Java Reference
In-Depth Information
XMLSchemawasintroducedbytheW3CtoovercomelimitationswithDTD,suchas
DTD'slackofsupportfornamespaces.Also,XMLSchemaprovidesanobject-oriented
approachtodeclaringanXMLdocument'sgrammar.Thisgrammarlanguageprovides
a much larger set of primitive types than DTD's CDATA and PCDATA types. For ex-
ample, you'll find integer, floating-point, various date and time, and string types to be
part of XML Schema.
Note
XML Schema predefines 19 primitive types, which are expressed via the
following identifiers:
anyURI
,
base64Binary
,
boolean
,
date
,
dateTime
,
decimal
,
double
,
duration
,
float
,
hexBinary
,
gDay
,
gMonth
,
gMonthDay
,
gYear
,
gYearMonth
,
NOTATION
,
QName
,
string
, and
time
.
XML Schema provides
restriction
(reducing the set of permitted values through
constraints),
list
(allowing a sequence of values), and
union
(allowing a choice of
valuesfromseveraltypes)derivationmethodsforcreatingnew
simple types
fromthese
primitive types. For example, XML Schema derives 13 integer types from
decim-
al
through restriction; these types are expressed via the following identifiers:
byte
,
int
,
integer
,
long
,
negativeInteger
,
nonNegativeInteger
,
nonPos-
itiveInteger
,
positiveInteger
,
short
,
unsignedByte
,
un-
signedInt
,
unsignedLong
, and
unsignedShort
. It also provides support for
creating
complex types
from simple types.
AgoodwaytobecomefamiliarwithXMLSchemaistofollowthroughanexample,
such as creating a schema for
Listing 10-1
'
s recipe language document. The first step
increatingthisrecipelanguageschemaistoidentifyallitselementsandattributes.The
elements are
recipe
,
title
,
ingredients
,
instructions
, and
ingredi-
ent
;
qty
is the solitary attribute.
ThenextstepistoclassifytheelementsaccordingtoXMLSchema's
content model
,
which specifies the types of child elements and text
nodes
(see
ht-
tp://en.wikipedia.org/wiki/Node_(computer_science)
)
that can be
includedinanelement.Anelementisconsideredtobe
empty
whentheelementhasno
childelementsortextnodes,
simple
whenonlytextnodesareaccepted,
complex
,when
onlychildelementsareaccepted,and
mixed
whenchildelementsandtextnodesareac-
cepted.Noneof
Listing10-1
'
selementshaveemptyormixedcontentmodels.However,
the
title
,
ingredient
,and
instructions
elementshavesimplecontentmod-
els; and the
recipe
and
ingredients
elements have complex content models.
Forelementsthathaveasimplecontentmodel,wecandistinguishbetweenelements
having attributes and elements not having attributes. XML Schema classifies elements
havingasimplecontentmodelandnoattributesassimpletypes.Furthermore,itclassi-
