1. XML – Basic Concepts (modified version from Dr. Praveen Madiraju)
2018, Fall
Pusan National University
Ki-Joune Li

2. W3SCHOOLS.COM a very nice material is found at

3. XML vs. HTML HTML is a HyperText Markup language
Designed for a specific application, namely, presenting and linking hypertext documents
XML describes structure and content (“semantics”)
The presentation is defined separately from the structure and the content

4. An Address Book as an XML document
<addresses>
<person>
<name> Donald Duck</name>
<tel> </tel>
< > </ >
</person>
<name> Miki Mouse</name>
<tel> </tel>
</addresses>

5. Main Features of XML No fixed set of tags
New tags can be added for new applications
An agreed upon set of tags can be used in many applications
Namespaces facilitate uniform and coherent descriptions of data
For example, a namespace for address books determines whether to use <tel> or <phone>

6. Main Features of XML (cont’d)
XML has the concept of a schema
DTD and the more expressive XML Schema
XML is a data model
Similar to the semistructured data model
cf. DB Schema
XML supports internationalization (Unicode) and platform independence (an XML file is just a character file)

7. XML is the Standard for Data Exchange
Web services (e.g., ecommerce) require exchanging data between various applications that run on different platforms
XML (augmented with namespaces) is the preferred syntax for data exchange on the Web

8. XML is not Alone
XML Schemas strengthen the data-modeling capabilities of XML (in comparison to XML with only DTDs)
XPath is a language for accessing parts of XML documents
XLink and XPointer support cross-references
XSLT is a language for transforming XML documents into other XML documents (including XHTML, for displaying XML files)
Limited styling of XML can be done with CSS alone
XQuery is a lanaguage for querying XML documents

9. The Two Facets of XML
Some XML files are just text documents with tags that denote their structure and include some metadata (e.g., an attribute that gives the name of the person who did the proofreading)
See an example on the next slide
XML is a subset of SGML (Standard Generalized Markup Language)
Other XML documents are similar to database files (e.g., an address book)

10. XML can Describe the Structure of a Document
<book year="1994">
<title>TCP/IP Illustrated</title>
<author>
<last>Stevens</last>
<first>W.</first>
</author>
<publisher>Addison-Wesley</publisher>
<price>65.95</price>
</book>

11. W3Schools Resources on XML Syntax

12. The Structure of XML XML consists of tags and text
Tags come in pairs <date> ... </date>
They must be properly nested
good
<date> ... <day> ... </day> ... </date>
bad
<date> ... <day> ... </date>... </day>
(You can’t do <i> ... <b> ... </i> ...</b> in HTML)

13. A Useful Abbreviation
Abbreviating elements with empty contents:
<br/> for <br></br>
<hr width=“10”/> for <hr width=“10”></hr>
For example:
<family>
<person id = “lisa”>
<name> Lisa Simpson </name>
<mother idref = “marge”/>
<father idref = “homer”/>
</person>
...
</family>
Note that a tag may have a set of attributes, each consisting of a name and a value

14. XML Text XML has only one “basic” type – text
It is bounded by tags, e.g.,
<title> The Big Sleep </title>
<year> 1935 </ year> – 1935 is still text
XML text is called PCDATA
(for parsed character data)

15. XML Structure
Nesting tags can be used to express various structures, e.g., a tuple (record):
<person>
<name> Lisa Simpson</name>
<tel> </tel>
<tel> </tel>
< > </ >
</person>

16. XML Structure (cont’d)
We can represent a list by using the same tag repeatedly:
<addresses>
<person> … </person> …
</addresses>

17. XML Structure (cont’d)
<addresses>
<person>
<name> Donald Duck</name>
<tel> </tel>
< > </ >
</person>
<name> Miki Mouse</name>
<tel> </tel>
</addresses>

18. Terminology
The segment of an XML document between an opening and a corresponding closing tag is called an element
element
element,
a sub-element of
<person>
<name> Bart Simpson </name>
<tel> 02 – </tel>
<tel> 051 – </tel>
< > </ >
</person>

19. An XML Document is a Tree
person
name
tel
tel
Bart Simpson
051 –
02 –
Leaves are either empty or contain PCDATA

20. Mixed Content <airline>
An element may contain a mixture of sub-elements and PCDATA
<airline>
<name> British Airways </name>
<motto>
World’s <dubious> favorite</dubious>
airline
</motto>
</airline>

21. XML Attributes XML elements can have attributes, just like HTML:
Attributes are designed to contain data related to a specific element.
Must be quoted
Example
<person gender="female">
Attributes vs. Elements: Example
<person>   <gender>female</gender> </person>
To consider
attributes cannot contain multiple values (elements can)
attributes cannot contain tree structures (elements can)
attributes are not easily expandable (for future changes)

22. XML Attributes as Metadata
<messages>   <note id="501">     <to>Tove</to>     <from>Jani</from>     <heading>Reminder</heading>     <body>Don't forget me this weekend!</body>   </note>   <note id="502">     <to>Jani</to>     <from>Tove</from>     <heading>Re: Reminder</heading>     <body>I will not</body>   </note> </messages>

23. XML Namespaces Using a Prefix  leads to a conflict
<table>   <tr>     <td>Apples</td>     <td>Bananas</td>   </tr> </table>
<table>   <name>African Table </name>   <width>80</width>   <length>120</length> </table>
 leads to a conflict
Using a Prefix
<root  xmlns:h=" xmlns:f=" <h:table>   <h:tr>     <h:td>Apples</h:td>     <h:td>Bananas</h:td>   </h:tr> </h:table> <f:table>   <f:name>African Coffee</f:name>   <f:width>80</f:width>   <f:length>120</f:length> </f:table> </root>

24. The Header Tag
<?xml version="1.0" standalone="yes/no" encoding="UTF-8"?>
Standalone=“no” means that there is an external DTD
You can leave out the encoding attribute and the processor will use the UTF-8 default

25. Processing Instructions
<?xml version="1.0"?>
<?xml-stylesheet  href="doc.xsl" type="text/xsl"?>
<!DOCTYPE doc SYSTEM "doc.dtd">
<doc>Hello, world!<!-- Comment 1 --></doc>
<?pi-without-data?>
<!-- Comment 2 -->
<!-- Comment 3 -->

26. Well-Formed XML Documents
An XML document (with or without a DTD) is well- formed if
Tags are syntactically correct
Every tag has an end tag
Tags are properly nested
There is a root tag
A start tag does not have two occurrences of the same attribute
An XML document must be well formed

27. Representing relational databases
A relational database for school:
student: course:
enroll:

28. XML representation of relational DB
<school>
<student id=“001”>
<name> Joe </name> <gpa> </gpa>
</student>
<student id=“002”>
<name> Mary </name> <gpa> </gpa>
<course cno=“331”>
<title> DB </title> <credit> </credit>
</course>
<course cno=“350”>
<title> Web </title> <credit> 3.0 </credit>
<enroll>
<id> 001 </id> <cno> </cno>
</enroll>
<id> 001 </id> <cno> </cno>
<id> 002 </id> <cno> </cno>
</school>