is no requirement regarding uniqueness. If a title is not provided, the table name can be used for display purposes.
description	Value type: string: xs:token Semantic Meaning: A free-text description of the table's contents. Occurrences: optional
utype	Value type: string: xs:token Semantic Meaning: an identifier for a concept in a data model that the data in this table as a whole represent. Occurrences: optional Comments: The format defined in the VOTable standard, section 4.1 [VOTable] is strongly recommended; see "Note on UType Format above.
column	Value type: composite: vs:TableParam Semantic Meaning: A marked description of one of the table's columns. Occurrences: optional; multiple occurrences are allowed. Comments: See section 3.3.1 regarding unique names for schemas.

Each column in a table can be described using the vs:TableParam type which is described in section 3.4.

The definitions of the <tableset> elements used in the and vs:DataCollection and vs:CatalogService types constrain the use of unique names. In particular, all schema names within a <tableset> element must be unique, and all table names within a <tableset> element must be unique. (A schema and table may share a common name, such as "default".) These constraints makes it possible to uniquely locate the description of a schema or table within a VOResource description.

   schema[@name="default"]
   schema/table[@name="default"]

Name uniqueness is only required when the table set description is part of a VOResource description. The name uniqueness rules should also be applied to other uses of the vs:TableSet element outside of a VOResource description.

1. Use extended types by applying the xsi:type attribute to the <tableset>, <schema>, <table>, and/or <column> elements. The values provided in the attributes must refer to an XML type legally extended from the types associated with these elements according to the rules of XML Schema [schema] and the VOResource specification [VOR].
2. Apply a globally-defined attribute from a schema other than VODataService (i.e. from a namespace other than "http://www.ivoa.net/xml/VODataService/v1.1") to any of the <tableset>, <schema>, <table>, and/or <column> elements.
3. When the extended metadata is specific to how the table data is accessed via a particular service protocol, then the new metadata can be incorporated into a specific capability extension (as described in the VOResource specification [VOR]). This extension may make use of the various names within the <tableset> to indicate where the extension metadata apply.
4. Use the extendedType attribute of the <column> element (see section 3.4) to indicate a more specific data type then those defined by the vs:TableParam type.

The VODataService schema provides several tagging types for describing different kinds of data parameters used in datasets and services, including service input parameters and table columns. The parameter types allow one to fully describe a parameter in terms of metadata that includes name, data type, and meaning.

All the VODataService parameter types derive from a base type called vs:BaseParam which defines all the common parameter metadata except the data type.

<xs:complexType name="BaseParam">
   <xs:sequence>

      <xs:element name="name" type="xs:token" minOccurs="0"/>
      <xs:element name="description" type="xs:token" minOccurs="0"/>
      <xs:element name="unit" type="xs:token" minOccurs="0"/>
      <xs:element name="ucd" type="xs:token" minOccurs="0"/>
      <xs:element name="utype" type="xs:token" minOccurs="0"/>

   </xs:sequence>
   <xs:anyAttribute namespace="##other" />
</xs:complexType>

vs:BaseParam Metadata Elements
Element	Definition
name	Value type: string: xs:token Semantic Meaning: The name of the column. Occurrences: optional
description	Value type: string: xs:token Semantic Meaning: a free-text description of the column's contents Occurrences: optional
unit	Value type: string: xs:token Semantic Meaning: the unit associated with all values associated with this parameter or table column. Occurrences: optional
ucd	Value type: string: xs:token Semantic Meaning: the name of a unified content descriptor that describes the scientific content of the parameter. Occurrences: optional Comments: There are no requirements for compliance with any particular UCD standard. The format of the UCD can be used to distinguish between UCD1, UCD1+, and SIA-UCD. See [UCD] for the latest IVOA standard set.
utype	Value type: string: xs:token Semantic Meaning: an identifier for a concept in a data model that the data in this schema as a whole represent. Occurrences: optional Comments: The format defined in the VOTable standard, section 4.1 [VOTable] is strongly recommended; see "Note on UType Format above.

The vs:TableParam is a derived from vs:BaseParam; it adds a set of possible data types that are typical for table columns and can be encoded into VOTable-formatted documents.

<xs:complexType name="TableParam">
   <xs:complexContent>
      <xs:extension base="vs:BaseParam">
         <xs:sequence>

            <xs:element name="dataType" type="vs:TableDataType" 
                        minOccurs="0"/>
            <xs:element name="flag" type="xs:token" 
                        minOccurs="0" maxOccurs="unbounded"/>

         </xs:sequence>

         <xs:attribute name="std" type="xs:boolean"/>
      </xs:extension>
   </xs:complexContent>
</xs:complexType>

By fixing the <dataType> child element to of the vs:TableDataType, the possbile types are restricted to predefined set appropriate for tables.

vs:TableParam Extension Metadata Elements
Element	Definition
dataType	Value type: string with optional attributes: vs:TableDataType Semantic Meaning:       a type of data contained in the column. Occurrences: optional Allowed Values: The following type names correspond to the same data types defined in the VOTable standard [VOTable]: boolean, bit, unsignedByte, short, int, long, char, unicodeChar, float, double, floatComplex, and doubleComplex. The additional types, string and unicodeString, are equivalent the VOTable data types char and unicodeChar when arrayshape="*".
flag	Value type: string with optional attributes: vs:TableDataType Semantic Meaning: a keyword representing traits of the column. Occurrences: optional; multiple occurrences allowed Recommended Values: indexed The column has an index on it for faster search against its values. primary The values column in the column represents in total or in part a primary key for its table. nullable the column may contain null or empty values.

The <dataType> element accepts a several attributes that can modify the interpretation of the values found in a column:

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 1.12, IVOA Recommendation, http://www.ivoa.net/Documents/REC/ResMetadata/RM-20040426.htm

[RI]

Benson, Kevin, Plante, Ray, Auden, Elizabeth, Graham, Matthew, Greene, Gretchen, Hill, Martin, Linde, Tony, Morris, Dave, O'Mullane, Wil, Rixon, Guy, Andrews, Kona 2008, IVOA Registry Interfaces, v1.02, IVOA Recommendation, http://www.ivoa.net/Documents/latest/ResourceInterface.html

[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/

[SIA]

Tody, Doug and Plante, Ray 1997, Simple Image Access Specification Version 1.0, IVOA Working Draft, http://www.ivoa.net/Documents/WD/SIA/sia-20040524.html.

[STC]

Rots, Arnold 2007, Space-Time Coordinate Metadata for the Virtual Observatory, v1.33, IVOA Recommendation, href="http://www.ivoa.net/Documents/REC/STC/STC-20071030.html">

[SQLGuide]

Date, C.J. and Darwin, Hugh 1997, A Guide to the SQL Standard, Fourth Edition, (Addison-Wesley, Longman Inc.: Reading), p 24.

[UCD]

Martinez, A.P., Derriere, S., Delmotte, N., Gray, N., Mann, R., McGlynn, T., Ochsenbein, F., Osuna, P., Rixon, G., Williams, R. 2007, The UCD1+ Controlled Vocabulary, v1.23, IVOA Recommendation, http://www.ivoa.net/Documents/latest/UCDlist.html

[VOR]

Plante, R., Benson, K., Graham, M., Greene, G., Harrison, P., Lemson, G., Linde, T., Rixon, G., Stébé, A. 2008, VOResource: an XML Encoding Schema for Resource Metadata, v1.03, IVOA Recommendation, http://www.ivoa.net/Documents/REC/ReR/VOResource-20080222.html

[VOTable]

Ochsenbein, F., Williams, R., Davenhall, C., Durand, D., Fernique, P., Giaretta, D., Hanisch, R., McGlynn, T., Szalay, A., Taylor, M.B., Wicenec, A. 2008, VOTable Format Definition, version 1.20, IVOA Working Draft, http://www.ivoa.net/Documents/WD/VOTable/VOTable-20080914.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