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ece 627 intelligent web: ontology and beyond

ece 627 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.

amanda-beasley
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ece 627 intelligent web: ontology and beyond

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  1. ece 627intelligent web: ontology and beyond lecture 3: xml and xml schema

  2. XML, RDF, RDF Schemaoverview XML – simple introduction and XML Schema RDF – basics, language RDF Schema – basics, language Semantics of RDF and RDF Schema SPARQL – query language for RDF

  3. XMLintroduction 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

  4. XMLexample <? 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>

  5. XML prolog of a document the prolog: • an XML declaration • an optional reference to external structuring documents <?xml version="1.0" encoding="UTF-8"?>

  6. 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>

  7. XMLelements (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”)

  8. XMLcontent 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>

  9. 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"/>

  10. XML other components comments <!-- This is a comment --> processing instructions (define procedural attachments) <?stylesheet type="text/css” href="mystyle.css"?>

  11. XMLwell-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

  12. XMLtree 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>

  13. XMLtree model of XML documents

  14. 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

  15. 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)

  16. 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)>

  17. XMLDTD: 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)

  18. XMLDTD: its meaning a name element and a phone element may have any content in DTDs, #PCDATA is the only atomic type for elements

  19. 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)

  20. 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>

  21. XML Schemaelement types <element name=”…"/> type=“…” minOccurs=“x”(x may be any natural number) maxOccurs=“x”(any number of unbounded)

  22. XML Schemaelement types - examples <element name="email"/> <element name="head" minOccurs="1" maxOccurs="1"/> <element name="to" minOccurs="1"/>

  23. XML Schemaattribute types <attribute name=”…"/> type=“…” use=“x”(x may be optional or required or prohibited) default value

  24. XML Schemaattribute 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 orrequired default value: use="x" value="...", where x may be default or fixed

  25. XML Schemadata types built-in 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

  26. XML Schemadata 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

  27. XML Schemadata 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>

  28. XML Schemadata 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)

  29. XML Schemadata 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>

  30. XML Schemarestriction of simple data types <simpleType name="dayOfMonth"> <restriction base="integer"> <minInclusive value="1"/> <maxInclusive value="31"/> </restriction> </simpleType>

  31. XML Schemanamespaces 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

  32. XML Schemanamespaces 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

  33. XML Schemanamespaces – 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"/> </…>

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