Introduction to XML and RSS

1
Introduction to XML and RSS

• Data Management Issues

2
Types of data

• Structured
• Semi-structured

3
Structured Data

• data is organized in entities
• similar entities are grouped together (tables)
• entities in the same group have the same
  descriptions (attributes)

4
Current Database World

• Structure
• Relational Database Management System (DBMS)
• everything is a relation
• Query languages SQL
• Software MS Access, Oracle.

5
Example of a table (patients)
6
Example ofa group of tables
7
(No Transcript)
8
World of Web Data

• Easy document exchange
• Unstructured (or poorly structured) data
• Everything is a document
• No standard for query languages

9
World of Web Data

• Example
• An organization A publishes financial data on its
  web pages (HTML), generated from DBMS.
• A second organization B wants some financial
  analyses can access only web data.

A
B
HTML
RDBMS
10
Semi-structured Data

• data can be of any type
• not necessarily following any format
• does not follow any rules
• is not predictable
• examples include
• text
• video
• sound
• images

11
Characteristics of Semi-Structured Data

• structure is irregular missing or additional
  attributes (labels)
• parts of data lack structure, e.g., images
• some may yield little structure, e.g., plain text
  

12
Semi-structured Data ( Contd)

• Data that is inherently self-describing and does
  not conform to an explicit and fixed schema is
  known as Semistructured Data
• information is contained within data itself

13
Semi-structured Data ( Contd)

• The structure of the data is rapidly and
  dynamically changing
• It includes data as found in several application
  areas such as Web Information Systems and Digital
  Libraries

14
Example of Semi-Structured Data

• name Peter Wood
• email ptw_at_dcs.bbk.ac.uk, p.wood_at_bbk.ac.uk
• --------------------------------------------------
  ----------------
• name
• first name Mark
• last name Levene
• email mark_at_dcs.bbk.ac.uk
• --------------------------------------------------
  ----------------
• name Alex Smith
• affiliation StFX

15
IMDb A Motivating Example

• The Internet Movie Database is a classical
  example of a collection of semistructured data
• Although the information pertaining to different
  movies may be essentially similar, their
  structure may be different!
• Let us consider an example movie database

16
An Example Movie Database
17
Irregularity In Structure

• Example Some movie may annotate information
  about the actors, choreographer, director and
  producer, while another movie may annotate
  additional information about the lyricist and the
  music director

18
Irregularity In Structure

• The same kind of data may be typified differently
• For ex An actors name may be represented as a
  string or as a tuple (first_name, last_name)
• Since data gets added to this database
  dynamically, the structure of the database as a
  whole, also keeps changing dynamically

19
Traditional Data Management
Universe of Discourse
Model of the UoD
Database
Query
20
Post-Internet Data Management
Universe of Discourse
Retrieval?
Data
Query
21
XML An Embodiment of Semistructured Data

• XML can be used to represent semistructured data

22
What is XML?

• XML stands for EXtensible Markup Language
• XML is a markup language much like HTML
• XML was designed to describe data
• XML tags are not predefined. You must define your
  own tags

23
The main difference between XML and HTML

• XML and HTML were designed with different goals
• XML was designed to describe data and to focus on
  what data is.
• HTML was designed to display data and to focus on
  how data looks.
• It is important to understand that XML is not a
  replacement for HTML.

24
XML does not DO anything

• Maybe it is a little hard to understand, but XML
  does not DO anything. XML is created to
  structure, store and to send information.
• The note has a header and a message body. It also
  has sender and receiver information. But still,
  this XML document does not DO anything. It is
  just pure information wrapped in XML tags.
  Someone must write a piece of software to send,
  receive or display it.

John Mary
Reminder Don't forget
me this weekend!
25
XML is free and extensible

• XML tags are not predefined. You must "invent"
  your own tags.
• The tags used to mark up HTML documents and the
  structure of HTML documents are predefined. (like
  , , etc.).
• XML allows authors to define their own tags and
  their own document structure.
• The tags in the example above (like and
  ) are not defined in any XML standard.
  These tags are "invented" by the author of the
  XML document.

26
XML is used to Exchange Data

• With XML, data can be exchanged between
  incompatible systems.
• In the real world, computer systems and databases
  contain data in incompatible formats. One of the
  most time-consuming challenges for developers has
  been to exchange data between such systems over
  the Internet.
• Since XML data is stored in plain text format,
  XML provides a software- and hardware-independent
  way of sharing data.

27
XML can be used to Create new Languages

• XML is the mother of WAP( Wireless Application
  Protocol) and WML (The Wireless Markup
  Language).
• WML used to markup Internet applications for
  handheld devices like mobile phones.
• MathML, for creating Math formula and CML
  (Chemical Markup language) is written in XML.

28
XML Syntax

• The syntax rules of XML are very simple and very
  strict. The rules are very easy to learn, and
  very easy to use.
• Because of this, creating software that can read
  and manipulate XML is very easy to do.

29
All XML elements must have a closing tag

• With XML, it is illegal to omit the closing tag.
• In HTML some elements do not have to have a
  closing tag. The following code is legal in HTML
• This is a paragraph
• In XML all elements must have a closing tag,
  like this
• This is a paragraph

30
XML tags are case sensitive

• Unlike HTML, XML tags are case sensitive.
• With XML, the tag is different from the
  tag .
• Opening and closing tags must therefore be
  written with the same case
• This is incorrect
  This is correct

31
All XML elements must be properly nested

• Improper nesting of tags makes no sense to XML.
• In HTML some elements can be improperly nested
  within each other like this
• This text is bold and italic
• In XML all elements must be properly nested
  within each other like this
• This text is bold and
  italic

32
All XML documents must have a root element (tag)

• All XML documents must contain a single tag pair
  to define a root element.
• All other elements must be within this root
  element.
• All elements can have sub elements (child
  elements). Sub elements must be correctly nested
  within their parent element
• .....

33
With XML, white space is preserved

• With XML, white space is preserved
• With XML, the white space in your document is not
  truncated.
• This is unlike HTML. With HTML, a sentence like
  this
• Hello              my name is John,
• will be displayed like this
• Hello my name is John,
• because HTML strips off the white space.

34
Element Naming

• XML elements must follow these naming rules
• Names can contain letters, numbers, and other
  characters
• Names must not start with a number or punctuation
  character
• Names must not start with the letters xml (or XML
  or Xml ..)
• Names cannot contain spaces

35
Element Naming

• Any name can be used, no words are reserved, but
  the idea is to make names descriptive
• XML documents often have a corresponding
  database, in which fields exist corresponding to
  elements in the XML document. A good practice is
  to use the naming rules of your database for the
  elements in the XML documents.

36
Comments in XML

• The syntax for writing comments in XML is similar
  to that of HTML.

37
XML Attributes

• XML elements can have attributes in the start
  tag, just like HTML.
• Attributes are used to provide additional
  information about elements.
• In HTML (and in XML) attributes provide
  additional information about elements

38
XML Attributes

• Attribute values must always be enclosed in
  quotes

39
XML Attributes Cont.

• John
• Mary
• --------------------------------------------------
  --------------------
• John
• Mary
• The error in the first document is that the date
  attribute in the note element is not quoted.
• The first line in the document - the XML
  declaration

40
Use of Elements vs. Attributes

• Data can be stored in child elements or in
  attributes.
• Take a look at these examples
• Anna
• Smith
• --------------------------------------------------
  
• female
• Anna
• Smith
• In the first example sex is an attribute. In the
  last, sex is a child element. Both examples
  provide the same information.

41
Errors in XML will stop the XML program

• The World Wide Web Consortium (W3C) XML
  specification states that a program should not
  continue to process an XML document if it finds a
  validation error. The reason is that XML software
  should be easy to write, and that all XML
  documents should be compatible.
• With HTML it was possible to create documents
  with lots of errors (like when you forget an end
  tag). One of the main reasons that HTML browsers
  are so big and incompatible, is that they have
  their own ways to figure out what a document
  should look like when they encounter an HTML
  error.
• With XML this should not be possible.

42
XML and Browsers

• Netscape 6 or higher supports XML
• Internet Explorer 5.0 or higher supports XML

43
Viewing XML Files

• If you open an XML document in IE, it will
  display the document with color coded root and
  child elements. A plus () or minus sign (-) to
  the left of the elements can be clicked to expand
  or collapse the element structure.
•  
• If you want to view the raw XML source, you must
  select "View Source" from the browser menu.
• If an erroneous XML file is opened, the browser
  will report the error.

44
Other Examples

• Viewing some XML documents will help you get the
  XML feeling.
• An XML CD catalogThis is some CD collection,
  stored as XML data
• An XML plant catalogThis is a plant catalog from
  a plant shop, stored as XML data.
• A Simple Food MenuThis is a breakfast food menu
  from a restaurant, stored as XML data.

45
Why does XML display like this?

• XML documents do not carry information about how
  to display the data.
• Since XML tags are "invented" by the author of
  the XML document, browsers do not know if a tag
  like describes an HTML table or a dining
  table.
• Without any information about how to display the
  data, most browsers will just display the XML
  document as it is.

46
The XML Rules (Summary)

• Single, unique root element
• Matching open/close tags
• Consistent capitalisation
• Correctly nested elements (no overlapping
  elements)
• Attribute values enclosed in quotes
• No repeating attributes in an element

• 3Months.com
• Web Development
• Wakefield st
• Wellington
• New Zealand

47
Authoring XML Documents

• A basic XML document is an XML element that can,
  but might not, include nested XML elements.
• Example
• Second Chance
• Matthew Dunn

48
Converting Relational Database to XML

• Example Export the following data into XML and
  group books by store
• Relational Database
• Store (sid, name, phone)
• Book (bid, title, authors)
• StoreBook (sid , bid, price, stock)

49
Converting Relational Database to XML (Contd)

• XML

50
Examples

• example of database
• Example of database converted to XML

51
XML representation of a sample Movie Database

• standaloneyes?
• The Notebook
• Ryan Gosling
• Rachel McAdams
• Nick Cassavetes
• FRIENDS
• Seinfeld

52
RSS ( Really Simply Synidication)

• RSS is a family of web feed formats used to
  publish frequently updated digital content, such
  as blogs, news feeds or podcasts.
• Users of RSS content use programs called feed
  "readers" or "aggregators" the user "subscribes"
  to a feed by supplying to their reader a link to
  the feed the reader can then check the user's
  subscribed feeds to see if any of those feeds
  have new content since the last time it checked,
  and if so, retrieve that content and present it
  to the user.
• RSS formats are specified in XML (a generic
  specification for data formats). RSS delivers its
  information as an XML file called an "RSS feed,"
  "webfeed," "RSS stream," or "RSS channel".

53
RSS Feed representation

• On Web pages, web feeds (RSS) are typically
  linked with the word "Subscribe", an orange
  square,
• or a rectangle with the letters
• Or
• Many news aggregators such as msnbc.com publish
  subscription buttons for use on Web pages to
  simplify the process of adding news feeds.

54
Podcasting

• A podcast is a media file that is distributed
  over the Internet using syndication feeds, for
  playback on portable media players and personal
  computers.
• The term "podcast" is derived from Apple's
  portable music player, the iPod.
• Though podcasters' web sites may also offer
  direct download or streaming of their content, a
  podcast is distinguished from other digital audio
  formats by its ability to be downloaded
  automatically, using software capable of reading
  feed formats such as RSS.

55
Podcasting

• Podcasting is an automatic mechanism whereby
  multimedia computer files are transferred from a
  server to a client, which pulls down XML files
  containing the Internet addresses of the media
  files. In general, these files contain audio or
  video, but also could be images, text, PDF, or
  any file type.
• Example StFX Podcasts

56
XML Joke

• Question When should I use XML?
• Answer When you need a buzzword in your resume.