ece 720 intelligent web: ontology and beyond Lecture 3: xml and xml schema
XML, RDF, RDF Schema overview XML – simple introduction and XML Schema RDF – basics, language RDF Schema – basics, language Semantics of RDF and RDF Schema SPARQL – query language for RDF ece 720, winter '12
XML introduction XML – Extensible Markup Language designed to describe structured documents users may create their own tags (they can create their own specific languages) tags have no semantics indicting how to present documents through a Web browser ece 720, winter '12
XML example <? xml version=“1.0” encoding=“UTF-8” ?> <book> <title>Semantic Web is Cool</title> <author>John Smith</author> <publisher>Springer</publisher> <year>1993</year> <ISBN>0387976892</ISBN> </book> ece 720, winter '12
XML prolog of a document the prolog: an XML declaration an optional reference to external structuring documents <?xml version="1.0" encoding="UTF-8"?> ece 720, winter '12
<author>John Smith</author> XML elements “things” the XML document talks about books, authors, publishers, … each element contains three parts an opening tag the content a closing tag <author>John Smith</author> ece 720, winter '12
XML elements (2) tag names can be chosen almost freely the first character must be a letter, an underscore, or a colon no name may begin with the string “xml” in any combination of cases (“Xml”, “xML”) ece 720, winter '12
XML content of elements content may be text, or other elements, or nothing <author> <name>John Smith</name> <phone> +1 − 780 − 492 5507 </phone> </author> if no content <author/> for <author></author> ece 720, winter '12
XML attributes an empty element is not necessarily meaningless it may have some properties in terms of attributes an attribute is a name-value pair inside the opening tag of an element <author name=”John Smith" phone="+1 − 780 − 492 5507"/> ece 720, winter '12
XML other components comments <!-- This is a comment --> processing instructions (define procedural attachments) <?stylesheet type="text/css” href="mystyle.css"?> ece 720, winter '12
XML well-formed documents syntactically correct documents – ones that obey some syntactic rules: there is only one outermost element (called root element) each element has an opening and a corresponding closing tag tags may not overlap <author><name>Lee Hong</author></name> attributes have unique names names of elements and tags must be permissible ece 720, winter '12
XML tree model of XML documents <email> <head> <from name=”John Smith" address=”johnsmith@gmail.com"/> <to name=”Jenny Doe" address=”jennydoe@hotmail.com"/> <subject>How are you?</subject> </head> <body> Hi, it was nice … </body> </email> ece 720, winter '12
XML tree model of XML documents ece 720, winter '12
XML structure of documents definition of all element and attribute names that may be used definition of structure what values an attribute may take which elements may or must occur within other elements, etc. if such structuring information exists, the document can be validated ece 720, winter '12
XML structure of documents (2) an XML document is valid if it is well-formed respects the structuring information it uses there are two ways of defining the structure of XML documents: DTDs (the older and more restricted way) XML Schema (offers extended possibilities) ece 720, winter '12
XML structure of documents: DTD <author> <name>John Smith</name> <phone> +1 − 780 − 492 5507 </phone> </author> DTD for above element (and all author elements): <!ELEMENT author (name,phone)> <!ELEMENT name (#PCDATA)> <!ELEMENT phone (#PCDATA)> ece 720, winter '12
XML DTD: its meaning the element types author, name, and phone may be used in the document an author element contains a name element and a phone element, in that order (sequence) ece 720, winter '12
XML DTD: its meaning a name element and a phone element may have any content in DTDs, #PCDATA is the only atomic type for elements ece 720, winter '12
XML Schema richer language for defining the structure of XML documents its syntax is based on XML itself sophisticated set of data types, compared to DTDs (which only supports strings) ece 720, winter '12
XML Schema (2) it is like an element with an opening tag like <xsd:schema xmlns:xsd=“http://www.w3.org/2001 XMLSchema” version=“1.0”> ... </xsd:schema> ece 720, winter '12
XML Schema element types <element name=”…"/> type=“…” minOccurs=“x” (x may be any natural number) maxOccurs=“x” (any number of unbounded) ece 720, winter '12
XML Schema element types - examples <element name="email"/> <element name="head" minOccurs="1" maxOccurs="1"/> <element name="to" minOccurs="1"/> ece 720, winter '12
XML Schema attribute types <attribute name=”…"/> type=“…” use=“x” (x may be optional or required or prohibited) default value ece 720, winter '12
XML Schema attribute types - examples <attribute name="id" type="ID“ use="required"/> < attribute name="speaks" type="Language" use="default" value="en"/> existence: use="x", where x may be optional or required default value: use="x" value="...", where x may be default or fixed ece 720, winter '12
XML Schema data types built-in data types user-defined data types numerical data: integer, Short, … string: string, ID, IDREF, CDATA, … date and time: time, Month, … user-defined data types simple data types, which cannot use elements or attributes complex data types, which can use these ece 720, winter '12
XML Schema data types (2) complex data types are defined from already existing data types by defining some attributes (if any) and using: sequence, a sequence of existing data type elements (order is important) all, a collection of elements that must appear (order is not important) choice, a collection of elements, of which one will be chosen ece 720, winter '12
XML Schema data type extension already existing data types can be extended by new elements or attributes <complexType name="extendedLecturerType"> <extension base="lecturerType"> <sequence> <element name="email" type="string" minOccurs="0" maxOccurs="1"/> </sequence> <attribute name="rank" type="string" use="required"/> </extension> </complexType> ece 720, winter '12
XML Schema data type restriction an existing data type may be restricted by adding constraints on certain values (it is not the opposite process from extension) the following hierarchical relationship still holds: instances of the restricted type are also instances of the original type (they satisfy at least the constraints of the original type and some new ones) ece 720, winter '12
XML Schema data type restriction – example <complexType name="restrictedLecturerType"> <restriction base="lecturerType"> <sequence> <element name="firstname" type="string" minOccurs="1" maxOccurs="2"/> </sequence> <attribute name="title" type="string" use="required"/> </restriction> </complexType> ece 720, winter '12
XML Schema restriction of simple data types <simpleType name="dayOfMonth"> <restriction base="integer"> <minInclusive value="1"/> <maxInclusive value="31"/> </restriction> </simpleType> ece 720, winter '12
XML Schema namespaces a single XML document may use more than one DTD or schema in order to avoid clashes a different prefix for each DTD or schema can/should be used prefix:name ece 720, winter '12
XML Schema namespaces namespaces are declared within an element and can be used in that element and any of its children (elements and attributes) a namespace declaration has the form: xmlns:prefix="location" location is the address of the DTD or schema if a prefix is not specified: xmlns="location" then the location is used by default ece 720, winter '12
XML Schema namespaces – example <… xmlns="http://www.ua.ca/basic.xsd" xmlns:staff="http://www.ua.ca/staff.xsd"> <staff:faculty staff:title=“professor" staff:name="John Smith" staff:department=”ECE"/> <academicStaff title="lecturer" name=”Jenny Doe" school="Information Technology"/> </…> ece 720, winter '12