module network-topology {

    yang-version 1;

    namespace
      "urn:TBD:params:xml:ns:yang:network-topology";

    prefix nt;

    import ietf-inet-types {
      prefix inet;
      revision-date "2010-09-24";
    }

    organization "TBD";

    contact "WILL-BE-DEFINED-LATER";

    description
      "This module defines a model for the topology of a network.
        Key design decisions are as follows:
        A topology consists of a set of nodes and links.
        Links are point-to-point and unidirectional.
        Bidirectional connections need to be represented through
        two separate links.
        Multipoint connections, broadcast domains etc can be represented
        through a hierarchy of nodes, then connecting nodes at
        upper layers of the hierarchy.";

    revision "2013-10-21" {
      description "Initial revision.";
    }


    typedef topology-id {
      type inet:uri;
      description
        "An identifier for a topology.";
    }

    typedef node-id {
      type inet:uri;
      description
        "An identifier for a node in a topology.
            The identifier may be opaque.
            The identifier SHOULD be chosen such that the same node in a
            real network topology will always be identified through the
            same identifier, even if the model is instantiated in separate
            datastores. An implementation MAY choose to capture semantics
            in the identifier, for example to indicate the type of node
            and/or the type of topology that the node is a part of.";
    }

    typedef link-id {
      type inet:uri;
      description
        "An identifier for a link in a topology.
            The identifier may be opaque.
            The identifier SHOULD be chosen such that the same link in a
            real network topology will always be identified through the
            same identifier, even if the model is instantiated in separate
            datastores. An implementation MAY choose to capture semantics
            in the identifier, for example to indicate the type of link
            and/or the type of topology that the link is a part of.";
    }

    typedef tp-id {
      type inet:uri;
      description
        "An identifier for termination points on a node.
            The identifier may be opaque.
            The identifier SHOULD be chosen such that the same TP in a
            real network topology will always be identified through the
            same identifier, even if the model is instantiated in separate
            datastores. An implementation MAY choose to capture semantics
            in the identifier, for example to indicate the type of TP
            and/or the type of node and topology that the TP is a part of.";
    }

    typedef tp-ref {
      type leafref {
        path "/network-topology/topology/node/termination-point/tp-id";
      }
      description
        "A type for an absolute reference to a termination point.
            (This type should not be used for relative references.
            In such a case, a relative path should be used instead.)";
    }

    typedef topology-ref {
      type leafref {
        path "/network-topology/topology/topology-id";
      }
      description
        "A type for an absolute reference a topology instance.";
    }

    typedef node-ref {
      type leafref {
        path "/network-topology/topology/node/node-id";
      }
      description
        "A type for an absolute reference to a node instance.
            (This type should not be used for relative references.
            In such a case, a relative path should be used instead.)";
    }

    typedef link-ref {
      type leafref {
        path "/network-topology/topology/link/link-id";
      }
      description
        "A type for an absolute reference a link instance.
            (This type should not be used for relative references.
            In such a case, a relative path should be used instead.)";
    }

    grouping tp-attributes {
      description
        "The data objects needed to define a termination point.
            (This only includes a single leaf at this point, used
            to identify the termination point.)
            Provided in a grouping so that in addition to the datastore,
            the data can also be included in notifications.";
      leaf tp-id {
        type tp-id;
      }

      leaf-list tp-ref {
        type tp-ref;
        config false;
        description
          "The leaf list identifies any termination points that the
                termination point is dependent on, or maps onto.
                Those termination points will themselves be contained
                in a supporting node.
                This dependency information can be inferred from
                the dependencies between links.  For this reason,
                this item is not separately configurable.  Hence no
                corresponding constraint needs to be articulated.
                The corresponding information is simply provided by the
                implementing system.";
      }
    }  // grouping tp-attributes

    grouping node-attributes {
      description
        "The data objects needed to define a node.
            The objects are provided in a grouping so that in addition to
            the datastore, the data can also be included in notifications
            as needed.";
      leaf node-id {
        type node-id;
        description
          "The identifier of a node in the topology.
                A node is specific to a topology to which it belongs.";
      }

      list supporting-node {
        key "node-ref";
        description
          "This list defines vertical layering information for nodes.
                It allows to capture for any given node, which node (or nodes)
                in the corresponding underlay topology it maps onto.
                A node can map to zero, one, or more nodes below it;
                accordingly there can be zero, one, or more elements in the list.
                If there are specific layering requirements, for example
                specific to a particular type of topology that only allows
                for certain layering relationships, the choice
                below can be augmented with additional cases.
                A list has been chosen rather than a leaf-list in order
                to provide room for augmentations, e.g. for
                statistics or priorization information associated with
                supporting nodes.";
        leaf node-ref {
          type node-ref;
        }
      }  // list supporting-node
    }  // grouping node-attributes

    grouping link-attributes {
      leaf link-id {
        type link-id;
        description
          "The identifier of a link in the topology.
                A link is specific to a topology to which it belongs.";
      }

      container source {
        leaf source-node {
          type node-ref;
          mandatory true;
          description
            "Source node identifier, must be in same topology.";
        }

        leaf source-tp {
          type tp-ref;
          description
            "Termination point within source node that terminates the link.";
        }
      }  // container source

      container destination {
        leaf dest-node {
          type node-ref;
          mandatory true;
          description
            "Destination node identifier, must be in same topology.";
        }

        leaf dest-tp {
          type tp-ref;
          description
            "Termination point within destination node that terminates the link.";
        }
      }  // container destination

      list supporting-link {
        key "link-ref";
        leaf link-ref {
          type link-ref;
        }
      }  // list supporting-link
    }  // grouping link-attributes

    container network-topology {
      list topology {
        key "topology-id";
        description
          "
                This is the model of an abstract topology.
                A topology contains nodes and links.
                Each topology MUST be identified by
                unique topology-id for reason that a network could contain many
                topologies.
            ";
        leaf topology-id {
          type topology-id;
          description
            "
                    It is presumed that a datastore will contain many topologies. To
                    distinguish between topologies it is vital to have UNIQUE
                    topology identifiers.
                ";
        }

        leaf server-provided {
          type boolean;
          config false;
          description
            "
                    Indicates whether the topology is configurable by clients,
                    or whether it is provided by the server.  This leaf is

                    populated by the server implementing the model.
                    It is set to false for topologies that are created by a client;
                    it is set to true otherwise.  If it is set to true, any
                    attempt to edit the topology MUST be rejected.
                ";
        }

        container topology-types {
          description
            "This container is used to identify the type, or types
                    (as a topology can support several types simultaneously),
                    of the topology.
                    Topology types are the subject of several integrity constraints
                    that an implementing server can validate in order to
                    maintain integrity of the datastore.
                    Topology types are indicated through separate data nodes;
                    the set of topology types is expected to increase over time.
                    To add support for a new topology, an augmenting module
                    needs to augment this container with a new empty optional
                    container to indicate the new topology type.
                    The use of a container allows to indicate a subcategorization
                    of topology types.
                    The container SHALL NOT be augmented with any data nodes
                    that serve a purpose other than identifying a particular
                    topology type.
                ";
        }  // container topology-types

        list underlay-topology {
          key "topology-ref";
          description
            "Identifies the topology, or topologies, that this topology
                    is dependent on.";
          leaf topology-ref {
            type topology-ref;
          }
        }  // list underlay-topology

        list node {
          must
            "boolean(../underlay-topology[*]/node[./supporting-nodes/node-ref])";
          key "node-id";
          description
            "The list of network nodes defined for the topology.";
          uses node-attributes;

          list termination-point {
            key "tp-id";
            description
              "A termination point can terminate a link.
                        Depending on the type of topology, a termination point could,
                        for example, refer to a port or an interface.";
            uses tp-attributes;
          }  // list termination-point
        }  // list node

        list link {
          must
            "boolean(../underlay-topology/link[./supporting-link])";
          must
            "boolean(../node[./source/source-node])";
          must
            "boolean(../node[./destination/dest-node])";
          must
            "boolean(../node/termination-point[./source/source-tp])";
          must
            "boolean(../node/termination-point[./destination/dest-tp])";
          key "link-id";
          description
            "
                    A Network Link connects a by Local (Source) node and
                    a Remote (Destination) Network Nodes via a set of the
                    nodes' termination points.
                    As it is possible to have several links between the same
                    source and destination nodes, and as a link could potentially
                    be re-homed between termination points, to ensure that we
                    would always know to distinguish between links, every link
                    is identified by a dedicated link identifier.
                    Note that a link models a point-to-point link, not a multipoint
                    link.
                    Layering dependencies on links in underlay topologies are
                    not represented as the layering information of nodes and of
                    termination points is sufficient.
                ";
          uses link-attributes;
        }  // list link
      }  // list topology
    }  // container network-topology
  }  // module network-topology