/**
 * @file    UnitDefinition.h
 * @brief   Definitions of UnitDefinition and ListOfUnitDefinitions.
 * @author  Ben Bornstein
 *
 * $Id: UnitDefinition.h 13124 2011-03-03 04:48:53Z mhucka $
 * $HeadURL: http://sbml.svn.sourceforge.net/svnroot/sbml/trunk/libsbml/src/sbml/UnitDefinition.h $
 *
 * <!--------------------------------------------------------------------------
 * This file is part of libSBML.  Please visit http://sbml.org for more
 * information about SBML, and the latest version of libSBML.
 *
 * Copyright (C) 2009-2011 jointly by the following organizations: 
 *     1. California Institute of Technology, Pasadena, CA, USA
 *     2. EMBL European Bioinformatics Institute (EBML-EBI), Hinxton, UK
 *  
 * Copyright (C) 2006-2008 by the California Institute of Technology,
 *     Pasadena, CA, USA 
 *  
 * Copyright (C) 2002-2005 jointly by the following organizations: 
 *     1. California Institute of Technology, Pasadena, CA, USA
 *     2. Japan Science and Technology Agency, Japan
 * 
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation.  A copy of the license agreement is provided
 * in the file named "LICENSE.txt" included with this software distribution
 * and also available online as http://sbml.org/software/libsbml/license.html
 * ------------------------------------------------------------------------ -->
 *
 * @class UnitDefinition
 * @brief LibSBML implementation of SBML's %UnitDefinition construct.
 *
 * Units of measurement may be supplied in a number of contexts in an SBML
 * model.  The SBML unit definition facility uses two classes of objects,
 * UnitDefinition and Unit.  The approach to defining units in SBML is
 * compositional; for example, <em>meter second<sup> &ndash;2</sup></em> is
 * constructed by combining a Unit object representing <em>meter</em> with
 * another Unit object representing <em>second<sup> &ndash;2</sup></em>.
 * The combination is wrapped inside a UnitDefinition, which provides for
 * assigning an identifier and optional name to the combination.  The
 * identifier can then be referenced from elsewhere in a model.  Thus, the
 * UnitDefinition class is the container, and Unit instances are placed
 * inside UnitDefinition instances.
 *
 * Two points are worth discussing in the context of SBML units.  First,
 * unit declarations in SBML models are @em optional.  The consequence of
 * this is that a model must be numerically self-consistent independently
 * of unit declarations, for the benefit of software tools that cannot
 * interpret or manipulate units.  Unit declarations in SBML are thus more
 * akin to a type of annotation; they can indicate intentions, and can be
 * used by model readers for checking the consistency of the model,
 * labeling simulation output, etc., but any transformations of values
 * implied by different units must be incorporated @em explicitly into a
 * model.
 * 
 * Second, the vast majority of situations that require new SBML unit
 * definitions involve simple multiplicative combinations of base units and
 * factors.  An example is <em>moles per litre per second</em>.  What
 * distinguishes these sorts of unit definitions from more complex ones is
 * that they may be expressed without the use of an additive offset from a
 * zero point.  The use of offsets complicates all unit definition systems,
 * yet in the domain of SBML, the real-life cases requiring offsets are few
 * (and in fact, to the best of our knowledge, only involve temperature).
 * Consequently, the SBML unit system has been consciously designed to
 * simplify implementation of unit support for the most common cases in
 * systems biology.  The cost of this simplification is to require units
 * with offsets to be handled explicitly by the modeler.
 *
 * @section unitdef-summary Summary of the UnitDefinition construct
 *
 * UnitDefinition has two attributes and one subelement.  The two
 * attributes are "id" and "name", and the subelement is ListOfUnits.
 *
 * The required attribute "id" and optional attribute "name" are both
 * strings.  The "id" attribute is used to give the defined unit a unique
 * identifier by which other parts of an SBML model definition can refer to
 * it.  The "name" attribute is intended to be used for giving the unit
 * definition an optional human-readable name.  Please see the <a
 * href="#unitdef-id">next section</a> for information about the values
 * permitted for "id".
 *
 * A UnitDefinition must contain exactly one ListOfUnits, and this list
 * must contain one or more Unit definitions; see the definitions of these
 * other object classes for more information about them.  The following
 * example illustrates a complete unit definition (when written in XML)
 * when they all the pieces are combined together.  This defines "mmls"
 * to be millimoles per litre per second.
 * @code
 * <listOfUnitDefinitions>
 *     <unitDefinition id="mmls">
 *         <listOfUnits>
 *             <unit kind="mole"   scale="-3"/>
 *             <unit kind="litre"  exponent="-1"/>
 *             <unit kind="second" exponent="-1"/>
 *         </listOfUnits>
 *     </unitDefinition>
 * </listOfUnitDefinitions>
 * @endcode
 *
 * @section unitdef-id Special considerations for Unit object identifiers
 *
 * The attribute "id" in UnitDefinition cannot be given simply any value,
 * and the precise details of the values permitted differ slightly between
 * Levels of SBML:
 * <ul>
 *
 * <li> The "id" of a UnitDefinition must @em not contain a value from the
 * list of SBML's predefined base unit names (i.e., the strings @c gram, @c
 * litre, etc.).  In SBML Level&nbsp;3, this list consists of the
 * following:
 * 
 * @htmlinclude base-units2.html
 *
 * This list of predefined base units is nearly identical in SBML
 * Level&nbsp;2 Version&nbsp;4, the exception being that Level&nbsp;2 does
 * not define @c avogadro.  SBML Level&nbsp;2 Version&nbsp;1 (and @em only
 * this Level+Version combination) provides an additional predefined unit
 * name, @c Celsius, not available in Level&nbsp;3.  Finally, SBML
 * Level&nbsp;1 Versions&nbsp;2&ndash;3 provide two more additional
 * predefined unit names, @c meter and @c liter.  This is explained in
 * somewhat greater detail in the description of the Unit class.
 *
 * <li> In SBML Level&nbsp;2 (all Versions), there is an additional set of
 * reserved identifiers: @c substance, @c volume, @c area, @c length, and
 * @c time.  Using one of these values for the attribute "id" of a
 * UnitDefinition has the effect of redefining the model-wide default units
 * for the corresponding quantities.  The list of special unit names in
 * SBML Level&nbsp;2 is given in the table below:
 *
 *   @htmlinclude predefined-units.html
 *
 * Also, SBML Level&nbsp;2 imposes two limitations on redefining the
 * predefined unit @c substance, @c volume, @c area, @c length, and @c
 * time: (1) The UnitDefinition of a predefined SBML unit can only contain
 * a single Unit object within it.  (2) The value of the "kind" attribute
 * in a Unit instance must be drawn from one of the values in the second
 * column of the table above.
 *
 * The special unit names @c substance, @c volume, @c area, @c length, and
 * @c time are not defined by SBML Level&nbsp;3, which uses a different
 * approach to setting model-wide inherited units.
 *
 * </ul>
 * 
 *
 * @section sbml-units-limits Further comments about SBML's unit definition system
 * 
 * The vast majority of modeling situations requiring new SBML unit
 * definitions involve simple multiplicative combinations of base units and
 * factors.  An example of this might be <em>moles per litre per
 * second</em>.  What distinguishes these sorts of simpler unit definitions
 * from more complex ones is that they may be expressed without the use of
 * an additive offset from a zero point.  The use of offsets complicates
 * all unit definition systems, yet in the domain of SBML the real-life
 * cases requiring offsets are few (and in fact, to the best of our
 * knowledge, only involve temperature).  Consequently, the SBML unit
 * system has been consciously designed in a way that attempts to simplify
 * implementation of unit support for the most common cases in systems
 * biology.
 *
 * As of SBML Level&nbsp;2 Version&nbsp;2, Unit no longer has the
 * attribute called "offset" introduced in SBML Level&nbsp;2
 * Version&nbsp;1.  It turned out that the general case involving units
 * with offsets was incorrectly defined, and few (if any) developers even
 * attempted to support offset-based units in their software.  In the
 * development of Level&nbsp;2 Version&nbsp;2, a consensus among SBML
 * developers emerged that a fully generalized unit scheme is @em so
 * confusing and complicated that it actually @em impedes interoperability.
 * SBML Level&nbsp;2 Version&nbsp;2, Version&nbsp;3 and Version&nbsp;4 acknowledge this
 * reality by reducing and simplifying the unit system, specifically by
 * removing the "offset" attribute on Unit and @c Celsius as a pre-defined
 * unit.
 *
 * The following guidelines suggest methods for handling units that do
 * require the use of zero offsets for their definitions:
 * <ul>
 * <li> <em>Handling Celsius</em>.  A model in which certain quantities are
 *   temperatures measured in degrees Celsius can be converted
 *   straightforwardly to a model in which those temperatures are in
 *   kelvin.  A software tool could do this by performing a straightforward
 *   substitution using the following relationship: <em>T<sub> kelvin</sub> =
 *   T<sub>Celsius</sub> + 273.15</em>.  In every mathematical formula of the
 *   model where a quantity (call it @em x) in degrees Celsius appears,
 *   replace @em x with <em>x<sub>k</sub>+ 273.15</em>, where
 *   <em>x<sub>k</sub></em> is now in kelvin.  An alternative approach would 
 *   be to use a FunctionDefinition object to define a function encapsulating this
 *   relationship above and then using that in the rest of the model as
 *   needed.  Since Celsius is a commonly-used unit, software tools could
 *   help users by providing users with the ability to express temperatures
 *   in Celsius in the tools' interfaces, and making substitutions
 *   automatically when writing out the SBML.
 *
 * <li> <em>Other units requiring offsets</em>.  One approach to handling
 *   other kinds of units is to use a FunctionDefinition to define a function
 *   encapsulating the necessary mathematical relationship, then
 *   substituting a call to this function wherever the original quantity
 *   appeared in the model.  For example, here is a possible definition for
 *   converting Fahrenheit to Celsius degrees:
 *   @code
 * <functionDefinition id="Fahrenheit_to_kelvin">
 *     <math xmlns="http://www.w3.org/1998/Math/MathML">
 *         <lambda>
 *             <bvar><ci> temp_in_fahrenheit </ci></bvar>
 *             <apply>
 *                 <divide/>
 *                 <apply>
 *                     <plus/>
 *                     <ci> temp_in_fahrenheit </ci>
 *                     <cn> 459.67 </cn>
 *                 </apply>
 *                 <cn> 1.8 </cn>
 *             </apply>
 *         </lambda>
 *     </math>
 * </functionDefinition>
 *   @endcode
 *     
 * <li> An alternative approach not requiring the use of function definitions
 *   is to use an AssignmentRule for each variable in Fahrenheit units.
 *   The AssignmentRule could compute the conversion from Fahrenheit to
 *   (say) kelvin, assign its value to a variable (in Kelvin units), and
 *   then that variable could be used elsewhere in the model.
 *
 * <li> Still another approach is to rewrite the mathematical formulas of a
 *   model to directly incorporate the conversion formula wherever the
 *   original quantity appeared.
 * </ul>
 * 
 * Please consult the SBML specifications for more information about this
 * and other issues involving units.
 *  
 * <!-- leave this next break as-is to work around some doxygen bug -->
 */ 
/**
 * @class ListOfUnitDefinitions
 * @brief LibSBML implementation of SBML's %ListOfUnitDefinitions construct.
 * 
 * The various ListOf___ classes in SBML are merely containers used for
 * organizing the main components of an SBML model.  All are derived from
 * the abstract class SBase, and inherit the various attributes and
 * subelements of SBase, such as "metaid" as and "annotation".  The
 * ListOf___ classes do not add any attributes of their own.
 *
 * The relationship between the lists and the rest of an SBML model is
 * illustrated by the following (for SBML Level&nbsp;2 Version&nbsp;4):
 *
 * @image html listof-illustration.jpg "ListOf___ elements in an SBML Model"
 * @image latex listof-illustration.jpg "ListOf___ elements in an SBML Model"
 *
 * Readers may wonder about the motivations for using the ListOf___
 * containers.  A simpler approach in XML might be to place the components
 * all directly at the top level of the model definition.  The choice made
 * in SBML is to group them within XML elements named after
 * ListOf<em>Classname</em>, in part because it helps organize the
 * components.  More importantly, the fact that the container classes are
 * derived from SBase means that software tools can add information @em about
 * the lists themselves into each list container's "annotation".
 *
 * @see ListOfFunctionDefinitions
 * @see ListOfUnitDefinitions
 * @see ListOfCompartmentTypes
 * @see ListOfSpeciesTypes
 * @see ListOfCompartments
 * @see ListOfSpecies
 * @see ListOfParameters
 * @see ListOfInitialAssignments
 * @see ListOfRules
 * @see ListOfConstraints
 * @see ListOfReactions
 * @see ListOfEvents
 */

#ifndef UnitDefinition_h
#define UnitDefinition_h


#include <sbml/common/extern.h>
#include <sbml/common/sbmlfwd.h>


#ifdef __cplusplus


#include <string>

#include <sbml/SBase.h>
#include <sbml/ListOf.h>
#include <sbml/Unit.h>

LIBSBML_CPP_NAMESPACE_BEGIN

class SBMLVisitor;


class LIBSBML_EXTERN UnitDefinition : public SBase
{
public:

  /**
   * Creates a new UnitDefinition using the given SBML @p level and @p version
   * values.
   *
   * @param level an unsigned int, the SBML Level to assign to this UnitDefinition
   *
   * @param version an unsigned int, the SBML Version to assign to this
   * UnitDefinition
   * 
   * @note Upon the addition of a UnitDefinition object to an SBMLDocument
   * (e.g., using Model::addUnitDefinition(@if java UnitDefinition ud@endif)), the SBML Level, SBML Version
   * and XML namespace of the document @em override the values used
   * when creating the UnitDefinition object via this constructor.  This is
   * necessary to ensure that an SBML document is a consistent structure.
   * Nevertheless, the ability to supply the values at the time of creation
   * of a UnitDefinition is an important aid to producing valid SBML.
   * Knowledge of the intented SBML Level and Version determine whether it
   * is valid to assign a particular value to an attribute, or whether it
   * is valid to add an object to an existing SBMLDocument.
   */
  UnitDefinition (unsigned int level, unsigned int version);


  /**
   * Creates a new UnitDefinition using the given SBMLNamespaces object
   * @p sbmlns.
   *
   * The SBMLNamespaces object encapsulates SBML Level/Version/namespaces
   * information.  It is used to communicate the SBML Level, Version, and
   * (in Level&nbsp;3) packages used in addition to SBML Level&nbsp;3 Core.
   * A common approach to using this class constructor is to create an
   * SBMLNamespaces object somewhere in a program, once, then pass it to
   * object constructors such as this one when needed.
   *
   * @param sbmlns an SBMLNamespaces object.
   *
   * @note Upon the addition of a UnitDefinition object to an SBMLDocument
   * (e.g., using Model::addUnitDefinition(@if java UnitDefinition ud@endif)), the SBML XML namespace of
   * the document @em overrides the value used when creating the
   * UnitDefinition object via this constructor.  This is necessary to
   * ensure that an SBML document is a consistent structure.  Nevertheless,
   * the ability to supply the values at the time of creation of a
   * UnitDefinition is an important aid to producing valid SBML.  Knowledge
   * of the intented SBML Level and Version determine whether it is valid
   * to assign a particular value to an attribute, or whether it is valid
   * to add an object to an existing SBMLDocument.
   */
  UnitDefinition (SBMLNamespaces* sbmlns);


  /**
   * Destroys this UnitDefinition.
   */
  virtual ~UnitDefinition ();


  /**
  * Copy constructor; creates a copy of this UnitDefinition.
  */
  UnitDefinition(const UnitDefinition& orig);


  /**
   * Assignment operator.
   */
  UnitDefinition& operator=(const UnitDefinition& rhs);


  /**
   * Accepts the given SBMLVisitor for this instance of UnitDefinition.
   *
   * @param v the SBMLVisitor instance to be used.
   *
   * @return the result of calling <code>v.visit()</code>, which indicates
   * whether the Visitor would like to visit the next UnitDefinition in the
   * list of units within which this UnitDefinition is embedded (i.e., in
   * the ListOfUnitDefinitions located in the enclosing Model instance).
   */
  virtual bool accept (SBMLVisitor& v) const;


  /**
   * Creates and returns a deep copy of this UnitDefinition.
   * 
   * @return a (deep) copy of this UnitDefinition.
   */
  virtual UnitDefinition* clone () const;


  /**
   * Returns the value of the "id" attribute of this UnitDefinition.
   * 
   * @return the id of this UnitDefinition.
   */
  const std::string& getId () const;


  /**
   * Returns the value of the "name" attribute of this UnitDefinition.
   * 
   * @return the name of this UnitDefinition.
   */
  const std::string& getName () const;


  /**
   * Predicate returning @c true if this
   * UnitDefinition's "id" attribute is set.
   *
   * @return @c true if the "id" attribute of this UnitDefinition is
   * set, @c false otherwise.
   */
  bool isSetId () const;


  /**
   * Predicate returning @c true if this
   * UnitDefinition's "name" attribute is set.
   *
   * @return @c true if the "name" attribute of this UnitDefinition is
   * set, @c false otherwise.
   */
  bool isSetName () const;


  /**
   * Sets the value of the "id" attribute of this UnitDefinition.
   *
   * The string @p sid is copied.  Note that SBML has strict requirements
   * for the syntax of identifiers.  @htmlinclude id-syntax.html
   *
   * @param sid the string to use as the identifier of this UnitDefinition
   *
   * @return integer value indicating success/failure of the
   * function.  The possible values
   * returned by this function are:
   * @li @link OperationReturnValues_t#LIBSBML_OPERATION_SUCCESS LIBSBML_OPERATION_SUCCESS @endlink
   * @li @link OperationReturnValues_t#LIBSBML_INVALID_ATTRIBUTE_VALUE LIBSBML_INVALID_ATTRIBUTE_VALUE @endlink
   */
  int setId (const std::string& sid);


  /**
   * Sets the value of the "name" attribute of this UnitDefinition.
   *
   * The string in @p name is copied.
   *
   * @param name the new name for the UnitDefinition
   *
   * @return integer value indicating success/failure of the
   * function.  The possible values
   * returned by this function are:
   * @li @link OperationReturnValues_t#LIBSBML_OPERATION_SUCCESS LIBSBML_OPERATION_SUCCESS @endlink
   * @li @link OperationReturnValues_t#LIBSBML_INVALID_ATTRIBUTE_VALUE LIBSBML_INVALID_ATTRIBUTE_VALUE @endlink
   */
  int setName (const std::string& name);


  /**
   * Unsets the value of the "name" attribute of this UnitDefinition.
   *
   * @return integer value indicating success/failure of the
   * function.  The possible values
   * returned by this function are:
   * @li @link OperationReturnValues_t#LIBSBML_OPERATION_SUCCESS LIBSBML_OPERATION_SUCCESS @endlink
   * @li @link OperationReturnValues_t#LIBSBML_OPERATION_FAILED LIBSBML_OPERATION_FAILED @endlink
   */
  int unsetName ();


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit identifier @c "area".
   *
   * @return @c true if this UnitDefinition is a variant of the predefined
   * unit @c area, meaning square metres with only abritrary variations
   * in scale or multiplier values; @c false otherwise.
   */
  bool isVariantOfArea () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit identifier @c "length".
   *
   * @return @c true if this UnitDefinition is a variant of the predefined
   * unit @c length, meaning metres with only abritrary variations in scale
   * or multiplier values; @c false otherwise.
   */
  bool isVariantOfLength () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit identifier @c "substance".
   *
   * @return @c true if this UnitDefinition is a variant of the predefined
   * unit @c substance, meaning moles or items (and grams or kilograms from
   * SBML Level&nbsp;2 Version&nbsp;2 onwards) with only abritrary variations
   * in scale or multiplier values; @c false otherwise.
   */
  bool isVariantOfSubstance () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit identifier @c "time".
   *
   * @return @c true if this UnitDefinition is a variant of the predefined
   * unit @c time, meaning seconds with only abritrary variations in scale or
   * multiplier values; @c false otherwise.
   */
  bool isVariantOfTime () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit identifier @c "volume".
   *
   * @return @c true if this UnitDefinition is a variant of the predefined
   * unit @c volume, meaning litre or cubic metre with only abritrary
   * variations in scale or multiplier values; @c false otherwise.
   */
  bool isVariantOfVolume () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the unit @c "dimensionless".
   *
   * @return @c true if this UnitDefinition is a variant of @c
   * dimensionless, meaning dimensionless with only abritrary variations in
   * scale or multiplier values; @c false otherwise.
   */
  bool isVariantOfDimensionless () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit identifier @c "mass".
   *
   * @return @c true if this UnitDefinition is a variant of mass units,
   * meaning gram or kilogram with only abritrary variations in scale or
   * multiplier values; @c false otherwise.
   */
  bool isVariantOfMass () const;


  /**
   * Convenience function for testing if a given unit definition is a
   * variant of the predefined unit @c "substance" divided by the predefined
   * unit @c "time".
   *
   * @return @c true if this UnitDefinition is a variant of the predefined
   * unit @c substance per predefined unit @c time, meaning it contains two
   * units one of which is a variant of substance and the other is a
   * variant of time which an exponent of -1; @c false otherwise.
   */
  bool isVariantOfSubstancePerTime () const;


  /**
   * Adds a copy of the given Unit to this UnitDefinition.
   *
   * @param u the Unit instance to add to this UnitDefinition.
   *
   * @return integer value indicating success/failure of the
   * function.  The possible values
   * returned by this function are:
   * @li @link OperationReturnValues_t#LIBSBML_OPERATION_SUCCESS LIBSBML_OPERATION_SUCCESS @endlink
   * @li @link OperationReturnValues_t#LIBSBML_LEVEL_MISMATCH LIBSBML_LEVEL_MISMATCH @endlink
   * @li @link OperationReturnValues_t#LIBSBML_VERSION_MISMATCH LIBSBML_VERSION_MISMATCH @endlink
   * @li @link OperationReturnValues_t#LIBSBML_INVALID_OBJECT LIBSBML_INVALID_OBJECT @endlink
   * @li @link OperationReturnValues_t#LIBSBML_OPERATION_FAILED LIBSBML_OPERATION_FAILED @endlink
   * 
   * @note This method should be used with some caution.  The fact that
   * this method @em copies the object passed to it means that the caller
   * will be left holding a physically different object instance than the
   * one contained in this UnitDefinition.  Changes made to the original
   * object instance (such as resetting attribute values) will <em>not
   * affect the instance in the UnitDefinition</em>.  In addition, the
   * caller should make sure to free the original object if it is no longer
   * being used, or else a memory leak will result.  Please see
   * UnitDefinition::createUnit() for a method that does not lead to these
   * issues.
   *
   * @see createUnit()
   */
  int addUnit (const Unit* u);


  /**
   * Creates a new and empty Unit, adds it to this UnitDefinition's list of
   * units, and returns it.
   *
   * @return a newly constructed (and empty) Unit instance.
   * 
   * @note It is worth emphasizing that the attribute "kind" value of a
   * Unit is a required attribute for a valid Unit definition.  The
   * createUnit() method does not assign a valid kind to the constructed
   * unit (instead, it sets the "kind" to @link UnitKind_t#UNIT_KIND_INVALID UNIT_KIND_INVALID@endlink).
   * Callers are cautioned to set the newly-constructed Unit's kind using
   * Unit::setKind(@if java int kind@endif) soon after calling this method.
   *
   * @see addUnit(const Unit* u)
   */
  Unit* createUnit ();


  /**
   * Returns the list of Units for this UnitDefinition instance.
   * @return the ListOfUnits value for this UnitDefinition.
   */
  const ListOfUnits* getListOfUnits () const;


  /**
   * Returns the list of Units for this UnitDefinition instance.
   * @return the ListOfUnits value for this UnitDefinition.
   */
  ListOfUnits* getListOfUnits ();


  /**
   * Returns a specific Unit instance belonging to this UnitDefinition.
   *
   * @param n an integer, the index of the Unit to be returned.
   * 
   * @return the nth Unit of this UnitDefinition.
   *
   * @see getNumUnits()
   */
  Unit* getUnit (unsigned int n);


  /**
   * Returns a specific Unit instance belonging to this UnitDefinition.
   *
   * @param n an integer, the index of the Unit to be returned.
   * 
   * @return the nth Unit of this UnitDefinition.
   */
  const Unit* getUnit (unsigned int n) const;


  /**
   * Returns the number of Unit objects contained within this
   * UnitDefinition.
   * 
   * @return an integer representing the number of Units in this
   * UnitDefinition.
   */
  unsigned int getNumUnits () const;


  /**
   * Removes the nth Unit object from this UnitDefinition object and
   * returns a pointer to it.
   *
   * The caller owns the returned object and is responsible for deleting it.
   *
   * @param n the index of the Unit object to remove
   *
   * @return the Unit object removed, or @c NULL if the given index 
   * is out of range.
   *
   */
  Unit* removeUnit (unsigned int n);


  /** @cond doxygen-libsbml-internal */

  /**
   * Sets the parent SBMLDocument of this SBML object.
   *
   * @param d the SBMLDocument to use
   */
  virtual void setSBMLDocument (SBMLDocument* d);


  /**
   * Sets the parent SBML object of this SBML object.
   *
   * @param sb the SBML object to use
   */
  virtual void setParentSBMLObject (SBase* sb);

  /** @endcond */

  /**
   * Returns the libSBML type code for this object instance.
   * 
   * @if clike LibSBML attaches an identifying code to every kind of SBML
   * object.  These are known as <em>SBML type codes</em>.  The set of
   * possible type codes is defined in the enumeration #SBMLTypeCode_t.
   * The names of the type codes all begin with the characters @c
   * SBML_. @endif@if java LibSBML attaches an identifying code to every
   * kind of SBML object.  These are known as <em>SBML type codes</em>.  In
   * other languages, the set of type codes is stored in an enumeration; in
   * the Java language interface for libSBML, the type codes are defined as
   * static integer constants in the interface class {@link
   * libsbmlConstants}.  The names of the type codes all begin with the
   * characters @c SBML_. @endif@if python LibSBML attaches an identifying
   * code to every kind of SBML object.  These are known as <em>SBML type
   * codes</em>.  In the Python language interface for libSBML, the type
   * codes are defined as static integer constants in the interface class
   * @link libsbml@endlink.  The names of the type codes all begin with the
   * characters @c SBML_. @endif@if csharp LibSBML attaches an identifying
   * code to every kind of SBML object.  These are known as <em>SBML type
   * codes</em>.  In the C# language interface for libSBML, the type codes
   * are defined as static integer constants in the interface class @link
   * libsbml.libsbml@endlink.  The names of the type codes all begin with
   * the characters @c SBML_. @endif
   *
   * @return the SBML type code for this object, or @link SBMLTypeCode_t#SBML_UNKNOWN SBML_UNKNOWN@endlink (default).
   *
   * @see getElementName()
   */
  virtual SBMLTypeCode_t getTypeCode () const;


  /**
   * Returns the XML element name of this object, which for UnitDefinition,
   * is always @c "unitDefinition".
   * 
   * @return the name of this element, i.e., @c "unitDefinition".
   */
  virtual const std::string& getElementName () const;


  /** 
   * Simplifies the UnitDefinition such that any given kind of Unit object
   * occurs only once in the ListOfUnits.
   *
   * For example, the following definition,
   * @code
   * <unitDefinition>
   *  <listOfUnits>
   *    <unit kind="metre" exponent="1"/>
   *    <unit kind="metre" exponent="2"/>
   *  </listOfUnits>
   * <unitDefinition>
   * @endcode
   * will be simplified to 
   * @code
   * <unitDefinition>
   *   <listOfUnits>
   *     <unit kind="metre" exponent="3"/>
   *   </listOfUnits>
   * <unitDefinition>
   * @endcode
   *
   * @param ud the UnitDefinition object to be simplified.
   */
  static void simplify(UnitDefinition * ud);


  /** 
   * Alphabetically orders the Unit objects within the ListOfUnits of a
   * UnitDefinition.
   *
   * @param ud the UnitDefinition object whose units are to be reordered.
   */
  static void reorder(UnitDefinition * ud);

  
  /**
   * Convert a given UnitDefinition into a new UnitDefinition object
   * that uses SI units.
   * 
   * @param ud the UnitDefinition object to convert to SI
   *
   * @return a new UnitDefinition object representing the results of the
   * conversion.
   */
  static UnitDefinition * convertToSI(const UnitDefinition *ud);


  /** 
   * Predicate returning @c true if two
   * UnitDefinition objects are identical.
   *
   * For the purposes of performing this comparison, two UnitDefinition
   * objects are considered identical when they contain identical lists of
   * Unit objects.  Pairs of Unit objects in the lists are in turn
   * considered identical if they satisfy the predicate
   * Unit::areIdentical(@if java Unit u1, %Unit u2@endif).
   * The predicate compares every attribute of the
   * Unit objects.
   *
   * @param ud1 the first UnitDefinition object to compare
   * @param ud2 the second UnitDefinition object to compare
   *
   * @return @c true if all the Unit objects in ud1 are identical to the
   * Unit objects of ud2, @c false otherwise.
   *
   * @see areEquivalent(const UnitDefinition * ud1, const %UnitDefinition * ud2)
   * @see Unit::areIdentical(Unit * unit1, %Unit * unit2)
   */
  static bool areIdentical(const UnitDefinition * ud1, const UnitDefinition * ud2);


  /** 
   * Predicate returning @c true if two
   * UnitDefinition objects are equivalent.
   *
   * For the purposes of performing this comparison, two UnitDefinition
   * objects are considered equivalent when they contain @em equivalent
   * list of Unit objects.  Unit objects are in turn considered equivalent
   * if they satisfy the predicate
   * Unit::areEquivalent(@if java Unit u1, %Unit u2@endif).
   * The predicate tests a subset of the objects's attributes.
   *
   * @param ud1 the first UnitDefinition object to compare
   * 
   * @param ud2 the second UnitDefinition object to compare
   *
   * @return @c true if all the Unit objects in ud1 are equivalent
   * to the Unit objects in ud2, @c false otherwise.
   *
   * @see areIdentical(const UnitDefinition * ud1, const %UnitDefinition * ud2)
   * @see Unit::areEquivalent(Unit * unit1, %Unit * unit2)
   */
  static bool areEquivalent(const UnitDefinition *ud1 , const UnitDefinition * ud2);


  /** @cond doxygen-libsbml-internal */

  static bool areIdenticalSIUnits(const UnitDefinition * ud1, 
    const UnitDefinition * ud2);
  /** @endcond */


  /** 
   * Combines two UnitDefinition objects into a single UnitDefinition.
   *
   * This takes UnitDefinition objects @p ud1 and @p ud2, and creates a
   * UnitDefinition object that expresses the product of the units of @p
   * ud1 and @p ud2.
   *
   * @param ud1 the first UnitDefinition object 
   * @param ud2 the second UnitDefinition object
   *
   * @return a UnitDefinition which represents the product of the 
   * units of the two argument UnitDefinitions.
   */
  static UnitDefinition* combine(UnitDefinition * ud1, UnitDefinition * ud2);


  /** 
   * Expresses the given definition in a plain-text form.
   *
   * For example,
   * UnitDefinition::printUnits(@if java UnitDefinition u@endif)
   * applied to
   * @code
   * <unitDefinition>
   *  <listOfUnits>
   *    <unit kind="metre" exponent="1"/>
   *    <unit kind="second" exponent="-2"/>
   *  </listOfUnits>
   * <unitDefinition>
   * @endcode
   * will return the string <code>"metre (exponent = 1, multiplier = 1,
   * scale = 0) second (exponent = -2, multiplier = 1, scale = 0)"</code>
   * or, if the optional parameter @p compact is given the value @c true,
   * the string <code>"(1 metre)^1 (1 second)^-2"</code>.  This method may
   * be useful for printing unit information to human users, or in
   * debugging software, or other situations.
   *
   * @param ud the UnitDefinition object
   * @param compact boolean indicating whether the compact form
   * should be used (defaults to false)
   *
   * @return a string expressing the unit definition defined by the given
   * UnitDefinition object @p ud.
   */
  static std::string printUnits(const UnitDefinition * ud, 
                                bool compact = false);


  /** @cond doxygen-libsbml-internal */
  /**
   * Subclasses should override this method to write out their contained
   * SBML objects as XML elements.  Be sure to call your parents
   * implementation of this method as well.
   */
  virtual void writeElements (XMLOutputStream& stream) const;
  /** @endcond */


  /**
   * Predicate returning @c true if
   * all the required attributes for this UnitDefinition object
   * have been set.
   *
   * @note The required attributes for a UnitDefinition object are:
   * @li "id"
   *
   * @return a boolean value indicating whether all the required
   * attributes for this object have been defined.
   */
  virtual bool hasRequiredAttributes() const ;


  /**
   * Predicate returning @c true if
   * all the required elements for this UnitDefinition object
   * have been set.
   *
   * @note The required elements for a Constraint object are:
   * @li "listOfUnits" (required in SBML Level&nbsp;2 only, optional in Level&nbsp;3)
   *
   * @return a boolean value indicating whether all the required
   * elements for this object have been defined.
   */
  virtual bool hasRequiredElements() const ;


protected:
  /** @cond doxygen-libsbml-internal */

  /* this is a constructor that takes no arguments and 
   * only exists because the validator code needs it
   */
  UnitDefinition ();


  /**
   * @return the SBML object corresponding to next XMLToken in the
   * XMLInputStream or @c NULL if the token was not recognized.
   */
  virtual SBase* createObject (XMLInputStream& stream);


  /**
   * Subclasses should override this method to read values from the given
   * XMLAttributes set into their specific fields.  Be sure to call your
   * parents implementation of this method as well.
   */
  virtual void readAttributes (const XMLAttributes& attributes);


  /**
   * Subclasses should override this method to write their XML attributes
   * to the XMLOutputStream.  Be sure to call your parents implementation
   * of this method as well.
   */
  virtual void writeAttributes (XMLOutputStream& stream) const;


  std::string mId;
  std::string mName;
  ListOfUnits mUnits;

  /* the validator classes need to be friends to access the 
   * protected constructor that takes no arguments
   */
  friend class Validator;
  friend class ConsistencyValidator;
  friend class IdentifierConsistencyValidator;
  friend class InternalConsistencyValidator;
  friend class L1CompatibilityValidator;
  friend class L2v1CompatibilityValidator;
  friend class L2v2CompatibilityValidator;
  friend class L2v3CompatibilityValidator;
  friend class L2v4CompatibilityValidator;
  friend class MathMLConsistencyValidator;
  friend class ModelingPracticeValidator;
  friend class OverdeterminedValidator;
  friend class SBOConsistencyValidator;
  friend class UnitConsistencyValidator;


  /** @endcond */
};



class LIBSBML_EXTERN ListOfUnitDefinitions : public ListOf
{
public:

  /**
   * Creates and returns a deep copy of this ListOfUnitDefinitions instance.
   *
   * @return a (deep) copy of this ListOfUnitDefinitions.
   */
  virtual ListOfUnitDefinitions* clone () const;


  /**
   * Returns the libSBML type code for this SBML object.
   *
   * @if clike LibSBML attaches an identifying code to every kind of SBML
   * object.  These are known as <em>SBML type codes</em>.  The set of
   * possible type codes is defined in the enumeration #SBMLTypeCode_t.
   * The names of the type codes all begin with the characters @c
   * SBML_. @endif@if java LibSBML attaches an identifying code to every
   * kind of SBML object.  These are known as <em>SBML type codes</em>.  In
   * other languages, the set of type codes is stored in an enumeration; in
   * the Java language interface for libSBML, the type codes are defined as
   * static integer constants in the interface class {@link
   * libsbmlConstants}.  The names of the type codes all begin with the
   * characters @c SBML_. @endif@if python LibSBML attaches an identifying
   * code to every kind of SBML object.  These are known as <em>SBML type
   * codes</em>.  In the Python language interface for libSBML, the type
   * codes are defined as static integer constants in the interface class
   * @link libsbml@endlink.  The names of the type codes all begin with the
   * characters @c SBML_. @endif@if csharp LibSBML attaches an identifying
   * code to every kind of SBML object.  These are known as <em>SBML type
   * codes</em>.  In the C# language interface for libSBML, the type codes
   * are defined as static integer constants in the interface class @link
   * libsbml.libsbml@endlink.  The names of the type codes all begin with
   * the characters @c SBML_. @endif
   *
   * @return the SBML type code for this object, or @link SBMLTypeCode_t#SBML_UNKNOWN SBML_UNKNOWN@endlink (default).
   *
   * @see getElementName()
   */
  virtual SBMLTypeCode_t getTypeCode () const { return SBML_LIST_OF; };


  /**
   * Returns the libSBML type code for the objects contained in this ListOf
   * (i.e., UnitDefinition objects, if the list is non-empty).
   *
   * @if clike LibSBML attaches an identifying code to every kind of SBML
   * object.  These are known as <em>SBML type codes</em>.  The set of
   * possible type codes is defined in the enumeration #SBMLTypeCode_t.
   * The names of the type codes all begin with the characters @c
   * SBML_. @endif@if java LibSBML attaches an identifying code to every
   * kind of SBML object.  These are known as <em>SBML type codes</em>.  In
   * other languages, the set of type codes is stored in an enumeration; in
   * the Java language interface for libSBML, the type codes are defined as
   * static integer constants in the interface class {@link
   * libsbmlConstants}.  The names of the type codes all begin with the
   * characters @c SBML_. @endif@if python LibSBML attaches an identifying
   * code to every kind of SBML object.  These are known as <em>SBML type
   * codes</em>.  In the Python language interface for libSBML, the type
   * codes are defined as static integer constants in the interface class
   * @link libsbml@endlink.  The names of the type codes all begin with the
   * characters @c SBML_. @endif@if csharp LibSBML attaches an identifying
   * code to every kind of SBML object.  These are known as <em>SBML type
   * codes</em>.  In the C# language interface for libSBML, the type codes
   * are defined as static integer constants in the interface class @link
   * libsbml.libsbml@endlink.  The names of the type codes all begin with
   * the characters @c SBML_. @endif
   * 
   * @return the SBML type code for the objects contained in this ListOf
   * instance, or @link SBMLTypeCode_t#SBML_UNKNOWN SBML_UNKNOWN@endlink (default).
   *
   * @see getElementName()
   */
  virtual SBMLTypeCode_t getItemTypeCode () const;


  /**
   * Returns the XML element name of this object.
   *
   * For ListOfUnitDefinitions, the XML element name is @c
   * "listOfUnitDefinitions".
   * 
   * @return the name of this element, i.e., @c "listOfUnitDefinitions".
   */
  virtual const std::string& getElementName () const;


  /**
   * Get a UnitDefinition from the ListOfUnitDefinitions.
   *
   * @param n the index number of the UnitDefinition to get.
   * 
   * @return the nth UnitDefinition in this ListOfUnitDefinitions.
   *
   * @see size()
   */
  virtual UnitDefinition * get(unsigned int n); 


  /**
   * Get a UnitDefinition from the ListOfUnitDefinitions.
   *
   * @param n the index number of the UnitDefinition to get.
   * 
   * @return the nth UnitDefinition in this ListOfUnitDefinitions.
   *
   * @see size()
   */
  virtual const UnitDefinition * get(unsigned int n) const; 


  /**
   * Get a UnitDefinition from the ListOfUnitDefinitions
   * based on its identifier.
   *
   * @param sid a string representing the identifier 
   * of the UnitDefinition to get.
   * 
   * @return UnitDefinition in this ListOfUnitDefinitions
   * with the given id or @c NULL if no such
   * UnitDefinition exists.
   *
   * @see get(unsigned int n)
   * @see size()
   */
  virtual UnitDefinition* get (const std::string& sid);


  /**
   * Get a UnitDefinition from the ListOfUnitDefinitions
   * based on its identifier.
   *
   * @param sid a string representing the identifier 
   * of the UnitDefinition to get.
   * 
   * @return UnitDefinition in this ListOfUnitDefinitions
   * with the given id or @c NULL if no such
   * UnitDefinition exists.
   *
   * @see get(unsigned int n)
   * @see size()
   */
  virtual const UnitDefinition* get (const std::string& sid) const;


  /**
   * Removes the nth item from this ListOfUnitDefinitions items and returns a pointer to
   * it.
   *
   * The caller owns the returned item and is responsible for deleting it.
   *
   * @param n the index of the item to remove
   *
   * @see size()
   */
  virtual UnitDefinition* remove (unsigned int n);


  /**
   * Removes item in this ListOfUnitDefinitions items with the given identifier.
   *
   * The caller owns the returned item and is responsible for deleting it.
   * If none of the items in this list have the identifier @p sid, then @c
   * NULL is returned.
   *
   * @param sid the identifier of the item to remove
   *
   * @return the item removed.  As mentioned above, the caller owns the
   * returned item.
   */
  virtual UnitDefinition* remove (const std::string& sid);


  /** @cond doxygen-libsbml-internal */

  /**
   * Get the ordinal position of this element in the containing object
   * (which in this case is the Model object).
   *
   * The ordering of elements in the XML form of SBML is generally fixed
   * for most components in SBML.  So, for example, the
   * ListOfUnitDefinitions in a model is (in SBML Level&nbsp;2
   * Version&nbsp;4) the second ListOf___.  (However, it differs for
   * different Levels and Versions of SBML.)
   *
   * @return the ordinal position of the element with respect to its
   * siblings, or @c -1 (default) to indicate the position is not significant.
   */
  virtual int getElementPosition () const;

  /** @endcond */


protected:
  /** @cond doxygen-libsbml-internal */

  /**
   * @return the SBML object corresponding to next XMLToken in the
   * XMLInputStream or NULL if the token was not recognized.
   */
  virtual SBase* createObject (XMLInputStream& stream);

  friend class Unit;
  /** @endcond */
};

LIBSBML_CPP_NAMESPACE_END

#endif  /* __cplusplus */


#ifndef SWIG

LIBSBML_CPP_NAMESPACE_BEGIN
BEGIN_C_DECLS


/* ----------------------------------------------------------------------------
 * See the .cpp file for the documentation of the following functions.
 * --------------------------------------------------------------------------*/


LIBSBML_EXTERN
UnitDefinition_t *
UnitDefinition_create (unsigned int level, unsigned int version);


LIBSBML_EXTERN
UnitDefinition_t *
UnitDefinition_createWithNS (SBMLNamespaces_t *sbmlns);


LIBSBML_EXTERN
void
UnitDefinition_free (UnitDefinition_t *ud);


LIBSBML_EXTERN
UnitDefinition_t*
UnitDefinition_clone (const UnitDefinition_t *ud);


LIBSBML_EXTERN
const XMLNamespaces_t *
UnitDefinition_getNamespaces(UnitDefinition_t *c);


LIBSBML_EXTERN
const char *
UnitDefinition_getId (const UnitDefinition_t *ud);


LIBSBML_EXTERN
const char *
UnitDefinition_getName (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isSetId (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isSetName (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfArea (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfLength (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfSubstance (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfTime (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfVolume (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int 
UnitDefinition_isVariantOfDimensionless (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfMass (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_isVariantOfSubstancePerTime (const UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_setId (UnitDefinition_t *ud, const char *sid);


LIBSBML_EXTERN
int
UnitDefinition_setName (UnitDefinition_t *ud, const char *name);


LIBSBML_EXTERN
int
UnitDefinition_unsetName (UnitDefinition_t *ud);


LIBSBML_EXTERN
int
UnitDefinition_addUnit (UnitDefinition_t *ud, const Unit_t *u);


LIBSBML_EXTERN
Unit_t *
UnitDefinition_createUnit (UnitDefinition_t *ud);


LIBSBML_EXTERN
ListOf_t *
UnitDefinition_getListOfUnits (UnitDefinition_t *ud);


LIBSBML_EXTERN
Unit_t *
UnitDefinition_getUnit (UnitDefinition_t *ud, unsigned int n);


LIBSBML_EXTERN
Unit_t *
UnitDefinition_removeUnit (UnitDefinition_t *ud, unsigned int n);


LIBSBML_EXTERN
unsigned int
UnitDefinition_getNumUnits (const UnitDefinition_t *ud);


LIBSBML_EXTERN
void 
UnitDefinition_simplify(UnitDefinition_t * ud);

LIBSBML_EXTERN
void 
UnitDefinition_reorder(UnitDefinition_t * ud);

LIBSBML_EXTERN
UnitDefinition_t * 
UnitDefinition_convertToSI(UnitDefinition_t * ud);

LIBSBML_EXTERN
int 
UnitDefinition_areIdentical(UnitDefinition_t * ud1, UnitDefinition_t * ud2);

LIBSBML_EXTERN
int 
UnitDefinition_areEquivalent(UnitDefinition_t *ud1 , UnitDefinition_t * ud2);

LIBSBML_EXTERN
UnitDefinition_t * 
UnitDefinition_combine(UnitDefinition_t * ud1, UnitDefinition_t * ud2);

LIBSBML_EXTERN
const char *
UnitDefinition_printUnits(UnitDefinition_t * ud, int compact);


LIBSBML_EXTERN
UnitDefinition_t *
ListOfUnitDefinitions_getById (ListOf_t *lo, const char *sid);


LIBSBML_EXTERN
UnitDefinition_t *
ListOfUnitDefinitions_removeById (ListOf_t *lo, const char *sid);


END_C_DECLS
LIBSBML_CPP_NAMESPACE_END

#endif  /* !SWIG */
#endif  /* UnitDefinition_h */
