CS561XML & XML Query 1 Ling Wang Luping Ding. CS561XML & XML Query 2 The Web opens a new challenges in: - information technology - database framework

CS561 XML & XML Query 1

XML & XML Query

Ling WangLuping Ding


• The Web opens a new challenges in: - information technology - database framework.

• Why? - Data sources on the Web do NOT typically conform to any well-known structure. - Traditional databases technology is not adequate in dealing with rich data:

eg: audio, video, nested data structures …

Introduction


Web data characteristics, called semistructured :

•Object-likea collection of complex objects from CODM.

• Schema-lessNot typically conform to any type traditional structure.

• Self-describing meaning of the data is carried along with the data itself.

So, we need new database technologies to support those Web-based applications.

Features of Web Data


• XML---- Extensible Markup Language

- A mark up language for documents containing structured information. - Universal format for structured documents and data on the Web. - An HTML-like language.

• XML specification defines a standard way to add markup to documents.

• Note: Structured information , Markup language

What is XML?


A XML example for customer information:

<customer-details id="AcPharm39156"> <name>Acme Pharmaceuticals Co.</name> <address country="US"> <street>7301 Smokey Boulevard</street>

<city>Smallville</city> <state>Indiana</state> <postal>94571</postal>

</address> </customer-details>

What is XML ---- example


XML vs. HTML?

XML HTML

XML is extensible

- NOT specifies semantics or tag set

- Just facility

Not extensible

- Fix tag semantics and tag set

- Defined by W3C(the World Wide Web Consortium).

XML document is well formed:

- A root element.

- Opening tag is followed by a matching closing tag.

- Element properly nested.

Not strict required.

- Tags are not required to be closed.

- Browsers will forgive

etc.


Overview of XML

• Mechanisms for specifying document structure: ---- a set of rules for structuring an XML document.

DTD ---- Document type definition language (A part of XML standard )

XML Schema ---- A more recent specification • Query languages for XML: XPath , XSLT, XQuery


• XML element Any properly nested piece of text of the form <sometag>…</sometag>.

eg: <street>7301 Smokey Boulevard</street>

• XML Attributes also a tools for datapresentation.

eg: <customer-details id="AcPharm39156"> </customer-details>

Basic concept in XML ---- element & attributes

name content

name Attribute Value


• Namespaces • - Why?

Element names in XML are not fixed, name conflict. - How? Different authors use different namespace identifiers for different domains. The general structure “namespace:local-name”

Namespace ---- URI (uniform resource identifier): URL (uniform resource locator) or URN (universal resource name). Local name ---- same form as regular XML tags.

No a “:” in it.

Basic concept in XML ---- namespace


• An example of Namespaces :

<item xmlns="http://www.acmeinc.com/jp#supplies">xmlns:toy=“http://www.acmeinc.com/jp#toys”> <name>African Coffee Table</name> <feature>

<toy:item><toy:name>cyberpet</toy:name>

</toy:item> </feature>

</item>

Basic concept in XML ---- namespace

default namespace


• Why DTD? - XML files carry a description of its own format with it. - Independent groups of people can agree with interchanging data. - Application verify received data from the outside world - Also verify own data.

• How? - DTD is included in your XML source file <!DOCTYPE root-element [element-declarations]> - DTD is external to your XML source file <!DOCTYPE root-element SYSTEM "filename">

DTD ---- Document Type Definitions


Example XML document with a DTD:

<?xml version="1.0"?><!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)>]><note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend</body></note>

DTD ---- example


XML document with an external DTD:

<?xml version="1.0"?><!DOCTYPE note SYSTEM "note.dtd"><note><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note>

"note.dtd" containing the DTD:

<!ELEMENT note (to,from,heading,body)><!ELEMENT to (#PCDATA)><!ELEMENT from (#PCDATA)><!ELEMENT heading (#PCDATA)><!ELEMENT body (#PCDATA)>

DTD ---- example


• Inadequacy of DTD:

- Not designed with namespaces.. - Use syntax ---- quite different from XML document. - A very limited set of basic types - Provide only limited means for expressing data consistency constraints. No keys

Referential integrity is weak:Attributes can be type ID, IDREF,

IDREFS. No for element.

DTD ---- Inadequacy


• Inadequacy of DTD:

- No ways of enforcing referential integrity for elements.

- Use alternatives to state that the order of elements is immaterial. Terrible as the number of attributes grows.

- Element definitions are global to the entire document.

DTD ---- Inadequacy


• XML Schemas An attempt to solve all those problems in DTD

- Powerful data typing - Range checking - Namespace-aware validation based on namespace URIs rather than on prefixes - Extensibility and scalability

XML Schema


• Here is a simple example about XML Schema:

<?xml version="1.0"?><xsd:schema

xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="SONG" type="SongType"/> <xsd:complexType name="SongType"> <xsd:sequence> <xsd:element name="TITLE" type="xsd:string"/> <xsd:element name="COMPOSER" type="xsd:string"/> <xsd:element name="PRODUCER" type="xsd:string"/> <xsd:element name="PUBLISHER" type="xsd:string"/> <xsd:element name="LENGTH" type="xsd:string"/> <xsd:element name="YEAR" type="xsd:string"/> <xsd:element name="ARTIST" type="xsd:string"/> <xsd:element name="PRICE" type="xsd:string"/> </xsd:sequence> </xsd:complexType></xsd:schema>

XML Schema ---- example


• The root element ---- “schema”.• Default namespace ---- http://www.w3.org/2001/XMLSchema with prefix xsd or xs.

• Elements ---- xsd:element. divided into simple type and complex type.

simple type element is one that can only contain text and does not have any attributes. It cannot contain any child elements.

Syntax: <xs:element name="name" type="type"/>Examples: <xs:element name="to"

type="xs:string"/>



Complex type define a new type which can have attributes and can have child elements. This is very flexible.

Syntax: <xs:element name="name"> <xs:complexType>

. element content </xs:complexType></xs:element>

Example: <xs:element name="note"> <xs:complexType> <xs:sequence>

<element name="to" type="xs:string"/><element name="from" type="xs:string"/><element name="heading" type="xs:string"/><element name="body" type="xs:string"/>

</xs:sequence> </xs:complexType></xs:element>



• Simple Types

- 44 built-in simple types in the W3C XML Schema language. - Divided into seven groups:

Numeric types Time types XML types String types The boolean type The URI reference type The binary types

XML Schema ---- features


• Deriving Simple Types Not limited to the 44 simple types Create new data types by deriving from the

existing types -restrict a type to a subset of its normal values.

eg: A schema that derives a Str255 data type from xsd:string

<xsd:simpleType name="Str255"> <xsd:restriction base="xsd:string"> <xsd:minLength value="1"/> <xsd:maxLength value="255"/> </xsd:restriction> </xsd:simpleType>



• create enumerated types

Example:

<xsd:simpleType name="PublisherType"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="Warner-Elektra-Atlantic"/> <xsd:enumeration value="Universal Music Group"/> <xsd:enumeration value="Sony Music

Entertainment,Inc."/> <xsd:enumeration value="Capitol Records, Inc."/> <xsd:enumeration value="BMG Music"/> </xsd:restriction> </xsd:simpleType>



• create new types by join existing types through a union.

Example:

<xsd:simpleType name="MoneyOrDecimal"> <xsd:union> <xsd:simpleType> <xsd:restriction base="xsd:decimal"> </xsd:restriction> </xsd:simpleType> <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:pattern value="\p{Sc}\p{Nd}+(\.\p{Nd}\

p{Nd})?"/> </xsd:restriction> </xsd:simpleType> </xsd:union></xsd:simpleType>



• Namespaces

- http://www.w3.org/2001/XMLSchema the namespace that identifies the names of tags and attributes used in a schema. The name is understood by all schema aware XML processors.- http://www.w3.org/2001/XMLSchema-instance a small number of special names used in instance documents, not schema.- target namespace the set of names defined by a particular schema document the user-defined names that are to be used in the instance documents.



• Grouping- Does order really mattered? ?

- How? xsd:all group ---- each element in the group

must occur at most once, but that order is not important. xsd:choice group ---- any one element from the

group should appear. xsd:sequence group ---- each element in the

group appear exactly once, in the specified order.



Example for xsd:all group

<xsd:complexType name="PersonType"> <xsd:sequence> <xsd:element name="NAME"> <xsd:complexType> <xsd:all> <xsd:element name="GIVEN" type="xsd:string" minOccurs="1" maxOccurs="1"/> <xsd:element name="FAMILY" type="xsd:string" minOccurs="1" maxOccurs="1"/> </xsd:all> </xsd:complexType> </xsd:element> </xsd:sequence></xsd:complexType>



Example for XML Choice group:

<xsd:complexType name="SongType"> <xsd:sequence> <xsd:element name="TITLE" type="xsd:string"/> <xsd:choice> <xsd:element name="COMPOSER" type="PersonType"/> <xsd:element name="PRODUCER" type="PersonType"/> </xsd:choice> <xsd:element name="PUBLISHER" type="xsd:string" minOccurs="0"/> <xsd:element name="LENGTH" type="xsd:string"/> <xsd:element name="YEAR" type="xsd:string"/> <xsd:element name="ARTIST" type="xsd:string" maxOccurs="unbounded"/> <xsd:element name="PRICE" type="xsd:string"

minOccurs="0"/> </xsd:sequence></xsd:complexType>



• Schemas address limitations of DTDs: a strange, non-XML syntaxnamespace incompatibilitylack of data typinglimited extensibility and scalability.

• XML Schemas - Powerful data typing - Range checking - Namespace-aware validation based on namespace URIs rather than on prefixes - Extensibility and scalability



• DTD No keys, its Referential integrity is weak

Attributes :ID, IDREF, IDREFS. ID ---- Unique valueIDREF ---- Valid ID declared in same document IDREFS ---- Valid ID, space-separated

But these are also based on type string.

Element: no corresponding parts.

XML Constrains ---- DTD


XML Constrains ---- Schema

• XML keys: Similar with SQL, but complicated.

- complex structures- a key might be composed of a sequence of values- located at different depths inside an element.

Two ways: - tag unique ---- UNIQUE constraint- tag key ---- PRIMARY KEY , not null

eg: <key name=“PrimaryKeyForClass”><selector xpath=“Classes/Class”/><field xpath=“CrsCode”/><field xpath=“Semester”/>

</key>


XML Constrains ---- Schema

• Foreign keys:

eg: <complexType> …… <keyref name=“NoBogusTranscripts” refer=“adm:PrimaryKeyForClass”>

<selector xpath=“Students/Student/CrsTaken”/><field xpath=“@CrsCode”/><field xpath=“@Semester”/>

</keyref> … … </complexType>

• Powerful?


•Is XML data model relational or object-relational?• Is XML a database?

Question


References

[1] Chapter 17, XML and Web Data

[2] Chapter 24, XML Bible (2nd edition): Schemas

http://www.ibiblio.org/xml/books/bible2/index.html#toc

[3] http://www.w3schools.com

http://www.w3.org/

http://www.xml.com/


Part II XML Query Language

Counterpart of SQL in XML World


XML Query Language Desired Characteristics for XML Query

Language - also Requirements Good candidate: XQuery Language Use Cases for XQuery Language


Desired Characteristics XML Output Declarative - what has to be done? Query Operation No Schema Required Preserve Order and Association Mutually Embedding with XML Support for New Datatypes Suitable for Metadata Ability to add update capabilities in future versions


Details XML Output

define derived database (virtual views) provide transparency to application (why?)

The XML Query Language MUST be declarative - like SQL specifies what has to be done it MUST not enforce a particular evaluation

strategy


Details (cont.) Query Operation

Projection, selection, join, and restructuring should all be possible in a single XML Query (why?)

for optimization reason


Query Operations

XML QUERY

Details Relational Algebra

Projection Extract particular sub-elements or attributes of an element

Projection

Selection Select values that satisfy some predicate Selection

Join Join values from one or more documents Join

Restructuring Constructing a new set of element instances to hold queried data

Create view


Example - Sample Data <bib> <book year="1999" isbn="1-55860-622-X"> <title>Data on the Web</title> <author>Abiteboul</author> <author>Buneman</author> <author>Suciu</author> </book> <book year="2001" isbn="1-XXXXX-YYY-Z"> <title>XML Query</title> <author>Fernandez</author> <author>Suciu</author> </book> </bib>


Example - XML Schema <xs:group name="Bib"> <xs:element name="bib"> <xs:complexType> <xs:group ref="Book" minOccurs="0" maxOccurs="unbounded"/> </xs:complexType> </xs:element> </xs:group>


Example - XML Schema (Cont.) <xs:group name="Book"> <xs:element name="book"> <xs:complexType> <xs:attribute name="year" type="xs:integer"/> <xs:attribute name="isbn" type="xs:string"/> <xs:element name="title" type="xs:string"/> <xs:element name="author"type="xs:string"

maxOccurs="unbounded"/> </xs:complexType> </xs:element> </xs:group>


Variable Binding LET $bib0 := <bib> <book year="1999" isbn="1-55860-622-X"> <title>Data on the Web</title> <author>Abiteboul</author> <author>Buneman</author> <author>Suciu</author> </book> <book year="2001" isbn="1-XXXXX-YYY-Z"> <title>XML Query</title> <author>Fernandez</author> <author>Suciu</author> </book>), </bib>


Projection $bib0/book/author

==> <author>Abiteboul</author>, <author>Buneman</author>, <author>Suciu</author>, <author>Fernandez</author>, <author>Suciu</author>

Notes: the document order of author elements is preserved


Selection FOR $b IN $bib0/book WHERE $b/@year/data() <= 2000 RETURN $b

==> <book year="1999" isbn="1-55860-622-X"> <title>Data on the Web</title> <author>Abiteboul</author> <author>Buneman</author> <author>Suciu</author> </book>


Join - Sample Data LET $review0 := <reviews> <book> <title>XML Query</title> <review>A darn fine book.</review> </book>, <book> <title>Data on the Web</title> <review>This is great!</review> </book> </review> : Reviews


Join FOR $b IN $bib0/book, $r IN $review0/book WHERE $b/title/data() = $r/title/data() RETURN <book>{ $b/title, $b/author, $r/review }</book> ==> <book> <title>Data on the Web</title> <author>Abiteboul</author> <author>Buneman</author> <author>Suciu</author> <review>A darn fine book.</review> </book>, <book> <title>XML Query</title> <author>Fernandez</author> <author>Suciu</author> <review>This is great!</review> </book>


Restructuring FOR $a IN distinct-value($bib0/book/author/data())

RETURN <biblio> <author>{ $a }</author> { FOR $b IN $bib0/book, $a2 IN $b/author/data() WHERE $a = $a2 RETURN $b/title } </biblio>


Restructuring (Cont.) ==> <biblio> <author>Abiteboul</author> <title>Data on the Web</title> </biblio>, <biblio> <author>Buneman</author> <title>Data on the Web</title> </biblio>, <biblio> <author>Suciu</author> <title>Data on the Web</title> <title>XML Query</title> </biblio>, <biblio> <author>Fernandez</author> <title>XML Query</title> </biblio>


Details (cont.) No Schema Required

XML Query should be usable on XML data when there is no schema (DTD or XML Schema) known in advance. But it should be able to exploit the schema if the schema is available.

Preserve Order and Association XML Query should preserve order and

association of elements in XML data (why?)


Details (cont.) Mutually Embedding with XML

An XML Query should be able to contain arbitrary XML data, and an XML document should be able to hold arbitrary XML Queries

Support for New Datatypes XML Query should have an extension

mechanism for conditions and operations specific to a particular datatypes (e.g. multimedia data).


Details (cont.) Suitable for Metadata

XML Query should be useful as a part of metadata descriptions (how?)

Question: how about metadata in relational database?

The current version MUST not preclude the ability to add update capabilities in future versions


Your Idea? Any other characteristics you desire?


XQuery Language Overview XPath XQuery 1.0 Semantics Future work for XQuery


Overview Combine the best features of XPath, SQL

and ideas borrowed from object query language.


XPath Language for navigation with tree-

structured documents XPath data model

XML document Tree Element Attribute Node text comment


Navigation in XPath Operators

Root: / Parent: .. Child (descendant): / or // Attribute value: @ Comment: comment() function Text: text() function Element: <element name>

Wildcards *: all e-children of a node irrespective of type, not

including text nodes @*: all attributes //: all descendants of current node


XPath expression Combination of XPath operators Input: a document tree Output: a set of nodes Absolute path expression

start from the root node Relative path expression

start from the current node


XPath query Selection conditions Built-in functions Aggregate functions


Example – XML file

<students> <student studid=“996341111”> <name><first>John</first><last>Doe</last></name> <status>U2</status> <crstaken crscode=“CS503” semester=“S2002”/> <crstaken crscode=“CS561” semester=“S2002”/> </student> <student studid=“996342222”> <name><first>Bart</first><last>Simpson</last></name> <status>U4</status> <crstaken crscode=“CS504” semester=“S2002”/> </student> </students>


XPath Document Tree

root

comment commentstudents

name

student

studid

crscode semestercrscodesemester

student

status

crstaken

crstaken

first

last

John Doe U2


Example – XPath Query

//student[status=“U2” and start-with(.//last, “D”) and not (.//last=.//first)]

//student[count(crstaken) >=5]

//student[crstaken/@crscode=“CS561”] [crstaken/@semester=“S2002”]


Why XPath is not satisfying? Just for navigating, can only support limited

queries Cannot express join Cannot work on multiple XML documents Cannot filter unwanted elements Not support user-defined functions Not support importation and use of the types defined

in various XML schemas

Any other limitations you can think of?


A better candidate for XML Query? XQuery Language incorporates all the

above characteristics Any other characteristics you can think

of?

XQuery engine: Kweelt http://kweelt.sourceforge.net/


XQuery expressions – Path expressions – FLWR expressions – Element constructors – Expressions involving operators and

functions – Conditional expressions – Quantified expressions – List constructors – Expressions that test or modify datatypes


XQuery FLWR Expressions A FLWR expression binds some

expressions, applies a predicate, and constructs a new result.

FOR var IN expr …. LET var := expr …. WHERE expr …. RETURN expr ….

FOR and LET clauses grnerate a list of tuples of bound exprs,

preserving document order

WHERE clause applies a predicate, eliminating some of the tuples

RETURN clause is executing for each surviving tuple, generating

an ordered list of outputs


Example - DTD <!ELEMENT reviews (entry*)> <!ELEMENT entry (title, price, review)> <!ELEMENT title (#PCDATA)> <!ELEMENT price (#PCDATA)> <!ELEMENT review (#PCDATA)>


Example – Sample Data http://www.amazon.com/reviews.xml <reviews> <entry> <title>Data on the Web</title> <price>34.95</price> <review> a good discussion of database systems and XML. </review> </entry> <entry> <title>Advanced Unix Programming </title> <price>65.95</price> <review> a good discussion of UNIX programming. </review> </entry> </reviews>


Example - Request For each book found at both www.bn.com

and www.amazon.com, list the title of the book and its price from each source


Example - Query <books-with-prices> { for $b in document("www.bn.com/bib.xml")//book, $a in document("www.amazon.com/reviews.xml")//entry where $b/title = $a/title return <book-with-prices> { $b/title } <price-amazon>{ $a/price/data() }</price-amazon> <price-bn>{ $b/price/data() }</price-bn> </book-with-prices> } </books-with-prices>


Example - Result <books-with-prices> <book-with-prices> <title>Advanced Unix Programming</title> <price-amazon>65.95</price-amazon> <price-bn>65.95</price-bn> </book-with-prices> <book-with-prices> <title>Data on the Web</title> <price-amazon>34.95</price-amazon> <price-bn> 39.95</price-bn> </book-with-prices> </books-with-prices>


Use Cases Use Case 1: Queries that reserve hierarchy Use Case 2: Access to relational data


Use Case 1: Queries that reserve hierarchy

XML document has flexible structure Text is mixed with elements Many elements are optional Wide variation in structure from one

document to another The ways in which elements are ordered

and nested are quite important (Can you give me an example?)


Use Case 1 - DTD <!DOCTYPE book [

<!ELEMENT book (title, author+, section+)> <!ELEMENT title (#PCDATA)> <!ELEMENT author (#PCDATA)> <!ELEMENT section (title, (p | figure |

section)* )> <!ATTLIST section

id ID #IMPLIED difficulty CDATA #IMPLIED>

<!ELEMENT p (#PCDATA)> <!ELEMENT figure (title, image)> <!ATTLIST figure

width CDATA #REQUIRED height CDATA #REQUIRED >

<!ELEMENT image EMPTY> <!ATTLIST image

source CDATA #REQUIRED > ]>


<book> <title>Data on the Web</title> <author>Serge Abiteboul</author> <author>Peter Buneman</author> <section id="intro" difficulty="easy" >

<title>Introduction</title> <p>Text ... </p> <section>

<title>Audience</title> <p>Text ... </p>

</section> <section>

<title>Web Data and the Two Cultures</title> <p>Text ... </p> <figure height="400" width="400">

<title>Traditional client/server architecture</title> <image source="csarch.gif"/>

</figure> <p>Text ... </p>

</section> </section> <section id="syntax" difficulty="medium" >

... </section>

</book>


Use Case 1 - Request List all the sections and their titles.

Preserve the original attributes of each <section> element, if any.

Questions Do we need all the elements? How could we eliminate unwanted

elements? How could we preserve the original

attributes?


Use Case 1 - Solution <toc>

{Let $b := document(“book1.xml”)Return

Filter($b//section | $b//section/title | $b//section/title/data())

} </toc>


Use Case 1 - Result <toc>

<section id="intro" difficulty="easy"> <title>Introduction</title> <section>

<title>Audience</title> </section> <section>

<title>Web Data and the Two Cultures</title> </section>

</section> <section id="syntax" difficulty="medium">

... </section>

</toc>


Use Case 2 - Access to Relational Data Questions

How to represent relational tables as XML document?

Do we need multiple XML documents? How does XQuery work on multiple XML

documents?


Use Case 2 - Access to Relational Data

Represent database table as XML document Document element <-> table Tuple <-> nested element Column <-> nested element inside tuple-

element Column that allow null values are represented by

optional elements, and a missing element denotes a null value


Use Cases 2 - Online Auction Tables

USERS (userid, name, rating) Contains info on registered users

ITEMS (itemno, description, offered_by, start_date, end_date, reserve_price) Lists items currently or recently for sale

BIDS (userid, itemno, bid, bid_date) Contains all bids on record


Simplified E-R Diagram

USERS ITEMS

BIDS

userid

userid itemno

itemno


Use Case 2 - DTD <!DOCTYPE users [ <!ELEMENT users (user_tuple*)> <!ELEMENT user_tuple (userid, name,

rating?)> <!ELEMENT userid (#PCDATA)> <!ELEMENT name (#PCDATA)> <!ELEMENT rating (#PCDATA)> ]>


Use Case 2 - DTD

<!DOCTYPE items [ <!ELEMENT items (item_tuple*)> <!ELEMENT item_tuple (itemno, description,

offered_by, start_date?, end_date?, reserve_price? )> <!ELEMENT itemno (#PCDATA)> <!ELEMENT description (#PCDATA)> <!ELEMENT offered_by (#PCDATA)> <!ELEMENT start_date (#PCDATA)> <!ELEMENT end_date (#PCDATA)> <!ELEMENT reserve_price (#PCDATA)> ]>


Use Case 2 - DTD <!DOCTYPE bids [ <!ELEMENT bids (bid_tuple*)> <!ELEMENT bid_tuple (userid, itemno, bid, bid_date)> <!ELEMENT userid (#PCDATA)> <!ELEMENT itemno (#PCDATA)> <!ELEMENT bid (#PCDATA)> <!ELEMENT bid_date (#PCDATA)>

]>


Use Case 2 - Sample Data USER

USERID NAME RATING

U01 Tom Jones B

U02 Mary Doe A

U04 Roger Smith C

U05 Rip Sprat B


Use Case 2 - Sample Data ITEMS

ITEMNO DESCRIPTION OFFERED_BY START_DATE

END_DATE RESERVE_

PRICE

1001 Red Bicycle

U01 01-01-05 01-01-20 40

1002 Motorcycle U02 01-02-11 01-03-15 500

1003 Old Bicycle

U02 01-01-10 01-02-20 25


Use Case 2 – Sample Data BIDS

USERID ITEMNO BID BID_DATE

U02 1001 35 01-01-07

U04 1001 40 01-01-08

U02 1001 45 01-01-11

U04 1001 55 01-01-15

U01 1002 400 01-02-14

U02 1002 600 01-02-16

U04 1002 1000 01-02-25

U02 1002 1200 01-03-02

U04 1003 15 01-01-22

U05 1003 20 01-02-03


Use Case 2 - Request Request

For all bicycles, list the item number, description, and highest bid (if any), ordered by item number.


Use Case 2 – Solution <result> { for $i in document("items.xml")//item_tuple let $b := document("bids.xml")//bid_tuple[itemno =

$i/itemno] where contains($i/description, "Bicycle") return <item_tuple> { $i/itemno } { $i/description } <high_bid>{ max($b/bid) }</high_bid> </item_tuple> sortby(itemno) } </result>


Use Case 2 – Result (Bingo!) <result> <item_tuple> <itemno>1001</itemno> <description>Red Bicycle</description> <high_bid> <bid>55</bid> </high_bid> </item_tuple> <item_tuple> <itemno>1003</itemno> <description>Old Bicycle</description> <high_bid> <bid>20</bid> </high_bid> </item_tuple> </result>


Future Work about XQuery Add support for new desired characteristics

What are they? Any other future work?


Bibliography Chapter 17, XML and Web Data XML Query Requirements

http://www.w3.org/TR/2001/WD-xmlquery-req-20010215 XML Query Use Cases, W3C Working Draft 20

December 2001 http://www.w3.org/TR/2001/WD-xmlquery-use-cases-

20011220

Database Desiderata for an XML Query Language, David Maier, Oregon Graduate Institute

Documents

CS561XML & XML Query 1 Ling Wang Luping Ding. CS561XML & XML Query 2 The Web opens a new challenges in: - information technology - database framework