1 Dr Alexiei Dingli XML Technologies DTD. 2 Document Type Definition Defines –the legal building...

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Dr Alexiei Dingli

XML Technologies

DTD

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• Document Type Definition

• Defines – the legal building blocks of an XML document– the document structure– The legal elements and attributes

• A DTD can be defined inside an xml document or outside

What’s in a DTD?

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• An XML file can carry a description of its own format

• Independent groups of people can agree to use a standard DTD for interchanging data

• Applications can use a standard DTD to verify that the data received from the outside world is valid

• A DTD can be used to verify the data

Why do we need a DTD?

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<!DOCTYPE root-element [element-declarations]>

An inside DTD (1)

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An inside DTD (2)

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• !DOCTYPE note defines that the root element of this document is note.

• !ELEMENT note defines that the note element contains four elements: "to,from,heading,body".

• !ELEMENT to defines the to element  to be of the type "#PCDATA".

• !ELEMENT from defines the from element to be of the type "#PCDATA".

• !ELEMENT heading defines the heading element to be of the type "#PCDATA".

• !ELEMENT body defines the body element to be of the type "#PCDATA".

An inside DTD (3)

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<!DOCTYPE root-element SYSTEM "filename">

<!DOCTYPE note SYSTEM "note.dtd">

External DTD

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• Elements

• Attributes

• Entities

• PCDATA

• CDATA

The building blocks

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• Main building block

• Can contain text, other elements or be empty

• The elements b, title and br can be used as follows:

<b>Hello world</b>

<title>Hello <b>Tom</b></title>

<br />

Elements

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• Provide extra information about elements

• Always placed inside the opening tag

• Always have a name/value pair

Which is the element, attribute and value?

<img src="computer.gif" />

Attributes

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Entity References Character

&lt; <

&gt; >

&amp; &

&quot; "

&apos; '

Entities

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• Text that will NOT be parsed by a parser

• Tags inside the text will NOT be treated as markup and entities will not be expanded

CDATA

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• Parsed character data• Character data is the text found between the start tag

and the end tag of an XML element• Text that WILL be parsed by a parser

– The text will be examined by the parser for entities and markup

• Tags inside the text will be treated as markup and entities will be expanded

• However, parsed character data should not contain any &, <, or > characters; these need to be represented by the &amp; &lt; and &gt; entities, respectively

PCDATA

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<!ELEMENT element-name category>

Different Elements

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<!ELEMENT br EMPTY>

<br />

The Empty Element

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<!ELEMENT element-name (#PCDATA)>

<!ELEMENT from (#PCDATA)>

Element with PCDATA

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<!ELEMENT element-name ANY>

<!ELEMENT note ANY>

Element with Any

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<!ELEMENT element-name (child1,child2,...)>

<!ELEMENT note (to,from,heading,body)>

*Sequence must be respected

Elements with Children

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<!ELEMENT element-name (child-name)>

<!ELEMENT note (message)>

Element with one child

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• One or more

– <!ELEMENT element-name (child-name+)>

– <!ELEMENT note (message+)>

• Zero or more

– <!ELEMENT element-name (child-name*)>

– <!ELEMENT note (message*)>

• Zero or One

– <!ELEMENT element-name (child-name?)>

– <!ELEMENT note (message?)>

Occurrences

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• Either or

– <!ELEMENT note (to,from,header,(message|body))>

• Mixed content

– <!ELEMENT note (#PCDATA|to|from|header|message)*>

Mixing ...

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<!ATTLIST element-name attribute-name attribute-type default-value>

<!ATTLIST payment type CDATA "check">

<payment type="check" />

Declaring Attributes

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Type Description

CDATA The value is character data

(en1|en2|..) The value must be one from an enumerated list

ID The value is a unique id

IDREF The value is the id of another element

IDREFS The value is a list of other ids

NMTOKEN The value is a valid XML name

NMTOKENS The value is a list of valid XML names

ENTITY The value is an entity

ENTITIES The value is a list of entities

NOTATION The value is a name of a notation

xml: The value is a predefined xml value

Atribute Type

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Value Explanation

value The default value of the attribute

#REQUIRED The attribute is required

#IMPLIED The attribute is not required

#FIXED value The attribute value is fixed

Attribute Value

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<!ATTLIST mountain country CDATA "New Zealand">

<mountains>

<mountain country="New Zealand">

<name>Mount Cook</name>

</mountain>

CDATA example

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<!ATTLIST tutorial published (yes | no) "no">

<tutorial published="yes">

<name>XML Tutorial</name>

</tutorial>

Enumerated Example

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<!ATTLIST mountain mountain_id ID #REQUIRED>

<mountain mountain_id="m10001">

<name>Mount Cook</name>

</mountain>

ID example

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<!ATTLIST employee employee_id ID #REQUIRED manager_id IDREF #IMPLIED>

<employees>

<employee employee_id="e10001" manager_id="e10002"> <first_name>Homer</first_name>

<last_name>Flinstone</last_name>

</employee>

<employee employee_id="e10002"> <first_name>Fred</first_name> <last_name>Burns</last_name>

</employee>

</employees>

ID Ref example

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<!ATTLIST individual individual_id ID #REQUIRED parent_id IDREFS #IMPLIED>

<individual individual_id="e10001" parent_id="e10002 e10003">

<first_name>Bart</first_name> <last_name>Simpson</last_name>

</individual>

ID Refs example

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<!ATTLIST tutorial published NMTOKEN #REQUIRED>

* Can contain only letters, digits, points, hyphen, underline and colon

<mountain country="NZ">

<name>Mount Cook</name>

</mountain>

NMTOKEN example

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<!NOTATION name SYSTEM "external_id"> * Allow you to add data which is not XML

<!NOTATION GIF SYSTEM "image/gif">

<!NOTATION JPG SYSTEM "image/jpeg">

<!NOTATION PNG SYSTEM "image/png">

<!ATTLIST mountain photo ENTITY #IMPLIED photo_type NOTATION (GIF | JPG | PNG) #IMPLIED>

Notation example

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<!ATTLIST mountain photo ENTITY #IMPLIED>

<!ENTITY mt_cook_1 SYSTEM "mt_cook1.jpg">

<mountain photo="mt_cook_1">

<name>Mount Cook</name>

</mountain>

Entity example

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• Entities are variables used to define shortcuts to standard text or special characters– Entity references are references to entities– Entities can be declared internal or external

More about Entities

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<!ENTITY writer “Alexiei Dingli">

<!ENTITY copyright "Copyright Dingli@UOM">

<author>&writer;&copyright;</author>

Internal Entities

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<!ENTITY writer SYSTEM "http://www.um.edu.mt/entities.dtd">

<!ENTITY copyright SYSTEM "http://www.um.edu.mt/entities.dtd">

<author>&writer;&copyright;</author>

External Entities

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Example

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• Define an XML Vocabulary for a Toaster Markup Language (TML)

• It must support features such as:– Print message on toast– Display on LCD– Time stamp

Exercise

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Questions?