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XML

XML. Aynur Abdurazik. DTD. DTD ( Document Type Definition ) is a set of rules that defines a custom markup language in XML. An XML document for a particular custom markup language is not considered valid if it does not adhere to the DTD that language.

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XML

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  1. XML Aynur Abdurazik

  2. DTD • DTD (Document Type Definition) is a set of rules that defines a custom markup language in XML. • An XML document for a particular custom markup language is not considered valid if it does not adhere to the DTD that language. • A DTD defines the structure and contentof elements, child elements, and their attributes for a given markup language. Copyrigth Aynur Abdurazik

  3. DTD • DTD is a text-only document and is saved with a .dtd extension. • It is not an XML document itself and does not start with the standard XML declaration. Copyrigth Aynur Abdurazik

  4. DTD • DTD is a way to insure the consistency of shared XML data. DTDs are used to validate XML documents before their usage. • An XML editor or DTD processor will be needed to validate an XML document against a given DTD. Copyrigth Aynur Abdurazik

  5. DTD Syntax • Defining an element that contains text: • <!ELEMENT tag (#PCDATA) > • Tag is the name of the element you wish to define. • PCDATA (Parsed Character Data) refers to the text value of an element • XML is case sensitive – ELEMENT! and Element! are different. Copyrigth Aynur Abdurazik

  6. DTD Syntax • Defining an Empty Element: • <!ELEMENT tag EMPTY> • Tag is the name of the element you wish to define. • EMPTY indicates that the element will not contain a text value of its own. • No parenthesis around EMPTY. • EMPTY elements can have attributes that are used to store data. • Example: <!ELEMENT main_image EMPTY> Copyrigth Aynur Abdurazik

  7. DTD Syntax • Defining an Element that contains a child: • <!ELEMENT tag (child)> • Tag is the name of the element you wish to define • Child is the name of the element that will be contained in the element being defined • This element cannot contain anything other than the child element, and it must contain the child element every time • Example: <!ELEMENT students (student) > Copyrigth Aynur Abdurazik

  8. DTD Syntax • Defining an Element that contains children: • <!ELEMENT tag (child1, child2, child3)> • Example: <ELEMENT course (name, location, instructor) > • The most important thing in a sequence is comma. • (#PCDATA) cannot be used in any part of a sequence; sequences must only contain elements. • Elements contained in a sequence can have their own child elements. Copyrigth Aynur Abdurazik

  9. DTD Syntax • Defining how many occurrences: • After elements name add one of the following: • * - zero or more • + - one or more • ? – zero or one • Elements without a quantifier must appear exactly once. • There is no way to define a specific quantity of an element • <!ELEMENT course (name, location+, instructor+)> Copyrigth Aynur Abdurazik

  10. DTD Syntax • Defining Choices: • <!ELEMENT tag (child1 | child2 | child3) > • Defining an element that contains anything: • <!ELEMENT tag ANY> • ANY allows the element to contain any combination of elements and parsed character data. • If the element contains child element, children should be defined in the DTD. Copyrigth Aynur Abdurazik

  11. DTD Attributes • Attributes provide additional data about an element. • Elements are better used for information to be displayed • Attributes are better used for information about information. • Attributes are often used with empty elements. Copyrigth Aynur Abdurazik

  12. Defining Attributes • <!ELEMENT tag att_name CDATA #IMPLIED|#REQUIRED > • Att_name is the name of an attribute • CDATA (character data) will not be parsed by the processor. • #IMPLIED indicates the attribute may be omitted • #REQUIRED indicates the attribute may not be omitted and must contain a value • Definitions are case sensitive Copyrigth Aynur Abdurazik

  13. XML Entities • Entities are like autotext entries or shortcuts • Define entity name and the text it represents, • entity reference is expanded into the defined text • Two main types of entities: • General entities: can be expanded only in XML doc • Further divided into internal and external, parsed or unparsed • Parameter entities: can be expanded only in DTDs • Can be divided into internal and external, but are always parsed. Copyrigth Aynur Abdurazik

  14. Creating an External General Entity • Larger entities or entities could be reused in multiple DTDs can be saved in a separate, external text file with .ent extension. • <!ENTITY ent_name SYSTEM “entity.uri”> • “entity.uri” specifies the location of the entity file. Copyrigth Aynur Abdurazik

  15. XML Schema • Associating and XML Schema with an XML document: <?xml version=“1.0”?> <root_namexmlns:xsi=http://www.w3.org/2001/XMLSchema-instancexsi:noNamespaceSchemaLocation=“xsd.uri”> … </root_name> Copyrigth Aynur Abdurazik

  16. Deriving Custom Simple Types <xs:element name=“label”> • “label” is the name of XML element <xs:simpleType name=“custom_type_name”> <xs:restriction base=“foundation”> - “foundation” is any of the built-in simple types Specify restrictions </xs:restriction> </xs:simpleType> </xs:element> Copyrigth Aynur Abdurazik

  17. Named Custom Type <xs:simpleType name=“custom_type_name”> <xs:restriction base=“foundation”> - “foundation” is any of the built-in simple types Specify restrictions </xs:restriction> </xs:simpleType> <xs:element name=“label” type=“custom_type_name”> Copyrigth Aynur Abdurazik

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