[PDF] - XML <Foo> <Bars> XML and databases <Bar Number=2 PDF Document

SLIDE 1

1 XML and databases

Dennis Andersson, FOI Andreas Borg, LiU/IDA/PELAB

XML

<Foo> <Bars> <Bar Number=2 String=”ABC” /> <Bar Number=1 /> <Bar String=”XTC”> Baz </Bar> </Bars> <Bar> Booze </Bar> </Foo>

XML database

XML in RDBs

– Adding semi+structured features to strongly typed databases – Example: MS SQL Server 2005 – Dense vs. sparse

XML as DBs

– An XML file IS a database – A set of XML files is also a database – Semi+structured

XML as a DB

In order to effectively use an XML

document as a database we need:

– A method for persistance

(a filesystem?)

– To allow placing constraints on data

(a data model)

– A method for querying

(a query language)

XQuery background

W3C defines several XML standards:

– XML Schema: notation for defining new types

f elements and documents

– XSLT: notation for transforming XML documents from one representation to another – XPath: notation for selecting elements within an XML document – XQuery: a query language designed expressly for XML data sources

XQuery

Design in progress

– Only retrieval – Updating existing XML documents may follow

XQuery 1.0

– W3C recommendation 23 January 2007

Two syntaxes:

– Expressed in XML – Human+oriented version

SLIDE 2

2 XQuery data model

Sequence: An ordered collection of zero or more items
Item: Node or atomic value

– Node

Element
Attribute
Text
Document
Comment
Processing instruction
Namespace nodes

– Atomic value: E.g. strings, integers, decimals

Typed value: A sequence of zero or more typed values
Document order: Each node appears before its children

XQuery Expressions

Basics (literals, variables, core function library)
Path expressions (child, descendant, parent …)
Predicates (e.g. ” ”)
Element constructors (to construct new

elements)

Iteration and sorting (FLWR: for+let+where+

return)

Arithmetic (+,+,*,div)
Operations on sequences
Conditional expressions
Quantified expressions (some, every)

Example data: items.xml

document element attribute text node

Example data: bids.xml Path expressions

The result of each step is a sequence of nodes
The value is the node sequence resulting from the last

step

Q1: List the descriptions of all items offered for sale by

Smith.

– XML

– Human+oriented
Predicates
Q3:Find the status attribute of the item that is the

parent of a given description

variable

parent attribute node

SLIDE 3

3 Iteration and sorting

Q4: For each item that has more than ten bids, generate a popular+

item element containing the item number, description, and bid count.

! "#$
%&"

' ( ( % &"' )% &" ) %&"

* & + F L W R

A model for XML databases

An XML document is

– tags are properly nested – no need to conform to a particular schema – semi+structured data – relational and object+oriented modeling techniques becomes complex – efficient data models are needed

XDD, XML Declarative Description

A simple yet expressive mechanism

– explicit and implicit info

A description in XDD consists of

– XML elements – XML expressions (extended XML elements with variables) – XML clauses (constraints and relationships)

XML elements

Ground XML expression XML element
Example:

<Element id=1 type=”foo”>

<SubElement>Bar</SubElement> <SubElement>Baz</SubElement> <SubElement>Boz</SubElement>

</Element>

Example:

<AnotherElement />

(Non+ground) XML expressions

XML element with variable

– Name

– String
– Attribute+value+pair
– XML+expression
– Intermediate+expression
Example:

<$N:element id=$S:id $P:att1>

$E:subelements

</$N:element>

Generalization

<AirTrip from=”Bangkok” to=”London”> <Path> <City>Bangkok</City> <City>Singapore</City> <City>London</City> </Path> <Price>650</Price> </AirTrip> <AirTrip from= to=”London”>

</AirTrip>

<> <City>Singapore</City> </> (ground XML expression) (generalization of a) (another generalization of a)

SLIDE 4

4 Specialization

</AirTrip>

</AirTrip>

</AirTrip>

!

"

</AirTrip>

!

" #$%& # </AirTrip>

XDD database modeling

XML document

– Formalized as an XDD description containing ground XML unit clauses (facts, see definition 5)

Extensional XML DB (XDBE)

– 1+ XML documents formalized as above

Intensional XML DB (XDBI)

– Comprised of XML non+unit clauses defining axioms, relationships or deductible knowledge (XML non+unit clauses)

Set of structural and integrity constraints (XDBC)

– XML non+unit clauses defining particular constraints

XDD Description: XDB = XDBE υ XDBI υ XDBC

Extensional XML DB (XDBE)

<Flight number=”TG916” airline=”TG”> <Origin>Bangkok</Origin> <Destination>London</Destination> <Price>750</Price> </Flight> <Flight number=”SQ61” airline=”SQ”> <Origin>Bangkok</Origin> <Destination>Singapore</Destination> <Price>150</Price> </Flight> <Flight number=”SQ320” airline=”SQ”> <Origin>Singapore</Origin> <Destination>London</Destination> <Price>500</Price> </Flight>

Intensional XML DB (XDBI)

Example axiom

– Minimum waiting time between two connecting flights is 1 hour

Example deductible information

– There is a flight from Singapore to Bangkok – There is a flight from Bangkok to London – Hence there is a 2+step flight from Singapore to London

Can be expressed in XML

– see definition 5 and figure 4

Constraints (XDBC)

Example constraints

– A flight can not have the same origin and destination – The price of a flight must be an integer – The price of a flight must be less than 1500 – The flight number must be unique – Elements in the database must conform to a certain schema

Can be expressed in XML

– see definition 4 and figure 5

XDD querying

An XML query can be formalized as an

XML non+unit clause ( )

The result of the query is a sequence of all

possible specializations of the query clause in the database.

An example query is presented in figure 7

SLIDE 5

5 XQuery exercises

Ex1: Find the names of all conflicts where

Great Britain was a party.

Ex2: For each ongoing conflict (that has

no end+date), generate a conflict+ publication element containing the conflict name and publication titles.

! "#

XDD Exercises

Ex4: Create a non+ground XML expression that covers,

at the highest possible level of detail, any conflict in conflict.xml

Ex5: Using the expression from Ex4, show through

specialization how the following entity can be derived:

<conflict id="WW3" start="2050" type="fiction"> <name>World war 3</name> <parties> <party>Blue side</party> <party>Red side</party> </parties> <casualties>1000000</casualties> <civiliansKilled>10000</civiliansKilled> </conflict>