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Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
Document Type Definitions
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Document Type Definitions

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DTD's in XML

DTD's in XML

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  • 1. Document Type Definitions
    XML
  • 2. DTD stands for Document Type Definition
    Allows an XML document to go further than meeting the requirements of being well-formed
    Specifies requirements to be valid
    A valid XML document matches definitions of allowable elements, attributes
    DTD Overview
  • 3. Validation can be done in code (i.e. using javascript, VB and DOM)
    DTD’s allow use of a validating parser that compares the document against specifications
    Typically makes application changes and maintenance easier
    Less tied to a particular programming language/environment
    Validation
  • 4. Declarations are used to specify document requirements
    Document type declaration
    Element declaration
    Attribute List declaration
    Entity declaration
    Declarations
  • 5. Includes name of root element
    Allows specification of where the DTD is located
    DTD can be embedded in the XML file (local)
    DTD can refer to external file, Uniform Resource Identifier (URI)
    Local takes precedence over external
    Document Type Declaration
  • 6. Element Declaration has 3 parts:
    Declaration
    Element name
    Element content
    Element content can include a list of child elements or data
    Element Declaration
  • 7. DTD included in XML document
    Definition of a student:
    <!DOCTYPE student[
    <!ELEMENT student(first, last, studentID)>
    <!ELEMENT first (#PCDATA)>
    <!ELEMENT last(#PCDATA)>
    <ELEMENT studentID(#PCDATA)>
    ]>
    LocalDTD
    Document Type Declaration
    Element Declaration
    A student element is made up of first name, last name, and student id elements
  • 8. DTD exists in external file/location
    Must use keyword to specify type of location
    SYSTEM is a reference to local file system
    PUBLIC is reference to DTD accessed through a catalog
    Can use both together
    If can’t find catalog reference can use specified file
    External Definition
  • 9. Reference in XML file:
    <!DOCTYPE student SYSTEM “student.dtd”>
    External file:
    <!ELEMENT student(first, last, studentID)>
    <!ELEMENT first (#PCDATA)>
    <!ELEMENT last(#PCDATA)>
    <ELEMENT studentID(#PCDATA)>
    ]>
    Sample External Definition
    Document Type Declaration
    Element Declaration
  • 10. Element name must match name in XML document
    If using namespaces, prefixes must match
    Content Model defines what the element can store
    An element
    Mixed (i.e. data and element)
    Empty
    Any
    Working With Elements
  • 11. One element can contain another
    Can specify the elements contained by sequence
    Can specify the elements contained as a choice
    Element Content
  • 12. Error raised if an element is missing
    Error raised if there are extra elements
    Error raised if elements in a different order
    For a student, our content must be in firstname, lastname, studentID order
    If find an element “major”, error
    If order varies, error
    If missing first, last, or studentID, error
    Content by Sequence
  • 13. Can allow content to vary between elements
    | (vertical bar or pipe) indicates OR
    If add a Grade element to a student that can be a letter or percent:
    <!ELEMENT grade (letter | percent)>
    <!ELEMENT letter (#PCDATA)>
    <!ELEMENT percent (#PCDATA)
    Indicates that must have letter or percent element
    Content by Choice
  • 14. A name may be a full name (first, middle, last) or just first and last:
    <!ELEMENT name (fullName | (first, last))>
    <!ELEMENT fullName (first, middle, last)>
    <!ELEMENT first (#PCDATA)>
    <!ELEMENT middle (#PCDATA)>
    <!ELEMENT last (#PCDATA)>
    By Choice: Example
  • 15. Allows combination of elements and parsed character data
    Can include additional information within an element, eg. how to display
    Rules:
    Managed by using Choice (or)
    PCDATA must appear first in list of elements
    List cannot include inner content model (only simple elements)
    If there are child elements, include *
    * Indicates that may appear zero or more times
    Mixed Content
  • 16. If want to include emphasis with the letter grade
    Data: <letter><em>4</em></letter>
    Declaration:
    <!ELEMENT letter (#PCDATA | em)*>
    Describes a letter element as the content (pcdata) plus emphasis element
    Mixed Content -2
  • 17. An element can be empty
    <br /> (never has child, content)
    Declaration includes EMPTY:
    <!ELEMENT br EMPTY>
    Means that the element CANNOT contain content
    Empty Content
  • 18. An element can contain any kind of value (or be empty)
    Any elements declared in the DTD can occur, any number of times
    Only elements that are part of the DTD can be part of the document!
    May be empty
    May contain PCDATA
    Least restrictive model
    Any Content
  • 19. How many times can an element occur?
    How many times must an element occur?
    Cardinality
  • 20. A student must have a first name
    A student may or may not have a last name
    A student may have one or more majors, or none (undeclared)
    <!ELEMENT student (first, last?, major*)>
    Note: Cardinality indicator doesn’t affect the element declaration (i.e. major)
    Cardinality: Example
  • 21. Elements tend to be used to describe a logical unit of information
    Attributes are typically used to store data about characteristics (properties)
    May have a Movie element with attributes for Title, Rental Price, Rental Days
    No specific rules about how to use elements and attributes
    Attributes and DTD’s
  • 22. Attributes allow more limits on data
    Can have a list of acceptable values
    Can have a default value
    Some ability to specify a data type
    Concise, about a single name/value pair
    Attributes have limits
    Can’t store long strings of text
    Can’t nest values
    Whitespace can’t be ignored
    Attributes and Elements
  • 23. Declaration:
    <!ATTLISTElementNameAttrNameAttrType Default>
    Specify the Element the attribute belongs to
    Specify the Name of the attribute
    Specify the Type of data the attribute stores
    Specify characteristics of the values (Default or attribute value)
    List either the default value or other characteristic of value – required, optional
    Specifying Attributes
  • 24. CDATA – unparsed character data
    Enumerated – series/list of string values
    Entity/Entities – reference entity definition(s)
    ID – unique identifier for the element
    IDREF – refer to the ID of another element
    IDREFS – list of ID’s of other elements separated by whitespace
    NMTOKEN/NMTOKENS – value(s) of attribute can be anything that follows rules for XML name
    Sample Attribute Data Types
  • 25. Specifies that attribute value must be found in a particular list
    Each value in list must be valid XML name
    Limits on spaces, characters
    Use | (pipe) to separate members of list
    If specifying list letter grades for a student:
    <!ATTLIST student grade (A | B | C | D | F | V | W | I) #IMPLIED>
    Enumerated Attributes
    Element
    Attribute
    Enumerated List
  • 26. An ID specifies that the element must have a unique value within the document
    Allows reliable way to refer to a specific element
    No spaces allowed in value
    Typically replace space with underscore
    Attribute list can include only one ID
    IDREF, IDREFS allows an element to be associated with another or multiple other elements
    A student element must have a student ID:
    <!ATTLIST student studentID ID #REQUIRED>
    ID, IDREF, IDREFS
  • 27. Attributes can refer to entities
    “Entity” refers to substituting a reference for a text value
    & refers to the & character
    Unparsed Entity is a reference that isn’t parsed
    Can reuse references for long values, or hard to manage characters (i.e. tab, line feed)
    Entity must be declared in the DTD
    <!ENTITY classTitle “XML”>
    When classTitle found in document, replaced with XML
    Entities and Attributes
  • 28. Can specify how the value will appear in the document
    Must always specify a value declaration
    DEFAULT sets a value for an attribute if a value isn’t provided
    Include default value in double quotes
    FIXED sets a value that must occur; if an attribute has a different value, a validation error occurs
    REQUIRED specifies that the attribute (and value) must exist
    IMPLIED means the attribute is optional
    Attribute Value Declarations

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