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Representing Data with XML
February 26, 2004
Neal Arthorne
Data Representation
Design goals for data representation:Portable (platform independent)Easy for machines to processHuman legibleFlexible and usable over the Internet and
other networksConcisely defined with formal rules
Extensible Markup Language
World Wide Web Consortium (W3C) defines the Extensible Markup Language (XML)W3C also defined HTML, CSS, HTTP, SVG
and other markup languagesXML Working group formed in 1996XML 1.0 (Third Edition) 4 February 2004
(original Recommendation in 1998)
XML Example
<?xml version="1.0" encoding="UTF-8"?><stamps title="Queen Victoria Jubilee issue - 5 cents"> <name>Queen Victoria Jubilee issue - 5 cents</name> <description>Two portraits of Queen Victoria 1837 and 1867.
The portrait on the left...</description> <country>Canada</country> <dateOfIssue>1897-06-19</dateOfIssue> <denomination>1 x 5¢</denomination> <design>Lyndwode Charles Pereira, Peleg Franklin
Brownell</design> <perforations>12</perforations> <quantity>750,000</quantity> <printer>American Bank Note Company, Ottawa</printer> <picture>file://test/stamps/1850-1900/Jubilee-1897-
5_cents.jpg</picture></stamps>
Prolog
Element
Attribute
Entity reference
XML
XML documents should be well-formed (syntax, closing tags etc)
XML documents are “valid” if they are validated with a Document Type Definition (DTD)
DTDs provide a grammar for the XML by defining elements, attributes and entities
XML Advantages
XML provides: Logical structure for data in a textual representation Formal rules for validating documents Flexibility to define your own markup language Portability across networks and platforms Becoming a widely accepted data interchange format Processed with off-the-shelf tools
XML Disadvantages
XML drawbacks: Not a binary format so it requires a lot of overhead for
a little bit of data Very little support for binary or mixed media data
formats (hex or base64 encoding) Only for data and holds no semantics or reasoning
DTDs do not provide: Data types for each element or attribute Complex structural rules for documents
XML Schema
XML Schema defines a new schema language to replace DTD
Standardized by W3C in 2001 Provides data typing and logical structure Written in XML (easy to process) Higher complexity than DTD
XML Schema Example
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="stamps"> <xsd:complexType> <xsd:all> <xsd:element name="name" type="xsd:string"/> <xsd:element name="description" type="xsd:string"/> <xsd:element name="country" type="xsd:string"/> <xsd:element name="dateOfIssue" type="xsd:date"/> <xsd:element minOccurs="0" name="denomination" type="xsd:string"/> <xsd:element minOccurs="0" name="design" type="xsd:string"/> <xsd:element minOccurs="0" name="perforations" type="xsd:string"/> <xsd:element minOccurs="0" name="printer" type="xsd:string"/> <xsd:element minOccurs="0" name="quantity" type="xsd:string"/> <xsd:element minOccurs="0" name="picture" type="xsd:anyURI"/> </xsd:all> <xsd:attribute name="title" type="xsd:string"/> </xsd:complexType> </xsd:element></xsd:schema>
Element name Data type
Attribute name Data type
•An XML document is an ‘instance document’ of an XML Schema
Simple Types
Simple Types are of three varieties: Atomic: Built-in or derived, e.g.
<xsd:simpleType name="myInteger"> <xsd:restriction base="xsd:integer"> <xsd:minInclusive value="10000"/> <xsd:maxInclusive value="99999"/> </xsd:restriction></xsd:simpleType>
List: multiple items of the same type Union: Union or two or more Simple Types
Built-in Types
XML Schema defines numerous built-in types: integer, decimal, token, byte, boolean, date, time, short, long, float, anyURI, language
Derived types use facets to restrict existing types: min/maxInclusive, min/maxExclusive, pattern, enumeration, min/maxLength, length, totalDigits, fractionDigits
Complex Types
Complex Types define logical structures with attributes and nested elements
They use a sequence, choice or all containing elements that use Simple Types or other Complex Types
May reference types defined elsewhere in the schema or imported using import statement
In the Schema of Things
XML Schema supersedes DTD Defines a typed data format with no
semantics or relations between data Next step: higher level of abstraction and
the ability to define objects and relations
Resource Description Framework
W3C standard for describing resources on the World Wide Web (1999, revised 2004)
Generalized to identify objects that may not be retrievable on the Web
Objects identified by Uniform Resource Identifiers (URIs)
RDF represented by a directed graph and in XML syntax
RDF Example
In English: http://www.example.com/people/diaz/contact has the full name Federico Diaz and has an employer called Fisher and Sons.
http://www.example.com/people/diaz/contact
Federico Diaz
http://www.w3.org/2000/10/pim/contact#fullName
http://www.fisherandsons.com/contact
http://www.w3.org/2000/10/work#employer
RDF Parts
Each RDF statement is a triple containing a subject (identifier by URI), a predicate (e.g.
creator, title, full name) and an object An object can be either a literal value (e.g.
Federico Diaz) or another RDF resource All three parts can be identified with an
URI and fragment identifier #
RDF Semantics
RDF attaches no specific meaning to RDF statements – just like the name of a database field is meaningless to an SQL engine
RDF does provide a way to attach data types to literal values, but RDF does not define data types
Generally RDF software uses the XML Schema data types <size rdf:datatype=“xsd#int”>10</size>
Arbitrary XML can also be used as a literal <x:prop rdf:parseType="Literal“>
<a:size>10</a:size></x:prop>
RDF Schema
RDF Schema is a ‘vocabulary description language’ that relates resources to each other using RDF
RDFS uses ‘classes’ of objects like in Object-Oriented (OO) systems
Class properties relate to other classes using OO concepts such as generalization
RDF Schema Use
Differs from OO in that Properties are defined in terms of the resources to which they apply (their domain) – they are not restricted to the scope of a single class domain: Classes to which a Property applies range: The Class of a Property (i.e. type)
Allows new Properties to be created that apply to the same domain without redefining the domain
RDFS Classes
Classes introduced by RDFS: Resource - top level class Literal – all literal values like text strings Class – the class of all classes Datatype – top level RDF datatype
Properties introduced by RDFS: subClassOf subPropertyOf domain – domain of a Property range – range of a Property label, comment, seeAlso – human readable labels
inheritance
RDF/RDFS
Lets authors create vocabularies of Classes and Properties and show how the terms should be used to describe resources, e.g. Property ‘author’ applies to class ‘Book’ Class ‘Employee’ is a subclass of ‘Person’
Does not define descriptive properties such as ‘dateOfIssue’ or ‘title’ but references them using URIs
Like in XML/XML Schema, an RDF instance document can be validated against its RDF Schema
Machines Understanding the Web
RDF/RDFS along with XML/XML Schema provide a means to describe resources on the web with basic generalization
For a higher conceptual level, applications require semantic information
Ontologies serve as a starting point for understanding
Ontologies on the Web
“Ontologies define the terms used to represent an area of knowledge.” – OWL Use Cases & Requirements, 2004
Example use cases: A web portal that needs to classify information Multimedia archive that requires a taxonomy of media
or content-specific properties Corporate portal website that integrates vocabularies
from different departments
Web Ontology Language (OWL)
Supersedes DAML+OIL DARPA Agent Markup Language (DAML) was based
on RDF/RDFS and includes much of what is now OWL
Adds terms used to better describe relations between classes of RDF resources
With OWL ontologies can be integrated, extended and shared
OWL Features
OWL improvements on RDF/RDFS: Cardinality
min/maxCardinality for Properties with respect to a Class Equality, disjointness
equivalentClass, equivalentProperty, sameAs, differentFrom, disjointWith
Transitive, Symmetric, Functional Properties labelling a Property allows for reasoning
A has B and B has C implies A has C (Transitive) A has B implies B has A (Symmetric)
OWL Features con’t
Boolean expressions of Class relations unionOf, complementOf, intersectionOf
Property restrictions Limits how properties can be used by an instance
of a class
Versioning priorVersion, versionInfo, incompatibleWith,
backwardCompatibleWith
Conclusion
XML XML Schema
RDF RDF Schema
OWL
Unicode/ISO byte streams
Data formatting and data types
Machine data representation
Resource description and vocabulary
Knowledge processing and reasoning
??? Conceptual level reasoning – ‘smart’ applications
Knowledge
Data
References
World Wide Web Consortium http://www.w3.org
XML http://www.w3.org/TR/REC-xml
XML Schema Part 0: Primer http://www.w3.org/TR/xmlschema-0/
RDF Primer http://www.w3.org/TR/rdf-primer/
RDF Concepts http://www.w3.org/TR/rdf-concepts/
RDF/XML Syntax http://www.w3.org/TR/rdf-syntax-grammar/
RDF Schema http://www.w3.org/TR/rdf-schema/
OWL Use Cases & Requirements http://www.w3.org/TR/webont-req/
OWL Overview http://www.w3.org/TR/owl-features/
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