In package javax.xml.datatype, classes XMLGregorianCalendar and Duration
were added to provide a Java representation for the XML Schema builtin
datatypes xsd:dateTime and xsd:duration.

The proposed approach introduced a class javax.xml.datatype.XMLGregorianCalendar
that extended java.util.GregorianCalendar, attempting to address
the mismatch in binding via overrides in the subclass.

Central to a majority of the issues raised
is that it is not appropriate to have XMLGregorianCalendar extend
java.util.GregorianCalendar. There are too many differences between
Java calendar representation, java.util.GregorianCalendar, and XML Schema
definition of xsd:dateTime.


Issues:

1. XMLGregorianCalendar data representation for xsd:dateTime "year" and
   "fractionalSecond" field is insufficient.

   - The value space of xsd:dateTime "year" requires a Java representation of
     BigInteger. java.util.Calendar.YEAR field can only be accessed as int.

   - The value space of xsd:dateTime "fractionalSeconds" requires a Java
     representation of BigDecimal.
     java.util.Calendar.MILLISECOND only has precision for three fields.

2. No way to determine partial-order relation between instances
   of XMLGregorianCalendar. (Same issue for Duration.)

   xsd:duration and xsd:dateTime are specified as partially
   ordered in XML Schema specification. Thus, a comparator that
   returns 4 values, not just the typical three that a totally
   ordered comparator returns. New method also would return
   a value denoting INDETERMINATE.

3. XMLGregorianCalendar equals and hashcode methods be defined relative
   to the XML Schema comparison methods.

4. Incompatibility between java.util.Calendar TimeZone and
   xsd:dateTime timezone offset.
   Major differences:
   - java.util.Calendar daylight savings timezones are not representable
     in XML Schema datatype xsd:dateTime.
   - java.util.Calendar default for timezone is current machines default.
     XML Schema xsd:dateTime has no default timezone, it is significant
     to remember that no time zone exists when specifying comparison
     (see issue 2 and 3).
     The existence of daylight savings timezone in an XMLGregorianCalendar
     implementation that extends java.util.Calendar would be undefined
     for both addition of duration and comparison as defined in XML
     Schema Part 2.

5. Add method XMLGregorianCalendar.add(Duration) that is documented to
   work as specified in XML Schema Part 2.

6. Parse/printing

(a)Have only one parse method for all XML Schema builting datatypes
   representing date/time datatypes instead of one for each of
   8 datatypes. XML Schema lexical representation is unique for
   all 8 datatypes: dateTime, date, time, gYearMonth, gMonthDay,
   gYear, gMonth and gDay.

   from<XMLdatetime_datatypes>(String) ==> parse(String lexicalRep).

   This change eliminates a lot of API and simplifies handling of
   XML Schema union over XML Schema date/time datatypes.

(b)Have only one print method for all XML Schema datatypes
   representing date/time datatypes.

   String to<XMLDatatime_datatypes() ==> String toXMLFormat()

(c)introduce a method that allows one to determine which XML Schema builtin
   datatype an XMLGregorianCalendar instance represents at any point in time.
   Proposed method name is getXMLSchemaType().