Changki Kim July 14 2005 MSE

XML Query Language Changki Kim July 14 2005 MSE

Contents • Introduction • XQuery Data Model • XQuery Expression Types • Implementations of XQuery • XQuery API for Java • Conclusion

Introduction • XML (Extensible Markup language) • the format of choice for the exchange of information among various applications on the Internet • Its flexibility for representing many different kinds of information (multimedia presentation, database tables, web pages) • World Wide Web Consortium(W3C) • A series of standard : XML Schma, XPath,XSLT, and XQuery • XQuery • A requirement for a query language against data in XML data format. • Early Attempts to define a query language for XML data(XQL,XML-QL, Quilt) • In October 1999, W3C convened the XML QUery Working Group • XQuery 1.0:An XML Query Language.(2002)

Introduction • SQL & XQuery • XQuery goes beyond the functionality of relational query language • It is often thought of as a native XML programming language • Only XML data is complex, the operations for processing XML are simple. • XQuery can easily search any XML structure with predefined expressions. • Even when the data is not physically stored as XML, XQuery can be used with middleware that provides an XML view of the data.  XQUery is widely used for data integration!!!!!

XQuery Data Model • The input and output is defined in terms of the XQuery1.0 and XPath2.0 data model • The data model is based on the notion of a sequence. (sequence>item>node or atomic value) • The output sequence may be heterogeneous. However the result of the operation is single-level sequence of nodes and atomic values.

XQuery Expression Types • There are 7 types of expressions in XQuery • Path expressions. • Element constructors. • FLWR expression, • Expressions involving operators and functions • Conditional expression. • Quantified expression. • The expressions can be used together both sequentially and nested • Path expression • It is used to locate nodes in XML data. • It consists of a series of one or more steps, separated by slash ,/, or double slash , // • Example : document(“books.xml”)//book, document(“books.xml”)/bib/book/author[last=“Stevens”]

XQuery Expression Types • Element constructors • It is used when a query needs to create new elements. • Example : date(“2005-5-31”) • FLWR expressions • It is the analogue of the SELECT FROM-WHERE construction in SQL. • Example : for $b in document(“books.xml”)//book where $b/@year = “2000” return $$b/title • Expressions involving operators and functions • Built-in function (AVG,SUM,COUNT,DOCUMENT,EMPTY) • Conditional expressions • IF-THEN-ELSE • Quantified expressions • SOME(existential) and EVERY(universial)

Implementation of XQuery • Currently several implementations of XQuery are available. • References to Xquery Implementations. • X-Hive: http://www.x-hive.com/xquery/ • Fatdog: http://www.fatdog.com • Kawa-XQuery: http://www.gnu.org/software/kawa/xquery/ • Kweelt: http://db.cis.upenn.edu/Kweelt/ • Lucent: http://db.bell-labs.com/galax/ • Microsoft: http://131.107.228.20 • Openlink Software: http://demo.openlinksw.com:8391/xquery/demo.vsp • QuiP (Software AG): http://www.softwareag.com/developer/quip/default.htm • XQuench: http://sourceforge.net/projects/xquench/ • The goal of implementation is to investigate implementability and usability of XQuery and to provide feedback to the W3C XML Query Working Group.

Implementation of XQuery • X-Hive (active member of W3C) • This company provides on-line XQuery demo. • The Query I wrote on the browser is running on top X-Hive/DB • The result is returned in less than 5 seconds

XQuery API for Java(XQJ) • XQJ is an API designed to support the XQuery language, just like the JDBC API supports the SQL query language. • The XQJ standard (JSR 225) is being developed under the Java Community Process. • For more information, http://www.jcp.org/en/jsr/detail?id=225. • DataDirect XQuery is a Java implementation of XQuery that uses the XQuery API for Java (XQJ) for accessing both XML and relational sources.

XQuery API for Java(XQJ) • XQJ sample Java code to execute an XQuery query //import the XQJ classes import com.ddtek.xquery.alpha.*; import com.ddtek.xquery.xqj.mediator.DDXQDataSource; // establish a connection to a DataDirect XQuery data source DDXQDataSource ds = new DDXQDataSource( ); ds.setConfigFile("stockconfigfile.xml"); XQConnetion conn = ds.getConnection("myuserid", "mypswd"); // create an expression object that is used to execute // an XQuery query XQExpression expr = conn.createExpression(); // the XQuery query String es = "for $h in collection('HOLDINGS')/Holdings“ + "where ($h/STOCKTICKER='AMZN'“ + "return $h"; // execute the XQuery query XQResultSequence result = expr.executeQuery(es); System.out.println(result.getSequenceAsString()); // free all resources result.close(); expr.close(); conn.close();

Shortcomings • XQuery is still in the W3C Working Draft stage. • Update query (including insert query) is not specified in the current XQuery 1.0 drafts. • It does not contain full text search facilities ”Find all elements containing a particular word” . • It has backward compatibility with XPath1.0 • There are other minor issues( inconsistencies with and between the working drafts)

Conclusion • XQuery is a very promising initiative in defining the standard for query and retrieval of XML. • It is a functional language consisting of several types of expressions. • It is defined in terms of a data model based on heterogeneous sequences of nodes and atomic values. • Currently, Design of the XQuery is an ongoing activity of the W3C XML Query Working Group. • XQuery will help XML to realize its potential as a universal in formation representation.

Reference • Useful web site. • http://www.w3.org/TR/xquery/ • http://hake.stanford.edu/~widom/cs145/. • http://www.perfectxml.com/articles/xml/xquery.asp • http://www.ipedo.com/html/xquery/xquery_tutorial/ • http://www.datadirect.com/products/xquery/xquerybetahome/index.ssp (XQJ) • Paper • D.Chamberlin.”Xquery: An XML Query Language,” IBM System Journal, Vol 41, No 4, 2002

Changki Kim July 14 2005 MSE