1. Introduction to XQuery

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1 Introduction to XQuery Introduction to XQuery Background Purpose SKILLBUILDERS

2 Introduction to XQuery Background Language for querying XML documents Can accept input from diverse sources and treat them uniformly Has received strong support from major database vendors such as Oracle, Microsoft, and IBM, and many other vendors XQuery W3C working group second largest in W3C Syntax shares similarities with SQL Certain to be industry standard "SQL of XML" in a short time.

3 Introduction to XQuery What is XQuery? A declarative language for extracting information stored in XML documents Supports: Navigation through XML document (using XPath) Filtering Iteration and has a built-in iteration counter Sorting Joining data from multiple XML documents User-defined reusable functions Most modern databases can present an XML view of their data. Packaged software can frequently export data in XML. WebServices are already XML based. All these data can be used as input for XQuery.

4 Introduction to XQuery A Simple Example XQuery query in file test.xq for $i $i in in doc("report.xml")//name return $i $i List the customer names in the document Run the query C:\xquery-class>myxquery test.xq <?xml version="1.0" encoding="utf-8"?> <name>mad Hatter</name> <name>alice Liddle</name> <name>aloysius Swenson</name> <name>homer Twombly</name> Query output This is an example of an XQuery FLWOR (pronounced flower ) expression. FLWOR stands for: For Let Where Order By Return At this point, let s not worry about the details and syntax of the query we ll study that in detail in the XQuery Data lesson later in this course. However, let s understand what this query does: reads the XML document (report.xml) iterates through the document and returns all customer names. The command myxquery is actually a BAT file that runs the Saxon class Query which will read, interpret and execute XQuery queries. See the Appendix of this course book for information on installing and running Saxon.

5 Introduction to XQuery Why use XQuery? Easier to learn and requires much less coding than procedural languages such as Java or C Easier to learn and requires much less coding than XSLT Bears resemblance to SQL which is already widely known Some XQuery syntax similar to SQL syntax Includes a rich set of built-in functions XML is increasingly being used as the preferred format for exchanging data. Accordingly, there is a need for a language that can combine data from multiple sources without the need of ad-hoc programming. XQuery is an ideal language for Enterprise Information Integration. Before the advent of XML, such a query language was not possible except in narrow niches (e.g. databases) because most data were unstructured or in proprietary formats. This data had to be put in a structured format before it could be processed.

6 Introduction to XQuery Other similar languages SQL/XML (SQLX, SQL:2003) ISO standard, extends SQL not to be confused with Microsoft s SQLXML XSLT XPath XQueryX SQL/XML is an extension to standard SQL to support XML. Input for SQL/XML is normally relational tables so its support is usually integrated by database vendors to their products. Output is XML. XQuery implementations, on the other hand, do not have dependencies on databases although it can work with them. XSLT was not designed to accept multiple XML as input. It was designed for XML transformation, not data integration. XSLT is also harder to learn by programmers coming from procedural languages. XQuery is built on XPath. XQuery shares most built in functions with XSLT version 2. XQueryX is an alternative syntax for XQuery expressed in pure XML. Semantically it is completely equivalent to XQuery and the two syntaxes can be transformed either way without losing information. It is meant to be consumed and generated by programs.

7 Introduction to XQuery XQuery vs. XSLT XSLT is designed to accept only one primary XML input XQuery much easier to learn XQuery less verbose than XSLT Although strictly speaking, you could have XSLT accept more than one XML document as input (through the document() function), the design center of XSLT is to have only one primary XML document for transformation. XQuery, on the other hand, is designed to be able to perform joins and process multiple XML input. XSLT is also harder for most programmers to learn. XSLT can be coded using different styles, such as using templates (rule based) or in a more procedural way. Code written in one style may be difficult for others, used to a different style, to understand. XSLT, being XML based, is also more verbose than XQuery. XQuery, on the other hand, shares a lot of similarity with SQL, which most programmers are already familiar with.

8 Introduction to XQuery XQuery vs. SQL XQuery is currently only for queries update capability to be added in the future XQuery searches hierarchies XQuery is case sensitive Node order is significant in XQuery XQuery can return nodes, not just values XQuery shares many similarities with SQL. Both are declarative languages and both are set oriented. In the case of SQL, the sets are made up of relational rows whereas in XQuery, it is made up of sequences. But there are many differences also. SQL is very good to manipulate structured data but most information is not structured. XML can represent both structured and non-structured data. Whereas relational rows do not have intrinsic ordering (unless explicitly requested with the order by clause), XQuery data always have an implicit ordering, the document order. Like SQL, this order can be changed with the use of the order by clause.

9 Introduction to XQuery XQuery Status XQuery currently a W3C "Candidate Recommendation" More and more implementations becoming available W3C XQuery specification and documentation available at We will use Saxon XQuery in the class workshop. This is just one of several implementations of XQuery now available. See the appendix of this course book for information on installing and running Saxon. Another nice open source implementation of XQuery is Qizx/Open, available at Much additional information on XQuery is available at

10 Introduction to XQuery XQuery API Will allow XQuery to be embedded in code (inline) in several programming languages JSR-225 is the Java XQuery API (XQJ) Analogous to JDBC for SQL.NET will also provide a similar API Although there is currently no standard API for embedding XQuery, Saxon has provided its own API for Java. See the appendix of this course book for more information on using Saxon's XQuery API for Java. DataDirect is a commercial product that provides an API for XQuery. For more information visit:

11 Introduction to XQuery 1.11 XQueryX An alternate syntax to the XQuery language Completely equivalent to regular XQuery but written in XML instead One syntax can be converted to the other and vice versa Meant mostly to be read and processed by programs e.g. development tools, etc Because XQueryX is XML, it can be queried using XQuery 1.11

12 Introduction to XQuery Oracle Oracle 10g Release 2 includes an XQuery engine Supports the April 2005 draft and will provide full compliance later However, XQuery s regex will not be included initially Oracle Application Server 10g will also include an XQuery component Oracle XML Data Synthesis or XML Query Services Oracle s XQuery support is provided in both the middle and backend (database) tiers. The middle tier will be typically used for data integration, combining XML from multiple sources. It is expected that the volume of input data involved in these queries will be kept low to avoid transferring large amounts of data over the network. In the backend (database), XQuery will be used to process data which is mostly stored in the database itself. The volume of input data in this case can be much larger than in the previous case, as this input data is not sent over the network. Also, when running queries in the database, the XQuery parser can take advantage of indexes and other optimizations of the SQL engine. Typically, only the result of the query (presumably, with less data) would be sent to the middle tier.

13 Introduction to XQuery Microsoft SQL Server 2005 will also include an XQuery engine SQL Server will support the July 2004 draft Will provide full compliance later Although XML updates are not yet supported in XQuery, SQL Server will offer extensions that will allow updates

14 Introduction to XQuery Where We've Been XQuery is a tool for retrieving data or XML from XML documents Based on XPath 2.0 Provides basis for declarative rather than procedural access to XML data -- what is wanted rather than how to get it -- similar in this respect to SQL and XSLT Rich set of built-in functions to facilitate data retrieval and modification

15 Introduction to XQuery XQuery Intro Workshop Become familiar with SAXON Your Objective In this workshop you will familiarize yourself with Saxon, a popular open source implementation of XQuery. In this workshop you will use it to run a simple XQuery query. Follow the steps below to prepare your environment for the use of Saxon. Saxon is written in Java and requires a Java. If you don't already have Java 5 installed on your workstation you will need to download it from and install it. Before doing this or the other workshops in this course you must install the course files that accompany this course. These files include example XQuery files, XML source documents, the Saxon XQuery engine, and some DOS batch files. The course files are distributed in a self-extracting file. Simply run the file from windows or from a DOS command window. Accept the default directory for the extracted files ("\xquery-class"). If you don't accept the default you may have to change settings in some of your DOS batch files. If you do not have the self-extracting course file or are unsure how to install it talk to your instructor. When the class files are installed correctly, you will have a directory \xquery-class. This will have several sub-directories. In your \xquery-class directory you will find a file called setenv.bat. If necessary, modify that file. Your instructor will explain what, if anything, needs to be changed. Run setenv.bat every time you open a new DOS command window. You should give your XQuery files the suffix ".xq". While any file extension will work, the standard naming convention for an XQuery file extension is.xq. When using Saxon, you must provide the full name (".xq" will not be assumed). Workshop continues on the next page

16 Introduction to XQuery 1.16 A convenience DOS batch file (myxquery.bat) has been provided for running Saxon XQuery. Some Saxon XQuery command line options are mentioned in the Appendix. For most of the examples and workshops in this course we will be using an XML document called report.xml. It is located in the xml and work sub-directories of \xquery-class. Take a few moments to look it over to familiarize yourself with it. To keep your XQuery workshop exercises in a separate directory use the work directory below \xqueryclass Test your environment by coding and running the XQuery query shown previously in this lesson. As shown previously in this lesson, run the Saxon XQuery engine as follows: myxquery name-of-xquery-file