XML Documents and Database
Different approaches for storing XML documents are as given below:
- A RDBMS or object-oriented database management system is used to store XML document in the form of text.
- A tree model is very useful to store data elements located at leaf level in tree structure.
- The large amount of data is stored in the form of relational database or object-oriented databases. A middleware software is used to manage communication between XML document and relational database.
XML query is based on two methods.
- Xpath is a syntax for defining parts or elements of XML documents.
- Xpath is used to navigate between elements and attributes in the XML documents.
- Xpath uses path of expressions to select nodes in XML documents.
In this example, the tree structure of employee is represented in the form of XML document.
<First name>Brian</First name>
<Last name>Lara<</Last name>
<Zip code>4110</Zip code>
In the above example, a (/) is used as </Employee> where Employee is a root node and Name, Contact and Address are descendant nodes.
- Xquery is a query and functional programming language. Xquery provides a facility to extract and manipulate data from XML documents or any data source, like relational database.
- The Xquery defines FLWR expression which supports iteration and binding of variable to intermediate results.
FLWR is an abbreviation of FOR, LET, WHERE, RETURN. Which are explained as follows:
FOR: Creates a sequence of nodes.
LET: Binds a sequence to variable.
WHERE: Filters the nodes on condition.
RETURN: It is query result specification.
Xquery comparisons: The two methods for Xquery comparisons are as follows:
1. General comparisons: =, !=, <=, >, >=
In this example, the expression (Query) can return true value if any attributes have a value greater than or equal to 15000.
$ TVStore//TV/price > =15000
2. Value comparisons: eq, ne, lt, le, gt , ge
In this example, the expression (Query) can return true value, if there is only one attribute returned by the expression, and its value is equal to 15000.
$ TVStore//TV/price eq 15000
Lets take an example to understand how to write a XMLquery.
FOR $x in doc (“student.xml”)/student information /marks
WHERE $x/marks >700
The queries in the above example can return true value ( Name of the students) only if the value (marks) is greater than 700.