More XML XML schema, XPATH, XSLT

More XMLXML schema, XPATH, XSLT CS 502 – 20020214 Carl Lagoze – Cornell University

Semantic Web Xpath Data Decomposition RDF Semantic Relationships XSLT Data Transformation DAML+OIL Concept Building Schema Type Definition Namespaces Concept Integration Traditional Library Central control Uniform expertise Traditional Web Distributed, interlinked Viewable Documents XML Markup Syntax URIs Name Convention HTTP Access Method A little context DTD Tag Sets

XML Schema Define… • elements • attributes • Nesting structure (parent/child rela.) • Sibling sequence • Sibling cardinality • Presence or absence of text values • Element and attribute data types • Element and attribute default values

Simple vs. Complex Values • Element with complex value contains other elements (has children) • Element with simple value does not have children (e.g. text).

Simple Value Types • Restriction on type of content • Syntax • <xs:element name=“xxx” type=“yyy”/> • Examples • <xs:element name=“lastname” type=“xs:string”/> • <xs:element name=“age” type=“xs:number”/> • <xs:element name=“age” type=“xs:date”/>

Facets • Restrictions on values within type context • Examples

Simple Example • Memo Schema • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/memo.xsd • Memo Instance Document • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/memo.xml

Type extension/restriction

Type Reuse

Type Reuse Example • Base Type Definition • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/address.xsd • Type Use • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/person.xsd • Instance Document • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/person.xml

DTD & XML Schema Equivalence • DTD Example • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/channel.dtd • Equivalent Schema • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/channel.xsd • Instance Document • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xmlschema/channel.xml

XPath • Language for addressing parts of an XML document • XSLT • Xpointer • Tree model similar to DOM • W3C Recommendation (1999) • http://www.w3.org/TR/xpath

Xpath Concepts • Context Node • current node in XML document that is basis of path evaluation • Default to root • Location Steps – selection from context node • Axis – sub-tree(s) selection from context node • Node Test – select specific elements or node type(s) • Predicates – predicate for filtering after axis and node tests

Axis • child: all children of context • descendent: all children, grandchildren, … • parent: • ancestor

Node Test • Element name: e.g. “Book” • Wildcard: * • Type(): where type is “node”, “text”, etc.

Predicate • Boolean and comparative operators • Types • Numbers • Strings • node-sets • Functions • Examples • boolean starts-with(string, string) • number count(node-set)

Combining all into a location set specification • Syntax: axis::node-test[predicate] • Examples: • child::Book[position() <= 3] – first three <Book> child elements of context • child::Book/attribute::color – “color” attributes of <Book> child elements of context

Abbreviations • Child axis is default • child::Book  Book • Attribute axis  @ • Book[position() = 1]/@color • “.” (self), “..” (parent), “//” (descendent-or-self) • position() = n  n • Example • Book[2]/@color

XML Transformations (XSLT) • Origins: separate rendering from data • Roots in CSS • W3C Recommendation • http://www.w3.org/TR/xslt • Generalized notion of transformation for: • Multiple renderings • Structural transformation between different languages • Dynamic documents • XSLT – rule-based (declarative) language for transformations

XSLT Capabilities • Generate constant text • Filter out content • Change tree ordering • Duplicate nodes • Sort nodes • Any computational task (XSLT is “turing complete”)

XSLT Processing Model XSLT serialize parse Input XMLdoc Parsedtree Xformedtree Outputdoc(xml, html, etc)

XSLT “engine” XML input XSLT Engine (SAXON) Output Document (xml, html, …) XSLT “program”

Stylesheet Document or Program • XML document rooted in <stylesheet> element • Body is set of templates • Xpath expression specifies elements in source tree • Body of template specifies contribution of source elements to result tree • Not sequential execution

Template Form • Elements from xsl namespace are transform instructions • Match attribute value is xpath expression • Non-xsl namespace elements are literals.

A simple example • XML base file • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xslt/simple.xml • XSLT file • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xslt/simple.xsl

XSLT Recursive Programming Style • Document driven, template matching • Conflict resolution rules • Mode setting • <xsl:apply-templates mode=“this”> • <xsl:template match=“foo” mode=“this”> • <xsl:template match=“foo” mode=“that”> • Context setting • <xsl:apply-templates select=“//bar”>

XSLT Procedural Programming • Sequential programming style • Basics • for-each – loop through a set of elements • call-template – like a standard procedure call

For-each programming example • XML base file • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xslt/foreach.xml • XSLT file • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xslt/foreach.xsl

Call-template programming example • XML base file • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xslt/call.xml • XSLT file • http://www.cs.cornell.edu/Courses/cs502/2002SP/Demos/xslt/call.xsl

Result Tree Creation • Literals – any element not in xsl namespace • <xsl:text> - content directly to output • <xsl:value-of> - expression processing • <xsl:copy> and <xsl:copyof> - Copy current node or selected nodes into result tree • <xsl:element> - instantiate an element • <xsl:attribute> - instantiate an attribute

Various other programming constructs • Conditionals • Variables (declaration and use) • Some type conversion • Sorting

Resources • XSLT – WROX Press • ISBN 1-861005-06-7 • W3C XSLT Page • http://www.w3.org/Style/XSL/ • Arbortext XSL Tutorial • http://www.nwalsh.com/docs/tutorials/xsl/

More XML XML schema, XPATH, XSLT