Lecture Outline

We shall study Extensible Markup Language (XML) 1.0 (Fourth Edition) which is a W3C Recommendation published on August 16, 2006.
Link: http://www.w3.org/TR/2006/REC-xml-20060816
For a gentle introduction to XML, read pages 1-85 of XML in a Nutshell (3rd edition) by Elliotte Rusty Harold & W. Scott Means. This desktop reference is published by O'Reilly and is highly recommended.
Subjects to be covered this week:
1. The structure of an XML document
2. Character data and markup
3. Entity reference and character reference
4. Document type definition (DTD)
5. Well-formedness and validity
Case studies:
1. Rich Site Summary (RSS) 0.91
2. Question and Answer Markup Language (QAML)
3. XHTML (some part only)

The Structure of An XML Document

Document:
```
document  ::=  prolog element Misc*
```

Prolog:

prolog       ::=  XMLDecl? Misc* (doctypedecl  Misc*)?
XMLDecl      ::=  '<?xml' VersionInfo EncodingDecl? SDDecl? S? '?>'
VersionInfo  ::=  S 'version' Eq ("'" VersionNum "'" | '"' VersionNum '"')
Eq           ::=  S? '=' S?
VersionNum   ::=  '1.0'
Misc         ::=  Comment | PI | S

Element & Content:

element  ::=  EmptyElemTag |  STag content ETag
content  ::=  CharData? ((element | Reference | CDSect | PI | Comment) CharData?)*

White Space:
```
S  ::=  (#x20 | #x9 | #xD | #xA)+
```

The Text in An XML Document

The text in an XML document consists of intermingled character data and markup. All text that is not markup constitutes the character data of the document.

Character Data:

CharData  ::= [^<&]* - ([^<&]* ']]>' [^<&]*)

Markup takes the form of:
- start-tags,
- end-tags,
- empty-element tags,
- entity references,
- character references,
- comments,
- CDATA section delimiters,
- document type declarations,
- processing instructions,
- XML declarations,
- text declarations, and
- any white space that is at the top level of the document entity (that is, outside the document element and not inside any other markup).

Entity References and Character References

(General) Entity references (for example):

"<" is used for "<"
"&" is used for "&"
">" is used for ">"
" is used for "
' is used for '

(Numeric) Character references (for example):

"&" is used for "&"
"&" is used for "&"
"堃" is used for "堃"

More Markup

Comments (for example):

<!-- declarations for <head> & <body> -->

CDATA sections (for example):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN"
             "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd" [
	<!ATTLIST polygon
		area CDATA #IMPLIED
		circumference CDATA #IMPLIED>
]>
<svg width="100" height="100" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <defs>
		<style type="text/css"><![CDATA[
		polygon { fill: green;    stroke: black;  stroke-width: 1}
		]]>
		</style>
  </defs>
  <polygon id="_10001001" points="10,10 10,90 90,90 90,10" area="6400" circumference="320"/>
</svg>

Processing instructions (for example):

<?xml-stylesheet href="person.css" type="text/css"?>

Document Type Declarations

A valid document includes a document type declaration that identifies the DTD (Document Type Definition) that the document satisfies. A DTD contains or points to the following kinds of markup declarations.

Element Type declarations: An element type can have element content, mixed content, EMPTY content, or ANY content.

<!ELEMENT br EMPTY>
<!ELEMENT container ANY>
<!ELEMENT div1 (head, (p | list | note)*, div2*)>
<!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
<!ELEMENT b (#PCDATA)>

Attribute-List declarations specify the name, data type, and default value (if any) of each attribute associated with a given element type. There are 10 attribute types: CDATA, NMTOKEN, NMTOKENS, enumeration, ENTITY, ENTITIES, ID, IDREF, IDREFS, NOTATION.
General Entity declarations (for example):
```
<!ENTITY lt     "&#38;#60;">
```

Attribute-List Declaration

CDATA:

<!ELEMENT img EMPTY>
<!ATTLIST img src CDATA #REQUIRED
                alt CDATA #REQUIRED>

<img src="../images/MonaLisa.png" alt="Mona Lisa"/>

NMTOKEN/NMTOKENS:

<!ELEMENT performance (#PCDATA)>
<!ATTLIST performance dates NMTOKENS #REQUIRED>

<performance dates="2001-08-21 2001-08-23 2001-08-27">King Lear</performace>

Enumeration:

<!ELEMENT date EMPTY>
<!ATTLIST date year  (2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008) #REQUIRED>
<!ATTLIST date month (Jan | Feb | Mar | Apr | May | Jun |
                      JUL | Aug | Sep | Oct | Nov | Dec) #REQUIRED>
<!ATTLIST date day   (1 |  2 |  3 |  4 |  5 |  6 |  7 |  8 |  9 | 10 |
                     11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
                     21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31) #REQUIRED>

<date year="2007" month="Mar" day="6" />

Attribute-List Declaration (Cont.)

ID/IDREF/IDREFS:

<!ELEMENT animal EMPTY>
<!ELEMENT person EMPTY>
<!ELEMENT angel  EMPTY>
<!ATTLIST animal name CDATA #REQUIRED
                 id   ID    #REQUIRED>
<!ATTLIST person name CDATA #REQUIRED
                 id   ID    #REQUIRED>
<!ATTLIST angel  name CDATA #REQUIRED
                 id   ID    #REQUIRED>

<!ELEMENT team EMPTY>
<!ATTLIST team name    CDATA  #REQUIRED
               members IDREFS #REQUIRED>

<animal name="pooh"   id="777"/>
<animal name="dodo"   id="778"/>
<person name="andrea" id="012"/>
<person name="dodo"   id="013"/>
<angel  name="winnie" id="912"/>

<team name="fantasy" members="777 912 012 013"/>

Attribute-List Declaration (Cont.)

Attribute Defaults: #IMPLIED, #REQUIRED, #FIXED, Literal.

<!ATTLIST termdef
          id      ID      #REQUIRED
          name    CDATA   #IMPLIED>
<!ATTLIST list
          type    (bullets|ordered|glossary)  "ordered">
<!ATTLIST form
          method  CDATA   #FIXED "POST">

#IMPLIED: This attribute is optional. An element may or may not provide a value for the attribute. No default value is provided.
#REQUIRED: This attribute is required. Each element must provide a value for the attribute. No default value is provided.
#FIXED: The attribute value is a constant. An element may or may not include this attribute. If included, it must have the specific value.
Literal: The actual value is given as a quote string.

External/Internal DTDs

An example of external DTD:

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xml:lang="en-US">
<head><title>An Example</title></head>
<body><p>This is a test.</p></body>
</html>

An example of internal DTD:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE greeting [
  <!ELEMENT greeting (#PCDATA)>
]>
<greeting>Hello, world!</greeting>

Both used at the same time:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE greeting SYSTEM "hello.dtd" [
  <!ELEMENT greeting (#PCDATA)>
]>
<greeting>Hello, world!</greeting>

Entity and attribute-list declarations in the internal subsets take precedence over those in the external subset.

A standalone XML document: External markup declarations have no effect on the XML document.
```
<?xml version="1.0" standalone="yes"?>
```

Well-formedness and Validity

Every XML document must be well-formed. The document must adhere to rules like the following:
1. Every start-tag must have a matching end-tag.
2. Elements may nest but not overlap.
3. There must be exactly one root element.
4. Attribute values must be quoted.
5. An element may not have two attributes with the same name.
6. No unescaped < or & signs may occur in the character data of an element or attribute.
This is not an exhausted list! For a complete list of well-formedness constraints, check out the XML Recommendation.
An XML document is valid if, in addition to being well-formed, the document satisfies all the constraints specified in the XML document's DTD. Such constraints state, for example, that an element's children must occur in an order as required by the element's content model, and that the an element can only have attributes that are specified. For a complete list of validity constraints, check out the XML Recommendation.

XML Basics, Part 1

Lecture Outline

The Structure of An XML Document

The Text in An XML Document

Entity References and Character References

More Markup

Document Type Declarations

Attribute-List Declaration

Attribute-List Declaration (Cont.)

Attribute-List Declaration (Cont.)

External/Internal DTDs

Well-formedness and Validity