Native XML Database for Information Systems Chris Wallace ISD3 March 2006

Chris Wallace, ISD3 2 Exploring the design space 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. “design as a conversation with the materials in the situation” (Schon)

Chris Wallace, ISD3 3 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, ISD3 4 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)meta-databirths, deaths and marriages ISD3 Assignment –a web-based calculator –e.g. a currency convertercurrency converter State-machine simulator –Coke machineCoke machine

Chris Wallace, ISD3 5 ISD3 Coursework 1 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, ISD3 6 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 ISO4217XE.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, ISD3 7 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, ISD3 8 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, ISD3 9 Development Process for currency converter XP Practices: –‘Spike’ Simple end to end implementation –Incremental development Setup eXist databaseeXist 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.xqlcur.xql Upload to eXist Execute in browser

Chris Wallace, ISD3 10 Currency Data in XML Start MS Excel 2003 Create the spreadsheet with column headings Convert to List (needs XML add-in) Save as XML dataXML data CodeNameRate GBPSterling1 USDUS Dollars EUREuro NZDNZ Dollars JPYYen

Chris Wallace, ISD3 11 XQuery W3C candidate recommendation – Designed by, amongst others, Don Chamberlin – rlin.pdfhttp:// rlin.pdf A functional programming Language –Based on XPath (tree-access language) –Integrate, select, update, compute and construct XML documents –cf PL/SQL

Chris Wallace, ISD3 12 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, ISD3 13 Executing an XQuery eXist DB cur.xql XQuery Engine parameters html Client BrowsereXist: Server Get cur.xql + parameters servlet fetch cur.xql render User clicks link cur.xql?fromAmount=100&fromCode=USD&toCode=EUR XSLT

Chris Wallace, ISD3 14 XQuery Script (1) declare namespace request=" let $fromAmount := request:request-parameter("fromAmount",“100"), $fromCode := request:request-parameter("fromCode","GBP"), $toCode := request:request-parameter("toCode","EUR"), $currencies := collection('/db/calculator/currencies')//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, ISD3 15 XQuery Script (1) declare namespace request=" let $fromAmount := request:request-parameter("fromAmount",“100"), $fromCode := request:request-parameter("fromCode","GBP"), $toCode := request:request-parameter("toCode","EUR"), $currencies := collection('/db/calculator/currencies')//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, ISD3 16 XQuery Script (2) return Currency Calculator Currency Calculator Amount to Convert <input type="text" name="fromAmount“ value="{$fromAmount}"/> Embedded XQuery XML

Chris Wallace, ISD3 17 XQuery (3) From Currency {for $currency in $currencies let $code := data($currency/Code), $name := data($currency/Name) return if ($code = $fromCode) then {$name} else {$name} } FLWOR expression conditional

Chris Wallace, ISD3 18 Round two - enhancements Add another currency –ZAR Rand Add new columns –Source and date/time Update spreadsheet –Add columns and data Update XQuery script – cur2.xqlXQuery script cur2.xql –Add source – Sources and oldest date

Chris Wallace, ISD3 19 Round 3 – Currency Table Same document used for different purpose: –currency.xslcurrency.xsl –curtable.xqlcurtable.xql –Run it curtable.xqlcurtable.xql

Chris Wallace, ISD3 20 The FOLD

Chris Wallace, ISD3 21 FOLD Design Some table data for maintenance in spreadsheet form. Forces some compromises in the data structure –Multi-valued fields (not nested) –Specific roles (not generic) Module specifications, Programme Structures, Organisational Groups –deeply structured documents –complex relationships

Chris Wallace, ISD3 22 Research Areas Design practice for NDX –‘Pattern language’ to help map from conceptual model to multiple XML schemes –Identifier design –Structuring documents by responsibility and versions NDX in organisational use –Social effects of distributed responsibility –Visualisation of complex relationships –Handling integrity problems – accept inconsistency as a way of life –Management of veracity

Chris Wallace, ISD3 23 Process support Short term – Process support –Form generation –Linkage to process documentation Medium term – Process monitoring –Online capture of significant dates Coursework hand-in date Date exam sent to moderator Date coursework returned to students –Derived information Workload prediction based on coursework schedule and student numbers Display of latest coursework returned and SMS message to students –State-based process modelling Exam moderation Long term- Process management –Workflow –Process enactment software

Chris Wallace, ISD3 24 Next 6 weeks Web Services – Application integration Process modelling –Use cases and scenarios –State machines Business Process Modelling