XML Query Language Changki Kim July MSE

2 2 Contents  Introduction  XQuery Data Model  XQuery Expression Types  Implementations of XQuery  XQuery API for Java  Conclusion

3 3 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)

4 4 Introduction  SQL & XQuery SQLXQuery Query language for relational tablesQuery language for XML Uses the table as basic modelUse the XML document as basic model Result is a table containing a set of row Result is complex XML sequence  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!!!!!

5 5 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.

6 6 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”]

7 7 XQuery Expression Types  Element constructors – It is used when a query needs to create new elements. – Example : date(“ ”)  FLWR expressions – It is the analogue of the SELECT FROM-WHERE construction in SQL. – Example : for $b in document(“books.xml”)//book where = “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)

8 8 Implementation of XQuery  Currently several implementations of XQuery are available. – References to Xquery Implementations. X-Hive: Fatdog: Kawa-XQuery: Kweelt: Lucent: Microsoft: Openlink Software: QuiP (Software AG): XQuench:  The goal of implementation is to investigate implementability and usability of XQuery and to provide feedback to the W3C XML Query Working Group.

9 9 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

10 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,  DataDirect XQuery is a Java implementation of XQuery that uses the XQuery API for Java (XQJ) for accessing both XML and relational sources.

11 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();

12 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)

13 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.

14 Reference  Useful web site. – – – – – (XQJ)  Paper – D.Chamberlin.”Xquery: An XML Query Language,” IBM System Journal, Vol 41, No 4, 2002