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XMLTA
Transparency No. 1
Query XML Documentswith XQuery
Cheng-Chia Chen
XMLTA
Transparency No. 2
Objectives
How XML generalizes relational databasesThe XQuery languageHow XML may be supported in databases
XMLTA
Transparency No. 3
XQuery 1.0
XML documents naturally generalize database relationsXQuery is the corresponding generalization of SQL
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Transparency No. 4
Queries on XML documents
XML documents generalize relational data:
A database is composed of many tables A table (relation) is composed of tuples A tuple (record; rows) is composed of attributes An attribute (field; column) contains a primitve data (,
which may serves as a key/key reference) .
XMLTA
Transparency No. 5
From Relations to Trees
XMLTA
Transparency No. 6
Only Some Trees are Relations
A relation is a tree of height two with an unbounded number of children (rows) all of which have the same fixed number of child nodes (columns)
The database community has been looking for a richer data model than relations. Hierarchical, object-oriented, or multi-dimensional databases have emerged, but neither has reached consensus.
A DTD for RDB : <!ELEMENT PeopleDataBase (PeopleTable, …) > <!ELEMENT PeopleTable (PeopleRow*) > <!ELEMENT PeopleRow (%Column;) >
<!ENTITY % Column “FirstName, LastName, Age “ > <!ELEMENT FirstName (#PCDATA)> <!ELEMENT LastName (#PCDATA)> <!ELEMENT Age (#PCDATA)>
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Transparency No. 7
Trees Are Not Relations
Not all XML Document trees satisfy the previous characterization Trees are ordered, while both rows and columns of tables
may be permuted without changing the meaning of the data
Trees may have height > 2. Trees is in general not homogeneous.
Elements of the same type may have different number and types of children.
This does not mean that we cannot store these documents in traditional data base but only means that a more complex encoding of xml documents into data base tables is required.
XMLTA
Transparency No. 8
An examlpe student grade records
<students> <student id="100026"> <name>Joe Average</name> <age>21</age> <major>Biology</major> <grades> <result course="Math 101" grade="C-"/> <result course="Biology 101" grade="C+"/> <result course="Statistics 101" grade="D"/> </grades> </student> <student id="100078"> <name>Jack Doe</name> <age>18</age> <major>Physics</major><major>XML Science</major> <grades> <result course="Math 101" grade="A"/> <result course="XML 101" grade="A-"/> <result course="Physics 101" grade="B+"/> <result course="XML 102" grade="A"/> </grades> </student></students>
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Transparency No. 9
A Corresponding Student Database
key point of data base design: decompose general xml tree into flat data base tables
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Transparency No. 10
For Relational Data base, we have well-established theory and practice, but can we have the same achievement for XML ? database XML DDL(DataDefintionLang) XML Schema DQL(DataQueryLang;SQL) XQuery
How should query languages like SQL be similarly generalized?
XMLTA
Transparency No. 11
XQuery Design Requirements
Must have at least one XML syntax and at least one human-readable syntax
Must be declarativeMust be namespace awareMust coordinate with XML SchemaMust support simple and complex datatypesMust be able to combine information from multiple
documentsMust be able to transform and create XML trees
XMLTA
Transparency No. 12
The XQuery language
Developed by W3C Recommendation.
Derived from several previous proposals: XML-QL ,YATL ,Lorel,Quilt
which all agree on the fundamental principles. XQuery relies on XPath and XML Schema
datatypes. There have been many
commercial/non-commerical implementations released. Exist : http://exist.sf.net AltovaXML (free) …
Two formats XQuery : plaintext syntax XQueryX : XML syntax.
XMLTA
Transparency No. 13
Relationship to XPath
XQuery 1.0 is a strict superset of XPath 2.0 Every XPath 2.0 expression is directly an XQuery 1.0
expression (a query)The extra expressive power is the ability to
join information from different sources and generate new XML fragments
XMLTA
Transparency No. 14
Relationship to XSLT
XQuery and XSLT are both domain-specific languages (DSL) for combining and
transforming XML data from multiple sourcesThey are vastly different in design, partly for historical
reasons XQuery is designed from scratch, XSLT is an intellectual descendant of CSS (cascaded
StyleSheet) – about how to render a document.Technically, they may emulate each other.XQuery Grammar
XMLTA
Transparency No. 15
XQuery conceptsA query in XQuery is an expression that:
reads a sequence of XML nodes or atomic values returns a sequence of XML nodes or atomic values
The principal forms of XQuery expressions are: path expressions element constructors
FLWOR ("flower") expressions list expressions (for,let) conditional expressions (where ) order by (o) return expr(r)
Xpath 2.0 + constructor: quantified expressions (some/every) datatype expressions (xs:int(“123”)); <e attr={…}>{…}</e>
XMLTA
Transparency No. 16
XQuery Modules and Prologs
An XQuery is a main module: Module ::= VersionDecl? ( MainModule | LibraryModule) VersionDecl:
xquery version "1.0" encoding "UTF-8" ; (: this is versiondecl; encoding is optional :)
a module may import other library modules. MainModule ::= Prolog QueryBoby LibraryModule ::= ModuleDecl Prolog
Ex: module namespace math = "http://example.org/math-functions";
Like XPath expressions, XQuery expressions are evaluated relatively to a context This is explicitly provided by a prolog Settings define various parameters for the XQuery
processor language, such as: declare bounndary-space (preserve | strip );
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Transparency No. 17
More From the Prolog
Prolog ::= (: Prolog consists of two parts. :)( ( DefaultNamespaceDecl // declare default function or element/type NSs | Setter // settings for XQuery processing | NamespaceDecl // declare prefix-URI bindings | Import // import schema or other modules ) Separator // each ends with ‘;’ )*
( ( (: Second part contains variable decl, function decl and options :)
VarDecl // global variable declarations | FunctionDecl // function declarations | OptionDecl // implementation-defined options declaration ) Separator // each ends with ';')* optionDecl ::= declare option QName “aLiteral”
XMLTA
Transparency No. 18
Namespace Declarations
Format: // declare prefix-namexpace bindingdeclare namespace prefix = ”aURI” ;
Ex: declare namespace bk = ”http://www.book.org/” ; Predeclared namespaces prefixes:
(: for xml:lang, xml:space, etc :) declare namespace xml = "http://www.w3.org/XML/1998/namespace"; (: for xml schema and schema instance :) xs = "http://www.w3.org/2001/XMLSchema"; xsi = "http://www.w3.org/2001/XMLSchema-instance"; (: for xpath fucntion and data types ; this is the default function
namespace:) fn = "http://www.w3.org/2005/xpath-functions"; (: for xquery fucntions :) local="http://www.w3.org/2005/xquery-local-functions";
only xml prefix cannot be redefined.
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Transparency No. 19
Setter [7] Setter ::= BoundarySpaceDecl | // preserve space b/t elements
declare boundary-space (preserve | strip); DefaultCollationDecl | // default collation for ordering declare default collation "aURILiteral" BaseURIDecl | declare base-uri "http://example.org"; ConstructionDecl | // preserve type of copied constructs? declare construction (strip | preserve); OrderingModeDecl | // ordered or not for return values declare ordering (ordered | unordered) ; EmptyOrderDecl | //empty or NaN as least/greatest key declare default order empty (greatest | least); CopyNamespacesDecl // copy prefix-NS bindings
see (here. and (3.7.1.3.1.e.2.D) for details) cf: constructed node ;copied nodes; original elements ex: <cn>{.//book}</cn>
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Transparency No. 20
Default namespace declarations
Default namespace Defautl element/type namespace Default function namespace
Ex: (: can be disabled by ”” for element (and type as well) :) declare default element namespace ”http://a.b.c/d” ; declare default function namespace “aURI”; (: default is "http://www.w3.org/2005/xpath-functions" if not specified
or disabled by "" So f1(.) has the same effect as fn:f1(.) :)
Unprefixed attribute names and variable names are in no namespace.
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Transparency No. 21
Import declarations
Import declarations // import element/type/attribute declared in a schema // may also declare prefix/default namespace for the target namespace // default namespace uri can be "" for importing noNamespaceSchema import schema import (library) module
Ex: import schema "targetNamespaceURI" ( at "schema_loc_uri1",
"schema_loc_uri2" )? ; import schema namespace prefix = "targetNamespaceURI" (at "loc1" )?; import schema default element namespace "targetNamespaceURI" ( at
"loc_uri" )? ; Ex:
// import a schema and use it as the default element/type namespace import schema default element namespace "http://example.org/abc"; // import a schema which has no target namespace and use it as default
namespace. import schema default element namespace "" at
"http://example.org/xyz.xsd";
XMLTA
Transparency No. 22
Module imports
Import declarations // import function/global variables declared in an XQ library module import (library) module // may also declare its namespace prefix
Notes: Only variables and functions are imported; Hence in scope schema
definition and statically known namespaces are not imported. Module imports are not transitive: A imports B and B imports C do not imply
A imports C. Ex:
import module "http://book.org/ ";
// can give hints about module locations import module "http://book.org/” (at "http://www.book.org/book.xq",
"book2.xq” )? ;
// can also bind a prefix for imported module namespace uri. import module namespace book="http://book.org/” ( at "book2.xq” )? ;
import module namespace math = "http://example.org/math-functions";
XMLTA
Transparency No. 23
Variable and function declarations
VarDecl ::= declare variable $QName TypeDeclaration? ((":="
ExprSingle) | "external")
declare variable $math:pi xs:decimalopt := 3.14159 ; declare variable $math:e xs:double := 2.71E0 declare variable $ext:var1 external ;
FunctionDecl ::= declare function QName ( ParamList? ) (as SequenceType
)? (EnclosedExpr | external)
XMLTA
Transparency No. 24
Ex :
declare function local:summary // name
( $emps as element(employee)* ) // parameters
as element(dept) * // return type
{ //body
for $d in fn:distinct-values($emps/deptno) //a FLWOR expression
let $e := $emps[deptno = $d]
return
<dept>
<deptno>{$d}</deptno>
<headcount> {fn:count($e)} </headcount>
<payroll> {fn:sum($e/salary)} </payroll>
</dept>
};
Direct element
construction!
XMLTA
Transparency No. 25
Example
Suppose we have the file at loc "employee.xml"<employees> <employee>
<depno>dept2</depno><name>Wang</name><salary>100000</salary></employee>
<employee>
<depno>dept1</depno><name>Lee</name><salary>50000</salary></employee>
<employee>
<depno>dept3</depno><name>Chen</name><salary>100000</salary></employee>
<employee>
<depno>dept1</depno><name>Cheng</name><salary>150000</salary></employee>
<employees>
The following query sho how to use the function summary
xquery version "1.0" encoding "UTF-8" ;
(: Definition of fun summary inserted here or import it here :)
let $emps := doc("employees.xml")/employees/employee
return <summary>{summary($emps)}</summary> Result: <summary>
<dept><deptno>dept2</deptno><headCount>1</headcount><payroll>100000</payroll></dept>
<dept><deptno>dept1</deptno><headCount>2</headcount><payroll>200000</payroll></dept>
<dept><deptno>dept3</deptno><headCount>1</headcount><payroll>100000</payroll></dept>
</summary>
XMLTA
Transparency No. 26
Xquery Conecpts
QueryBody = Expr[31] Expr ::= ExprSingle ("," ExprSingle)*[32] ExprSingle ::=
FLWORExpr | QuantifiedExprxpath20
| TypeswitchExpr | IfExprxpath20 | OrExprxpath20+construction
Expressions are evaluated relative to a expression context: namespaces variables functions date and time context item,context position, context size …
XMLTA
Transparency No. 27
XPath Expressions
XPath expressions are also legal XQuery expressions same data model : sequence of items items : nodes or atomic data
The XQuery prolog gives the required static context namespace, function library, variable bindings
The initial context node, position, and size are undefined Since XQuery is intended to operate on multple
docuemnts. initial context info can be obtained by starting from
fn:doc()
XMLTA
Transparency No. 28
Datatype Expressions
Same atomic values as XPath 2.0Also lots of primitive simple values: xs:string("XML is fun") xs:boolean("true") xs:decimal("3.1415") xs:float("6.02214199E23") xs:dateTime("1999-05-31T13:20:00-05:00") xs:time("13:20:00-05:00") xs:date("1999-05-31") xs:gYearMonth("1999-05") xs:gYear("1999") xs:hexBinary("48656c6c6f0a") xs:base64Binary("SGVsbG8K") xs:anyURI("http://www.brics.dk/ixwt/") xs:QName("rcp:recipe") Functions for theses types can be found in fn:XXX().
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Transparency No. 29
XML Expressions
XQuery expressions may produce new XML nodes, which do not exist in input documents.
Expressions may denote element, character data, comment, and processing instruction nodes
Each node is created with a unique node identityConstructors may be either
direct (called literal result element in XSLT) or computed Both may be nested with each other.
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Transparency No. 30
Uses the standard XML syntaxEx:
The expression
<foo><bar/>baz</foo> evaluates to the given XML fragment
Note that the expression (containing two direct elements)
<foo/> is <foo/> evaluates to false why ? ( unique identity of each node )
Direct Constructors
XMLTA
Transparency No. 31
Namespaces in Constructors (1/3)
The following four constructions have the same effect.
declare default element namespace "http://businesscard.org";
<card>
<name>John Doe</name>
<title>CEO, Widget Inc.</title>
<email>[email protected]</email>
<phone>(202) 555-1414</phone>
<logo uri="widget.gif"/>
</card>
XMLTA
Transparency No. 32
Namespaces in Constructors (2/3)
declare namespace b = "http://businesscard.org";
<b:card>
<b:name>John Doe</b:name>
<b:title>CEO, Widget Inc.</b:title>
<b:email>[email protected]</b:email>
<b:phone>(202) 555-1414</b:phone>
<b:logo uri="widget.gif"/>
</b:card>
XMLTA
Transparency No. 33
Namespaces in Constructors (3/3)
<card xmlns="http://businesscard.org">
<name>John Doe</name>
<title>CEO, Widget Inc.</title>
<email>[email protected]</email>
<phone>(202) 555-1414</phone>
<logo uri="widget.gif"/>
</card>
<b:card xmlns:b="http://businesscard.org">
<b:name>John Doe</b:name>
<b:title>CEO, Widget Inc.</b:title>
<b:email>[email protected]</b:email>
<b:phone>(202) 555-1414</b:phone>
<b:logo uri="widget.gif"/>
</b:card>
XMLTA
Transparency No. 34
Enclosed Expressions
XQ also allow us to embed some XQ expressions into direct elements : Such expression is called attribuate value template in XSLT. but can be appled to atribute value as well as element contents.
<foo>1 2 3 4 5</foo>
<foo>{1, 2, 3, 4, 5}</foo>
<foo>{1, "2", 3, 4, 5}</foo>
<foo>{1 to 5}</foo>
<foo>1 {1+1} {" "} {"3"} {" "} {4 to 5}</foo>
<foo bar="1 2 3 4 5"/>
<foo bar="{1, 2, 3, 4, 5}"/>
<foo bar="1 {2 to 4} 5"/> ‘{‘ and '}' now have special meaning and must be escaped
using { ( or {{ ) and } (or }} ).
XMLTA
Transparency No. 35
Direct Constructors v.s Computed constructors
Direct construction in XML syntax :
<card xmlns="http://businesscard.org">
<name>John Doe</name>
<title>CEO, Widget Inc.</title>
<email>[email protected]</email>
<phone>(202) 555-1414</phone>
<logo uri="widget.gif"/>
</card>• Non-XML alternative syntax (Computed Constructors)• syntaxdeclare default element namespace http://businesscard.org" ;element card { <name>John Doe</name>, (: may use direct contructor :) element title { text { "CEO, Widget Inc." } } , element email { text { "[email protected]" } }, element phone { text { "(202) 555-1414" } }, element logo { attribute uri { "widget.gif" } }}
XMLTA
Transparency No. 36
Computed QNames
Names of elements/attributes may need to be computed! Syntax: nodeType (QName| {NameExpr})? { ContentExpr } nodeType : element | attribute | processing-instruction – need a name | document | comment | text -- no name
declare default element namespace "http://businesscard.org"
element { lower-case("CARD") } {
element { "name" } { text { "John Doe" } },
element { "title" } { text { "CEO, Widget Inc." } },
element { "email" } { text { "[email protected]" } },
element { "phone" } { text { "(202) 555-1414" } },
element { "logo" } {
attribute { "uri" } { "widget.gif" },
"aLogo" } }
XMLTA
Transparency No. 37
Biliingual Business Cards
xquery version "1.0" encoding "big5" ;
declare default element namespace "uri:businesscard.org";
declare variable $lang := "zh_TW" ;
element { if ($lang="zh_TW") then "名片 " else "card" } {
element { if ($lang="zh_TW") then "姓名 " else "name" }{ "John Doe" },
element { if ($lang="zh_TW") then "頭銜 " else "title" }{ "CEO, Widget Inc." },
element { "email" }{ "[email protected]" },
element { if ($lang="zh_TW") then "電話 " else "phone" }
{"(202) 456-1414" },
element logo { attribute { "uri" } { "widget.gif" }}
}
XMLTA
Transparency No. 38
FLWOR Expressions
Used for general queries:Find the names of all students which have more than
one major and order them by student id. <doubles>
{ for $s in fn:doc("students.xml")//student
let $m := $s/major
where fn:count($m) ge 2
order by $s/@id
return <double>
{ $s/name/text() }
</double>
}
</doubles>
XMLTA
Transparency No. 39
The Difference Between For and Let (1/4)
for $x in (1, 2, 3, 4)
let $y := ("a", "b", "c")
return ($x, $y)
1, a, b, c, 2, a, b, c, 3, a, b, c, 4, a, b, c
XMLTA
Transparency No. 40
The Difference Between For and Let (2/4)
let $x in (1, 2, 3, 4)
for $y := ("a", "b", "c")
return ($x, $y)
1, 2, 3, 4, a, 1, 2, 3, 4, b, 1, 2, 3, 4, c
XMLTA
Transparency No. 41
The Difference Between For and Let (3/4)
for $x in (1, 2, 3, 4)
for $y in ("a", "b", "c")
return ($x, $y)
1, a, 1, b, 1, c, 2, a, 2, b, 2, c,
3, a, 3, b, 3, c, 4, a, 4, b, 4, c
XMLTA
Transparency No. 42
The Difference Between For and Let (4/4)
let $x := (1, 2, 3, 4)
let $y := ("a", "b", "c")
return ($x, $y)
1, 2, 3, 4, a, b, c
XMLTA
Transparency No. 43
Computing Joins
Find distinct names of recipses that make use of at least one stuff in a refrigerator?
declare namespace rcp = "http://www.brics.dk/ixwt/recipes";
fn:distinct-values(
for $r in fn:doc("recipes.xml")//rcp:recipe,
$i in $r//rcp:ingredient/@name,
$s in fn:doc("frige.xml")//stuff[text()=$i]
return $r/rcp:title/text() )<fridge> <stuff>eggs</stuff> <stuff>olive oil</stuff> <stuff>ketchup</stuff> <stuff>unrecognizable moldy thing</stuff></fridge>
XMLTA
Transparency No. 44
Computing Joins
Find distinct names of recipses that make use of at least one stuff in a refrigerator?
more efficient version:declare namespace rcp = "http://www.brics.dk/ixwt/recipes";
for $r in fn:doc("recipes.xml")//rcp:recipe
let $names := $r//rcp:ingredient/@name
let $stuffs := fn:doc("fridge.xml")//stuff/text() (: may be put at 2nd line:)
where $names = $s (: general comparison :)
return $r/rcp:title/text()
XMLTA
Transparency No. 45
Inverting a Relation
From Recipe ingredients to ingredients recipes
declare namespace rcp = "http://www.brics.dk/ixwt/recipes";
<ingredients>
{ for $i in distinct-values( (: for each ingredient i :)
fn:doc("recipes.xml")//rcp:ingredient/@name (: find all ingredients :)
)
return <ingredient name="{$i}">
{ for $r in fn:doc("recipes.xml")//rcp:recipe (: for each receipe :)
where $r//rcp:ingredient[@name=$i] (: which uses ingrediwent i :)
return <title>$r/rcp:title/text()</title>
}
</ingredient>
}
</ingredients>
XMLTA
Transparency No. 46
Sorting the Results
declare namespace rcp = "http://www.brics.dk/ixwt/recipes";
<ingredients>
{ for $i in distinct-values(
fn:doc("recipes.xml")//rcp:ingredient/@name
)
order by $i
return <ingredient name="{$i}">
{ for $r in fn:doc("recipes.xml")//rcp:recipe
where $r//rcp:ingredient[@name=$i]
order by $r/rcp:title/text()
return <title>$r/rcp:title/text()</title>
}
</ingredient>
}
</ingredients>
XMLTA
Transparency No. 47
A More Complicated Sorting
for $s in document("students.xml")//student
order by
fn:count($s/results/result[fn:contains(@grade,"A")]) descending,
fn:count($s/major) descending,
xs:integer($s/age/text()) ascending
return $s/name/text()
XMLTA
Transparency No. 48
Using Functions
declare function local:grade($g as xs:string ) {
if ($g="A") then 4.0 else if ($g="A-") then 3.7
else if ($g="B+") then 3.3 else if ($g="B") then 3.0
else if ($g="B-") then 2.7 else if ($g="C+") then 2.3
else if ($g="C") then 2.0 else if ($g="C-") then 1.7
else if ($g="D+") then 1.3 else if ($g="D") then 1.0
else if ($g="D-") then 0.7 else 0
};
declare function local:gpa($s as element(student) ) {
fn:avg( for $g in $s/results/result/@grade return local:grade($g) )
};
<gpas>
{ for $s in fn:doc("students.xml")//student
return <gpa id="{ $s/@id }" gpa="{local:gpa($s) }"/> }
</gpas>
XMLTA
Transparency No. 49
A Height Function
Find the height of an node tree. can use recursion !
declare function local:height($x as node() ) {
if (fn:empty($x/*))
then 0 (: an element without child element has height 0:)
else
fn:max(for $y in $x/* return local:height($y) )+1
} ;
XMLTA
Transparency No. 50
A Textual Outline
intended textual outline of a recipe unusual in that it generate plain text instead of xml output.
Cailles en Sarcophages //recipe title
pastry // ingredient
chilled unsalted butter // sub ingredient
flour
salt
ice water
filling
baked chicken
marinated chicken
small chickens, cut up
Herbes de Provence
dry white wine
orange juice
minced garlic
truffle oil
...
XMLTA
Transparency No. 51
Computing Textual Outlines
declare namespace rcp = "http://www.brics.dk/ixwt/recipes";
declare function local:ingredients($i,$p){ fn:string-join( (:$p is ident spaces :) for $j in $i/rcp:ingredient return fn:string-join( ($p, $j/@name,"
", local:ingredients($j, fn:concat($p,"
"))), ""), "") };declare function local:recipes($r) { fn:concat( $r/rcp:title/text(), "
", local:ingredients($r," ") )};(: Query body :) for $r in
fn:doc("http://www.brics.dk/ixwt/examples/recipes.xml")//rcp:recipe[5] return local:recipes($r)
XMLTA
Transparency No. 52
Sequence Types
2 instance of xs:integer2 instance of item()2 instance of xs:integer?() instance of empty()() instance of xs:integer*(1,2,3,4) instance of xs:integer*(1,2,3,4) instance of xs:integer+<foo/> instance of item()<foo/> instance of node()<foo/> instance of element()<foo/> instance of element(foo)<foo bar="baz"/> instance of element(foo)<foo bar="baz"/>/@bar instance of attribute()<foo bar="baz"/>/@bar instance of attribute(bar)fn:doc("recipes.xml")//rcp:ingredient instance of element()+fn:doc("recipes.xml")//rcp:ingredient instance of element(rcp:ingredient)+
XMLTA
Transparency No. 53
An Untyped Function
declare function local:grade($g) { if ($g="A") then 4.0 else if ($g="A-") then 3.7 else if ($g="B+") then 3.3 else if ($g="B") then 3.0 else if ($g="B-") then 2.7 else if ($g="C+") then 2.3 else if ($g="C") then 2.0 else if ($g="C-") then 1.7 else if ($g="D+") then 1.3 else if ($g="D") then 1.0 else if ($g="D-") then 0.7 else 0};
XMLTA
Transparency No. 54
A Default Typed Function
declare function local:grade($g as item()*) as item()* { if ($g="A") then 4.0 else if ($g="A-") then 3.7 else if ($g="B+") then 3.3 else if ($g="B") then 3.0 else if ($g="B-") then 2.7 else if ($g="C+") then 2.3 else if ($g="C") then 2.0 else if ($g="C-") then 1.7 else if ($g="D+") then 1.3 else if ($g="D") then 1.0 else if ($g="D-") then 0.7 else 0};
XMLTA
Transparency No. 55
A Precisely Typed Function
declare function local:grade($g as xs:string) as xs:decimal { if ($g="A") then 4.0 else if ($g="A-") then 3.7 else if ($g="B+") then 3.3 else if ($g="B") then 3.0 else if ($g="B-") then 2.7 else if ($g="C+") then 2.3 else if ($g="C") then 2.0 else if ($g="C-") then 1.7 else if ($g="D+") then 1.3 else if ($g="D") then 1.0 else if ($g="D-") then 0.7 else 0};
XMLTA
Transparency No. 56
Another Typed Function
declare function local:grades($s as element(students)) as attribute(grade)* { $s/student/results/result/@grade};
XMLTA
Transparency No. 57
Runtime Type Checks
Type annotations are checked during runtimeA runtime type error is provoked when
an actual argument value does not match the declared type a function result value does not match the declared type a valued assigned to a variable does not match the
declared type
XMLTA
Transparency No. 58
Built-In Functions Have Signatures
fn:contains($x as xs:string?, $y as xs:string?) as xs:boolean
op:union($x as node()*, $y as node()*) as node()*
XMLTA
Transparency No. 59
XQueryX
for $t in fn:doc("recipes.xml")/rcp:collection/rcp:recipe/rcp:titlereturn $t
<xqx:module xmlns:xqx="http://www.w3.org/2003/12/XQueryX" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2003/12/XQueryX xqueryx.xsd"> <xqx:mainModule> <xqx:queryBody> <xqx:expr xsi:type="xqx:flwrExpr"> <xqx:forClause> <xqx:forClauseItem> <xqx:typedVariableBinding> <xqx:varName>t</xqx:varName> </xqx:typedVariableBinding> <xqx:forExpr> <xqx:expr xsi:type="xqx:pathExpr"> <xqx:expr xsi:type="xqx:functionCallExpr"> <xqx:functionName>doc</xqx:functionName> <xqx:parameters> <xqx:expr xsi:type="xqx:stringConstantExpr"> <xqx:value>recipes.xml</xqx:value> </xqx:expr> </xqx:parameters>
<xqx:stepExpr> <xqx:xpathAxis>child</xqx:xpathAxis> <xqx:elementTest> <xqx:nodeName> <xqx:QName>rcp:collection</xqx:QName> </xqx:nodeName> </xqx:elementTest> </xqx:stepExpr> <xqx:stepExpr> <xqx:xpathAxis>child</xqx:xpathAxis> <xqx:elementTest> <xqx:nodeName> <xqx:QName>rcp:recipe</xqx:QName> </xqx:nodeName> </xqx:elementTest> </xqx:stepExpr> <xqx:stepExpr> <xqx:xpathAxis>child</xqx:xpathAxis>
xqx:nodeName> <xqx:QName>rcp:title</xqx:QName> </xqx:nodeName> </xqx:elementTest> </xqx:stepExpr> </xqx:expr> </xqx:forExpr> </xqx:forClauseItem> </xqx:forClause> <xqx:returnClause> <xqx:expr xsi:type="xqx:variable"> <xqx:name>t</xqx:name> </xqx:expr> </xqx:returnClause> </xqx:expr> </xqx:elementContent> </xqx:expr> </xqx:queryBody> </xqx:mainModule></xqx:module>
XMLTA
Transparency No. 60
XML Databases
How can XML and databases be merged?
Several different approaches: extract XML views of relations use SQL to generate XML shred XML into relational databases
XMLTA
Transparency No. 61
The Student Database Again
XMLTA
Transparency No. 62
Automatic XML Views (1/2)
Columns as attributes
<Students>
<record id="100026" name="Joe Average" age="21"/>
<record id="100078" name="Jack Doe" age="18"/>
</Students>
XMLTA
Transparency No. 63
Automatic XML Views (2/2)
Column as elements
<Students>
<record>
<id>100026</id>
<name>Joe Average</name>
<age>21</age>
</record>
<record>
<id>100078</id>
<name>Jack Doe</name>
<age>18</age>
</record>
</Students>
XMLTA
Transparency No. 64
Programmable Views
wrap query results by xml elements SQL/XML (http://sqlx.org)
An extension of SQL allowing constructin of XML data as a resultof SQL queries.
xmlelement(name "Students",
select xmlelement(name "record",
xmlattributes(s.id, s.name, s.age) )
from Students s
)
xmlelement(name "Students",
select xmlelement(name "record",
xmlforest(s.id, s.name, s.age) )
from Students s
)
XMLTA
Transparency No. 65
XML Shredding
Shredding an XML documents into multiple data base Tables
Each element type is represented by a relationEach element node is assigned a unique key in
document order so siblings can be ordered.
Each element node contains the key of its parent so parent –child relations can be maintained
The possible attributes are represented as fields, where absent attributes have the null value
Contents consisting of a single character data node (#PCDATA only) is inlined as a field.
XMLTA
Transparency No. 66
From XQuery to SQL
Any XML document can be faithfully representedThis takes advantage of the existing database
implementationQueries must now be phrased in ordinary SQL rather
than XQueryBut an automatic translation is possible
//rcp:ingredient[@name="butter"]/@amount
select ingredient.amountfrom ingredientwhere ingredient.name="butter"
XMLTA
Transparency No. 67
Summary
XML trees generalize relational tablesXQuery similarly generalizes SQL
XQuery and XSLT have roughly the same expressive power
But they are suited for different application domains: data-centric vs. document-centric
XMLTA
Transparency No. 68
Essential Online Resources
http://www.w3.org/TR/xquery/http://www.w3.org/XML/Query/implementations:
http://www.galaxquery.org/ http://exists.sf.net http://saxon.sf.net AltovaXML