XSDL – Part II

XML Foundations (INFO 242)

Erik Wilde, UC Berkeley School of Information
2007-10-25

This work is licensed under a CC
Attribution 3.0 Unported License

Abstract

XSDL Complex Types describe element content if this content is using attributes and/or element content other than only character data. Thus, complex types are used to define the allowed markup structures for a class of documents. Using XSDL's type concepts, it is easier to represent model-level information in a schema, because type hierarchies can represent model-level specializations.

Outline (Complex Types)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

What is a Complex Type?

Complex types describe the allowed element content
- they describe what the element may contain (the element's content model)
- they describe the attributes that an element may have (the element's attribute list)
Complex types do not define the element name
- the complex type defines which content is allowed for the element
- the element definition uses the complex type to define the allowed element content
Complex types have similar properties to simple types
- they can be named or anonymous
- Complex Type Derivation can be used to construct a type hierarchy

Complex Type Example

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 <xs:element name="billingAddress" type="addressType"/>
 <xs:element name="shippingAddress" type="addressType"/>
 <xs:complexType name="addressType">
  <xs:sequence>
   <xs:element name="name" type="xs:string"/>
   <xs:element name="street" type="xs:string"/>
   <xs:element name="city" type="xs:string"/>
   <xs:element name="state" type="xs:string" minOccurs="0"/>
   <xs:element name="zip" type="xs:decimal"/>
  </xs:sequence>
  <xs:attribute name="country" type="xs:NMTOKEN"/>
 </xs:complexType>
</xs:schema>

Complex Types & Content Types

Complex types can have different kinds of content
- simple content refers to simple type content using additional attributes
- complex content is anything else (anything beyond simple type content)
Complex Type Derivation heavily depends on this classification

Simple Types	Complex Types
	Simple Content	Complex Content
	Simple Content	Element Only	Mixed	Empty

Outline (Content Models)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

DTD Content Models

Defining Elements in DTDs uses a compact syntax
- XSDL supports the same facilities with a more verbose syntax
- XSDL adds features which DTDs do not support
DTDs allow elements to be mandatory, optional, repeatable, or optional and repeatable
- XSDL allows the cardinality to be specified
DTDs allow sequences (,) and alternatives (|)
- XSDL introduces a (very limited) operator for all groups
Apart from the syntax, XSDL content models are not very different

Mixed Content

DTDs define mixed content by mixing #PCDATA into the content model
- DTDs always require mixed content to use the form ( #PCDATA | a | b )*
- the occurrence of elements in mixed content cannot be controlled
XSDL defines mixed content outside of the content model
- the content model is defined like an element-only content model
- the mixed attribute on the type marks the type as being mixed
XSDL mixed content can use all model groups
- it is possible to constrain element occurrences in the same way as in element-only content
- in practice, this feature is rarely used (mixed content often is very loosely defined)

 <xs:element name="p" type="mixedType"/>
 <xs:complexType name="mixedType" mixed="true">
  <xs:choice maxOccurs="unbounded" minOccurs="0">
   <xs:element ref="b"/>
   <xs:element name="i" type="xs:string"/>
   <xs:element name="u" type="xs:string"/>
  </xs:choice>
  <xs:attribute ref="class"/>
 </xs:complexType>

Empty Content

DTDs have a special keyword for empty elements
- instead of the content model, the keyword EMPTY is used
- empty elements may still have attribute lists associated with them
XSDL empty types are defined implicitly
- there is no explicit keyword for defining an empty type
- if a type has no model group inside it, it is empty (it still may have attributes)

Outline (XSDL Design Patterns)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

Global Elements? Named Types?

XSDL's design dimensions allow different strategies
Elements/attributes can be defined as local or global
- local elements/attributes are defined where they are used
- global elements/attributes are globally defined and then referenced
- elements/attributes which should be reused must be defined as global
Types can be defined as anonymous or named
- anonymous types are defined where they are used
- named types are globally defined and then referenced
- types which should be reused must be defined as named
XSDL design patterns can favor one type of definition
- reuse always required global elements/attributes and named types
- having everything global/named results in bigger schema

Sample XML

<?xml version="1.0" encoding="UTF-8"?>
<person>
 <name>
  <givenname>Erik</givenname>
  <givenname>Thomas</givenname>
  <surname>Wilde</surname>
 </name>
 <address>
  <company>ETH Zürich</company>
  <email>net.dret@dret.net</email>
 </address>
</person>

Outline (Russian Doll)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

Russian Doll XSDL

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
 <xs:element name="person">
  <xs:complexType>
   <xs:sequence>
    <xs:element name="name">
     <xs:complexType>
      <xs:sequence>
       <xs:element name="givenname" type="xs:token" maxOccurs="unbounded"/>
       <xs:element name="surname" type="xs:string"/>
      </xs:sequence>
     </xs:complexType>
    </xs:element>
    <xs:element name="address">
     <xs:complexType>
      <xs:sequence>
       <xs:element name="company" type="xs:string"/>
       <xs:element name="email" minOccurs="0">
        <xs:simpleType>
         <xs:restriction base="xs:string">
          <xs:pattern value=".*@.*\..*"/>
         </xs:restriction>
        </xs:simpleType>
       </xs:element>
      </xs:sequence>
     </xs:complexType>
    </xs:element>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
</xs:schema>

Russian Doll Structure

Outline (Venetian Blinds)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

Venetian Blinds XSDL

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
 <xs:element name="person" type="personType"/>
 <xs:complexType name="personType">
  <xs:sequence>
   <xs:element name="name" type="nameType"/>
   <xs:element name="address" type="addressType"/>
  </xs:sequence>
 </xs:complexType>
 <xs:complexType name="nameType">
  <xs:sequence>
   <xs:element name="givenname" type="givennameType" maxOccurs="unbounded"/>
   <xs:element name="surname" type="surnameType"/>
  </xs:sequence>
 </xs:complexType>
 <xs:simpleType name="givennameType">
  <xs:restriction base="xs:token"/>
 </xs:simpleType>
 <xs:simpleType name="surnameType">
  <xs:restriction base="xs:string"/>
 </xs:simpleType>
 <xs:complexType name="addressType">
  <xs:sequence>
   <xs:element name="company" type="companyType"/>
   <xs:element name="email" type="emailType" minOccurs="0"/>
  </xs:sequence>
 </xs:complexType>
 <xs:simpleType name="companyType">
  <xs:restriction base="xs:string"/>
 </xs:simpleType>
 <xs:simpleType name="emailType">
  <xs:restriction base="xs:string">
   <xs:pattern value=".*@.*\..*"/>
  </xs:restriction>
 </xs:simpleType>
</xs:schema>

Venetian Blinds Structure

Outline (Salami Slice)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

Salami Slice XSDL

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
 <xs:element name="person">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="name"/>
    <xs:element ref="address"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
 <xs:element name="name">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="givenname" maxOccurs="unbounded"/>
    <xs:element ref="surname"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
 <xs:element name="givenname" type="xs:token"/>
 <xs:element name="surname" type="xs:string"/>
 <xs:element name="address">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="company"/>
    <xs:element ref="email" minOccurs="0"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
 <xs:element name="company" type="xs:string"/>
 <xs:element name="email">
  <xs:simpleType>
   <xs:restriction base="xs:string">
    <xs:pattern value=".*@.*\..*"/>
   </xs:restriction>
  </xs:simpleType>
 </xs:element>
</xs:schema>

Salami Slice Structure

Outline (Garden of Eden)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

Garden of Eden XSDL

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
 <xs:element name="person" type="personType"/>
 <xs:element name="name" type="nameType"/>
 <xs:element name="givenname" type="givennameType"/>
 <xs:element name="surname" type="surnameType"/>
 <xs:element name="address" type="addressType"/>
 <xs:element name="company" type="companyType"/>
 <xs:element name="email" type="emailType"/>
 <xs:complexType name="personType">
  <xs:sequence>
   <xs:element ref="name"/>
   <xs:element ref="address"/>
  </xs:sequence>
 </xs:complexType>
 <xs:complexType name="nameType">
  <xs:sequence>
   <xs:element ref="givenname" maxOccurs="unbounded"/>
   <xs:element ref="surname"/>
  </xs:sequence>
 </xs:complexType>
 <xs:simpleType name="givennameType">
  <xs:restriction base="xs:token"/>
 </xs:simpleType>
 <xs:simpleType name="surnameType">
  <xs:restriction base="xs:string"/>
 </xs:simpleType>
 <xs:complexType name="addressType">
  <xs:sequence>
   <xs:element ref="company"/>
   <xs:element ref="email" minOccurs="0"/>
  </xs:sequence>
 </xs:complexType>
 <xs:simpleType name="companyType">
  <xs:restriction base="xs:string"/>
 </xs:simpleType>
 <xs:simpleType name="emailType">
  <xs:restriction base="xs:string">
   <xs:pattern value=".*@.*\..*"/>
  </xs:restriction>
 </xs:simpleType>
</xs:schema>

Garden of Eden Structure

Outline (Conclusions)

Complex Types [6]
1. Content Models [3]
XSDL Design Patterns [10]
1. Russian Doll [2]
2. Venetian Blinds [2]
3. Salami Slice [2]
4. Garden of Eden [2]
Conclusions [1]

Typed XML Structures

XSDL introduces a type layer to schema languages
Types facilitate abstractions (and thus modeling)
Complex types define how elements have to be used
Designing XSDL can be done in many different ways