<!--
  The 'xsd' namespace is the "schema of schemas" as defined by the XSchema
  standard.  The 'xlink' namespace defines the namespace for XLink attributes
  and elements.  The targetNamespace defines the URI of the namespace
  which THIS XSchema is defining.  Other XSchemas should use this URL
  when referring to things defined in this XSchema.
 -->
<xsd:schema xmlns="http://www.ics.uci.edu/pub/arch/xArch/instance.xsd"
            xmlns:xsd="http://www.w3.org/2000/10/XMLSchema"
            xmlns:xlink="http://www.w3.org/1999/xlink"
            targetNamespace="http://www.ics.uci.edu/pub/arch/xArch/instance.xsd">

  <xsd:annotation>
    <xsd:documentation>
      xArch Instances XML Schema 1.0

      Change Log:
         2000-12-06: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Fixed cardinality of 'member' in type Group.
         2000-12-04: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Removed explicit collections from the schema
           and replaced them with Kleene-star type elements
           for more flexibility/extensibility.
         2000-11-18: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Added InterfaceInstanceMappingCollection between
           subarchitecture and set of interface instance
           mappings.
         2000-10-24: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Changed 'archInstances' to 'archInstance'
           Changed interface mapping names from 'from' and
           'to' to 'inner' and 'outer.'
         2000-10-24: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Added xArch root element.
         2000-10-19: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Changed names of Interface to InterfaceInstance.
           Added subarchitectures in connector, component
           instances with interface mappings.
         2000-10-13: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Changed names of Component, Connector, and Link
           to ComponentInstance, ConnectorInstance, and LinkInstance,
           respectively.
         2000-10-12: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Added grouping mechanism with appropriate types.
           Changed name of element archStructure to archInstances.
           Changed name of type ArchStructure to ArchInstances.
           Changed name of file from structure.xsd to instance.xsd
         2000-10-02: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Changed "anchorInterface" name to "anchorOnInterface."
           Changed name of element archCore to archStructure.
           Changed name of type ArchCore to ArchStructure.
           Added id + description to ArchStructure type.
           Changed name from core.xsd to structure.xsd.
         2000-09-28: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Fixed some syntax errors and validated with XSV.
         2000-09-27: Eric M. Dashofy [edashofy@ics.uci.edu]:
           Initial Development

    </xsd:documentation>
  </xsd:annotation>

  <!--
    ELEMENT: xArch

    The xArch element must be the root (top-level) element of an xArch
    document.  Because of the single-inheritance model of XML Schema
    1.0, the contents of xArch are not restricted.  It is expected that
    xArch will contain only tags that are declared as xsd:element in
    this and other schemas (archInstances, for example).
   -->
  <xsd:element name="xArch">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:any minOccurs="0" maxOccurs="unbounded"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <!--
    ELEMENT: archInstance
    
    The archInstance element (of type ArchInstance) is the root element
    that is the aegis over all other elements in the architecture
    structure.  It has four groups of subelements: componentInstances,
    connectorInstances, linkInstances, and groups.  It represents instantiated 
    components, connectors, links, and interfaces in an architecture, as well 
    as different logical groupings of these entities.
   -->
  <xsd:element name="archInstance" type="ArchInstance"/>
  
  <!--
    TYPE: Identifier

    An Identifier is currently defined as an XML ID type.  
    It must be unique in the space of identified things.  
    Most unique entities in this schema and
    extensions to it will have an identifier.  The Identifier
    must be used as an attribute because it is of the 
    xsd:ID type, and this must exist only in attributes, 
    never elements, to retain compatibility with XML 
    1.0 DTD's.
   -->
  <xsd:simpleType name="Identifier">
    <xsd:restriction base="xsd:ID">
      <xsd:minLength value="1"/>
    </xsd:restriction>
  </xsd:simpleType>

  <!--
    TYPE: Description

    A Description is a human-readable string describing
    an entity.
   -->
  <xsd:simpleType name="Description">
    <xsd:restriction base="xsd:string">
    </xsd:restriction>
  </xsd:simpleType>

  <!--
    TYPE: Direction

    A direction specifies the direction of an interface
    entity.  An interface can be "in" (provided) or
    "out" (required).  An "inout" interface represents
    an interface that has parts that are both provided
    and required.
   -->
  <xsd:simpleType name="Direction">
    <xsd:restriction base="xsd:string">
      <xsd:enumeration value="none"/>
      <xsd:enumeration value="in"/>
      <xsd:enumeration value="out"/>
      <xsd:enumeration value="inout"/>
    </xsd:restriction>
  </xsd:simpleType>

  <!--
    TYPE: XMLLink
  
    This type is a schema definition that encapsulates
    the parts of the XLink definition that are useful
    in the xArch context.
   -->
  <xsd:complexType name="XMLLink">
    <xsd:attribute name="type" type="xlink:type"/>
    <xsd:attribute name="href" type="xlink:href"/>
  </xsd:complexType>

  <!--
    TYPE: InterfaceInstance

    The InterfaceInstance type describes an opaque interface for use
    at the instance level.  No semantic information is provided
    at this level.  An opaque interface instance contains an ID,
    description, and a direction.  This may be connected
    to other interface instances via a link.  The direction is
    optional.
   -->
  <xsd:complexType name="InterfaceInstance">
    <xsd:sequence>
      <xsd:element name="description" type="Description"/>
      <xsd:element name="direction"   type="Direction"
                   minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="id"          type="Identifier"/>
  </xsd:complexType>

  <!--
    TYPE: ComponentInstance
  
    The ComponentInstance type describes an opaque component for use
    at the structural level.  No semantic information is provided
    at this level.  An opaque component contains an ID,
    description, and zero or more interface instances.

    A component instance may also have substructure, described
    in the optional subArchitecture tag.  In this case, the
    interfaces on this component are mapped to interfaces
    on subcomponents/subconnectors of this component.
   -->
  <xsd:complexType name="ComponentInstance">
    <xsd:sequence>
      <xsd:element name="description" type="Description"/>
      <xsd:element name="interfaceInstance" 
                   type="InterfaceInstance"
                   minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="subArchitecture"   
                   type="SubArchitecture"
                   minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="id"          type="Identifier"/>
  </xsd:complexType>

  <!--
    TYPE: ConnectorInstance

    The ConnectorInstance type describes an opaque connector for use
    at the structural level.  No semantic information is provided
    at this level.  An opaque connector contains an ID,
    description, and zero or more interface instances.

    A connector instance may also have substructure, described
    in the optional subArchitecture tag.  In this case, the
    interfaces on this connector are mapped to interfaces
    on subcomponents/subconnectors of this connector.
   -->
  <xsd:complexType name="ConnectorInstance">
    <xsd:sequence>
      <xsd:element name="description"       
                   type="Description"/>
      <xsd:element name="interfaceInstance" 
                   type="InterfaceInstance"
                   minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="subArchitecture"   
                   type="SubArchitecture"
                   minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="id"                type="Identifier"/>
  </xsd:complexType>

  <!--
    TYPE: Point

    The Point type describes an endpoint of a link.  All
    links at the instance level exist between interfaces on
    components and connectors.  A Point has an XLink to
    exactly one interfaceInstance.
   -->
  <xsd:complexType name="Point">
    <xsd:sequence>
      <xsd:element name="anchorOnInterface" type="XMLLink"/>
    </xsd:sequence>
  </xsd:complexType>

  <!--
    TYPE: LinkInstance

    The LinkInstance type describes a link between two interface
    instances. All links at the instance level exist between 
    interfaces on components and connectors.  A LinkInstance 
    has an ID, a description, and exactly two endpoints.
   -->
  <xsd:complexType name="LinkInstance">
    <xsd:sequence>
      <xsd:element name="description" type="Description"/>
      <xsd:element name="point" type="Point"
                   minOccurs="2" maxOccurs="2"/>
    </xsd:sequence>
    <xsd:attribute name="id"          type="Identifier"/>
  </xsd:complexType>

  <!--
    TYPE: Group
    
    The Group type describes a logical grouping of architecture
    elements (components, connectors, and links).  Groups may
    also be members of other groups.  As such, the member XLink
    may point at a component instance, a connector instance,
    a link instance, or another group.
   -->
  <xsd:complexType name="Group">
    <xsd:sequence>
      <xsd:element name="description" type="Description"/>
      <xsd:element name="member" type="XMLLink"
                   minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attribute name="id"          type="Identifier"/>
  </xsd:complexType>

  <!-- 
    TYPE: InterfaceInstanceMapping

    The InterfaceInstanceMapping type defines a mapping
    between an interface on a component/connector that has
    a subarchitecture, and the interface within that
    component/connector that the higher-level interface
    represents.  The 'from' XMLLink points to the interface
    on the component with substructure, and the 'to' XMLLink
    points to the interface within the substructure.
  -->
  <xsd:complexType name="InterfaceInstanceMapping">
    <xsd:sequence>
      <xsd:element name="outerInterfaceInstance" type="XMLLink"/>
      <xsd:element name="innerInterfaceInstance" type="XMLLink"/>
    </xsd:sequence>
  </xsd:complexType>

  <!-- 
    TYPE: SubArchitecture

    The SubArchitecture type describes how subarchitectures are included
    at the structure level. The substructure contains an archStructure 
    (containing the subarchitecture) and a set of interface instance
    mappings that map interfaces at the higher-level component/connector
    onto interfaces of one of the lower-level components/connectors.
  -->
  <xsd:complexType name="SubArchitecture">
    <xsd:sequence>
      <xsd:element name="archInstance" type="ArchInstance"/>
      <xsd:element name="interfaceInstanceMapping"
                   type="InterfaceInstanceMapping"
                   minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
  </xsd:complexType>

  <!--
    TYPE: ArchInstance

    The ArchInstance type describes the structural description of
    an architecture instance.  It has no semantic information associated 
    with it.  It is composed of three collections of instances: of connector 
    instances, component instances, and link instances.  It also contains a 
    collection of logical groupings of connector, component, and link instances, 
    which may be used to indicate substructure, distribution, or any other kind
    of group.
    
    This also forms the basis for schema extensions that can more 
    richly describe this skeleton architecture.
   -->
  <xsd:complexType name="ArchInstance">
    <xsd:sequence>
      <xsd:element name="description"       type="Description"/>
      <xsd:element name="componentInstance" type="ComponentInstance"
                   minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="connectorInstance" type="ConnectorInstance"
                   minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="linkInstance"      type="LinkInstance"
                   minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element name="group"             type="Group"
                   minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attribute name="id"                          type="Identifier"/>
  </xsd:complexType>

</xsd:schema>