XML

1
XML

• Introducing XML

2
What is XML?

• XML is the Extensible Markup Language. It is
  designed to improve the functionality of the Web
  by providing more flexible and adaptable
  information identification.
• It is called extensible because it is not a fixed
  format like HTML (a single, predefined markup
  language). Instead, XML is actually a
  metalanguage' a language for describing other
  languageswhich lets you design your own
  customized markup languages for limitless
  different types of documents. XML can do this
  because it's written in SGML, the international
  standard metalanguage for text markup systems
  (ISO 8879).

3
Why not just carry on extending HTML?

• HTML is already overburdened with dozens of
  interesting but incompatible inventions from
  different manufacturers, because it provides only
  one way of describing your information.
• XML allows groups of people or organizations to
  create their own customized markup applications
  for exchanging information in their domain
  (music, chemistry, electronics, hill-walking,
  finance, surfing, petroleum geology, linguistics,
  cooking, knitting, stellar cartography, history,
  engineering, rabbit-keeping, mathematics,
  genealogy, etc).
• HTML is at the limit of its usefulness as a way
  of describing information, and while it will
  continue to play an important role for the
  content it currently represents, many new
  applications require a more robust and flexible
  infrastructure.

4
XML Parsers

• An XML processor (also called XML parser)
• evaluates the document to make sure it conforms
• to all XML specifications for structure and
  syntax.
• XML parsers are strict. It is this rigidity
  built into
• XML that ensures XML code accepted by the
• parser will work the same everywhere.
• Microsofts parser is called MSXML and is built
• directly in IE versions 5.0 and above.
• Netscape developed its own parser, called
  Mozilla,
• which is built into version 6.0 and above.

5
The Document Creation Process
6
Creating an XML Document

• There are two categories of XML documents
• Well-formed
• Valid
• An XML document is well-formed if it contains
  no syntax errors and fulfills all of the
  specifications for XML code as defined by the
  W3C.
• An XML document is valid if it is well-formed
  and also satisfies the rules laid out in the DTD
  or schema attached to the document.

7
The Structure of an XMLDocument

• XML documents consist of three parts
• The prolog
• The document body
• The epilog
• The prolog is optional and provides information
  about the document.
• The document body contains the documents
• content in a hierarchical tree structure.
• The epilog is also optional and contains any
  final
• comments or processing instructions.

8
The XML Declaration

• The XML declaration at the beginning of an XML
  document is not necessary, but it's the best way
  to say "this is definitely an XML document and
  here's the release of XML it conforms to." The
  following is typical
• lt?xml version"1.0"?gt

9
Elements and Attributes

• XML supports two types of elements
• Closed elements, and
• empty elements
• A closed element, has the following syntax
• ltelement_namegtContentlt/element_namegt
• Example
• ltArtistgtMiles Davislt/Artistgt
• An attribute is a feature or characteristic of
  an
• element. Attributes are text strings and must
  be
• placed in single or double quotes. The syntax
  is ltelement_name attributevaluegt
  lt/element_namegt

10
Linking to a Style Sheet

• . A stylesheet is a separate document that
  provides hints and algorithms for rendering or
  transforming the data in the XML document.
• 1-The CSS stylesheet language is general and
  powerful enough to be applied to XML documents,
  although it is oriented toward visual rendering
  of the document and does not allow for complex
  processing of the document's data.
• 2-more complex and powerful stylesheet language
  is XSLT, the Transformations part of the
  Extensible Stylesheet Language, which can be used
  to transform XML to other formats, including
  HTML, other forms of XML, and plain text .

11
Binding XML Data withInternet Explorer

• Data in a data source is organized by
  fields,records, and recordsets.
• A field is an element that contains a single
  item of information such as an employees last
  name.
• A record is a collection of those fields.
• A recordset is a collection of records.
• The first step in data binding is to attach the
  Web page to a recordset. The attached data is
  called a data island. They can be either external
  files or code entered into the HTML file.
• The syntax to create a data island from an
  external file is
• ltxml idid srcURLgtlt/xmlgt
• For example
• ltxml idCompany srcCompany.xmlgtlt/xmlgt
• ActiveX Data Objects (ADO) is a data-access
  technology
• developed by Microsoft. ADO allows you to work
  with the
• Data Source Object by applying a method or by
  changing
• one of the properties of the DSO.
• For example, if you want to display the last
  record in a DSO whose id is Staff_Info, run the
  following method
• Staff_Info.recordset.moveLast

12
Creating a Valid Document

• An XML document can be validated using either
  DTDs (Document Type Definitions) or schemas.
• A DTD can be used to
• Ensure all required elements are in present the
  document
• Prevent undefined elements from being used
• Enforce a specific data structure
• Specify the use of attributes and define their
  possible values
• Define default values for attributes
• Describe how the parser should access non-XML
  or
• non-textual content
• DTDs define five different types of element
• content
• Any elements. No restrictions on the elements
  content.
• Empty elements. The element cannot store any
  content.
• Character data. The element can only contain a
  text string.
• Elements. The element can only contain child
  elements.
• Mixed. The element contains both a text string
  and child elements.

13
How do I create my own DTD?

• You need to use the XML Declaration Syntax
  (very simple declaration keywords begin with lt!
  rather than just the open angle bracket, and the
  way the declarations are formed also differs
  slightly). Here's an example of a DTD for a
  shopping list,
• lt!ELEMENT Shopping-List (Item)gt lt!ELEMENT
  Item (PCDATA)gt
• It says that there shall be an element
  called Shopping-List and that it shall contain
  elements called Item there must be at least one
  (that's the plus sign) but there may be more than
  one. It also says that the Item element may
  contain parsed character data (PCDATA, ie text).
• Because there is no other element which
  contains Shopping-List, that element is assumed
  to be the root' element, which encloses
  everything else in the document. You can now use
  it to create an XML file give your editor the
  declarations
• lt?xml version"1.0"?gt lt!DOCTYPE
  Shopping-List SYSTEM "shoplist.dtd"gt (assuming
  you put the DTD in that file). Now your editor
  will let you create files according to the
  pattern
• ltShopping-Listgt
• ltItemgtChocolatelt/Itemgt
• ltItemgtSugarlt/Itemgt
• ltItemgtButterlt/Itemgt
• lt/Shopping-Listgt
• See http//www.w3.org/QA/2002/04/valid-dtd-list.ht
  ml

14
Working with Namespaces and Schemas

• A namespace is a collection of element
  and attribute names identified by a Uniform
  Resource Identifier reference. The reference may
  appear in the root element as a value of the
  xmlns attribute. For example, the namespace
  reference for an XML document with a root element
  x might appear like this
• ltx xmlns"http//www.company.com/company-schema
  "gt.
• More than one namespace may appear in a
  single XML document, to allow a name to be used
  more than once. Each reference can declare a
  prefix to be used by each name, so the previous
  example might appear as
• ltx xmlnsspc"http//www.company.com/companys
  chema"gt, which would nominate the namespace for
  the spc' prefix
• ltspcnamegtMr. Biglt/spcnamegt.

15
schema

• A schema is a model for describing the
  structure of information. It's a term borrowed
  from the database world to describe the structure
  of data in relational tables. In the context of
  XML, a schema describes a model for a whole class
  of documents. The model describes the possible
  arrangement of tags and text in a valid document.
  A schema might also be viewed as an agreement on
  a common vocabulary for a particular application
  that involves exchanging documents.
• Schemas may sound a little technical, but we
  use them to analyze the world around us. For
  example, suppose I ask you, "is this a valid
  postal address?"
• ltaddressgt
• ltnamegtYoussef Hijazilt/namegt
• ltstreetgt1469 alphada avelt/streetgt
• ltcitygtAkronlt/citygt
• ltstategtOHlt/stategt
• ltzipgt12481lt/zipgt
• lt/addressgt

16
Schema ..cont

• Mentally, you compare the address
  presented with a schema that you have in your
  head for addresses. It probably goes something
  like this a postal address consists of a person,
  possibly at a company or organization, one or
  more lines of street address, a city, a state or
  province, a postal code, and an optional country.
  So, yes, this address is valid.In schemas, models
  are described in terms of constraints. A
  constraint defines what can appear in any given
  context. There are basically two kinds of
  constraints that you can give content model
  constraints describe the order and sequence of
  elements and datatype constraints describe valid
  units of data.
• For example, a schema might describe a
  valid ltaddressgt with the content model constraint
  that it consist of a ltnamegt element, followed by
  one or more ltstreetgt elements, followed by
  exactly one ltcitygt, ltstategt, and ltzipgt element.
  The content of a ltzipgt might have a further
  datatype constraint that it consist of either a
  sequence of exactly five digits or a sequence of
  five digits, followed by a hyphen, followed by a
  sequence of exactly four digits. No other text is
  a valid ZIP code.
• The purpose of a schema is to allow machine
  validation of document structure. Every specific,
  individual document which doesn't violate any of
  the constraints of the model is, by definition,
  valid according to that schema.Using the schema
  described (informally) above, a parser would be
  able to detect that the following address is not
  valid
• ltaddressgt
• ltnamegtYoussef Hijazilt/namegt
• ltstreetgt1469 alphada avelt/streetgt
• ltcitygtAkronlt/citygt
• ltstategtMAlt/stategt
• ltstategtOHlt/stategt
• ltzipgtbluelt/zipgt
• lt/addressgt
• It violates two constraints of our
  schema it does not contain exactly one ltstategt
  and the ZIP code is not of the proper form. A
  formal definition of this schema for addresses is
  presented in the syntax section.

17
How do I use graphics in XML?

• Graphics have traditionally just been
  links which happen to have a picture file at the
  end rather than another piece of text. They can
  therefore be implemented in any way supported by
  the XLink and XPointer specifications , including
  using similar syntax to existing HTML images.
  They can also be referenced using XML's built-in
  NOTATION and ENTITY mechanism in a similar way to
  standard SGML, as external unparsed entities.
• The linking specifications, however,
  give you much better control over the traversal
  and activation of links, so an author can
  specify, for example, whether or not to have an
  image appear when the page is loaded, or on a
  click from the user, or in a separate window,
  without having to resort to scripting.
• XML itself doesn't predicate or
  restrict graphic file formats GIF, JPG, TIFF,
  PNG, CGM, and SVG at a minimum would seem to make
  sense however, vector formats are normally
  preferred for non-photographic images

18
Examples

• http//www.cs.kent.edu/yhijazi/xml/question.xml
• http//www.cs.kent.edu/yhijazi/xml/home.html
• Dr. Arvind Bansals lectures
• http//www.cs.kent.edu/yhijazi/xml/xml-tutorials/
  a1.pdf
• http//www.cs.kent.edu/yhijazi/xml/xml-tutorials/
  a2.pdf
• http//www.cs.kent.edu/yhijazi/xml/xml-tutorials/
  a3.pdf
• http//www.cs.kent.edu/yhijazi/xml/xml-tutorials/
  a4.pdf