ITR3%20lecture%202:%20XML

1
ITR3 lecture 2 XML

• Thomas Krichel
• 2002-10-16

2
Structure

• URIs (we will come back to them in lecture 3)
• XML
• Sofix xml example

3
Literature

• Castro, Elizabeth (2001) XML for the World Wide
  Web Peachpit Press
• RFC 2396
• http//openlib.org/home/krichel/lis900gp02i

4
Uniform Resource Identifiers URI

• A Uniform Resource Identifier (URI) is a compact
  string of characters for identifying an abstract
  or physical resource.
• They provide a simple and extensible means for
  identifying a resource.

5
Universal concept of resource

• A resource can be anything that has identity.
  Not all resources are network retrievable''.
• The resource identifier identifies a resource,
  not necessarily the state in which the resource
  is in at a particular point in time.

6
Benefits of uniformity

• it allows different type of resource identifiers
  to be used in the same context, even when the
  mechanisms used to access those resources may
  differ
• it allows uniform semantic interpretation of
  common syntactic conventions across different
  types of resource identifiers

7
Benefits of extensibility

• allows introduction of new types of resource
  identifiers without interfering with the way that
  existing identifiers are used
• it allows the identifiers to be reused in many
  different contexts, thus permitting new
  applications or protocols to leverage a
  pre-existing, large, and widely-used set of
  resource identifiers.

8
transcribability

• The URI syntax was designed with global
  transcribability as one of its main concerns.
• A URI is a sequence of characters, not a sequence
  of bytes
• A URI may be transcribed from a non-network
  source, and thus should consist of characters
  that are most likely to be able to be typed into
  a computer
• A URI often needs to be remembered by people, and
  it is easier for people to remember a URI when it
  consists of meaningful components.
• Therefore it has a restricted set of characters,
  only US ASCII.

9
XML

• Stands for eXtensible Markup Language
• It is a recommendation by the World Wide Web
  Consortium (W3C). It is a new (1998) markup
  language that will transport a lot of contents
  over the Internet in the future.
• As its level of complexity goes it sits in
  between HTML and SGML.

10
Importance of XML

• XML will be, for the information industry, what
  the container is for international shipping.
• A uniform syntactic convention for the encoding
  of any piece of information expressed as textual
  data (i.e. as characters)
• Default character set is the UTF-8 encoding of
  Unicode.

11
HTML and XML

• HTML comes with predefined tags such as HTML,
  HEAD, TITLE, BODY, H1, H2, P, UL, LI, IMG, A, EM,
  B etc
• XML allows to use any tags.
• XML has not yet replaced HTML. It lacks native
  support for images and links.

12
XML and SGML

• SGML is the standard general markup language
  developed by an industry consortium
• Very complicated, to extent that there is no full
  implementation software ever written
• XML specs written by SGML aficionados who were
  aware of its problems

13
Original design goals

• XML shall be straightforwardly usable over the
  Internet.
• XML shall support a wide variety of applications.
• XML shall be compatible with SGML.
• It shall be easy to write programs which process
  XML documents.
• The number of optional features in XML is to be
  kept to the absolute minimum, ideally zero.
• XML documents should be human-legible and
  reasonably clear.
• The XML design should be prepared quickly.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance

14
Well-formed valid XML

• Every piece of data that wants be be xml has to
  obey a set of rules. Otherwise it is just not XML
• These rules ensure that the document is
  well-formed.
• In addition, the XML document may obey to other
  rules, in that case it is called valid.

15
XML element

• Syntax ltnamegtcontentslt/namegt
• Where name is the name of the element and
  contents is the contents of the element.
• ltnamegt is called the opening tag
• lt/namegt is called the closing tag
• Examples
• ltsexgtFlt/sexgt
• ltstorygtOnce upon a time there was. lt/storygt
• Element names are case-sensitive. They must start
  with a letter or _.
• Element names must not start with xml in any
  capitalization.

16
Attributes to XML elements

• Are name/value pairs that further qualify element
  contents
• Syntax ltname attribute_nameattribute_valuegt
  contentslt/namegt
• Example
• lttemperature unitFgt64lt/temperaturegt
• ltswearword languagefrgtconlt/swearwordgt
• Attribute names have to obey the same rules as
  element names.
• Attribute values must be surrounded by single or
  double quotes.

17
Empty elements

• Elements that are empty may be written as
  ltname/gt. This is a shorthand for ltnamegtlt/namegt.
• Empty names may have attributes.
• Example
• ltgrade valueA/gt

18
Processing instructions

• They are instructions to the software reading the
  XML.
• General syntax is
• lt?name attribute_name1attribute_value1
  attribute_name2attribute_value2 ?gt

19
comments

• Start with lt!--
• End with --gt
• May not contain a double hyphen
• Comments may not be nested i.e. no comments
  inside other comments.

20
Nesting elements

• Elements are allowed to contain other elements.
• Elements that contain other elements are called
  parent elements.
• Elements that are contained in another element
  are children of that element.
• Elements must be properly nested, i.e. child
  element closing tag must appear before parent
  element closing tag.

21
Root and prolog

• There must be one root element that contains all
  other element is the document.
• The prolog is what appears before the root
  element.
• The prolog may contain the XML declaration.

22
XML declaration

• The XML declaration is a special case of a
  processing instruction, it is written as
• lt?xml version1.0?gt
• If the XML declaration is there, it must be the
  first line.
• You can declare your character set in the XML
  declaration, like
• lt?xml version1.0 encodingucs-2?gt

23
Quote special symbols

• is written as amp
• lt is written as lt
• gt is written as gt
• is written as quot
• is written as apos
• Example ltstory contentshe pronounced the
  quotl-wordquot/gt

24
Document Type Definition DTD

• DTDs are a legacy SGML tool to further define and
  refine the contents of an XML document. XML can
  be defined by an SGML
• Still in use by the technologically retarded.
• Not covered here, because there are more powerful
  replacements.

25
Example application sofix

• Sofix is an XML based cataloging format for
  classical music CDs.
• It is named after Sophie C. Rigny.
• It is a creation of Thomas Krichel.
• Used for teaching purposes only.

26
Key concepts in Sofix

• Item an individual CD or a collection of CDs
  kept physically together (i.e. sold together)
• Work a piece of music as recorded on a CD. For
  simplicity, we do not distinguish between
  composition and recording of that composition.
• Track semantics associated with physical
  separation of tracks on the disk

27
Sofix in XML

• ltitemgt
• ltworkgt
• lttrackgt
• lt/trackgt
• lt/workgt
• ltitemgt

28
Sofix general rules

• Record all titles in English. If no English title
  provided, use a translation if it is obvious. If
  the translation is not obvious, use original
  language.
• All personal names as Lastname, Firstname
• Translatable names in English.

29
Contents of ltitemgt

• ltlabelnamegtname of labellt/labelnamegt
• ltnumbergtnumber of the CDlt/numbergt
• (followed by the works on the CD)

30
Contents of ltworkgt

• lttitlegttitle of the worklt/titlegt
• ltcompositionyeargt year when work was
  composedlt/compositionyeargt
• ltrecordingyeargt year when the recording was made
  lt/recordingyeargt
• ltcontributor rolecontributor rolegt name of
  contributor lt/contributorgt
• Possibly many contributor, followed by a series
  of tracks

31
Contributor roles

• alto, alto_sax, bariton, bass, bassoon,
  chamber orchestra, cello, choir, choir_master,
  clarinett,composer, conductor, flute,
  french_horn, horn, oboe, orchestra, organ, piano,
  piano_trio, prepared_piano, recorder, soprano,
  speaker, string_orchestra, string_quartett,
  viola, violin, xylophone

32
Attributes of lttrackgt

• lttitlegt full title as given on CDlt/titlegt
• lttimegt minutessecondslt/timegt
• where minutes and seconds are numbers.

33
http//openlib.org/home/krichel

• Thank you for your attention!