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: Example:

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 2.May begin with a a)Letter b)Colon c)Underscore 3.Subsequent to the 1rst character, may also include a period and hyphen

1.Build the DTD hierarchically– i.e. from the outside/in 2.Identify the root ELEMENT e.g. Example 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. oAn element that has no content. i.e. no child elements.  oReferred 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.

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 book lang CDATA #REQUIRED >

Attribute that indicates a reference/link: <!ATTLIST RESOURCES type CDATA "href" > Note: xsl:

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:

Common Attributes types 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 tag in the DTD In the XML document: Start with a “&” Ends with a “;” Once defined, you may use the entity anywhere within your XML document.

Lab Assignment To Be Added!