introduction to xml and databases

Introduction to XML

Kristian Torp

Department of Computer ScienceAalborg University

people.cs.aau.dk/˜[email protected]

November 3, 2015

daisy.aau.dk

Kristian Torp (Aalborg University) Introduction to XML November 3, 2015 1 / 42

http://people.cs.aau.dk/~torp

mailto:[email protected]

http://daisy.aau.dk

Outline

1 Introduction

2 Anatomy of an XML DocumentDocument PrologElementsAttributesEntitiesComplete XML Document

3 Well-Formed and Valid XML Documents

4 Summary


Learning Goals

GoalsKnow the basic differences between a table and an XML document

Know the different representations of an XML document

Know the basic parts of an XML document

Know the goals of designing XML

Know data centric from document centric

Be able to construct your own basic XML documents


Outline

1 Introduction



4 Summary


Text Files, (a Deja Vu?)

Example (A Text File)

P4 OOP 3 Object−or ien ted programmingP2 DB 7 Databases i n c l u d i n g SQL

Open QuestionsWhat does the columns mean?

When does white space matter?

What are the types of the columns?

NoteNo metadata what so everNeed additional information to parse the text file!

Could be a human looking at the file

Lowest common denominator a CSV fileKristian Torp (Aalborg University) Introduction to XML November 3, 2015 5 / 42

A First Look

Example (Table Look)

Id Name Semester Desc

P4 OOP 3 Object-oriented programmingP2 DB 7 Databases including SQL

Example (XML Look)<?xml vers ion= ” 1.0 ” ?>< !DOCTYPE coursecata log SYSTEM ” coursecata log . dtd ”><coursecata log>

<course c id= ’P4 ’><name>OOP< / name><semester>3< / semester><desc>Object−or ien ted programming< / desc>

< / course><course c id= ’P2 ’>

<name>DB< / name><semester>7< / semester><desc>Databases i n c l u d i n g SQL< / desc>

< / course>< / coursecata log>

A Second LookExample (XML Look (again))<?xml vers ion= ” 1.0 ” ?>< !DOCTYPE coursecata log SYSTEM ” coursecata log . dtd ”><coursecata log>

<course c id= ’P4 ’><name>OOP< / name><semester>3< / semester><desc>Object−or ien ted programming< / desc>

< / course><course c id= ’P2 ’>



Example (Tree Look)/coursecatalog

course

id=4 name:OOP sem:3 dsc

course

id=2 name:DB sem:7 dsc

Something Well Known?

Example (XHTML)<?xml vers ion= ” 1.0 ” encoding= ”UTF−8” ?>< !DOCTYPE html PUBLIC ” − / /W3C/ / DTD XHTML 1.0 T r a n s i t i o n a l / / EN”

” h t t p : / /www.w3 . org /TR/ xhtml1 /DTD/ xhtml1− t r a n s i t i o n a l . dtd ”><html xmlns= ” h t t p : / /www.w3 . org /1999/ xhtml ”>

<head>< t i t l e>A Simple XHTML Document< / t i t l e>

< / head><body>

Hel lo XHTML!< / body>

< / html>[Source: examples/xhtml_simple.xhtml]

XHTML versus HTMLXHTML is a cleaned-up version of HTML

Looks a lot like HTML

Much stricter requirements to XHTML than to HTML


examples/xhtml_simple.xhtml

Data versus Document Centric

Example (Data Centric)<rows><row><name>Hans< / name><address>Denmark< / address>

< / row><row><name>Marge< / name><address>Sweden< / address>

< / row>< / rows>

Example (Document Centric)< l y r i c>I s i t g e t t i n g b e t t e r?Or do you f e e l the same?W i l l i t make i t eas ie r on you now?You got someone to blameYou say

One loveOne l i f e< / l y r i c>

Data CentricDatabase table like

Content in leafs

Inflexible, but simple

Document CentricFree format (almost)

Mixed content

Flexible, but complex

Goals of XML

GoalsXML shall be straight forwardly usable over the Internet

XML shall support a wide variety of applicationsXML shall be compatible with SGML

SGML = Standard Generalized Markup Language

Easy to write programs which process XML documents

Keep the number of optional features low (0)

XML documents should be reasonably clear

The XML design should be prepared quickly

The design of XML shall be formal and concise

XML documents shall be easy to create

[Source: www.w3.org/TR/REC-xml/]


http://en.wikipedia.org/wiki/Standard_Generalized_Markup_Language

www.w3.org/TR/REC-xml/

XML Family of Products

ProductsCore

The basic XML recommendation

Add-onsDTD, XML Namespace, XPath, XLink, XPointer, XQuery, etc.

Focus on layoutCSS, XSLT, and XSL-FO

XML ApplicationsXHTML, DocBook, SVG, XForms, etc.

XML ApplicationsWeb Content Syndication: RSS (www.rssboard.org)

Education: SCORM for teaching material (www.scorm.com)

Document metadata: Dublin Core (www.dublincore.org)


www.rssboard.org

www.scorm.com

www.dublincore.org

Summary: Introduction

Main PointsAn XML document compared to a text file

More readable (without help)More complicated to handle (if you are familiar with content)Higher space usageData and metadata embedded in the same documentMarkup and content clearly separated

An XML document can be represented in two waysTextual structureTree structure

The goals of the XML design were made in an Internet age!

There is a very large set of XML technologies and applications

NoteXML and databases are not competing technologies

XML is not a replacement of HTML


Outline

1 Introduction



4 Summary


Main Parts of an XML Document

ConceptsDocument prologElements

A root

Attributes

Entities

Example (XML Document)<?xml vers ion= ” 1.0 ” encoding= ”UTF−8” ?>< !DOCTYPE coursecata log

SYSTEM ” coursecata log . dtd ” [<!ENTITY prg ” programming ”>< ! ENTITY sq l ”SQL”> ]>

<coursecata log><course i d = ”P4”>

<name>OOP< / name><semester>3< / semester><desc>Object−or ien ted &prg ;< / desc>

< / course><course i d = ”P2”>

<name>DB< / name><semester>7< / semester><desc>Databases i n c l u d i n g &sq l ;< / desc>


NoteElements more flexible than attributes

XML supports UTF out-of-the box

Outline

1 Introduction



4 Summary


Document Prolog

Example<?xml vers ion= ” 1.0 ” ?>< !DOCTYPE coursecata log SYSTEM ” coursecata log . dtd ”><coursecata log>

Consists ofVersion number and text encoding

Document type definition declaration

Instruction to the XML processor

Root element of the XML document

Outline

1 Introduction



4 Summary


Elements

ExampleStart tag <state> or <course>

State tag with attributes <state id=”1” abbr=”GA”>

End tag </state>

Element with content <state>Georgia</state>

Empty element <state/>

Empty element with attributes <state id=”1” abbr=”GA”/>

Case matters <state> , <State> , <STaTE>

Consists ofStart tag

Some content called character data

End tag

Elements, cont.

RulesStart tag must be before end tagAn elements start and end tag must have the same parent

Wrong: <state><city></state></ city>

Right: <state><city></ city></state>

ContentSimple <outer><one>stuff</one></outer>

Mixed content <outer>More <one>stuff</one></outer>

Tag versus Element<msg>Hello World</msg>

Element: <msg>Hello World</msg>

Tag: msg

Outline

1 Introduction



4 Summary


Attributes

Example<state id=”1” abbr=”GA”>

<country id=”DK”date=”2006−02−01”>

Consists ofName/value pairs

NoteAttributes cannot stand alone

Only start tags can have attributes

There can be any number of attributes

Attribute names must be unique <state id=”GA”id=”GE”>

Attribute values must be in quotes <state id=GA>

Elements versus Attributes

Example (Elements versus Attributes)<box he igh t= ” 20 ”

width= ” 20 ”depth= ” 30 ”u n i t = ”cm”><content>S t u f f< / content>

< / box>

<box><he igh t>

<sca la r>20< / s ca la r>cm

< / he igh t><width>


< / w id th><depth>


< / depth><content>S t u f f< / content>

< / box>

NoteAttributes can always be converted to elements

Elements can sometimes be converted to attributes

Elements versus Attributes, cont.

Example (Elements versus Attributes)<box>

<he igh t><sca la r>20< / s ca la r>cm

< / he igh t><width>


< / w id th><depth>


< / depth><content>S t u f f< / content>

< / box>

<box><he igh t u n i t = ”cm”>20< / he igh t><width u n i t = ”cm”>20< / w id th><depth u n i t = ”cm”>30< / depth><content>S t u f f< / content>

< / box>

NoteAttributes good for identify, units and so on

Elements good if variable number of “stuff”

Outline

1 Introduction



4 Summary


Entities

Example<! ENTITY company ”XML Lovers Inc.”>

<! ENTITY sql ”SQL”>

PurposeTo make XML document easier to maintain

Recurring text

Are place holders for content (abbreviations)

TypesParameter entities used in DTD

General entities used in the XML document itself

There are a lot of details about entities!

Using Entities

Example<?xml vers ion= ” 1.0 ” encoding= ”UTF−8” ?>< !DOCTYPE coursecata log

SYSTEM ” coursecata log . dtd ” [<!ENTITY prg ” programming ”>< ! ENTITY sq l ”SQL”> ]>

<coursecata log><course i d = ”P4”>

<name>OOP< / name><semester>3< / semester><desc>Object−or ien ted &prg ;< / desc>


<name>DB< / name><semester>7< / semester><desc>Databases i n c l u d i n g &sq l ;< / desc>


[Source: examples/coursecatalog_with_entity.xml]

NoteThe entities prg and sql


examples/coursecatalog_with_entity.xml

More Entity Examples

Entity TypesPredefined character entities amp = & gt = >

Usage: <msg>Hello & and ></msg>

Numbered character entities #145 = æ

Usage: <msg>This is a Danish letter </msg>

External entities definition is in another file

Internal entities

Unparsed entity <!ENTITY logo SYSTEM ”logo.gif”NDATA gif>

NoteThere are a lot of details about entities!

Various Comments on XML Documents

CommentsAre always in UTF

Whitespace is preserved (not the case in HTML)Carriage return and line feed converted to line feed

Weird when used to MS Windows

This is a comment <!−−a comment in XML −−>

Example (Comments in XML)<?xml vers ion= ” 1.0 ”><doc>

< !−− A comment −−><row> < / row><row> < !−− Another comment −−> < / row>

< / doc>

Outline

1 Introduction



4 Summary


First Design

Example (1-n Relationship)<order−db>

<orders><order i d = ” 117 ”>

<customer−name>Ann< / customer−name>< / order><order i d = ” 341 ”>

<customer−name>Jim< / customer−name>< / order>

< / orders><o r d e r l i n e s>

<o r d e r l i n e i d = ” 117 ” l i n e −no= ” 1 ”><d e s c r i p t i o n>pizza< / d e s c r i p t i o n><q u a n t i t y>1< / q u a n t i t y><pr ice −each>10.50

< / o r d e r l i n e>< / o r d e r l i n e s>

< / order−db>

NoteToo much first normal form, does not use tree hierarchy

Second Design

Example (1-n Relationship)<order−db>

<orders><order i d = ”O117”>

<customer−name>Ann< / customer−name><o r d e r l i n e s>

<o r d e r l i n e l i n e −no= ” 1 ”><d e s c r i p t i o n>pizza< / d e s c r i p t i o n><q u a n t i t y>1< / q u a n t i t y><pr ice −each>10.50

< / o r d e r l i n e>< / o r d e r l i n e s>

< / order><order i d = ”O341”>

<customer−name>Jim< / customer−name>< / order>

< / orders>< / order−db>

NoteAll information related to single order is stored together

Summary: Anatomy

Main PointsElements

One is the root

AttributeLimited set

EntitiesSimilar to a macroThere are many details

The prolog

NoteIn doubt element or attribute? Pick element

Remember good comments, for humans!


Outline

1 Introduction



4 Summary


Non Well-Formed XML Document

Example (Missing Root)<course i d = ”P4”>

<name>OOP< / name><semester>3< / semester><desc>Object−or iented Prog .< / desc>



< / course>

Example (Nesting Wrong)<person ssn= ” 43 ”>

<name>< f i r s t>James< / f i r s t> < l a s t>Bond< / name>< / l a s t>< j ob>agent< / job>

< / person>

Example (Missing Quotes)<person ssn=43>

<name> . . . < / name>< / person>

Well-Formed XML and Valid Document

Well-Formed XML DocumentAll XML elements must have a closing tag

Empty elements are allow

Tags must be properly nestedStart and end tag must have the same parent

The XML document must have a root tag

Attribute values must be quoted

Valid XML DocumentIs well-formedAdheres to the rules of the specified DTD or XML Schema

Similar to a schema for a table, e.g., types and integrity constraints


Well-Formed and Valid

XML Documents

Well-Formed XML Documents

Valid XML Documents


Summary: Well-Formed and Valid

Main PointsWell-formed XML document

Structure must adhere to certain rules

Valid XML documentTypes and constraints must match a schema (DTD or XML Schema)Not covered in this lecture, more to come later

NoteTools check if documents are well-form and valid

The well-formedness is a huge plus over “flat” files


Outline

1 Introduction



4 Summary


Why XML?

Many Good ReasonsOpen

Specifications available to all

Platform neutralRuns on Apple, Linux, Unix, Windows, . . .

Vendor neutralCompetition among vendors

StandardChanges done in open forums

NoteXML has support for checking structure/types/integrity constraints

DTD and XML Schema

XML has support for querying text documentsXPath and XQuery


Data vs. Document Centric

Data CentricDatabase designer

Does not use document order

Only content at leaf level

Simple

Rigid

Example: Extract RDBMS

Document CentricText author

Document order, e.g., forchapters figure no

Mixed content

Complex

Flexible

Examples: DocBook, XHTML


XML vs. DBMS

RDBMSStructured data

Unordered

Flat information

Native format

Very compact format

SQL

Fine-grained modifications

Bad data exchange

Integrity via SQL DDL

Supports data types

Extreme data volumes

XMLStructured and unstructured

Ordered

Hierarchical information

Standard format

Very verbose format

XPath and XQuery

Coarse-grained modifications

Excellent data exchange

Integrity via XML Schema (DTD)

Supports data types

Large data volumes


Additional Information

Web SitesW3C Schools free online tutorials www.w3schools.com.

Quite good for getting an overview of the various XML technologies.

Interactive XML Tutorials www.xmlzoo.net.Covers several parts of XML

The Annotated XML 1.0 Specificationwww.xml.com/axml/testaxml.htm.

The XML 1.0 specification with a lot of comments.

W3C XML recommendations www.w3.org.The place to go if you want all the details.

Altova’s home page (maker of XMLSpy) www.altova.com. If you arelooking for a good XML tool.IBM developerWorks overview “New to XML”www.ibm.com/developerworks/xml/newto/

Many links to additional information.


www.w3schools.com

www.xmlzoo.net

www.xml.com/axml/testaxml.htm

www.w3.org

www.altova.com

www.ibm.com/developerworks/xml/newto/

introduction to xml and databases

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