What is XQuery
Xquery can be described as XML (Extensible query language) Query language. As the name suggests XQuery is a querying and functional programming language to play with data or pull out data from XML documents. It was developed by W3C (World wide web consortium) to pull out the data over the widespread worldwide web. The latest version is version 3.1 released in March 2017 after the previous release in 2014. XPath is the subset of XQuery which is also used to extract the data, but the syntax is different than XQuery. It works in line with SQL queries. So, the structure of it can be easily understood by SQL developers.
Why do we Need XQuery?
The use of XQuery can be well understood by the below-mentioned statements published under W3C by J.Robie when XQuery was introduced. “The mission of the XML Query project is to provide flexible query facilities to extract data from real and virtual documents on the World Wide Web, therefore finally providing the needed interaction between the Web world and the database world. Ultimately, collections of XML files will be accessed like databases”.
The primary use of XQuery is to extract data from XML databases. It is also capable of extracting data from relational databases that store XML data. XML follows the hierarchy structure containing nodes inside the node. These nodes are taken care of by the XML querying language. It is also used to change the data over the fly. That means we can update the data while transmitting itself. This functionality, when added up with querying language, provides enough power to XQuery to handle most of the XML data over the web.
How does XQuery Work?
We need to have a processor that helps us in rendering the usage of XQuery. We can use Saxon-HE (widely used). As this is open-source software, we can download it from the internet along with the guidebook for installation. We need to set up classpaths as we do for JAVA installation. This supports the latest version of XPath, XQuery, and XSLT (Extensible Stylesheet Language Transformations). We can have a database for querying or have an XML file to extract the data from.
It works around the concept of FLWOR. FLWOR stands for From, let, where, order by, and result. These 5 words make up the whole query. We can write simply to complex logic using these 5 keywords in XQuery. We select the source data from the “from” keyword. “Let” is used to declare and initialize the variable to be used while we create any control loops. “Order by” is used to arrange the data in ascending or descending order. “Where” is used to limit the scope by declaring the specific conditions of data pulling. This works like “from” keyword in SQL. “Return” will mark the end of the query and this keyword will transfer the control out of the query along with the output.
In case we have an XML data file named “test.xml”, we can create a query and save it in a separate file with the relevant expression. Here we can save our query in a file named “testquery.xqy”. We then need a driver program in JAVA that will establish a connection with the database using connection objects. Once the connection is maintained, the result set is initialized. We can run this query by including query files in the JAVA driver program. In this case, we can have a JAVA program named “querydriver.java”.
Syntax:
<html> {
let $fruit := document("checkingfruitcolor.xml") /Data about fruits and its color is stored in this file..
for $color in $fruit /discovering colors defined in the file.
return <h2> {$color /color name.. )</h2>
} </html>XQuery should be encompassed under <html> tags to function. Here variables like “fruit” and “color” are denoted by the “$” dollar symbol at the start. The return statement is at the end of the output value.
Features and Advantages of XQuery
Following are the different features and advantages of XQuery.
Features
Some of the noteworthy features of the XQuery language are pointed out below:
- XQuery is a functional programming language that not only supports querying language but also offers to do data changes thus promoting dynamic websites.
- XQuery has simple syntax on the lines of SQL language. It is easy to understand and powerful at the same time.
- XQuery works to dig into the hierarchical structure until it discovers the data. The same can be seen when we navigate through the path in the windows file manager. XPath used to pull out data based upon file path is the component of XQuery.
- It is a universal language. Thus, it is accepted worldwide with certain standards to be followed as defined by W3C. Its simplicity and syntax encourage coders to go with its implementation in projects.
Advantages
Some advantages are listed below:
- XQuery can be used to extract data from any type of structure like hierarchical, tabular or graphical data structure.
- It can be used to pull out the data directly from the website. This reduces a lot of work and saves time.
- Similarly, XQuery can be used to build websites. Reduces the number of efforts we put in to build a website.
- It works efficiently with relational databases.
- Along with querying, it can be used to transform the data while transmitting it. This is useful for dynamic data handling. Because of this functionality, we can XQuery as a functional programming language as well.
- It can be used with object-oriented databases as well as reducing impedance mismatch.
Conclusion
XQuery is one of the widely used universal languages capable of displaying, retrieving, and changing data over dynamic web pages. It was developed to challenge complex languages like C++, JAVA, etc. We can have logic written in XML and just use the JAVA file to establish and maintain a connection with the database.
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This is a guide to XQuery. Here we discuss the Introduction and why we need XQuery along with its working, features, and advantages. You may also have a look at the following articles to learn more –
