Java Reference
In-Depth Information
fieselementshavingasimplecontentmodelandattributes,orelementsfromothercon-
tentmodelsascomplextypes.Furthermore,XMLSchemaclassifiesattributesassimple
typesbecausetheyonlycontaintextvalues—attributesdon'thavechildelements.
List-
types. Its
recipe
,
ingredients
, and
ingredient
elements are complex types.
At this point, we can begin to declare the schema. The following example presents
the introductory
schema
element:
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
The
schema
elementintroducesthegrammar.Italsoassignsthecommonlyused
xs
namespace prefix to the standard XML Schema namespace;
xs:
is subsequently pre-
pended to XML Schema element names.
Next, we use the
element
element to declare the
title
and
instructions
simple type elements, as follows:
<xs:element name="title" type="xs:string"/>
<xs:element name="instructions" type="xs:string"/>
XMLSchemarequiresthateachelementhaveanameand(unlikeDTD)beassociated
with a type, which identifies the kind of data stored in the element. For example, the
first
element
declaration identifies
title
as the name via its
name
attribute and
string
asthetypeviaits
type
attribute(stringorcharacterdataappearsbetweenthe
<title>
and
</title>
tags). The
xs:
prefix in
xs:string
is required because
string
is a predefined W3C type.
Continuing,wenowusethe
attribute
elementtodeclarethe
qty
simpletypeat-
tribute, as follows:
<xs:attribute
name="qty"
type="xs:unsignedInt"
de-
fault="1"/>
This
attribute
element declares an attribute named
qty
. I've chosen
un-
signedInt
as this attribute's
type
because quantities are nonnegative values. Fur-
thermore,I'vespecified
1
asthe
default
valueforwhen
qty
isnotspecified—
at-
tribute
elements default to declaring optional attributes.
Note
The order of element and attribute declarations is not significant within a
schema.
Nowthatwe'vedeclaredthesimpletypes,wecanstarttodeclarethecomplextypes.
To begin, we'll declare
recipe
, as follows:
