<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="http://www.ivoa.net/xml/VOResource/v1.0" 
           xmlns="http://www.w3.org/2001/XMLSchema" 
           xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0" 
           xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
           elementFormDefault="unqualified"
           attributeFormDefault="unqualified"
           version="1.02">

   <xs:annotation>
     <xs:appinfo>
       <vm:schemaName>VOResource</vm:schemaName>
       <vm:schemaPrefix>xs</vm:schemaPrefix>
       <vm:targetPrefix>vr</vm:targetPrefix>
     </xs:appinfo>
      <xs:documentation>
        Implementation of an XML Schema describing a resource to 
        be used in the Virtual Observatory Project.  Based on "Resource 
        Metadata for the Virtual Observatory", Version 0.8, 
        February 2002 by Bob Hanisch et al.
      </xs:documentation>
   </xs:annotation>

   <xs:simpleType name="UTCTimestamp">
      <xs:annotation>
         <xs:documentation>
           A timestamp that is compliant with ISO8601 but disallows
           the use of a timezone indicator.
         </xs:documentation> 
      </xs:annotation>

      <xs:restriction base="xs:dateTime">
         <xs:pattern value="\d{4}-\d\d-\d\dT\d\d:\d\d:\d\d(\.\d+)?"/>
      </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="UTCDateTime">
      <xs:annotation>
         <xs:documentation>
           A date stamp that can be given to a precision of either a
           day (type xs:date) or seconds (type
           xs:dateTime)
         </xs:documentation> 
      </xs:annotation>
      <xs:union memberTypes="xs:date vr:UTCTimestamp"/>
   </xs:simpleType>

   <xs:complexType name="Resource">
      <xs:annotation>
         <xs:documentation>
           Any entity or component of a VO application that is
           describable and identifiable by a IVOA Identifier. 
         </xs:documentation>
      </xs:annotation>
      <xs:sequence>
         <xs:element name="validationLevel" type="vr:Validation"
                     minOccurs="0" maxOccurs="unbounded">
            <xs:annotation>
               <xs:documentation>
                  A numeric grade describing the quality of the
                  resource description, when applicable, 
                  to be used to indicate the confidence an end-user
                  can put in the resource as part of a VO application
                  or research study. 
               </xs:documentation>
               <xs:documentation>
                  See vr:ValidationLevel for an explanation of the
                  allowed levels.  
               </xs:documentation>
               <xs:documentation>
                  Note that when this resource is a Service, this
                  grade applies to the core set of metadata.
                  Capability and interface metadata, as well as the
                  compliance of the service with the interface
                  standard, is rated by validationLevel tag in the 
                  capability element (see the vr:Service complex
                  type).  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="title" type="xs:token">
            <xs:annotation>
               <xs:appinfo>
                 <vm:dcterm>Title</vm:dcterm>
               </xs:appinfo>           
               <xs:documentation>
                  the full name given to the resource
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="shortName" type="vr:ShortName" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                 a short name or abbreviation given to the resource.
               </xs:documentation>
               <xs:documentation>
                 This name will be used where brief annotations for
                 the resource name are required.  Applications may 
                 use to refer to this resource in a compact display.   
               </xs:documentation>
               <xs:documentation>
                 One word or a few letters is recommended.  No more
                 than sixteen characters are allowed.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="identifier" type="vr:IdentifierURI">
            <xs:annotation>
               <xs:appinfo>
                 <vm:dcterm>Identifier</vm:dcterm>
               </xs:appinfo>           
               <xs:documentation>
                 Unambiguous reference to the resource conforming to the IVOA
                 standard for identifiers
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="curation" type="vr:Curation">
           <xs:annotation>
             <xs:documentation>
               Information regarding the general curation of the resource
             </xs:documentation>
           </xs:annotation>
         </xs:element>

         <xs:element name="content" type="vr:Content">
           <xs:annotation>
             <xs:documentation>
               Information regarding the general content of the resource
             </xs:documentation>
           </xs:annotation>
         </xs:element>

      </xs:sequence>

      <xs:attribute name="created" type="xs:dateTime" use="required">
         <xs:annotation>
            <xs:documentation>
              The UTC date and time this resource metadata description
              was created. 
            </xs:documentation>
            <xs:documentation>
              This timestamp must not be in the future.  This time is
              not required to be accurate; it should be at least
              accurate to the day.  Any insignificant time fields
              should be set to zero. 
            </xs:documentation>
         </xs:annotation>
      </xs:attribute>

      <xs:attribute name="updated" type="xs:dateTime" use="required">
         <xs:annotation>
            <xs:documentation>
              The UTC date this resource metadata description was last updated.
            </xs:documentation>
            <xs:documentation>
              This timestamp must not be in the future.  This time is
              not required to be accurate; it should be at least
              accurate to the day.  Any insignificant time fields
              should be set to zero. 
            </xs:documentation>
         </xs:annotation>
      </xs:attribute>

      <xs:attribute name="status" use="required">
         <xs:annotation>
            <xs:documentation>
              a tag indicating whether this resource is believed to be still
              actively maintained.
            </xs:documentation>
         </xs:annotation>
         <xs:simpleType>
            <xs:restriction base="xs:string">
               <xs:enumeration value="active">
                 <xs:annotation>
                   <xs:documentation>
                      resource is believed to be currently maintained, and its
                      description is up to date (default). 
                   </xs:documentation>
                 </xs:annotation>
               </xs:enumeration>
               <xs:enumeration value="inactive">
                 <xs:annotation>
                   <xs:documentation>
                     resource is apparently not being maintained at the present.
                   </xs:documentation>
                 </xs:annotation>
               </xs:enumeration>
               <xs:enumeration value="deleted">
                 <xs:annotation>
                   <xs:documentation>
                      resource publisher has explicitly deleted the resource.
                   </xs:documentation>
                 </xs:annotation>
               </xs:enumeration>
            </xs:restriction>
         </xs:simpleType>
      </xs:attribute>
   </xs:complexType>

   <xs:simpleType name="ValidationLevel">
     <xs:annotation>
       <xs:documentation>
         the allowed values for describing the resource descriptions
         and interfaces.  
       </xs:documentation>
       <xs:documentation>
         See the RM (v1.1, section 4) for more guidance on the use of
         these values.  
       </xs:documentation>
     </xs:annotation>
     <xs:restriction base="xs:integer">
        <xs:whiteSpace value="collapse"/>
        <xs:enumeration value="0">
          <xs:annotation>
            <xs:documentation>
              The resource has a description that is stored in a
              registry. This level does not imply a compliant
              description. 
            </xs:documentation>
          </xs:annotation>
        </xs:enumeration>
        <xs:enumeration value="1">
          <xs:annotation>
            <xs:documentation>
              In addition to meeting the level 0 definition, the
              resource description conforms syntactically to this
              standard and to the encoding scheme used. 
            </xs:documentation>
          </xs:annotation>
        </xs:enumeration>
        <xs:enumeration value="2">
          <xs:annotation>
            <xs:documentation>
              In addition to meeting the level 1 definition, the
              resource description refers to an existing resource that
              has demonstrated to be functionally compliant. 
            </xs:documentation>
            <xs:documentation>
              When the resource is a service, it is consider to exist
              and functionally compliant if use of the
              service accessURL responds without error when used as
              intended by the resource. If the service is a standard
              one, it must also demonstrate the response is syntactically 
              compliant with the service standard in order to be
              considered functionally compliant. If the resource is
              not a service, then the ReferenceURL must be shown to
              return a document without error. 
            </xs:documentation>
          </xs:annotation>
        </xs:enumeration>
        <xs:enumeration value="3">
          <xs:annotation>
            <xs:documentation>
              In addition to meeting the level 2 definition, the
              resource description has been inspected by a human and
              judged to comply semantically to this standard as well
              as meeting any additional minimum quality criteria (e.g.,
              providing values for important but non-required
              metadata) set by the human inspector.
            </xs:documentation>
          </xs:annotation>
        </xs:enumeration>
        <xs:enumeration value="4">
          <xs:annotation>
            <xs:documentation>
              In addition to meeting the level 3 definition, the
              resource description meets additional quality criteria
              set by the human inspector and is therefore considered
              an excellent description of the resource. Consequently,
              the resource is expected to be operate well as part of a
              VO application or research study.
            </xs:documentation>
          </xs:annotation>
        </xs:enumeration>
     </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Validation">
     <xs:annotation>
       <xs:documentation>
         a validation stamp combining a validation level and the ID of 
         the validator.
       </xs:documentation>
     </xs:annotation>
     <xs:simpleContent>
       <xs:extension base="vr:ValidationLevel">
         <xs:attribute name="validatedBy" type="vr:IdentifierURI" 
                       use="required">
           <xs:annotation>
             <xs:documentation>
               The IVOA ID of the registry or organisation that
               assigned the validation level.  
             </xs:documentation>
           </xs:annotation>
         </xs:attribute>
       </xs:extension>
     </xs:simpleContent>
   </xs:complexType>

   <xs:simpleType name="AuthorityID">
     <xs:restriction base="xs:token">
       <xs:pattern value="[\w\d][\w\d\-_\.!~\*'\(\)\+=]{2,}"/>
     </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="ResourceKey">
     <xs:restriction base="xs:token">
       <xs:pattern value="[\w\d\-_\.!~\*'\(\)\+=]+(/[\w\d\-_\.!~\*'\(\)\+=]+)*"/>
     </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="IdentifierURI">
     <xs:restriction base="xs:anyURI">
       <xs:pattern value="ivo://[\w\d][\w\d\-_\.!~\*'\(\)\+=]{2,}(/[\w\d\-_\.!~\*'\(\)\+=]+(/[\w\d\-_\.!~\*'\(\)\+=]+)*)?"/>
     </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="ShortName">
     <xs:annotation>
       <xs:documentation>
         a short name or abbreviation given to something.
       </xs:documentation>
       <xs:documentation>
         This name will be used where brief annotations for
         the resource name are required.  Applications may 
         use to refer to this resource in a compact display.   
       </xs:documentation>
       <xs:documentation>
         One word or a few letters is recommended.  No more
         than sixteen characters are allowed.
       </xs:documentation>
     </xs:annotation>

     <xs:restriction base="xs:token">
        <xs:maxLength value="16"/>
     </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Curation">
     <xs:annotation>
       <xs:documentation>
         Information regarding the general curation of a resource
       </xs:documentation>
     </xs:annotation>

     <xs:sequence>
       <xs:element name="publisher" type="vr:ResourceName">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Publisher</vm:dcterm>
             </xs:appinfo>
             <xs:documentation>
               Entity (e.g. person or organisation) responsible for making the 
               resource available
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="creator" type="vr:Creator" 
                   minOccurs="0" maxOccurs="unbounded">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Creator</vm:dcterm>
             </xs:appinfo>
             <xs:documentation>
                The entity (e.g. person or organisation) primarily responsible 
                for creating the content or constitution of the resource.
             </xs:documentation>
             <xs:documentation>
                A logo need only be provided for the first occurance.
                When multiple logos are supplied via multiple creator 
                elements, the application is free to choose which to
                use. 
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="contributor" type="vr:ResourceName"
                   minOccurs="0" maxOccurs="unbounded">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Contributor</vm:dcterm>
             </xs:appinfo>
             <xs:documentation>
               Entity responsible for contributions to the content of
               the resource
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="date" type="vr:Date" 
                   minOccurs="0" maxOccurs="unbounded">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Date</vm:dcterm>
             </xs:appinfo>
             <xs:documentation>
               Date associated with an event in the life cycle of the
               resource.  
             </xs:documentation>
             <xs:documentation>
               This will typically be associated with the creation or 
               availability (i.e., most recent release or version) of
               the resource.  Use the role attribute to clarify.
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="version" type="xs:token" minOccurs="0">
          <xs:annotation>
             <xs:documentation>
               Label associated with creation or availablilty of a version of 
               a resource.
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="contact" type="vr:Contact" maxOccurs="unbounded">
          <xs:annotation>
             <xs:documentation>
               Information that can be used for contacting someone with
               regard to this resource.
             </xs:documentation>
          </xs:annotation>
       </xs:element>

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

   <xs:complexType name="ResourceName">
     <xs:annotation>
       <xs:documentation>
         the name of a potentially registered resource.  That is, the entity
         referred to may have an associated identifier.
       </xs:documentation>
     </xs:annotation>

     <xs:simpleContent>
       <xs:extension base="xs:token"> 

         <xs:attribute name="ivo-id" type="vr:IdentifierURI">
            <xs:annotation>
              <xs:documentation>
                The URI form of the IVOA identifier for the resource refered to
              </xs:documentation>
            </xs:annotation>
         </xs:attribute>

       </xs:extension>       
     </xs:simpleContent>
   </xs:complexType>   

   <xs:complexType name="Contact">
     <xs:annotation>
        <xs:documentation>
          Information that can be used for contacting someone
        </xs:documentation>
     </xs:annotation>
     <xs:sequence>
        <xs:element name="name" type="vr:ResourceName">
           <xs:annotation>
              <xs:documentation>
                  the name or title of the contact person.
              </xs:documentation>
              <xs:documentation>
                  This can be a person's name, e.g. "John P. Jones" or
                  a group, "Archive Support Team".
              </xs:documentation>
           </xs:annotation>
        </xs:element>

        <xs:element name="address" type="xs:token" minOccurs="0">
           <xs:annotation>
              <xs:documentation>the contact mailing address</xs:documentation>
              <xs:documentation>
                All components of the mailing address are given in one
                string, e.g. "3700 San Martin Drive, Baltimore, MD 21218 USA".
              </xs:documentation>
           </xs:annotation>
        </xs:element>

        <xs:element name="email" type="xs:token" minOccurs="0">
           <xs:annotation>
              <xs:documentation>the contact email address</xs:documentation>
           </xs:annotation>
        </xs:element>

        <xs:element name="telephone" type="xs:token" minOccurs="0">
           <xs:annotation>
              <xs:documentation>the contact telephone number</xs:documentation>
              <xs:documentation>
                Complete international dialing codes should be given, e.g.
                "+1-410-338-1234".
              </xs:documentation>
           </xs:annotation>
        </xs:element>

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

   <xs:complexType name="Creator">
      <xs:annotation>
         <xs:documentation>
            The entity (e.g. person or organisation) primarily responsible 
            for creating something
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
        <xs:element name="name" type="vr:ResourceName">
           <xs:annotation>
              <xs:documentation>
                  the name or title of the creating person or organization
              </xs:documentation>
              <xs:documentation>
                  Users of the creation should use this name in
                  subsequent credits and acknowledgements.
              </xs:documentation>
           </xs:annotation>
        </xs:element>

        <xs:element name="logo" type="xs:anyURI" minOccurs="0">
           <xs:annotation>
              <xs:documentation>
                URL pointing to a graphical logo, which may be used to help 
                identify the information source
              </xs:documentation>
           </xs:annotation>
        </xs:element>

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

   <xs:complexType name="Date">
      <xs:simpleContent>
         <xs:extension base="vr:UTCDateTime">
           <xs:attribute name="role" type="xs:string" default="representative">
             <xs:annotation>
               <xs:documentation>
                 A string indicating what the date refers to.  
               </xs:documentation>
               <xs:documentation>
                 While this vocabulary is uncontrolled, recognized strings 
                 include "creation", indicating the date that the resource 
                 itself was created, and "update", indicating when the
                 resource was updated last.  The default value, 
                 "representative", means that the date is a rough 
                 representation of the time coverage of the resource.
               </xs:documentation>
               <xs:documentation>
                 Note that this date refers to the resource; dates describing
                 the metadata description of the resource are handled by
                 the "created" and "updated" attributes of the Resource 
                 element. 
               </xs:documentation>
             </xs:annotation>
           </xs:attribute>
         </xs:extension>
      </xs:simpleContent>
   </xs:complexType>

   <xs:complexType name="Content">
     <xs:annotation>
       <xs:documentation>
         Information regarding the general content of a resource
       </xs:documentation>
     </xs:annotation>

     <xs:sequence>
       <xs:element name="subject" type="xs:token" maxOccurs="unbounded">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Subject</vm:dcterm>
             </xs:appinfo>           
             <xs:documentation>
               a topic, object type, or other descriptive keywords 
               about the resource.  
             </xs:documentation>
             <xs:documentation>
               Terms for Subject should be drawn from the IAU Astronomy 
               Thesaurus (http://msowww.anu.edu.au/library/thesaurus/).
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="description" type="xs:token">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Description</vm:dcterm>
             </xs:appinfo>           
             <xs:documentation>
               An account of the nature of the resource
             </xs:documentation>
             <xs:documentation>
               The description may include but is not limited to an abstract, 
               table of contents, reference to a graphical representation of
               content or a free-text account of the content.
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="source" type="vr:Source" minOccurs="0">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Source</vm:dcterm>
             </xs:appinfo>
             <xs:documentation>
                a bibliographic reference from which the present resource is 
                derived or extracted.  
             </xs:documentation>
             <xs:documentation>
                This is intended to point to an article in the published 
                literature.  An ADS Bibcode is recommended as a value when 
                available.    
             </xs:documentation>
          </xs:annotation>
       </xs:element>
       
       <xs:element name="referenceURL" type="xs:anyURI">
          <xs:annotation>
             <xs:documentation>
                URL pointing to a human-readable document describing this 
                resource.   
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="type" type="vr:Type" 
                   minOccurs="0" maxOccurs="unbounded">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Type</vm:dcterm>
             </xs:appinfo>
             <xs:documentation>
               Nature or genre of the content of the resource
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="contentLevel" type="vr:ContentLevel" 
                   minOccurs="0" maxOccurs="unbounded">
          <xs:annotation>
             <xs:appinfo>
               <vm:dcterm>Subject</vm:dcterm>
               <vm:dcterm>Subject.ContentLevel</vm:dcterm>
             </xs:appinfo>           
             <xs:documentation>
                Description of the content level or intended audience
             </xs:documentation>
          </xs:annotation>
       </xs:element>

       <xs:element name="relationship" type="vr:Relationship" 
                   minOccurs="0" maxOccurs="unbounded">
          <xs:annotation>
             <xs:documentation>
               a description of a relationship to another resource.  
             </xs:documentation>
             <xs:documentation>
                Because this element's type is abstract, an xsi:type must be 
                to indicate the set of relationship types that are valid.
             </xs:documentation>
          </xs:annotation>
       </xs:element>
       
     </xs:sequence>
      
   </xs:complexType>

   <xs:complexType name="Source">
      <xs:simpleContent>
         <xs:extension base="xs:token">
           <xs:attribute name="format" type="xs:string">
             <xs:annotation>
               <xs:documentation>
                 The reference format.  Recognized values include "bibcode", 
                 referring to a standard astronomical bibcode 
                 (http://cdsweb.u-strasbg.fr/simbad/refcode.html).  
               </xs:documentation>
             </xs:annotation>
           </xs:attribute>
         </xs:extension>
      </xs:simpleContent>
   </xs:complexType>

   <xs:simpleType name="Type">
     <xs:restriction base="xs:token">
         <xs:enumeration value="Other">
           <xs:annotation>
             <xs:documentation>
               resource that does not fall into any of the category names
               currently defined.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Archive">
           <xs:annotation>
             <xs:documentation>
               Collection of pointed observations
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Bibliography">
           <xs:annotation>
             <xs:documentation>
               Collection of bibliographic reference, abstracts, and 
               publications
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Catalog">
           <xs:annotation>
             <xs:documentation>
               Collection of derived data, primarily in tabular form
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Journal">
           <xs:annotation>
             <xs:documentation>
               Collection of scholarly publications under common editorial 
               policy
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Library">
           <xs:annotation>
             <xs:documentation>
               Collection of published materials (journals, books, etc.)
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Simulation">
           <xs:annotation>
             <xs:documentation>
               Theoretical simulation or model
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Survey">
           <xs:annotation>
             <xs:documentation>
               Collection of observations covering substantial and
               contiguous areas of the sky
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Transformation">
           <xs:annotation>
             <xs:documentation>
               A service that transforms data
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Education">
           <xs:annotation>
             <xs:documentation>
               Collection of materials appropriate for educational use, such
               as teaching resources, curricula, etc.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Outreach">
           <xs:annotation>
             <xs:documentation>
               Collection of materials appropriate for public outreach, such
               as press releases and photo galleries
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="EPOResource">
           <xs:annotation>
             <xs:documentation>
               Collection of materials that may be suitable for EPO
               products but which are not in final product form, as in Type 
               Outreach or Type Education.  EPOResource would apply,
               e.g., to archives with easily accessed preview images or to
               surveys with easy-to-use images.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Animation">
           <xs:annotation>
             <xs:documentation>
               Animation clips of astronomical phenomena
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Artwork">
           <xs:annotation>
             <xs:documentation>
               Artists' renderings of astronomical phenomena or objects
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Background">
           <xs:annotation>
             <xs:documentation>
               Background information on astronomical phenomena or objects
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="BasicData">
           <xs:annotation>
             <xs:documentation>
               Compilations of basic astronomical facts about objects,
               such as approximate distance or membership in constellation.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Historical">
           <xs:annotation>
             <xs:documentation>
               Historical information about astronomical objects
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Photographic">
           <xs:annotation>
             <xs:documentation>
               Publication-quality photographs of astronomical objects
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Press">
           <xs:annotation>
             <xs:documentation>
               Press releases about astronomical objects
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Organisation">
           <xs:annotation>
             <xs:documentation>
               An organization that is a publisher or curator of other 
               resources.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Project">
           <xs:annotation>
             <xs:documentation>
               A project that is a publisher or curator of other resources
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Registry">
           <xs:annotation>
             <xs:documentation>
               a query service for which response is a structured
               description of resources.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
       </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="ContentLevel">
       <xs:restriction base="xs:token">
         <xs:enumeration value="General">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for all users
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Elementary Education">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for use in elementary
               education (e.g. approximate ages 6-11)
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Middle School Education">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for use in middle
               school education (e.g. approximate ages 11-14)
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Secondary Education">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for use in elementary
               education (e.g. approximate ages 14-18)
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Community College">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for use in 
               community/junior college or early university education.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="University">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for use in
               university education
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Research">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for
               supporting scientific research.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Amateur">
           <xs:annotation>
             <xs:documentation>
               Resource provides information of interest to
               amateur astronomers.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="Informal Education">
           <xs:annotation>
             <xs:documentation>
               Resource provides information appropriate for education
               at museums, planetariums, and other centers of informal learning.
             </xs:documentation>
           </xs:annotation>
         </xs:enumeration>
       </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Relationship">
      <xs:annotation>
         <xs:documentation>
           A description of the relationship between one resource and one or
           more other resources.
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="relationshipType" type="xs:token">
            <xs:annotation>
               <xs:documentation>
                  the named type of relationship
               </xs:documentation>
               <xs:documentation>
                  The VOResource Core specification defines a standard
                  set of names that are not enforced by this schema,
                  but are otherwise required by the spec.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="relatedResource" type="vr:ResourceName" 
                     minOccurs="1" maxOccurs="unbounded">
            <xs:annotation>
               <xs:documentation>
                  the name of resource that this resource is related to.
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <!--
     -  The Organisation resource type
     -->

   <xs:complexType name="Organisation">
      <xs:annotation>
         <xs:documentation>
           A named group of one or more persons brought together to pursue 
           participation in VO applications.  
         </xs:documentation>
         <xs:documentation>
           According to the Resource Metadata Recommendation, organisations 
           "can be hierarchical and range in size and scope.  At a high level, 
           an organisation could be a university, observatory, or government
           agency.  At a finer level, it could be a specific scientific 
           project, mission, or individual researcher."  
         </xs:documentation>
         <xs:documentation>
           The main purpose of an organisation as a registered resource is 
           to serve as a publisher of other resources.  
         </xs:documentation>
      </xs:annotation>
      <xs:complexContent>
         <xs:extension base="vr:Resource">
            <xs:sequence>

               <xs:element name="facility" type="vr:ResourceName"
                           minOccurs="0" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:appinfo>
                       <vm:dcterm>Subject</vm:dcterm>
                     </xs:appinfo>
                     <xs:documentation>
                       the observatory or facility used to collect the data 
                       contained or managed by this resource.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="instrument" type="vr:ResourceName"
                           minOccurs="0" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:appinfo>
                       <vm:dcterm>Subject</vm:dcterm>
                       <vm:dcterm>Subject.Instrument</vm:dcterm>
                     </xs:appinfo>
                     <xs:documentation>
                       the Instrument used to collect the data contain or 
                       managed by a resource.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

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

   <!--
     -  The Service resource type
     -->

   <xs:complexType name="Service">
      <xs:annotation>
         <xs:documentation>
           a resource that can be invoked by a client to perform some action
           on its behalf.  
         </xs:documentation>
      </xs:annotation>
      <xs:complexContent>
         <xs:extension base="vr:Resource">
            <xs:sequence>

               <xs:element name="rights" type="vr:Rights" 
                           minOccurs="0" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:appinfo>
                       <vm:dcterm>Rights</vm:dcterm>
                     </xs:appinfo>           
                     <xs:documentation>
                       Information about rights held in and over the resource.
                     </xs:documentation>
                     <xs:documentation>
                       This should be repeated for all Rights values that apply.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="capability" type="vr:Capability" 
                           minOccurs="0" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        a description of a general capability of the
                        service and how to use it.
                     </xs:documentation>
                     <xs:documentation>
                        This describes a general function of the
                        service, usually in terms of a standard
                        service protocol (e.g. SIA), but not
                        necessarily.  
                     </xs:documentation>
                     <xs:documentation>
                        A service can have many capabilities
                        associated with it, each reflecting different
                        aspects of the functionality it provides.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>
            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:simpleType name="Rights">
      <xs:restriction base="xs:token">
         <xs:enumeration value="public">
            <xs:annotation>
               <xs:documentation>
                  unrestricted, public access is allowed without 
                  authentication.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="secure">
            <xs:annotation>
               <xs:documentation>
                  authenticated, public access is allowed.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>
         <xs:enumeration value="proprietary">
            <xs:annotation>
               <xs:documentation>
                  only proprietary access is allowed with authentication.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>
      </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Capability">
      <xs:annotation>
         <xs:documentation>
            a description of what the service does (in terms of 
            context-specific behavior), and how to use it (in terms of
            an interface)
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="validationLevel" type="vr:Validation"
                     minOccurs="0" maxOccurs="unbounded">
            <xs:annotation>
               <xs:documentation>
                  A numeric grade describing the quality of the
                  capability description and interface, when applicable, 
                  to be used to indicate the confidence an end-user
                  can put in the resource as part of a VO application
                  or research study. 
               </xs:documentation>
               <xs:documentation>
                  See vr:ValidationLevel for an explanation of the
                  allowed levels.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="description" type="xs:token" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  A human-readable description of what this capability 
                  provides as part of the over-all service 
               </xs:documentation>
               <xs:documentation>
                  Use of this optional element is especially encouraged when
                  this capability is non-standard and is one of several 
                  capabilities listed.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="interface" type="vr:Interface" 
                     minOccurs="0" maxOccurs="unbounded">
            <xs:annotation>
               <xs:documentation>
                  a description of how to call the service to access
                  this capability
               </xs:documentation>
               <xs:documentation>
                  Since the Interface type is abstract, one must describe
                  the interface using a subclass of Interface, denoting
                  it via xsi:type.
               </xs:documentation>
               <xs:documentation>
                  Multiple occurances can describe different interfaces to 
                  the logically same capability--i.e. data or functionality.
                  That is, the inputs accepted and the output provides should
                  be logically the same.  For example, a WebBrowser interface
                  given in addition to a WebService interface would simply 
                  provide an interactive, human-targeted interface to the 
                  underlying WebService interface.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>

      <xs:attribute name="standardID" type="xs:anyURI">
         <xs:annotation>
            <xs:documentation>
               A URI identifier for a standard service. 
            </xs:documentation>
            <xs:documentation>
               This provides a unique way to refer to a service
               specification standard, such as a Simple Image Access service.
               The use of an IVOA identifier here implies that a
               VOResource description of the standard is registered and 
               accessible.  
            </xs:documentation>
         </xs:annotation>
      </xs:attribute>
   </xs:complexType>

   <xs:complexType name="Interface" abstract="true">
      <xs:annotation>
         <xs:documentation>
            A description of a service interface.
         </xs:documentation>
         <xs:documentation>
            Since this type is abstract, one must use an Interface subclass
            to describe an actual interface.
         </xs:documentation>
         <xs:documentation>
           Additional interface subtypes (beyond WebService and WebBrowser) are 
           defined in the VODataService schema.
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="accessURL" type="vr:AccessURL"
                     minOccurs="1" maxOccurs="unbounded">
            <xs:annotation>
               <xs:documentation>
                 The URL (or base URL) that a client uses to access the
                 service.  How this URL is to be interpreted and used 
                 depends on the specific Interface subclass
               </xs:documentation>
               <xs:documentation>
                 When more than one URL is given, each represents an
                 alternative (i.e. mirror) endpoint whose behavior is
                 identical to all the other accessURLs listed.  
               </xs:documentation>
               <xs:documentation>
                 Editor's note: this element assumes that
                 all registered services are inherently web based.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="securityMethod" type="vr:SecurityMethod"
                     minOccurs="0" maxOccurs="unbounded">
            <xs:annotation>
               <xs:documentation>
                  the mechanism the client must employ to gain secure
                  access to the service.  
               </xs:documentation>
               <xs:documentation>
                  when more than one method is listed, each one must
                  be employed to gain access.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

      </xs:sequence>

      <xs:attribute name="version" type="xs:string" default="1.0">
         <xs:annotation>
            <xs:documentation>
               The version of a standard interface specification that this 
               interface complies with.  When the interface is
               provided in the context of a Capability element, then
               the standard being refered to is the one identified by
               the Capability's standardID element.  If the standardID
               is not provided, the meaning of this attribute is
               undefined.  
            </xs:documentation>
         </xs:annotation>
      </xs:attribute>

      <xs:attribute name="role" type="xs:NMTOKEN">
         <xs:annotation>
            <xs:documentation>
               A tag name the identifies the role the interface plays
               in the particular capability.  If the value is equal to
               "std" or begins with "std:", then the interface refers
               to a standard interface defined by the standard
               referred to by the capability's standardID attribute.  
            </xs:documentation>
            <xs:documentation>
               For an interface complying with some registered
               standard (i.e. has a legal standardID), the role can be
               match against interface roles enumerated in standard 
               resource record.  The interface descriptions in
               the standard record can provide default descriptions 
               so that such details need not be repeated here.  
            </xs:documentation>
         </xs:annotation>
      </xs:attribute>
   </xs:complexType>

   <xs:complexType name="AccessURL">
     <xs:simpleContent>
       <xs:extension base="xs:anyURI">
         <xs:attribute name="use">
           <xs:annotation>
             <xs:documentation>
               A flag indicating whether this should be interpreted as a base
               URL, a full URL, or a URL to a directory that will produce a 
               listing of files.
             </xs:documentation>
             <xs:documentation>
               The default value assumed when one is not given depends on the 
               context.  
             </xs:documentation>
           </xs:annotation>
           <xs:simpleType>
             <xs:restriction base="xs:NMTOKEN">
               <xs:enumeration value="full">
                 <xs:annotation>
                   <xs:documentation>
                     Assume a full URL--that is, one that can be invoked 
                     directly without alteration.  This usually returns a 
                     single document or file.  
                   </xs:documentation>
                 </xs:annotation>
               </xs:enumeration>
               <xs:enumeration value="base">
                 <xs:annotation>
                   <xs:documentation>
                     Assume a base URL--that is, one requiring an extra portion
                     to be appended before being invoked.  
                   </xs:documentation>
                 </xs:annotation>
               </xs:enumeration>
               <xs:enumeration value="dir">
                 <xs:annotation>
                   <xs:documentation>
                     Assume URL points to a directory that will return a listing
                     of files.  
                   </xs:documentation>
                 </xs:annotation>
               </xs:enumeration>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:extension>
     </xs:simpleContent>
   </xs:complexType>

   <xs:complexType name="SecurityMethod">
      <xs:annotation>
         <xs:documentation>
            a description of a security mechanism.
         </xs:documentation>
         <xs:documentation>
            this type only allows one to refer to the mechanism via a
            URI.  Derived types would allow for more metadata.  
         </xs:documentation>
      </xs:annotation>

      <xs:sequence/>

      <xs:attribute name="standardID" type="xs:anyURI">
         <xs:annotation>
            <xs:documentation>
               A URI identifier for a standard security mechanism. 
            </xs:documentation>
            <xs:documentation>
               This provides a unique way to refer to a security
               specification standard.  The use of an IVOA identifier here 
               implies that a VOResource description of the standard is 
               registered and accessible.  
            </xs:documentation>
         </xs:annotation>
      </xs:attribute>

   </xs:complexType>

   <xs:complexType name="WebBrowser">
      <xs:annotation>
         <xs:documentation>
            A (form-based) interface intended to be accesed interactively 
            by a user via a web browser.
         </xs:documentation>
         <xs:documentation>
            The accessURL represents the URL of the web form itself.
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="vr:Interface">
            <xs:sequence/>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="WebService">
      <xs:annotation>
         <xs:documentation>
            A Web Service that is describable by a WSDL document.
         </xs:documentation>
         <xs:documentation>
            The accessURL element gives the Web Service's endpoint URL.
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="vr:Interface">
            <xs:sequence>
               <xs:element name="wsdlURL" type="xs:anyURI"
                           minOccurs="0" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        The location of the WSDL that describes this
                        Web Service.  If not provided, the location is 
                        assumed to be the accessURL with "?wsdl" appended.
                     </xs:documentation>
                     <xs:documentation>
                        Multiple occurances should represent mirror copies of 
                        the same WSDL file.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>
            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

</xs:schema>
