MUSA M.AMEEN

18/12/2014

Outlines

Introduction

Why XML for databases?

What's XML database?

XML Structure

Types of XML databases

XML vs. Relational databases

Document Type Definition

XML Schema Definition

Xpath

Xquery

Demo

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Introduction

Data interchange is critical in today’s networked world

Each application area has its own set of standards for

representing information

XML has become the basis for all new generation data

interchange formats

Earlier generation formats were based on plain text with line

headers indicating the meaning of fields

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Why XML for databases?

It is more suitable for specifying structured data that is

extracted from databases than HTML

XML was developed was to allow the exchange of semi-structured documents.

Using a database system to store XML documents allows users

to be able to better access information.

XML is also very flexible

Data is maintained in a self-describing format to accommodate a variety of ever-evolving business needs.

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What’s XML?

XML stands for Extensible Markup Language.

It is designed to describe data and focus on what data is.

It is used to structure store and to send information.

It is easy to understand and is self describing.

XML is derived from Standard Generalized Markup Language

(SGML)

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<?xml version = "1.0"?>

Structure of XML Data

<library xmlns:mevlana=“http://mevlana.edu.tr”>

<book id="bk101">

<author>Gambardella, Matthew</author>

<title>XML Developer's Guide</title>

<genre>Computer</genre>

<price>44.95</price>

<publish_date>2000-10-01</publish_date>

</book>

</library>

<!-- comments -->

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Start tag

End tag

Element

Attribute

Namespace

Comments

tag

XML

Document

Node

Types of XML databases

There are two major types of XML databases:

XML-enabled: These map all XML to a traditional database,

accepting XML as input and rendering XML as output.

Native XML (NXD): The internal model depends on XML and

uses XML documents as the fundamental unit of storage.

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XML vs. Relational Database

XML Database

XML data is hierarchical

XML data is self-describing

XML data has inherent

ordering

An XML database contains

collections

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Relational Database

relational data is represented

in a model of logical relationships

relational data is not self-

describing

Relational data does not

have inherent ordering

A relational database

contains tables

XML vs. Relational Database

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<ORDER><ORDER_ID=’83492’ CUST_ID=’93457’><ITEM>

<PROD_ID>94872</PROD_ID><PROD_NAME>PEN</PROD_NAME><PRICE>19.95</PRICE><QUANTITY>30</QUANTITY>

</ITEM><ITEM>

<PROD_ID>94866</PROD_ID><PROD_NAME>BINDER</PROD_NAM

E><PRICE>7.95</PRICE><QUANTITY>26</QUANTITY>

</ITEM><ITEM>

<PROD_ID>92219</PROD_ID><PROD_NAME>LABELS</PROD_NAM

E><PRICE>12.95</PRICE><QUANTITY>250</QUANTITY>

</ITEM></ORDER>

Items

Order

XML Representation

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XML Document Schema

Database schemas constrain what information can be stored,

and the data types of stored values

XML documents are not required to have an associated schema

Schemas are very important for XML data exchange

Two mechanisms for specifying XML schema

Document Type Definition (DTD)

XML Schema Definition (XSD)

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Document Type Definition

DTD constraints structure of XML data

What elements can occur

What attributes can/must an element have

What subelements can/must occur inside each element, and how many

times.

DTD does not constrain data types

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Document Type Definition

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DTD XML

XML Schema Definition

Different data types

XML Schema is itself specified in XML syntax, unlike DTDs

XML Schema is integrated with namespaces

XML Schema is significantly more complicated than DTDs

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XML Schema is a more sophisticated schema language which addresses

the drawbacks of DTDs. Supports

XML Schema Definition

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XSD XML

Querying XML Data

There are several languages used to access XML data from XML

Documents, some are:

XPath

Xquery (most popular)

XML-QL

XQL

etc....

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XPath

XPath is used to address (select) parts of documents using path

expressions

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<?xml version="1.0">

<bookstore>

<book><title lang="en">Harry Potter</title><author>J K. Rowling</author> <year>2005</year><price>29.99</price>

</book></bookstore>

Document node

Element node

Attribute node

/bookstore Will select the root element bookstore

/bookstore/book Selects all book elements that are children of bookstore

/bookstore/book/text() Selects all book elements of bookstore without tags

XQuery

XQuery is a general purpose query language for XML data

XQuery is built on XPath expressions

XQuery is derived from the quilt query language, which itself borrows from SQL

XQuery is supported by all database engines (IBM, Oracle, Microsoft, etc.)

XQuery uses FLOWR (for, let, where, order by , result)

for SQL from

where SQL where

order by SQL order by

result SQL select

let allows temporary variables

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XQuery

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<?xml version="1.0">

<bookstore>

<book category="COOKING"><title lang="en">Everyday Italian</title><author>Giada De Laurentiis</author><year>2005</year><price>30.00</price>

</book>

</bookstore>

for $x in doc("books.xml")/bookstore/bookwhere $x/price>29return $x/title

Select title

From bookstore/book

Where price>29

Demo

Demonstration of XML Database using eXistdb

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