8. Updates + XSLT 8.1 Introduction 8. Updates + XSLT

Transcrição

16.12.2009
8. Updates + XSLT
8.1 Introduction
8.2 Full document replacement
XML Databases
8.3 XQuery Update Facility
8. Updates + XSLT, 16.12.09
8.4 XSLT & the XSLTRANSFORM function
Silke Eckstein
Andreas Kupfer
Institut für Informationssysteme
Technische Universität Braunschweig
http://www.ifis.cs.tu-bs.de
8.5 Overview
8.6 References
XML Databases – Silke Eckstein – Institut für Informationssysteme – TU Braunschweig
8.1 Introduction
8. Updates + XSLT
• Three general techniques for modifying XML
documents:
8.1 Introduction
– Full document replacement
• Replace existing document with an updated one
– XQueryUpdate Facility
• Standardized extension to XQuery
• Modify, insert or delete individual elements and attributes
within an XML document
8.5 Overview
– Extensible Stylesheet Language Transformation (XSLT)
• Apply a style sheet to an XML document
• Use XSLTRANSFORM function to do this in SQL
statements
[NK09]
8.6 References
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• Replacing a full XML document
• Example
– Use regular SQL UPDATE statement to replace a full XML
document in a table with a new document
UPDATE customer
SET info =
'<?xml version="1.0" encoding="UTF-8" ?>
<customerinfo Cid="1010">
<name>Larry Trotter</name>
<addr country="England">
<street>5 Rosewood</street>
...
</addr>
<phone type="work">416-555-1358</phone>
</customerinfo>'
WHERE cid = 1000;
• treats XML document as a "black box"
• application needs to provide new document
– UPDATE statement needs to select a single row
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•
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predicate on the relational columns of the table
predicates on an XML element value
predicates on an XML attribute value
predicates on XML and relational values
– New documents can be provided via parameter markers
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• Using parameter marker or host variables
• 2 more examples:
– to provide the new XML document:
UPDATE customer SET info = ?
UPDATE customer
SET info = ?
WHERE XMLEXISTS('$INFO/customerinfo[name = "Larry Trotter"]
AND cid = 1000;
WHERE cid = 1000
UPDATE customer SET info = :hvar WHERE cid = 1000
– ... and to provide the relational value:
UPDATE customer SET info = ?
UPDATE customer
SET info = ?
WHERE XMLEXISTS('$INFO/customerinfo/phone[type = "work"
and text()="416-555-1358"]');
WHERE cid = ?
UPDATE customer SET info = :hvar WHERE cid = :hvar2
• Replacing an existing XML document with a NULL value
– removes the document from the row without deleting the row:
UPDATE customer SET info = NULL WHERE cid = 1000
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8. Updates + XSLT
• XQuery Update Facility
8.1 Introduction
– Standardized extension to XQuery
– Allows to modify, insert or delete individual elements or
attributes within an XML document
– Makes updating easier and provides more performance
than full document replacements
– Allows to modify nodes in the following way:
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8.5 Overview
8.6 References
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• XQuery Update Facility: New XQuery expressions
• Node insertion
– An insert expression is an updating expression that inserts
copies of zero or more nodes into a designated position
with respect to a target node.
XQuery expressions
FLWORExpr
QuantifiedExpr
TypeswitchExpr
IfExpr
InsertExpr
DeleteExpr
RenameExpr
ReplaceExpr
TransformExpr
OrExpr
Replace the value of a node
Replace a node with a new one
Insert a new node (at a specific location)
Delete a node
Rename a node
Modify multiple nodes in a document in a single statement
Update multiple documents ib a single statement
ExprSingle ::=
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Syntax and examples
taken from the W3C
web site.
Syntax
InsertExpr ::= "insert" ("node" | "nodes")
SourceExpr InsertExprTargetChoice TargetExpr
InsertExprTargetChoice ::= (("as" ("first" | "last"))? "into")
| "after" | "before"
SourceExpr ::= ExprSingle
TargetExpr ::= ExprSingle
– N.B. Updating expressions (insert, delete, rename, replace) lead
to a loss of type/validation information at the affected nodes.
Such information may be recovered by revalidation.
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• Node deletion
• Node insertion: Examples
– A delete expression deletes zero or more nodes from an XDM
instance.
– The keywords node and nodes may be used interchangeably,
regardless of how many nodes are actually deleted.
Insert a year element after the publisher of the first book.
insert node <year>2005</year>
after fn:doc("bib.xml")/books/book[1]/publisher
Syntax
DeleteExpr ::= "delete" ("node" | "nodes") TargetExpr
Navigating by means of several bound variables, insert a new
police report into the list of police reports for a particular
accident.
Delete the last author of the first book in a given bibliography.
delete node
fn:doc("bib.xml")/books/book[1]/author[last()]
insert node $new-police-report
as last into fn:doc("insurance.xml")/policies
/policy[id = $pid]
/driver[license = $license]
/accident[date = $accdate]
/police-reports
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Delete all email messages that are more than 365 days old.
delete nodes /email/message
[fn:currentDate() - date > xs:dayTimeDuration("P365D")]
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• Node replacement
• Node replacement: Examples
Syntax
ReplaceExpr ::= "replace" ("value" "of")? "node"
TargetExpr "with" ExprSingle
Replace the publisher of the first book with the publisher of the second
book.
replace node fn:doc("bib.xml")/books/book[1]/publisher
with fn:doc("bib.xml")/books/book[2]/publisher
– Replace takes two forms, depending on whether value of is specified:
• If value of is not specified, a replace expression replaces one node with a
new sequence of zero or more nodes. The replacement nodes occupy the
position in the node hierarchy that was formerly occupied by the node that
was replaced.
– Hence, an attribute node can be replaced only by zero or more attribute
nodes, and an element, text, comment, or processing instruction node can be
replaced only by zero or more element, text, comment, or processing
instruction nodes.
• If value of is specified, a replace expression is used to modify the value
of a node while preserving its node identity.
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Increase the price of the first book by ten percent.
replace value of node fn:doc("bib.xml")/books/book[1]/price
with fn:doc("bib.xml")/books/book[1]/price * 1.1
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• Renaming is local!
– A rename expression replaces the name property of a data
model node with a new QName.
– The effects of a rename expression are limited to its target
node, descendants are not affected.
Global change of names or namespaces needs explicit iteration.
Syntax
RenameExpr ::= "rename" "node" TargetExpr "as"
NewNameExpr
Example (Change all QNames from prefix abc to xyz and new namespace URI
http://xyz/ns for node $root and its decendents.)
for $node in $root//abc:*
let $localName := fn:local-name($node),
$newQName := fn:concat("xyz:", $localName)
return
rename node $node as fn:QName("http://xyz/ns", $newQName),
for $attr in $node/@abc:*
let $attrLocalName := fn:local-name($attr),
$attrNewQName := fn:concat("xyz:", $attrLocalName)
return
rename node $attr as fn:QName("http://xyz/ns",
$attrNewQName)
Rename the first author element of the first book to principal-author.
rename node fn:doc("bib.xml")/books/book[1]/author[1]
as "principal-author"
Rename the first author element of the first book to the QName that
is the value of the variable $newname.
rename node fn:doc("bib.xml")/books/book[1]/author[1]
as $newname
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• Renaming nodes
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• Node transformation
• Node transformation: Examples
– . . . creates modified copies of existing nodes. Each copied node
obtains a new node identity. The resulting XDM instance can
contain both, newly created and previously existing nodes.
Node transformation is a non-updating expression, since it does
not modify existing nodes!
Syntax
TransformExpr ::= "copy" "$"VarName ":=" ExprSingle
("," "$"VarName ":=" ExprSingle)*
"modify" ExprSingle
"return" ExprSingle
Return a sequence consisting of all employee elements that have Java
as a skill, excluding their salary child-elements.
for $e in //employee[skill = "Java"]
return
copy $je := $e
modify delete node $je/salary
return $je
Copy a node, modify copy, then return original and modified copy.
let $oldx := /a/b/x
return
copy $newx := $oldx
modify (rename node $newx as "newx",
replace value of node $newx by $newx * 2)
return ($oldx, $newx)
– Idea:
1.
2.
3.
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Bind variables of copy clause (non-updating expressions),
update copies (only!) as per modify clause,
construct result by return (copied/modified and/or other nodes).
– N.B. Underlying persistent data not changed by these examples!
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• Formal update semantics are always a lot more involved
than retrieval semantics.
• Updates and bulk operations do not go together well (cf.
SQL set-oriented updates).
• XUF uses a notion of "snapshots" and "pending update lists"
to work around some of the subtleties.
• The details are beyond the scope of this lecture.
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8.4 XSLT – Intro
8.5 Overview
8.6 References
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8.4 XSLT – Intro
• XSL Languages
• CSS = Style Sheets for HTML
– It started with XSL and ended up with XSLT, XPath
and XSL-FO
– HTML uses predefined tags, and the meaning of each
tag is well understood.
– The <table> tag in HTML defines a table - and a
browser knows how to display it.
– Adding styles to HTML elements are simple. Telling a
browser to display an element in a special font or
color, is easy with CSS.
• It started with XSL
– XSL stands for EXtensible Stylesheet Language.
– The World Wide Web Consortium (W3C) started to
develop XSL because there was a need for an XMLbased Stylesheet Language.
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8.1 Introduction
– Formally specifying the exact semantics of the
XQuery UF is non-trivial for several reasons:
8. Updates + XSLT
• On the semantics of the XQuery Update
Facility
[Scholl07]
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8.4 XSLT – Intro
8.4 XSLT – Intro
• XSL = Style Sheets for XML
• XSL - More Than a Style Sheet Language
– XML does not use predefined tags (we can use any
tag-names we like), and therefore the meaning of each
tag is not well understood.
– A <table> tag could mean an HTML table, a piece of
furniture, or something else - and a browser does
not know how to display it.
– XSL describes how the XML document should be
displayed!
– XSL consists of three parts:
– XSLT - a language for transforming XML documents
– XPath - a language for navigating in XML documents
– XSL-FO - a language for formatting XML documents
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8.4 XSLT
8.4 XSLT
• XSLT
• XSLT processor
– Extensible Stylesheet Language – Transformations
– A language to describe transformations from source to
target tree structures (= XML documents)
– A transformation in XSLT
• Is described by a well-formed XML document called stylesheet
• Can use elements of the XSLT namespace as well as of other
namespaces
• Contains template rules to execute the transformation
XSLT stylesheet
XSLT tree
and
and
XML document
Source tree
Transformation
process
Result tree
Result
document
XML file
XSLT
Stylesheet
XSLT
Processor
XML file
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8.4 XSLT
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8.4 XSLT
• XSLT processing model
• Template rules
– A rule consists of a pattern and a template.
– The pattern is compared to the nodes of the source
document tree.
– The template can be instanciated to create a part of
the target tree. It can contain elements of the XSLT
namespace which are instructions to create fragments.
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– By processing a list of source nodes,
fragments of the target tree can be created.
– The list starts with the root node only.
– A node is processed
• By selecting the best matching pattern from all rules
(resolving any conflicts).
• The template of the best matching rule is instanciated with the
current node as context node.
– A template usually contains instructions to select further
source tree nodes for processing.
– Recursivly repeat the selection of matching rules,
instanciation and selecting of new source nodes
until the list is empty.
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8.4 XSLT
8.4 XSLT
• Structure of a stylesheet
• Top level elements
– E.g. xsl:import, xsl:include, and most
importantly xsl:template
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
id={id}
extension-element-prefixes={token}
exclude-result-prefixes={token}
version={number}>

</xsl:stylesheet>
<xsl:template
match = {pattern}
name = {qname}
priority = {number}
mode = {qname}

</xsl:template
– Elements and attributes with the XSLT namespace
must be recognized by the XSLT processor
– PIs and comments are ignored
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8.4 XSLT
• Multiple matching patterns
– Uses a set of alternative (|-seperated) address paths in
the child and attribute axis.
– The use of '/' and '//', 'id' and 'key' functions is possible.
– Pattern predicates ('[…]') can use all XPath
expressions.
– If multiple patterns match a node, the conflict is resolved
by priorities (cf. priority attribute)
• Imported rules have a lower priority than rules of the primary
stylesheet
• Alternatives are processed as if each alternative is defined by a
single rule
• ChildOrAttributeAxisSpecifier::QName patterns have priority 0
• ChildOrAttributeAxisSpecifier::NCName patterns have
priority -0.25
• ChildOrAttributeAxisSpecifier::NodeTest patterns have
priority -0.5
• All other patterns have priority 0.5
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8.4 XSLT
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8.4 XSLT
• Rules
• XSLT contains default rules
– Can be named and be called in templates of other rules
– Can have parameters which can be passed along on
their invocation, default values can be defined
– The mode attribute allows a rule to be processed multiple
times and with different results
– If the template is invoked directly with xsl:calltemplate or xsl:apply-template, the filter
attributes (match, mode, priority or name) are not
processed
– Process the document recursivly
– But have lower priority than rules in the stylesheet
– Example:
<xsl:template match="*|/">
<xsl:apply-templates/>
</xsl:template>
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8.4 XSLT
• A pattern specifies a set of conditions to a
node
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8.4 XSLT
8.4 XSLT
• Templates
• Instructions to process nodes recusively
– Can contain literal elements (non XSLT
namespace) and elements of the XSLT namespace
(instructions).
– If the rule is selected, the template can construct
fragments of the result tree.
– Processing depends on the context.
– Default behaviour is to write all elements which are
not in the XSLT namespace to the result tree.
– Must be valid XML.
– Can contain instructions.
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8.4 XSLT
<xsl:apply-template
select = {node set expression}
mode = {qname}>

</xsl:apply-template>
– Without the attribute select all children of the
context node are processed
– Select can be a (XPath-) expression to select nodes
• Could result in not terminating recursion!
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8.4 XSLT
• Instructions to create a node
• Instructions for flow control
<xsl:element
name = {qname}
namespace = {uri-reference}
use-attribute-sets = {qname} >

</xsl:element>
– Conditional processing
<xsl:if
test = {boolean expression}
</xsl:if>
required
– Test expression is evaluated and result is casted to a
boolean. If it is true the template will be instanciated
– Name attribute is required, but can be calculated
– Other create instructions are similar
• xsl:attribute, xsl:attribute-set, xsl:text
(to create a text/leaf node with whitespaces),
xsl:processing-instruction, xsl:comment
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8.4 XSLT
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8.4 XSLT
• Instructions for flow control
• Multiple choice ("if-then-else" / "switch")
• Repetition
<xsl:for-each
select = {node-set expression}

</xsl:for-each>
<xsl:choose

</xsl:choose>
<xsl:when
test = {boolean expression}
</xsl:when>
– The template is instanciated for each node selected by
the node set expression.
– On instanciation the current node becomes the
context node and all selected nodes are the node list.
– If there is no explicit sort statement, the nodes are
processed in document order.
<xsl:otherwise
</xsl:otherwise>
– If multiple xsl:when elements are true, only the first one is
processed (no "break" needed)
– If no xsl:when element is true and there is no xsl:otherwise, no
content is created
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8.4 XSLT
8.4 XSLT
• "Calculation" of output text
• Other statements for sorting, numbering,
variables, …
<xsl:value-of
select = {string expression}
disable-output-escaping = "yes" | "no" />
– see http://www.w3.org/TR/xslt
• Some advice
– The selected object is casted to a string value and is
inserted as content of the instanciated text node.
– Denomination "variable" is misleading!
– Context node is changed by for-each!
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8.4 XSLT
<?xml version="1.0"?>
<resultset statement="SELECT * FROM t1"
xmlns:xsi="http://www.w3.org/2001/XMLSchemainstance">
<row> <field name="Pid">1</field>
<field name="Name">Super Pizza</field>
<field name="Category">4</field>
<field name="Location">1</field> </row>
<row>…</row>
</resultset>
<xsl:template match="field[attribute::name='Name']">
<h2>
<xsl:value-of select="."/>
</h2>
</xsl:template>
</xsl:stylesheet>
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8. Updates + XSLT
46
8.5 Overview
Introduction and Basics
1. Introduction
2. XML Basics
3. Schema Definition
4. XML Processing
Querying XML
5. XPath & SQL/XML
Queries
6. XQuery Data Model
7. XQuery
XML Updates
8. XML Updates & XSLT
8.1 Introduction
8.5 Overview
8.6 References
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8.4 XSLT
<?xml version="1.1"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:template match="resultset">
<html>
<head/>
<body>
<h1>
<xsl:text>Summary about </xsl:text>
<xsl:value-of select="count(child::*)"/>
<xsl:text> Pizzeria</xsl:text>
<xsl:if test="count(child::*) > 1">
<xsl:text>s</xsl:text>
</xsl:if>
</h1>
<xsl:apply-templates/>
</body>
</html>
</xsl:template>
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Producing XML
9. Mapping relational
data to XML
Storing XML
10. XML storage
11. Relational XML storage
12. Storage Optimization
Systems
13. Technology Overview
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16.12.2009
7.6 References
Questions, Ideas, Comments
• "Database-Supported XML Processors", [Gru08]
• Now, or ...
– Th. Grust
– Lecture, Uni Tübingen, WS 08/09
• "XML und Datenbanken", [Tür08]
– Can Türker
– Lecture, University of Zürich, 2008
IZ 232
• Office our:
Tuesday, 12:30 – 13:30 Uhr
or on appointment
• DB2 pureXML CookBook [NK09]
• Email:
– Matthias Nicola and Pav Kumar-Chatterjee
– IBMPress, 2009, ISBN 9780138150471
• Room:
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[email protected]
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8. Updates + XSLT 8.1 Introduction 8. Updates + XSLT

Transcrição

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