Native XML Databasefor Information Systems

Chris WallaceIS School Research Seminar

Feb 2006

Chris Wallace, IS School Research Seminar, Feb 2006

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Exploring the design space

• “design as a conversation with the materials in the situation” (Schon)

• Native XML database (NXD)– Storing, querying and updating XML documents without

mapping into relations– Schema-free– Trees are to NXD what tables are to RDBMS– Tables are trees

• Information Systems– Focus on semi-structured data (mixture of simple data

items, text and complex nested structures)– Searching, derived data, visualisation– Process support– Large problem space variously supported by

spreadsheets, word documents, ad-hoc databases, increasingly web-integrated data.

Chris Wallace, IS School Research Seminar, Feb 2006

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eXist Native XML Database• Open source Java • European team of developers led by Wolfgang

Meier• Documents (files) are organised in collections

(folders) in a file store– XML Documents stored in an efficient, B+ tree structure

with indexes– Non-XML resources (XQuery, CSS, JPEG ..), etc can be

stored as binary• Deployable in different ways

– Embedded in a Java application– Part of a Cocoon pipeline– As web application in Apache/Tomcat– With embedded Jetty HTTPserver (as on stocks)

• Multiple Interfaces– REST – to Java servlet – SOAP– XML:RPC

Chris Wallace, IS School Research Seminar, Feb 2006

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NXD case studies

• FOLD– modules, programmes, scheme operations,

staff, organisational structures, events

• Family photos and history– Integration of meta-data on family photos with

family history (births, deaths and marriages)

• ISD3 Assignment – a web-based calculator– e.g. a currency converter

• The language patterns book

Chris Wallace, IS School Research Seminar, Feb 2006

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ISD3 Coursework

• Develop a simple web-based calculator• Not just a programming exercise

– User interface design • Users language, units, not raw data• User interaction design

– Data design• choice of representation of domain facts

– Veracity• Relationship between data in database and domain

being modelled• How is veracity monitored and maintained

– Process• Examine some of the XP processes

– Test-driven development

Chris Wallace, IS School Research Seminar, Feb 2006

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Application Design• Data model is one simple table:

– Currency code, name and symbol– Latest conversion rates from GBP to currency X

• Currency Coding– Use ISO4217 e.g. XE.COM list

• Core algorithm:– Conversion from N X to ? Y is

• N * rate(X to GBP) * rate(GBP to Y) i.e.• N * (1/rate (GBP to X) * rate(GBP to Y)

• Currency rates to be updated by an administrator– (not via a web-service)

• Interface is to be a sticky form:– Input form and output result on one page– Input form default values from last input

• Veracity management– Rates must be dated and sourced –

Chris Wallace, IS School Research Seminar, Feb 2006

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Technical Decisions

• Choice of platform:– PL/SQL and Oracle– ASP.NET and SQL Server– JSP (Java Servlet Page) and JDBC to

Postgres(say)– PHP and MySQL– XML and Native XML Database (eXist)

• Calculation location:– client-side in ECMAScript (aka JavaScript)– server-side

• with/without Ajax

Chris Wallace, IS School Research Seminar, Feb 2006

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Two approaches

• PHP-MySQL– Define and create MySQL table– Write PHP script to provide interface and

access the database using SQL– Write editor for the Currency table

• XML– Create MS Excel spreadsheet of

currencies – Convert to XML in Excel and save– Write XQuery script to provide interface

Chris Wallace, IS School Research Seminar, Feb 2006

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Development Processfor currency converter

• XP Practices:– ‘Spike’ Simple end to end implementation– Incremental development

• Setup eXist database – Using the Admin interface:

• Create a directory for application• Create a subdirectory for currency data

• Create XML dataset(s) in Excel • Upload to eXist• Write the XQuery script cur.xql• Upload to eXist• Execute in browser

Chris Wallace, IS School Research Seminar, Feb 2006

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Currency Data in XML

• Start MS Excel 2003• Create the spreadsheet with column headings• Convert to List (needs XML add-in)• Save as XML data

Code Name Rate

GBP Sterling 1

USD US Dollars 1.7423

EUR Euro 1.46331

NZD NZ Dollars 2.60665

JPY Yen 205.852

Chris Wallace, IS School Research Seminar, Feb 2006

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XQuery

• W3C candidate recommendation– http://www.w3.org/TR/xquery/

• Designed by, amongst others, Don Chamberlin– http://www.research.ibm.com/journal/sj/414/ch

amberlin.pdf• A functional programming Language

– Based on XPath (tree-access language)– Integrate, select, update, compute and

construct XML documents– cf PL/SQL

• http://www.w3.org/XML/Query/

Chris Wallace, IS School Research Seminar, Feb 2006

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Write the XQuery script

• Use the admin interface to test simple queries

• Use a syntax aware editor if possible– JEdit– Dreamweaver– Java Client interface to eXist– PFE32

Chris Wallace, IS School Research Seminar, Feb 2006

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Executing an XQuery

eXist DB

cur.xql

XQuery Engine

parameters

html

Client Browser eXist: Server

Get cur.xql +parameters

servlet

fetch cur.xql

render

User clickslink

cur.xql?fromAmount=100&fromCode=USD&toCode=EUR

XSLT

Chris Wallace, IS School Research Seminar, Feb 2006

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XQuery Script (1)declare namespace request="http://exist-db.org/xquery/request";

let $fromAmount := request:request-parameter("fromAmount",“100"), $fromCode := request:request-parameter("fromCode","GBP"), $toCode := request:request-parameter("toCode","EUR"),

$currencies := doc('/db/calculator/currencyTable.xml')//Currency,

$fromCurrency := $currencies[Code=$fromCode], $toCurrency := $currencies[Code=$toCode],

$toAmount := round(xs:decimal($fromAmount) * xs:decimal($toCurrency/Rate) div xs:decimal($fromCurrency/Rate) )return

Chris Wallace, IS School Research Seminar, Feb 2006

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XQuery Script (1)declare namespace request="http://exist-db.org/xquery/request";

let $fromAmount := request:request-parameter("fromAmount",“100"), $fromCode := request:request-parameter("fromCode","GBP"), $toCode := request:request-parameter("toCode","EUR"),

$currencies := doc('/db/calculator/currencyTable.xml')//Currency,

$fromCurrency := $currencies[Code=$fromCode], $toCurrency := $currencies[Code=$toCode],

$toAmount := round(xs:decimal($fromAmount) * xs:decimal($toCurrency/Rate) div xs:decimal($fromCurrency/Rate) )return …

Default

Return node sequence of all Currency

elements in this doc

Filter Condition

Cast

Chris Wallace, IS School Research Seminar, Feb 2006

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XQuery Script (2)

return<html><head><title>Currency Calculator</title></head><body><h1>Currency Calculator</h1><form method ="get"><table border="1"><tr><td>Amount to Convert</td> <td><input type="text" name="fromAmount“ value="{$fromAmount}"/> </td></tr>

Embedded XQuery

XML

Current script is

called by

default

Chris Wallace, IS School Research Seminar, Feb 2006

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XQuery (3)

<tr><td>From Currency</td><td><select name="fromCode">{for $currency in $currencies let $code := data($currency/Code), $name := data($currency/Name) return if ($code = $fromCode) then <option value="{$code}" selected="yes">{$name}</option> else <option value="{$code}" >{$name}</option>}</select></td></tr>

FLWOR expression

conditional

Chris Wallace, IS School Research Seminar, Feb 2006

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XQuery (4)

<tr><td><input type="submit" name="Convert"/></td></tr><tr><td>Converts to </td><td>{$toAmount}</td></tr></table></form></body></html>

Switch to XQuery again,In PHP this would be either $toAmount (if in PHP) or

<?php print $toAmount; ?> (if in HTML)

Chris Wallace, IS School Research Seminar, Feb 2006

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Round two - enhancements

• Add another currency– ZAR Rand 10.4767

• Add new columns– Meta data

• to convey the accuracy, timeliness and origin of the data itself

– Source and date/time• Update spreadsheet

– Add columns and data• Update XQuery script – cur2.xql

– Add source – Sources and oldest date

Chris Wallace, IS School Research Seminar, Feb 2006

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Round 3 – Currency Table

• Same document used for different purpose:– currency.xsl– curtable.xql– Run it curtable.xql

Chris Wallace, IS School Research Seminar, Feb 2006

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The Language Patterns book

• Local / Web-based • Work-in-progress• Should be converted to XML

– currently organised by • Pattern

– Language– But should be able to be viewed as

• Language– Pattern

– An XML database would solve this problem• As an exercise for next week, you will extend the

number of languages with ActionScript– Get you familiar with the on-line book– Extend the book