JSBSimSystem.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <!-- The systems definition -->
  <xs:element name="system">
    <xs:annotation>
      <xs:documentation>
            The system definition can be present any number of times in an aircraft definition. This
            section is used to define an arbitrary system, such as navigation, guidance, or control 
            avionics, electrical systems, etc. The system, autopilot, and flight_control sections of a
            configuration file are all built the same way, using channel elements that contain strings
            of component definitions.
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="property">
          <xs:complexType>
            <xs:simpleContent>
              <xs:extension base="xs:string">
                <xs:attribute name="value" use="optional" type="xs:double"/>
              </xs:extension>
            </xs:simpleContent>
          </xs:complexType>
        </xs:element>
        <xs:element minOccurs="0" maxOccurs="unbounded" ref="channel"/>
      </xs:choice>
      <xs:attribute name="name" use="optional" type="xs:string"/>
      <xs:attribute name="file" use="optional" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Channel -->

  <xs:element name="channel">
    <xs:complexType>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element ref="actuator"/>
        <xs:element ref="aerosurface_scale"/>
        <xs:element ref="integrator"/>
        <xs:element ref="kinematic"/>
        <xs:element ref="lag_filter"/>
        <xs:element ref="lead_lag_filter"/>
        <xs:element ref="pid"/>
        <xs:element ref="pure_gain"/>
        <xs:element ref="scheduled_gain"/>
        <xs:element ref="second_order_filter"/>
        <xs:element ref="sensor"/>
        <xs:element ref="summer"/>
        <xs:element ref="switch"/>
        <xs:element ref="washout_filter"/>
        <xs:element ref="deadband"/>
        <xs:element ref="fcs_function"/>
      </xs:choice>
      <xs:attribute name="name" use="required" type="xs:string">
        <xs:annotation><xs:documentation>
          The name for a channel is simply a brief, descriptive, name. The name
          is not used for anything other than display.
        </xs:documentation></xs:annotation>
      </xs:attribute>
      <xs:attribute name="execute" type="xs:string">
        <xs:annotation><xs:documentation>
          The execute attribute value refers to a property that evaluates to a
          boolean indicating whether the channel should execute or not. If this
          attribute is not supplied, the channel always executes.
        </xs:documentation></xs:annotation>
      </xs:attribute>
    </xs:complexType>
  </xs:element>

  <!-- Lag filter -->

  <xs:element name="lag_filter">
    <xs:complexType>
      <xs:all>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string"/>
        <xs:element name="c1" type="xs:double"/>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" type="xs:string" minOccurs="0"/>
      </xs:all>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Summer -->

  <xs:element name="summer">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" maxOccurs="unbounded"/>
        <xs:element name="bias" type="xs:float" minOccurs="0"/>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" type="xs:string" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Aerosurface scale -->

  <xs:element name="aerosurface_scale">
    <xs:annotation>
      <xs:documentation>
        The aerosurface scale component maps an input value (which must fall within the span specified in the domain element)
        to an output value that falls within the span specified in the range element. For example, if the actual input value is 30% of
        the distance from the minimum to the maximum domain value, the output would be the value corresponding
        to 30% of the span of the range, from the minimum range value.
      </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" minOccurs="1" maxOccurs="1"/>
        <xs:element ref="domain" minOccurs="0" maxOccurs="1"/>
        <xs:element ref="range" minOccurs="1" maxOccurs="1"/>
        <xs:element name="gain" minOccurs="0" maxOccurs="1">
          <xs:annotation>
            <xs:documentation>The Gain element may contain a fixed numeric value, or it may be a property name.</xs:documentation>
          </xs:annotation>
        </xs:element>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:choice>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Kinematic device -->

  <xs:element name="kinematic">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" minOccurs="1" maxOccurs="1"/>
        <xs:element ref="traverse"/>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>
  <xs:element name="traverse">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="setting" minOccurs="1" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:element name="setting">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="position" type="xs:double"/>
        <xs:element name="time" type="xs:double"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <!-- Lead lag filter -->

  <xs:element name="lead_lag_filter">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" minOccurs="1" maxOccurs="1"/>
        <xs:element name="c1" type="xs:double"/>
        <xs:element name="c2" type="xs:double" minOccurs="0"/>
        <xs:element name="c3" type="xs:double" minOccurs="0"/>
        <xs:element name="c4" type="xs:double"/>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Washout filter -->

  <xs:element name="washout_filter">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" maxOccurs="1" minOccurs="1"/>
        <xs:element name="c1" type="xs:double" minOccurs="1" maxOccurs="1"/>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Integrator -->

  <xs:element name="integrator">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" maxOccurs="1" minOccurs="1"/>
        <xs:element name="c1" type="xs:double" minOccurs="1" maxOccurs="1"/>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="trigger" type="xs:string" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- PID controller -->

  <xs:element name="pid">
    <xs:complexType>
      <xs:all>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string"/>
        <xs:element name="kp" type="xs:string" minOccurs="0">
          <xs:annotation><xs:documentation>Specifies the proportional constant value or property.</xs:documentation></xs:annotation>
        </xs:element>
        <xs:element name="ki" minOccurs="0">
          <xs:annotation><xs:documentation>The integrator control action gain.</xs:documentation></xs:annotation>
          <xs:complexType>
            <xs:simpleContent>
              <xs:extension base="xs:string">
                <xs:attribute name="type" default="ab2">
                  <xs:simpleType>
                    <xs:restriction base="xs:string">
                      <xs:enumeration value="rect"><xs:annotation><xs:documentation>Specifies a rectangular integrator.</xs:documentation></xs:annotation></xs:enumeration>
                      <xs:enumeration value="trap"><xs:annotation><xs:documentation>Specifies a trapezoidal integrator.</xs:documentation></xs:annotation></xs:enumeration>
                      <xs:enumeration value="ab2"><xs:annotation><xs:documentation>Specifies an Adams-Bashforth second order integrator. [default]</xs:documentation></xs:annotation></xs:enumeration>
                      <xs:enumeration value="ab3"><xs:annotation><xs:documentation>Specifies an Adams-Bashforth third order integrator.</xs:documentation></xs:annotation></xs:enumeration>
                    </xs:restriction>
                  </xs:simpleType>
                </xs:attribute>                
              </xs:extension>
            </xs:simpleContent>
          </xs:complexType>
        </xs:element>
        <xs:element name="kd" type="xs:float" minOccurs="0">
          <xs:annotation><xs:documentation>The derivative control action gain.</xs:documentation></xs:annotation>
        </xs:element>
        <xs:element name="trigger" type="xs:string" minOccurs="0">
          <xs:annotation><xs:documentation>
            The trigger element provides a way to specify a property that controls
            how the integrator works, and is designed for wind-up protection. If
            the value of the property supplied to the trigger element is 0, there
            is no effect. If the value of the trigger property is non-zero,
            (positive or negative) then the integrator does not integrate and
            holds the last value. If the trigger property value is negative, the
            integrator value is reset to 0.0.
          </xs:documentation></xs:annotation>
        </xs:element>
        <xs:element name="pvdot" type="xs:string" minOccurs="0">
          <xs:annotation>
            <xs:documentation>
              pvdot is the process variable time derivative. If not specified,
              the derivative control action will be determined from the change
              in the input from the last time step (divided by the time step
              size). If pvdot is specified, the specified value will be used
              instead. The difference may be minimal in practice - UNLESS there
              is an unnatural step change in the input value. For instance, if
              the control input (process variable) is alpha, an alphadot value
              is calculated as mentioned from the previous value. If pvdot is
              explicitly specified as alphadot (alphadot is calculated and is
              available as a native property in JSBSim) the results can be
              smoother - particularly if there is a step change in the error
              signal (the input) due to a step change in the target state. To
              be clear, pvdot is meant to be the time derivative of the
              input parameter. If the input to the PID controller is pitch rate
              then pvdot should be pitch acceleration. If altitude is the input
              then pvdot should be altitude rate.
            </xs:documentation>
          </xs:annotation>
        </xs:element>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:all>
      <xs:attribute name="name" type="xs:string" use="required"/>
      <xs:attribute name="type" use="optional">
        <xs:simpleType>
          <xs:restriction base="xs:string">
            <xs:enumeration value="standard">
              <xs:annotation>
                <xs:documentation>
                  Specifies a standard PID controller where the output is defined
                  as:  Output = Kp * (Input + Integrator_value + Kd*Dval), where
                  Dval is the time derivative of the input signel.
                </xs:documentation>
              </xs:annotation>
            </xs:enumeration>
          </xs:restriction>
        </xs:simpleType>
      </xs:attribute>
    </xs:complexType>
  </xs:element>
  
  <!-- Second order filter -->

  <xs:element name="second_order_filter">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string"/>
        <xs:element name="c1" type="xs:double"/>
        <xs:element name="c2" type="xs:double"/>
        <xs:element name="c3" type="xs:double"/>
        <xs:element name="c4" type="xs:double"/>
        <xs:element name="c5" type="xs:double"/>
        <xs:element name="c6" type="xs:double"/>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Pure gain -->

  <xs:element name="pure_gain">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string"/>
        <xs:element name="gain" type="xs:string">
          <xs:annotation>
            <xs:documentation>The Gain element may contain a fixed numeric value, or it may be a property name.</xs:documentation>
          </xs:annotation>
        </xs:element>
        <xs:element ref="clipto" minOccurs="0" maxOccurs="1"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Scheduled gain -->

  <xs:element name="scheduled_gain">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string"/>
        <xs:element ref="table"/>
        <xs:element name="gain" type="xs:string" minOccurs="0" maxOccurs="1">
          <xs:annotation>
            <xs:documentation>The Gain element may contain a fixed numeric value, or it may be a property name.</xs:documentation>
          </xs:annotation>
        </xs:element>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Switch -->

  <xs:element name="switch">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" minOccurs="0"/>
        <xs:element ref="default" minOccurs="0"/>
        <xs:element ref="test" minOccurs="1" maxOccurs="unbounded"/>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Sensor -->

  <xs:element name="sensor">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" maxOccurs="1"/>
        <xs:element name="lag" type="xs:float" maxOccurs="1"/>
        <xs:element ref="noise" maxOccurs="1"/>
        <xs:element ref="quantization" maxOccurs="1"/>
        <xs:element name="drift_rate" type="xs:float" maxOccurs="1"/>
        <xs:element name="bias" type="xs:float" maxOccurs="1"/>
        <xs:element ref="clipto" maxOccurs="1"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Actuator -->

  <xs:element name="actuator">
    <xs:annotation>
      <xs:documentation>
        An actuator component models a general purpose mechanical effector. The actuator can
        exhibit a lag, can be rate- and position-limited, can feature a bias, can have a deadband,
        and it can feature hysteresis.
      </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:all>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" minOccurs="1" type="xs:string"/>
        <xs:element name="lag" type="xs:float" minOccurs="0"/>
        <xs:element name="rate_limit" minOccurs="0" maxOccurs="2">
          <xs:annotation><xs:documentation>
            The rate limit can be specified as a numeric value or as a property.
            Further, an "incr" or "decr" sense attribute to specify which
            direction the rate limit should apply to.
          </xs:documentation></xs:annotation>
          <xs:complexType>
            <xs:simpleContent>
              <xs:extension base="xs:string">
                <xs:attribute name="sense">
                  <xs:annotation><xs:documentation>
                    The sense attribute determines which direction the rate
                    limit applies to. If no sense is given, the rate limit
                    applies to both directions equally. If "incr" is specified
                    then the rate limit applies only to the rate of increase. 
                    If "decr" is specified, then the rate limit applies only to
                    a decreasing rate. The decreasing rate limit - if given - is
                    assumed to be negative - no negative sign is required.
                  </xs:documentation></xs:annotation>
                  <xs:simpleType>
                    <xs:restriction base="xs:string">
                      <xs:enumeration value="incr"><xs:annotation><xs:documentation>Specify this type when the rate limit applies to an increasing rate.</xs:documentation></xs:annotation></xs:enumeration>
                      <xs:enumeration value="decr"><xs:annotation><xs:documentation>Specify this type when the rate limit applies to a decreasing rate.</xs:documentation></xs:annotation></xs:enumeration>
                    </xs:restriction>
                  </xs:simpleType>
                </xs:attribute>
              </xs:extension>
            </xs:simpleContent>
          </xs:complexType>
        </xs:element>
        <xs:element name="bias" type="xs:float" minOccurs="0"/>
        <xs:element name="deadband_width" type="xs:float" minOccurs="0"/>
        <xs:element name="hysteresis_width" type="xs:float" minOccurs="0"/>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:all>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- Deadband -->

  <xs:element name="deadband">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string"/>
        <xs:element name="width" type="xs:float"/>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <!-- FCS function -->
  <xs:element name="fcs_function">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="description" type="xs:string" minOccurs="0"/>
        <xs:element name="input" type="xs:string" minOccurs="0"/>
        <xs:element ref="function"/>
        <xs:element ref="clipto" minOccurs="0"/>
        <xs:element name="output" minOccurs="0" maxOccurs="unbounded" type="xs:string"/>
      </xs:sequence>
      <xs:attribute name="name" use="required" type="xs:string"/>
    </xs:complexType>

  </xs:element>

  <!--

  <xs:group name="functionGroup">
    <xs:sequence>
      <xs:element ref="input"/>
      <xs:element name="function"/>
    </xs:sequence>
  </xs:group>

  <xs:group name="deadbandGroup">
    <xs:sequence>
      <xs:element ref="input"/>
      <xs:element ref="width"/>
    </xs:sequence>
  </xs:group>
 
-->
  <xs:element name="test">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="logic" default="AND" use="optional">
            <xs:simpleType>
              <xs:restriction base="xs:string">
                <xs:enumeration value="OR"/>
                <xs:enumeration value="AND"/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
          <xs:attribute name="value" use="required" type="xs:string"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>
  <xs:element name="width" type="PositiveNumber">
    <xs:annotation>
      <xs:documentation>The width value specifies the width of the deadband - i.e. 
        the total span about zero where the input will be mapped to zero output.</xs:documentation>
    </xs:annotation>
  </xs:element>

  <xs:element name="noise">
    <xs:annotation>
      <xs:documentation>
        The noise can be entered as a percentage of the signal, or as an absolute value.        
      </xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="xs:float">
          <xs:attribute name="variation">
            <xs:simpleType>
              <xs:restriction base="xs:string">
                <xs:enumeration value="PERCENT"/>
                <xs:enumeration value="ABSOLUTE"/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

  <xs:element name="quantization">
    <xs:complexType>
      <xs:all>
        <xs:element name="bits" type="xs:int"/>
        <xs:element name="min" type="xs:float"/>
        <xs:element name="max" type="xs:float"/>
      </xs:all>
      <xs:attribute type="xs:string" name="name"/>
    </xs:complexType>
  </xs:element>

  <xs:element name="clipto">
    <xs:annotation><xs:documentation>
      This element specifies a minimum and/or a maximum limit that the
      associated component will be allowed to have. The result will be
      clipped to the specified limits.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:all>
        <xs:element name="min" type="xs:double" minOccurs="0" maxOccurs="1"/>
        <xs:element name="max" type="xs:double" minOccurs="0" maxOccurs="1"/>
      </xs:all>
    </xs:complexType>
  </xs:element>
  <xs:element name="domain">
    <xs:annotation><xs:documentation>
      The domain defines the minimum and maximum input value allowed.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:all>
        <xs:element name="min" type="xs:float" default="-1"/>
        <xs:element name="max" type="xs:float" default="1"/>
      </xs:all>
    </xs:complexType>
  </xs:element>
  <xs:element name="range">
    <xs:annotation>
      <xs:documentation>The range defines the minimum and maximum output value mapped..</xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:all>
        <xs:element name="min" type="xs:float" default="0"/>
        <xs:element name="max" type="xs:float" default="0"/>
      </xs:all>
    </xs:complexType>
  </xs:element>
  <xs:element name="default">
    <xs:complexType>
      <xs:attribute name="value" type="xs:string"/>
    </xs:complexType>
  </xs:element>

  <xs:element name="table">
    <xs:complexType>
      <xs:sequence>
        <xs:element maxOccurs="unbounded" ref="independentVar"/>
        <xs:element ref="tableData" minOccurs="1" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" use="optional" type="xs:string"/>
    </xs:complexType>
  </xs:element>
  <xs:element name="independentVar">
    <xs:complexType mixed="true">
      <xs:attribute name="lookup" type="xs:string"/>
    </xs:complexType>
  </xs:element>
  <xs:element name="tableData">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="breakPoint" type="xs:double" use="optional"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

  <!-- Functions -->
  <xs:group name="func_group">
    <xs:choice>
      <xs:element ref="table"/>
      <xs:element ref="product"/>
      <xs:element ref="difference"/>
      <xs:element ref="sum"/>
      <xs:element ref="quotient"/>
      <xs:element ref="pow"/>
      <xs:element ref="sqrt"/>
      <xs:element ref="abs"/>
      <xs:element ref="sin"/>
      <xs:element ref="cos"/>
      <xs:element ref="tan"/>
      <xs:element ref="asin"/>
      <xs:element ref="acos"/>
      <xs:element ref="atan"/>
      <xs:element ref="atan2"/>
      <xs:element ref="min"/>
      <xs:element ref="max"/>
      <xs:element ref="avg"/>
      <xs:element ref="fraction"/>
      <xs:element ref="integer"/>
      <xs:element ref="mod"/>
      <xs:element name="random"/>
      <xs:element name="urandom"/>
      <xs:element name="pi"/>
      <xs:element ref="toradians"/>
      <xs:element ref="todegrees"/>
      <xs:element ref="lt"/>
      <xs:element ref="le"/>
      <xs:element ref="gt"/>
      <xs:element ref="ge"/>
      <xs:element ref="eq"/>
      <xs:element ref="nq"/>
      <xs:element ref="and"/>
      <xs:element ref="or"/>
      <xs:element ref="not"/>
      <xs:element ref="ifthen"/>
      <xs:element name="switch"> <!-- Switch element has to go here to disambiguate from FCS switch component -->
        <xs:annotation><xs:documentation>
          Uses the integer value of the first immediate child element as an
          index to select one of the subsequent immediate child elements to
          return the value of.
        </xs:documentation></xs:annotation>
        <xs:complexType>
          <xs:choice minOccurs="3" maxOccurs="unbounded">
            <xs:group ref="func_group"/>
            <xs:element ref="value"/>
            <xs:element ref="property"/>
            <xs:element name="v"/>
            <xs:element name="p"/>
          </xs:choice>
        </xs:complexType>
      </xs:element>
    </xs:choice>
  </xs:group>
  <xs:element name="function">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="description" minOccurs="0" maxOccurs="1"/>
        <xs:group ref="func_group"/>
      </xs:sequence>
      <xs:attribute name="name" use="optional"/>
    </xs:complexType>
  </xs:element>
  <xs:element name="product">
    <xs:annotation><xs:documentation>
      Multiplies together the values of all immediate child elements.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="difference">
    <xs:annotation><xs:documentation>
      Subtracts from the value of the first immediate child element the values of all subsequent immediate child elements. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="sum">
    <xs:annotation><xs:documentation>
      Sums the values of all immediate child elements.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="quotient">
    <xs:annotation><xs:documentation>
      Divides the value of the first immediate child element by the value of the second immediate child element.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="abs">
    <xs:annotation><xs:documentation>
      Returns the absolute value of the immediate child element. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="sqrt">
    <xs:annotation><xs:documentation>
      Returns the square root of the value of the immediate child element.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="toradians">
    <xs:annotation><xs:documentation>
      Converts the argument presumed to be expressed in degrees to radians by
      multiplying the value of the immediate child element by pi/180.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="todegrees">
    <xs:annotation><xs:documentation>
      Converts the argument presumed to be expressed in radians to degrees by
      multiplying the value of the immediate child element by 180/pi.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="pow">
    <xs:annotation><xs:documentation>
      Raises the value of the first immediate child element to the power of the
      value of the second immediate child element.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="sin">
    <xs:annotation><xs:documentation>
      Calculates the sine of the value of the immediate child element (the
      argument is expected to be in radians). 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="cos">
    <xs:annotation><xs:documentation>
      Calculates the cosine of the value of the immediate child element (the
      argument is expected to be in radians). 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="tan">
    <xs:annotation><xs:documentation>
      Calculates the tangent of the value of the immediate child element (the
      argument is expected to be in radians). 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="asin">
    <xs:annotation><xs:documentation>
      Calculates the arcsine (inverse sine) of the value of the immediate child
      element. The value provided should be in the range from -1 to +1. The
      value returned will be expressed in radians, and will be in the range
      from -pi/2 to +pi/2.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="acos">
    <xs:annotation><xs:documentation>
      Calculates the arccosine (inverse cosine) of the value of the immediate
      child element. The value provided should be in the range from -1 to +1.
      The value returned will be expressed in radians, and will be in the range
      from 0 to pi.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="atan">
    <xs:annotation><xs:documentation>
      Calculates the inverse tangent of the value of the immediate child
      element. The value returned will be expressed in radians, and will be in
      the range from -pi/2 to +pi/2.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="1" minOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="atan2">
    <xs:annotation><xs:documentation>
      Calculates the inverse tangent of the value of the immediate child
      elements, Y/X (in that order). It even works for X values near zero.
      The value returned will be expressed in radians, and in the range
      -pi to +pi.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="min">
    <xs:annotation><xs:documentation>
      Returns the smallest value from all the immediate child elements.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="max">
    <xs:annotation><xs:documentation>
      Returns the largest value from all the immediate child elements.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="avg">
    <xs:annotation><xs:documentation>
      Returns the average value of all the immediate child elements. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="2" maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="fraction">
    <xs:annotation><xs:documentation>
      Returns the fractional part of the value of the immediate child element .
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice>
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="integer">
    <xs:annotation><xs:documentation>
      Returns the integer part of the value of the immediate child element. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice>
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="value" type="xs:double"/>
  <xs:element name="mod">
    <xs:annotation><xs:documentation>
      Returns the remainder from the integer division of the value of the first
      immediate child element by the second immediate child element, X/Y
      (X modulo Y). The value returned is the value X-I*Y, for the largest
      integer I such that if Y is nonzero, the result has the same sign as X
      and magnitude less than the magnitude of Y. For instance, the expression
      "5 mod 2" would evaluate to 1 because 5 divided by 2 leaves a quotient of
      2 and a remainder of 1, while "9 mod 3" would evaluate to 0 because the
      division of 9 by 3 has a quotient of 3 and leaves a remainder of 0.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="lt">
    <xs:annotation><xs:documentation>
      Returns a 1 if the value of the first immediate child element is less
      than the value of the second immediate child element, returns 0
      otherwise. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="le">
    <xs:annotation><xs:documentation>
      Returns a 1 if the value of the first immediate child element is less
      than or equal to the value of the second immediate child element,
      returns 0 otherwise. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="gt">
    <xs:annotation><xs:documentation>
      Returns a 1 if the value of the first immediate child element is greater
      than the value of the second immediate child element, returns 0
      otherwise. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="ge">
    <xs:annotation><xs:documentation>
      Returns a 1 if the value of the first immediate child element is greater
      than or equal to the value of the second immediate child element,
      returns 0 otherwise. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="eq">
    <xs:annotation><xs:documentation>
      Returns a 1 if the value of the first immediate child element is equal to
      the value of the second immediate child element, returns 0 otherwise. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="nq">
    <xs:annotation><xs:documentation>
      Returns a 1 if the value of the first immediate child element is not
      equal to the value of the second immediate child element, returns 0
      otherwise. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice maxOccurs="2" minOccurs="2">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="and">
    <xs:annotation><xs:documentation>
      Returns a 1 if the values of the immediate child elements are all 1,
      returns 0 otherwise. Values provided are expected to be either 1 or 0
      within machine precision.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="2" maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="or">
    <xs:annotation><xs:documentation>
      Returns a 1 if any of the values of the immediate child elements are 1,
      returns 0 otherwise. Values provided are expected to be either 1 or 0
      within machine precision.
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="2" maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="not">
    <xs:annotation><xs:documentation>
      Returns the inverse of the value of the supplied immediate child element
      (e.g., returns 1 if supplied a 0). 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="1" maxOccurs="1">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="ifthen">
    <xs:annotation><xs:documentation>
      If the value of the first immediate child element is 1, then the value of
      the second immediate child element is returned, otherwise the value of
      the third child element is returned. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="3" maxOccurs="3">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  <xs:element name="interpolate1d">
    <xs:annotation><xs:documentation>
      Returns the result from a 1-dimensional interpolation of the supplied
      values, with the value of the first immediate child element representing
      the lookup value into the table, and the following pairs of values
      representing the independent and dependent values. The first provided
      child element is expected to be a property. The interpolation does not
      extrapolate, but holds the highest value if the provided lookup value
      goes outside of the provided range. 
    </xs:documentation></xs:annotation>
    <xs:complexType>
      <xs:choice minOccurs="5" maxOccurs="unbounded">
        <xs:group ref="func_group"/>
        <xs:element ref="value"/>
        <xs:element ref="property"/>
        <xs:element name="v"/>
        <xs:element name="p"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
  
  <xs:simpleType name="PositiveNumber">
    <xs:restriction base="xs:double">
      <xs:minInclusive value="0"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:element name="property" type="xs:string"/>
  <xs:element name="description" type="xs:string">
    <xs:annotation>
      <xs:documentation>A simple text description of the item.</xs:documentation>
    </xs:annotation>
  </xs:element>
</xs:schema>