Hi~ I'm Anka!

Table of content#

• Review Week 1 Tutorial.
• Review XML structure.
• Review XML rules.
• Explain what an XML schema is.
• Explain what a document definition is.
• Create a DTD document definition.
• Understand the main elements of DTD.

XML Schema?#

• The schema describes the structure.
  • What data is allowed.
  • What data is required.
  • How data is organized.
• Example: maged#zy.cdut

Well Formed and Valid XML#

XML document is well-formed:

• structurally and syntactically correct.
• Adheres to the general XML rules.
• Not necessarily valid. XML document is valid:
• Satisfies the schema document.
• Validity can vary between schema documents.
• XML documents that fail validation are considered invalid.

XML Schema Types#

The XML schema has two types:

• DTD: Document Type Definition.
• XSD: XML Schema Definition.

DTDs#

Document Type Definition (DTD)#

DTD is a structure (standard)

• A DTD is a set of markup declarations that define the document structure.
• Uses a list of validated elements and attributes.
• What elements can/must appear.
• What order they must be in.

DTD basics#

DTD determines:

• What the root element is.
• Number of instances of elements. DTD does not determine:
• Data types.
• Meaning of an element.

Is DTD also an XML file?#

No, DTDs are NOT xml

DTD location#

Internal: declared inside the XML document.

• Appears after the XML declaration, and before the document body. External: declared outside the XML document (as an external reference).

DOCTYPE#

• internal

1
<!DOCTYPE Name [
2
    Document definition
3
]>

• external

1
<!DOCTYPE events SYSTEM "xxx.dtd">

The contents of a DTD#

DTD Elements:

• Elements are the allowed/required tags.
• Created with an Element declaration.
• ElementName = XML Tag.
• Type = Tag Type

1
<?xml version="1.0" standalone="yes"?>
2
<!DOCTYPE Foods [
3
    <!ELEMENT Foods (Food)*>
4
    <!ELEMENT Food (Fruits,Vegetables,Meat,Fish)>
5
    <!-- 上面的元素定义了食品的结构（Food内的标签及其顺序，即Fruits,Vegetables,Meat,Fish） -->
6
    <!ELEMENT Fruits (#PCDATA)>
7
    <!ELEMENT Vegetables (#PCDATA)>
8
    <!ELEMENT Meat (#PCDATA)>
9
    <!ELEMENT Fish (#PCDATA)>
10
]>
11
<!-- 在浏览器中查看XML文件时，DOCTYPE部分并不会显示 -->
12
<Foods>
13
    <Food>
14
        <Fruits>Apple</Fruits>
15
        <Vegetables>Carrot</Vegetables>
16
        <Meat>Lamb</Meat>
17
        <Fish>Salmon</Fish>
18
    </Food>
19
    <Food>
20
        <Fruits>Orange</Fruits>
21
        <Vegetables>Cucumber</Vegetables>
22
        <Meat>Mutton</Meat>
23
        <Fish>Cod</Fish>
24
    </Food>
25
</Foods>

1
<?xml version="1.0" standalone="no"?>
2
<!DOCTYPE Foods SYSTEM “FoodsDTD.dtd">
3
<Foods>
4
    <Food>
5
        <Fruits>Apple</Fruits>
6
        <Vegetables>Carrot</Vegetables>
7
        <Meat>Lamb</Meat>
8
        <Fish>Salmon</Fish>
9
    </Food>
10
    <Food>
11
        <Fruits>Orange</Fruits>
12
        <Vegetables>Cucumber</Vegetables>
13
        <Meat>Mutton</Meat>
14
        <Fish>Cod</Fish>
15
    </Food>
16
</Foods>

1
<!ELEMENT Foods (Food)*>
2
<!ELEMENT Food (Fruits,Vegetables,Meat,Fish)>
3
<!ELEMENT Fruits (#PCDATA)>
4
<!ELEMENT Vegetables (#PCDATA)>
5
<!ELEMENT Meat (#PCDATA)>
6
<!ELEMENT Fish (#PCDATA)>

Element type declarations#

Mixed content需要把#PCDATA写在最前面

• (#PCDATA): The content can be only character data.
  • e.g.,
    • DTD: <!ELEMENT first (#PCDATA)>
    • XML: <first> John </first>
• EMPTY: The element is declared to be an empty one - no content allowed.
  • e.g.,
    • DTD: <!ELEMENT empty_element EMPTY>
    • XML: <empty_element></empty_element> or <empty_element />
• ANY: The element can have any element or character data.
  • e.g.,
    • DTD: <!ELEMENT any_element ANY>
    • XML:

1
<any_element>
2
    This is a line of characters
3
    <other_element> ... </other_element>
4
</any_element>

• Child elements: The content can only contain the child elements (no character data). The sequence, alternative, and cardinality can be expressed using commas(,) Ors (|).
  • e.g. DTD: <!ELEMENT a (x,y,z)> Element a must have an element x, followed by y, followed by z.
  • e.g. DTD: <!ELEMENT b (x|y|z)> Element b must have an element x, or y, or z
• Mixed content
  • Must use OR | to separate elements
  • #PCDATA must come first
  • * Must appear at the end if there are child elements
  • e.g., DTD: <!ELEMENT mix_element (#PCDATA | first | last)*>

1
<mix_element>
2
    My first name is
3
    <first>John</first>
4
    and my last name is
5
    <last>smith </last>
6
</mix_element>

DTD Element Options (modifiers)#

• <!ELEMENT Foods (Food)*>
  • *: zero or more times.
  • +: one or more times.
  • ?: zero or one time.
  • No symbol means the element must appear only once.
  • e.g. DTD: <!ELEMENT c (x*, y+, z?) >

DTD Element Options#

Elements with children

1
<!ELEMENT person (child1,child2)>
2
<!ELEMENT person (child1+,child2)>
3
<!ELEMENT person (child1*,child2)>
4
<!ELEMENT person (child1?,child2)>
5
<!ELEMENT person (child1|(child2,child3))*>

DTD Attributes#

<!ATTLIST ElementName AttributeName AttType DefaultValue>

• Some common attribute data types:
  • CDATA: Character data (text values).
  • ID: unique key.
  • Enumerator: list of values (value1 | value2 | value3). e.g. DTD: <!ATTLIST event cancelled (y|n) #REQUIRED>
• Some common default values:
  • #REQUIRED: <!ATTLIST Food orderNo CDATA #REQUIRED>
  • #IMPLIED: the attribute is optional
  • “default character data” <!ATTLIST person sex CDATA “male">
  • #FIXED: <!ATTLIST Form language CDATA #FIXED “EN”>

1
<?xml version="1.0" standalone=“yes"?>
2
<!DOCTYPE Foods [
3
    <!ELEMENT Foods (Food)*>
4
    <!ELEMENT Food (Fruits,Vegetables,Meat,Fish)>
5
    <!ATTLIST Food orderNo CDATA "1">
6
    <!ELEMENT Fruits (#PCDATA)>
7
    <!ELEMENT Vegetables (#PCDATA)>
8
    <!ELEMENT Meat (#PCDATA)>
9
    <!ELEMENT Fish (#PCDATA)>
10
]>
11
<Foods>
12
    <Food orderNo ="1">
13
        <Fruits>Apple</Fruits>
14
        <Vegetables>Carrot</Vegetables>
15
        <Meat>Lamb</Meat>
16
        <Fish>Salmon</Fish>
17
    </Food>
18
    <Food orderNo ="2">
19
        <Fruits>Orange</Fruits>
20
        <Vegetables>Cucumber</Vegetables>
21
        <Meat>Mutton</Meat>
22
        <Fish>Cod</Fish>
23
    </Food>
24
</Foods>

Structure: CDATA#

CDATA / PCDATA sections can be declared in both DTD and XML files

• Attributes can be defined in DTD using CDATA
• Elements can be defined in DTD using #PCDATA
• You can also declare a CDATA section directly in an XML file with the following processing instruction : <![CDATA[<tags>content</tags>]]>

Entity declarations#

To declare in DTD: <!ENTITY entityName "Long string or other character">
To display: &entityName;
Predefined entities:

1
<?xml version="1.0" standalone="yes"?>
2
<!DOCTYPE Universities [
3
    <!ELEMENT Universities (University)*>
4
    <!ELEMENT University (#PCDATA)>
5
    <!ENTITY CDUT "Chengdu University of Technology">
6
    <!ENTITY OBU "Oxford Brookes University">
7
]>
8
<Universities>
9
    <University>&CDUT;</University>
10
    <University>&OBU;</University>
11
</Universities>

Result:

1
<Universities>
2
    <University>Chengdu University of Technology </University>
3
    <University>Oxford Brookes University </University>
4
</Universities>

Comments#

1
<!-- comments are written in the same way as XML and HTML comments-->

Issues with Document definitions#

• If your document contains a link to a definition and the definition changes your document may break.
• If you link to a document definition and the link breaks your XML will not work.

Remember#

XML Validation#

Check the validity of your XML

• Is it well formed?
• Is it valid?

Useful Information#

Once NP++ and XML tools are installed, go to: Plugins > XML Tools > Options
Set “Prohibit DTD” to FALSE. This allows the use of internal DTDs in your XML files. By default, these are disabled.