XML Validation II Schemas Robin Burke ECT 360. Outline Namespaces Documents Data types XML Schemas...
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Transcript of XML Validation II Schemas Robin Burke ECT 360. Outline Namespaces Documents Data types XML Schemas...
XML Validation IISchemas
Robin Burke
ECT 360
Outline
Namespaces Documents Data types XML Schemas
ElementsAttributesDerived data types
RELAX NG
XML so far
Languages defined by DTDsnames assigned by designers
OK for standalone systems Doesn't have
The ability to handle naming conflictsThe ability to partition work among
different developers
Namespaces
A way to identify a set of labelselement / attribute namesattribute values
As belonging to a particular application
Example
recordings title artist
• group | artist-name+ date label
artworks title artist date exhibit
books title author date publisher
Problem
Want to create a list of items related to 50s Beat-era cultureincludes music, art, literature
Could create a new DTDbetter to reuse existing ones
Namespace idea
Associate a short prefix with an applicationSchema or DTD
Use the prefix with a colon to "qualify" namesmusic:artistart:artistbook:author
Namespace idea, cont'd
A namespace is an association between a set of namesa unique identifier (URI)a prefix used to identify them
Namespace declaration
Standalone<?xml:namespace
ns="http://bookpeople.com/book" prefix="book"?>
Part of element<html xmlns="http://www.w3.org/1999/xhtml">
in this case, no prefix<book xmlns:book="http://bookpeople.com/book">
Namespace URI
Not a URLthere is no resource at the given
locationjust a unique identifier
URL-like identifiers are goodassociated with an organizationmust be unique on the Internet
Example
DTDs Document Problem
how to import the namespaces?
Solution
Fully-qualified names everywhereyuk!
DTDs & namespaces don't work well together
XML so far
Languages defined by DTDscontain text elementsstring attributes
OK for text documents Not enough for
DatabasesBusiness process integration
Other DTD problems
Not XMLdifferent syntaxdifferent processor
No support for namespaces
Solution
Write language definition in XML Allow more control over document
contents XML document becomes
a complex data type XML language definition becomes
complex data type specification
XML Schema
Always a separate documentno internal option
Written in XMLvery verbose
Can be complex
Schemas and namespaces
A schema uses elements from one application
• the XML Schema language to define another
Namespaces are necessary Namespaces apply to elements
not values Namespace of element assumed to apply to attributes
can have attributes from different namespaces<html xmlns="http://www.w3.org/1999/xhtml"
xml:lang="en">
Example 1, XML
<grades assignment="Homework 1"><grade>
<student id="1234-12345">Jane Doe</student><assigned-grade>A</assigned-grade>
</grade><grade>
<student id="5432-54321">John Doe</student><assigned-grade>B</assigned-grade>
</grade></grades>
Example 1, DTD
<!ELEMENT grades (grade*)>
<!ATTLIST gradesassignment CDATA #IMPLIED>
<!ELEMENT grade (student, assigned-grade)>
<!ELEMENT student (#PCDATA)>
<!ATTLIST student
id CDATA #REQUIRED>
<!ELEMENT assigned-grade (#PCDATA)>
Data types
grades a collection of items of type grade can never have more than 40 students
grade a structure containing a student and an
assigned grade student
a structure containing an id and some text probably should constrain the student id
assigned-grade is text probably should constrain to A-D,F,I
Built-in types
Part of the schema language Base types
19 fundamental typesExamples: string, decimal
Derived types25 more types that use the base typesExamples: ID, positiveInteger
Built-in types, cont'd
To declare an element
<xs:element name="assigned-grade"
type="string">
Equivalent to<!ELEMENT assigned-grade (#PCDATA)>
Simple data type
A renaming of an existing data type<xs:element name="assigned-grade"
type="xs:string">
Or a restriction of a existing typestrings beginning with "D"more on this later
Complex datatype
<xs:element name=“name”>
<xs:complexType>
compositor
element declarations
attribute declarations
</xs:complexType>
</xs:element>
Compositor
sequence choice all
Sequence compositor
like "," in DTD DTD
<!ELEMENT foo (bar, baz)>
Schema<xs:element name="foo"> <xs:complexType> <xs:sequence> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:sequence> </xs:complexType></xs:element>
Elements in sequences
Can specify optional / # of occurrences ?
<xs:element ref="bar" minOccurs="0" type="xs:string">
*<xs:element ref="bar" minOccurs="0"
maxOccurs="unbounded" /> +
<xs:element ref="bar" minOccurs="1" maxOccurs="unbounded" />
What about...<xs:element ref="bar" minOccurs="2"
maxOccurs="4" />
Choice compositor
like "|" in DTD DTD
<!ELEMENT foo (bar | baz)>
Schema<xs:element name="foo"> <xs:complexType> <xs:choice> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:choice> </xs:complexType></xs:element>
All compositor
no simple DTD equivalent DTD
<!ELEMENT foo ( (bar, baz?) | (baz, bar?) >
Schema<xs:element name="foo"> <xs:complexType> <xs:all> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:all> </xs:complexType></xs:element>
Nesting
Compositors can be combined DTD
<!ELEMENT foo ( (bar, baz) | (thud, grunt) )> Schema
<xs:element name="foo"> <xs:complexType> <xs:sequence> <xs:choice> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:choice> <xs:choice> <xs:element ref="thud" /> <xs:element ref="grunt" /> </xs:choice> </xs:sequence> </xs:complexType></xs:element>
Example
<!ELEMENT grades (grade*)><!ELEMENT grade (student, assigned-grade)><!ELEMENT student (#PCDATA)><!ELEMENT assigned-grade (#PCDATA)>
Local naming
Suppose we want to reuse an element namedifferent place in the structure
Example <!ELEMENT url-catalog (link*)><!ELEMENT link (link, description?)>
• not a legal DTD
schema?
Using namespaces
Schema must say to use schema namespace what namespace it is defining
• targetNamespace Document must say
that it is using the Schema Instance namespace
what namespace(s) it is using what prefix(es) are used where to find the relevant schemas
Multi-schema documents
Possible to validate multi-schema documents
Must use any element to import namespacecan't restrict to certain elements
Attributes
DTD attribute typesCDATA, enumeration, token
Schemacan be any of the basic or derived
typescan also be user-defined types
Declaration<xs:attribute name="x" type="xs:string" use="required" default="abc" />
Attribute declaration
Part of complex typefollows compositor(one exception)
Declaration<xs:attribute name="foo"
type="xs:positiveInteger" />
What if the attribute is a more complex type itself?we'll get to that
Example
grades element? add homework attribute
Exception: simple content
If an element has "simple content"no compositor usedinstead simpleContent element
• and extension to declare type of the content
Example
<!ELEMENT student (#PCDATA)><!ATTLIST student
id CDATA #REQUIRED>
<xs:element name="student"> <xs:complexType> <xs:simpleContent> <xs:extension base="xs:string"> <xs:attribute name="id" type="xs:string" use="required"/> </xs:extension> </xs:simpleContent> </xs:complexType></xs:element>
How to read this
student is a complex typeit is not simply a renaming of an
existing type its content is simple
being of only one type• string
but with an attribute• id of type string which is required
Standalone types
A type can stand outside of an element definition must have a name<xs:complexType name="bar-n-baz">
<xs:sequence>
<xs:element ref="bar" />
<xs:element ref="baz" />
</xs:sequence>
</xs:complexType>
Used in element definition<xs:element name="foo" type="bar-n-baz" />
Deriving types
DTDs do not allow types restrictionsbeyond enumeration, CDATA, token
• for attributes
PCDATA• for content
Schemas have built-in typesalso capability to create your own
Derivation operations
listsequence of values
unioncombine two types
• allowing either
restrictionplacing limits on the legal values
List
<xs:element name="partList">
<xs:simpleType>
<xs:list itemType="partNo" />
</xs:simpleType>
</xs:element>
<partList>PN334-04 PN223-89 PQ1112-03</partList>
Must be separated by spacesprobably more useful to do this with
document structurepartList -> partNo*
Union
Allows data of either type to be used Example<xs:simpleType name="xs:integer">
<xs:union memberTypes="xs:negativeInteger xs:nonNegativeInteger" />
</xs:simpleType>
Bogus!
Restriction
Most useful Allow design to state exactly what
values are legalprices must be non-negativeSSN must follow a certain patternin-stock must yes or noetc.
Restriction, cont'd
Restrict a base typeaccording to "facets"
Different facets available for different data types
Facets
Example: enumeration
<xs:simpleType name="grade"> <xs:restriction base="xs:string"> <xs:enumeration value="A"/> <xs:enumeration value="B"/> <xs:enumeration value="C"/> <xs:enumeration value="D"/> <xs:enumeration value="F"/> <xs:enumeration value="I"/> </xs:restriction></xs:simpleType>
Example: numeric
<xs:simpleType name="drinkingAge"><xs:restriction
base="xs:positiveInteger"><xs:minInclusive value="21"/>
</xs:restriction></xs:simpleType>
Example: pattern
Regular expressions againderived from perl
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="([A-D]|F|I)(\+|\-)?" />
</xs:restriction>
</xs:simpleType>
Extended example
Complete schema for grades
RELAX NG
XML Schemas are biga lot of the page consists of
• < > /• repeated element names
RELAX NGcreated as an alternate validation
languagecompact, non-XML syntax
• also XML syntax
Example
element grades
{ element grade
{ element student { text },
element assigned-grade { text }
}*
}
Equivalent to<!ELEMENT grades (grade*)>
<!ELEMENT grade (student, assigned-grade)>
<!ELEMENT student (#PCDATA)>
<!ELEMENT assigned-grade (#PCDATA)>
Attributes
element grades
{ element grade
{ element student
{ text,
attribute id { text }
},
element assigned-grade (text)
}*
attribute assignment { text }
}
Types
instead of { text }use appropriate built-in data typeattribute age { xsd:positiveInteger }
facetsqualify with name / value pairattribute drinkingAge
{ xsd:positiveInteger
{ minInclusive="21" }
}
What does this one say?
element grade
{ element student ....,
{ element assigned-grade
{ text { pattern="([A-D](\+|\-)?|F)" }
|
( element assigned-grade
{ text "I" },
element reason { text }
)
}
}
The point
A schema language has two purposeslets the language designer state a
designlets the system validate documents
against that design Any language that serves this
purposes can be used
Validation languages
DTD SGML holdover ugly a dead-end fairly simple to express
Schema complete extensible baroque unreadable
RELAX NG readable
• esp. compact syntax more expressive than Schema fewer tools
Homework #3
Create a schema for "Grills.xml" Generate a schema for your
"books.xml" fileusing XML Spy's "generate"
featureedit generated schema
Next week
CSS SVG
an XML application for generating graphics
online reading
