/* 
   This schema specifies the format for unit definitions.  Definitions occur
   in special-purpose documents containing nothing else, that are made
   accessible on the internet.  BrainML instance documents may refer to these
   by use of a 'unit' element that is defined in the main brainml schema.
   They may NOT define units themselves.  If a unit needs to be added, a schema
   authority should submit a unit definitions document to the schema repository.
*/
targetNamespace "urn:bml/brainml.org:internal/BrainMetaL/1"
namespace "urn:bml/brainml.org:internal/BrainMetaL/1"
namespace xlink "http://www.w3.org/1999/xlink"

import "http://brainml.org/schemas/internal/BrainMetaL/1/xlink.xsd" namespace "http://www.w3.org/1999/xlink"

/* 
   Allowable unit classes, representing the energy or characteristic being
   measured.  Unit class allows applications to specify a restriction on
   the kinds of units that may occur in a given context.
*/
simpleType class-type { xs:token { /absorbed-dose|electric-current|dimensionless|electric-capacitance|electric-charge|electric-conductance|electric-potential|electric-resistance|energy|force|frequency|illuminance|inductance|length|luminous-intensity|magnetic-flux|magnetic-flux-density|mass|plane-angle|power|pressure|radioactive-activity|solid-angle|substance-amount|temperature|time|unknown/  } }

/*
   Allowable unit base names.
*/
simpleType base-name-type { xs:token { /amp|becquerel|candela|coulomb|dimensionless|farad|gray|henry|hertz|joule|kelvin|gram|lumen|lux|meter|mole|newton|ohm|pascal|radian|second|siemens|steradian|tesla|volt|watt|weber|unknown/  } }

/*
   Alternative format using enumerations.
*/
simpleType base-name-type-alt { xs:token { "ampere", "becquerel"  } }

/*
   Allowable unit prefixes, expressing powers of 10.
*/
simpleType prefix-type { xs:token { /atto|centi|deca|deci|exa|femto|giga|hecto|kilo|mega|micro|milli|nano|none|peta|pico|tera/  } }

/*
   Single unit definition.  This could be used outside of a special-purpose
   unit-definition document if desired.
*/
element unit-definition {
   (
      /* Name of the unit.  E.g., "millisecond". */
      name,
      /* Quantity measured by unit.  E.g., "electric-potential". */
      class { class-type },
      /* Symbol used for unit.  E.g., "kg". */
      symbol { xs:normalizedString },
      /* Link to corresponding term or definition in an external system. */
      external-equivalent? )

   /* Name of a unit (composite). */
   element name {
      (
         /* Stem of unit name (e.g., "gram", "meter"). */
         base-name { base-name-type } &
         /* Power-of-ten prefix (e.g., "kilo", "centi"). */
         prefix { prefix-type }? )
   }
   /* This is the identifier by which the unit will be referenced.  Valid
      characters in identifiers are ONLY letters, numbers, underscore,
      period, and dash, and an identifier cannot start with a number.  The
      identifier for a domain should be unique within its containing document
      among both domains and terms.
   */
   required attribute id { xs:ID }
}

/*
  Supports linking of a unit declaration to a corresponding term or definition
  in an external system.
*/
element external-equivalent {
   required attribute xlink:href
}

/*
   Collection of unit definitions, and valid unit definition document root.
*/
element unit-definitions {
   ( unit-definition+, )
}