INFSY 547: WEB-Based Technologies

Gayle J Yaverbaum, PhD

Professor of Information Systems

Penn State Harrisburg

Document Type Definitions

XML Parsers

• Two types of parsers:– Validating: checks document against a DTD or

schema– Non-validating: recognizes syntax errors

• All parsers require well-formed documents

• Eclipse will check your document

DTD

• Describes the XML object to the processor • Models XML structure• Constrains the structure

– On sequence– On nesting of tags

• Content may be processed without a DTD

DTD’s:

1. Strict rule book for XML document

2. Each tag must be declared

3. Should not contain elements that are absent in the XML document

DTD• Schemas do the same and more

• Valid: Structure is correct

Ask Eclipse to check

• Well-formed: XML code may not be

be valid.

• DTD’s can be shared, guaranteeing consistency

DTD

• Provides a list of:– Elements– Attributes– Entities

• May be embedded in xml document file or in separate file– Always create an external DTD.

DTD

Attribute types:

PCDATA (parsed character data )• Only content

CDATA (character data that is not markup

DTD Document type declaration: refers to the external file:

<!DOCTYPE rootname SYSTEM “filename.dtd”>

Example: <!DOCTYPE PORTFOLIO SYSTEM “PortfolioProject.dtd”>

DTD keywords

ELEMENT Defines tags

ATTLIST Defines attributes

ENTITY Defines entities

DTD Element Declaration:

1. Element Type Declaration is main building block of a DTD

<!ELEMENT element name content specification>

2. May begin with a a) Letterb) Colonc) Underscore

3. Subsequent to the 1rst character, may also include a period and hyphen

1. Build the DTD hierarchically– i.e. from the outside/in2. Identify the root ELEMENT e.g. Example <!ELEMENT PORTFOLIO

(SECTION*,RESOURCES*,OTHER*)>

1) An * : 0..MANY 2) A + : 1..MANY 3) A ? : 1 TIME

DTD Element Declaration(describes document tree structure)

Element content/child element

Element Declarations:

1. Types of content within an ELEMENT

o A list of other elements (as per last page)

o Keyword EMPTY (if element will not

contain anything)

EMPTY e.g. <!ELEMENT ABC EMPTY>

o An element that has no content. i.e. no child elements.

<!ELEMENT group (app,author,title )>

o Referred to as having children specified.

Defining ELEMENT Content

1. Content specification

2. The right side (content specification/model) defines the left side (element name)

3. MIXED content specifies both PCDATA and other elements

4. <!ELEMENT distributorName (#PCDATA)>

Attribute declaration:

Can be located anywhere in the DTD

good practice: keep it close to the corresponding

element

Attributes cannot contain sub elements.

Attribute declaration

<!ATTLIST elementname attributename type default>

<!ATTLIST book lang CDATA

#REQUIRED >

Attribute that indicates a reference/link:

<!ELEMENT RESOURCES (address,title1)><!ATTLIST RESOURCES

type CDATA "href">

Note: xsl:

<xsl:template match="RESOURCES"> <xsl:for-each select=".">

<P><a> <xsl:attribute name="href">

<xsl:value-of select="address" />

</xsl:attribute> <xsl:value-of select="title1" />

</a></P></xsl:for-each>

Image!

DTD file:

PIC is listed in the appropriate ELEMENT list in the DTD

an attribute is then defined: ATTLIST elementname attributename CDATA #IMPLIED

Example of the attribute in the DTD file: <ATTLIST filename CDATA #IMPLIED>

Common Attributes types<!ATTLIST elementname attributename type

default>

1. #CDATA

• Stands for character/string data

• Contains any combination of characters except “<“ or “&”

• Is simple and easy to use

• May have multiple attributes for an element

2. #REQUIRED: attribute must contain some value

3. #IMPLIED: attribute has no default value and may be omitted

4. #FIXED fixedvalue: attribute must always be set to the value, fixedvalue

5. Default: merely type a default value instead of the above

Programmer Defined Entities

• An <!ENTITY> tag in the DTD

<!ENTITY univ “Penn State University”>• In the XML document:

Start with a “&” Ends with a “;” <school name=“&univ;”>• Once defined, you may use the entity

anywhere within your XML document.

Lab Assignment

To Be Added!