Friday, September 4 th, 2009 The Systems Group at ETH Zurich XML and Databases Exercise Session 6 courtesy of Ghislain Fourny/ETH © Department of Computer

Friday, September 4th, 2009

The Systems Groupat ETH Zurich

XML and DatabasesXML and DatabasesExercise Session 6Exercise Session 6

courtesy of Ghislain Fourny/ETHcourtesy of Ghislain Fourny/ETH

© Department of Computer Science | ETH Zürich

Friday, September 4th, 2009 PUL Algebra Theory

Previously, in XML&DatabasesPreviously, in XML&Databases

2

DTDXML Schema

InfosetPSVIXDM

<a/>

All of this should be familiar to you

by now.

All of this should be familiar to you

by now.

XMLwith/withoutnamespaces



3

DTDXML Schema

InfosetPSVIXDM

<a/>

So, now we can leverage the power

of XML.

So, now we can leverage the power

of XML.

XQueryXSLT

XMLwith/withoutnamespaces



4

XMLwith

namespaces

(XML Schema)optional

XDM

<a/>

This would be the typical setup.

This would be the typical setup.

XQuery


Reminder: XML and Data ModelsReminder: XML and Data Models

5

<a> <d e="f"/> <c>This is <b>text</b>.</c></a>

Physical view(syntax)

Logical view(data model)

a

d

This is

c

b .

text

e:f


Reminder: XQuery and XPath Data Reminder: XQuery and XPath Data ModelModel

6

In XQuery, anything that goes into or comes out of an expression is a sequence of items!In XQuery, anything that goes into or comes out of an expression is a sequence of items!

ExpressionExpression

for if thenelse where

order by

whileany

every

letreturn

exit with

=

+


Ever played Lego?Ever played Lego?

7



8

if( )

then

else



9

if( )

then

else

my:func( )my:func( )



10

if( )

then

else

my:func( )my:func( )



11

if( )

then

else

my:func( )my:func( )2



12

if( )

then

else

for $x in

let $y :=

return




13

if( )

then

else

for $x in

let $y :=

return




14

if( )

then

else

for $x in

let $y :=

return




15

if( )

then

else

for $x in

let $y :=

return




16

if( )

then

else

for $x in

let $y :=

return



XQuery ExpressionsXQuery Expressions

17

if( )

then

else



18

for $x in

let $y :=

for $z in

where

order by

return



19

/ / / / ...


PrecedencePrecedence

Some expressions have priority over others while parsing an XQuery program: Lowest priority: comma (,) Then FLWOR, if/then/else, ... on same level Operators (+,...) Path expressions (/) Highest priority: literals, variables, function calls,

element constructors...

Use parentheses when in doubt!


Exercise 1: Simple queriesExercise 1: Simple queries

21


Exercise 1: Simple queriesExercise 1: Simple queries

22


Exercise 1: Titles sorted by priceExercise 1: Titles sorted by price

23



24



25



26


Exercise 1: How many books Exercise 1: How many books written by Abiteboul?written by Abiteboul?

27



28



29



30

2


Exercise 1: Number of books by Exercise 1: Number of books by authorauthor

31



32



33



34



35

<?xml version="1.0" encoding="UTF-8"?><res> <name>Stevens</name>

</res><res> <name>Abiteboul</name>

</res><res> <name>Buneman</name>

</res><res> <name>Suciu</name>

</res>



36

<?xml version="1.0" encoding="UTF-8"?><res> <name>Stevens</name> <count>2</count></res><res> <name>Abiteboul</name> <count>2</count></res><res> <name>Buneman</name> <count>1</count></res><res> <name>Suciu</name> <count>1</count></res>


The document (from first exercise The document (from first exercise sheet)sheet)

37

You (should) know how namespaces work in XML (prefix-binding)You (should) know how namespaces work in XML (prefix-binding)


The document (from first exercise The document (from first exercise sheet)sheet)

38

How should we navigate a document which has namespaces with XQuery?

How should we navigate a document which has namespaces with XQuery?


Exercise 2: How prefixes are Exercise 2: How prefixes are bound to namespaces in XQuery bound to namespaces in XQuery (Basics)(Basics) Very simple! Just a prolog declaration...

And then you can use the prefix in the XQuery code (e.g., in path expressions).

39


Exercise 2: How prefixes are Exercise 2: How prefixes are bound to namespaces in XQuery bound to namespaces in XQuery (Basics)(Basics) Very simple! Just a prolog declaration...

And then you can use the prefix in the XQuery code (e.g., in path expressions).

Actually, you can also bind them in element constructors just like in XML.

40


Exercise 2: Let‘s try this out!Exercise 2: Let‘s try this out!

41



42



43



44



45



46



47



48



49



50



51



52



53



54



55



56


Exercise 2: The other wayExercise 2: The other way

57


Exercise 3: Comparison Operators Exercise 3: Comparison Operators in XQueryin XQuery

58



In XQuery, there are three kinds of comparisons General Comparisons

Value Comparisons

Node Comparisons

59




= < > <= >= Value Comparisons

Node Comparisons

60





eq lt gt le ge Node Comparisons

61





eq lt gt le ge Node Comparisons

is

62


Exercise 3: General ComparisonsExercise 3: General Comparisons

To compare sequences of items each item: atomic item or node item which is

atomized

63

In XQuery, if you receive a node item where an atomic item is expected, the node is atomized.

In XQuery, if you receive a node item where an atomic item is expected, the node is atomized.

= < > <= >=



To compare sequences of items each item: atomic item or node which is atomized

Answers to the question: does any combination of a value from the first sequence and a value from the second sequence

fulfil the condition?

64

=

= < > <= >=






(1,2) = (3,<a>1</a>)65

= < > <= >=






(1,2) = (3,<a>1</a>)66

= < > <= >=






(1,2) = (3,<a>1</a>) (1,2) > (3,4)67

= < > <= >=






(1,2) = (3,<a>1</a>) (1,2) > (3,4)68

= < > <= >=


Exercise 3: Value ComparisonsExercise 3: Value Comparisons

Compares one value to one value (Empty sequence allowed)

69

le

eq lt gt le ge




32 eq xs:integer(<a>32</a>)

70

eq lt gt le ge





71

eq lt gt le ge





31 gt xs:integer(<a>32</a>)

72

eq lt gt le ge





31 gt xs:integer(<a>32</a>)

73

eq lt gt le ge


Exercise 3: Node ComparisonsExercise 3: Node Comparisons

Compares node identities

74

is




let $a := <a/> let $b := $a return $a is $b

75

is





76

is





let $a := <a/> let $b := <b/> return $a is $b

77

is





let $a := <a/> let $b := <b/> return $a is $b

78

is


Exercise 3: General/Value Exercise 3: General/Value comparisonscomparisons

79



For both, values have to have comparable types (e.g., string is not comparable to integer)

80




Empty sequence treated differently General comparison returns false Value comparison returns ()

81




Empty sequence treated differently General comparison returns false Value comparison returns ()

Untyped data treated differently General comparison casts to type of other operand Value comparison casts to string

82


Exercise 3: 1=2Exercise 3: 1=2

Find $x s.t. $x = 1 and $x = 2

83


Exercise 3: 1=2Exercise 3: 1=2

Find $x s.t. $x = 1 and $x = 2

84

(1,2)


Exercise 3: Transitivity of >Exercise 3: Transitivity of >

Find $x, $y, $z s.t. $x > $y and $y > $z and not $x > $z

85


Exercise 3: Transitivity of >Exercise 3: Transitivity of >

Find $x, $y, $z s.t. $x > $y and $y > $z and not $x > $z

86

$x := 2$y := (1,4)$z := 3


Exercise 3: $x eq $x, $x = $xExercise 3: $x eq $x, $x = $x

Find $x so that both $x eq $x and $x = $x are not true.

87


Exercise 3: $x eq $x, $x = $xExercise 3: $x eq $x, $x = $x

Find $x so that both $x eq $x and $x = $x are not true.

88

()

Friday, September 4th, 2009 PUL Algebra Theory 89

Hope to see you next week!Hope to see you next week!

Documents

Friday, September 4 th, 2009 The Systems Group at ETH Zurich XML and Databases Exercise Session 6 courtesy of Ghislain Fourny/ETH © Department of Computer