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Native XML Database for Information Systems

Native XML Database for Information Systems. Chris Wallace ISD3 March 2006. 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

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Native XML Database for Information Systems

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  1. Native XML Databasefor Information Systems Chris Wallace ISD3 March 2006

  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) • ISD3 Assignment • a web-based calculator • e.g. a currency converter • State-machine simulator • Coke 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 • 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 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, 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 data Chris Wallace, ISD3

  11. XQuery • W3C candidate recommendation • http://www.w3.org/TR/xquery/ • Designed by, amongst others, Don Chamberlin • http://www.research.ibm.com/journal/sj/414/chamberlin.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, 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 cur.xql?fromAmount=100&fromCode=USD&toCode=EUR Client Browser eXist: Server User clicks link Get cur.xql + parameters servlet fetch cur.xql parameters cur.xql eXist DB html XQuery Engine render XSLT Chris Wallace, ISD3

  14. 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 := 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) Default 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 := 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 … Return node sequence of all Currency elements in this doc Filter Condition Cast Chris Wallace, ISD3

  16. XQuery Script (2) XML 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 Chris Wallace, ISD3

  17. XQuery (3) FLWOR expression <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> conditional Chris Wallace, ISD3

  18. Round two - enhancements • Add another currency • ZAR Rand 10.4767 • Add new columns • Source and date/time • Update spreadsheet • Add columns and data • Update XQuery script – cur2.xql • Add source – Sources and oldest date Chris Wallace, ISD3

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

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