1. XML Extensible Markup Language Aleksandar Bogdanovski Programing Enviroment LABoratory alebo@ida.liu.se

2. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language What is XML ? Unformal definition: XML is a markup language for representation of documents which contain stuctured information. http://www.w3.org/XML/1999/XML-in-10-points.html New in XML ?

3. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Document The word "document" refers not only to traditional documents, but also to the countless number of other XML "data formats". These include vector graphics, e-commerce transactions, mathematical equations, object meta- -data, server APIs, and a thousand other kinds of structured information.

4. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language SGML – XML – HTML SGML provides arbitrary structure. Full SGML systems solve large, complex problems that justify their expense. XML is defined as an application profile of SGML, or roughly speaking, a restricted form of SGML. XML specifies neither semantics nor a tag set. XML provides a facility to define tags and the structural relationships between them. In HTML, both the tag semantics and the tag set are fixed.

5. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language 10 Commandmend’s of XML 1.XML shall be straightforwardly usable over the Internet. 2.XML shall support a wide variety of applications. 3.XML shall be compatible with SGML. 4.It shall be easy to write programs which process XML documents. 5.The number of optional features in XML is to be kept to the absolute minimum, ideally zero. 6.XML documents should be human-legible and reasonably clear. 7.The XML design should be prepared quickly. 8.The design of XML shall be formal and concise. 9.XML documents shall be easy to create. 10.Terseness in XML markup is of minimal importance.

6. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Look and feel of XML Document A Simple XML Document : Say goodnight, Gracie. Goodnight, Gracie.

7. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Markup in XML There are six kinds of markup in XML: Elements Entity references Comments Processing instructions (Pis) Marked (CDATA) sections Document type declarations (DTD)

8. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Elements Elements are the most common form of markup. Elements identify the nature of the content they surround. Some elements may be empty, in which case they have no content. Element begins with a start-tag,, ends with an end-tag,, and has some content in between. Example : Say goodnight, Gracie. Attributes are name-value pairs that occur in start-tags after the element name. Example: In XML, all attribute values must be quoted.

9. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Entity references To represent special characters in XML, entities are used. Entities are also used to refer to often repeated or varying text and to include the content of external files. Every entity must have a unique name. A special form of entity reference, called a character reference, can be used to insert arbitrary Unicode characters into your document. Character references take one of two forms: decimal references, ℞, and hexadecimal references, ℞.

10. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Comments Comments begin with ” ”. Comments can contain any data except the literal string ”--”. Comments can be placed anywhere between markup in the document. Comments are not part of the textual content of an XML document. An XML processor is not required to pass them along to an application.

11. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Processing instructions (PIs) Like comments, Pis are not textually part of the XML document, but the XML processor is required to pass them to an application. Processing instructions have the form:. The name, called the PI target, identifies the PI to the application. Any data that follows the PI target is optional. The names used in PIs may be declared as notations in order to formally identify them. PI names beginning with xml are reserved for XML standardization.

12. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language CDATA sections CDATA section instructs the parser to ignore most markup characters. Example: <![CDATA[ *p = &q; b = (i <= 3); ]]> Between the start of the section,, all character data is passed directly to the application, without interpretation. The only string that cannot occur in a CDATA section is ]]>.

13. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Document Type Declaration (DTD) One of the greatest strengths of XML is that it allows you to create your own tag names. But it is not meaningful for tags to occur in a completely arbitrary order Example: Goodnight, Gracie Say goodnight, Gracie. This doesn’t make any sence, but syntactically there’s nothing wrong. For the document to have a meaning, some constraints on the sequence and nesting of tags should be imposed.

14. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Document Type Declaration (DTD) Constarints are expresed in the Declarations. Declarations allow a document to communicate meta-information to the parser about its content. There are four kinds of declarations in XML: Element Type Declarations Attribute List Declarations Entity Declarations Notation Declarations

15. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Element Type Declaration Element type declarations identify the names of elements and the nature of their content. Example:

16. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Attribute List Declarations Attribute list declarations identify which elements may have attributes, what attributes they may have, what values the attributes may hold, and what value is the default. Example: <!ATTLIST oldjoke name ID #REQUIRED label CDATA #IMPLIED status ( funny | notfunny ) 'funny'> Each attribute in a declaration has 3 parts: a name, a type, and default value.

17. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Attribute List Declarations CDATA CDATA attributes are strings, any text is allowed. ID The value of an ID attribute must be a name. All of the ID values used in document must be different. IDs uniquely identify individual elements in a document. Elements can have only a single ID attribute. IDREF or IDREFS An IDREF attribute's value must be the value of a single ID attribute on some element in the document. The value of an IDREFS attribute may contain multiple IDREF values separated by white space. There are six possible attribute types ENTITY or ENTITIES An ENTITY attribute's value must be the name of a single entity. The value of an ENTITIES attribute may contain multiple entity names separated by white space. NMTOKEN or NMTOKENS Restricted form of string attribute. NMTOKEN attribute must consist of a single word, but there are no additional constraints. The value of an NMTOKENS attribute may contain multiple NMTOKEN values separated by white space. A list of names The value of an attribute must be taken from a specific list of names. This is frequently called an enumerated type. Alternatively, you can specify that the names must match a notation name.

18. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Attribute List Declarations #REQUIRED The attribute must have an explicitly specified value on every occurrence of the element in the document. #IMPLIED The attribute value is not required, and no default value is provided. If a value is not specified, the XML processor must proceed without one. "value" An attribute can be given any legal value as a default. The attribute value is not required on each element in the document, and if it is not present, it will appear to be the specified default. #FIXED "value" An attribute declaration may specify that an attribute has a fixed value. In this case, the attribute is not required, but if it occurs, it must have the specified value. If it is not present, it will appear to be the specified default. There are four possible default values:

19. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Entity Declarations Entity declarations allow you to associate a name with some other fragment of content. That construct can be a chunk of regular text, a chunk of the document type declaration, or a reference to an external file containing either text or binary data. Example: There are three kinds of entities: Internal Entities External Entities Parameter Entities

20. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Internal Entities The internal entities associate a name with a string of literal text. Example: Internal entities allow to define shortcuts for frequently typed text or text that is expected to change, such as the revision status of a document. The XML specification predefines five internal entities: 1.< produces the left angle bracket, < 2.> produces the right angle bracket, > 3.& produces the ampersand, & 4.&apos; produces a single quote character (an apostrophe), ' 5." produces a double quote character, "

21. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language External Entities External entities associate a name with the content of another file. External entities contain either text or binary data. Example: The textual content of the external file is inserted at the point of reference and parsed as part of the referring document. Binary data is not parsed and may only be referenced in an attribute.

22. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Parameter Entities Parameter entities can only occur in the document type declaration. Parameter entity references are immediately expanded in the Document type declaration and their replacement text is part of the declaration. Example:

23. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Notation Declaration Notation declarations identify specific types of external binary data. This information is passed to the processing application, which may make whatever use of it it wishes. Example:

24. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Including a DTD The DTD must be the first thing in the document after the optional processing instructions and comments. The DTD identifies the root element of the document and may contain additional declarations. Example: <!DOCTYPE chapter SYSTEM "dbook.dtd” [ <!ATTLIST ulink xml:link CDATA #FIXED "SIMPLE" xml-attributes CDATA #FIXED "HREF URL" URL CDATA #REQUIRED> ]>...

25. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Well-formed Documents A document can only be well-formed if it obeys the syntax of XML. The document must meet all of the following conditions: The document instance must conform to the grammar of XML documents. The replacement text for all parameter entities referenced inside a markup declaration consists of zero or more complete markup declarations. No attribute may appear more than once on the same start-tag. String attribute values cannot contain references to external entities. Non-empty tags must be properly nested. Parameter entities must be declared before they are used. All entities except the following: amp, lt, gt, apos, and quot must be declared. A binary entity cannot be referenced in the flow of content, it can only be used in an attribute declared as ENTITY or ENTITIES. Neither text nor parameter entities are allowed to be recursive, directly or indirectly.

26. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Valid Documents A well-formed document is valid only if it contains a proper document type declaration and if the document obeys the constraints of that declaration (element sequence and nesting is valid, required attributes are provided, attribute values are of the correct type, etc.). The XML specification identifies all of the criteria in detail.

27. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language The XML family Set of modules that offer useful services to accomplish important and frequently demanded tasks. The XML family consists of: XLink XPointer XSchemas CSS – XSL – XSLT DOM etc.

28. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language XLink Some of the highlights of XLink are: XLink gives you control over the semantics of the link XLink introduces Extended Links. Extended Links can involve more than two resources. There are two types of links: Simple Links Extended Links

29. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Simple Links A Simple Link strongly resembles an HTML link: Example Link Text A Simple Link identifies a link between two resources, one of which is the content of the linking element itself. This is an in-line link. The locator identifies the other resource. The locator may be a URL, a query, or an Extended Pointer.

30. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Extended Links Extended Links allow you to express relationships between more than two resources: Example: The Text Annotations More Annotations Literary Criticism

31. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language XPointer XPointers offer a syntax that allows you to locate a resource by traversing the element tree of the document containing the resource. Example: child(2,oldjoke).(3,.) locates the third child (whatever it may be) of the second oldjoke in the document. XPointers can span regions of the tree. Example: span(child(2,oldjoke),child(3,oldjoke)) selects the second and third oldjoke s in the document.

32. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language XSchemas XML Schemas help developers to precisely define the structures of their own XML-based formats.

33. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language CSS – XSL – XSLT CSS the style sheet language, is applicable to XML as it is to HTML. XSL is the advanced language for expressing style sheets. It is based on XSLT a transformation language used for rearranging, adding and deleting tags and attributes.

34. February 2002Aleksandar Bogdanovski : XML Extensible Markup Language Conclusion XML isn't always the best solution, but it is always worth considering.