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Introduction to XML and RSS

Introduction to XML and RSS. Data Management Issues. Types of data. Structured Semi-structured. Structured Data. data is organized in entities ( or tables) similar entities are grouped together (tables) entities in the same group have the same descriptions (attributes).

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Introduction to XML and RSS

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  1. Introduction to XML and RSS Data Management Issues

  2. Types of data • Structured • Semi-structured

  3. Structured Data • data is organized in entities ( or tables) • 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 table • Query languages: SQL • Software: MS Access, Oracle….

  5. Example of a table (patients)

  6. Example ofa group of tables

  7. Example of relationships

  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 analysis; 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 ( Cont’d) • Definition: Data that is inherently self-describing and does not conform to an explicit and fixed schema is known as Semi-structured Data • information is contained within data itself

  13. Semi-structured Data ( Cont’d) • 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@dcs.bbk.ac.uk, p.wood@bbk.ac.uk ------------------------------------------------------------------ • name: • first name: Mark • last name: Levene • email: mark@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 semi-structured 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 example: An actor’s 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. <note> <to>John</to> <from>Mary</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>

  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 <b>, <h1>, etc.). • XML allows authors to define their own tags and their own document structure. • The tags in the example above (like <to> and <from>) 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: <p>This is a paragraph • In XML all elements must have a closing tag, like this: <p>This is a paragraph</p>

  30. XML tags are case sensitive • Unlike HTML, XML tags are case sensitive. • With XML, the tag <Letter> is different from the tag <letter>. • Opening and closing tags must therefore be written with the same case: <Message>This is incorrect</message> <message>This is correct</message>

  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: <b><i>This text is bold and italic</b></i> • In XML all elements must be properly nested within each other like this: <bold><italic> This text is bold and italic </italic></bold>

  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: <root> <child> <subchild>.....</subchild> </child> </root>

  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. <!-- This is a comment -->

  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: <img src="computer.gif"> <a href="demo.asp">

  38. XML Attributes • Attribute values must always be enclosed in quotes <person sex="female">

  39. XML Attributes Cont. <?xml version="1.0" encoding="ISO-8859-1"?> <note date=12/11/2002> <to>John</to> <from>Mary</from> </note> ---------------------------------------------------------------------- <?xml version="1.0" encoding="ISO-8859-1"?> <note date="12/11/2002"> <to>John</to> <from>Mary</from> </note> • 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: <person sex="female"> <firstname>Anna</firstname> <lastname>Smith</lastname> </person> -------------------------------------------------- <person> <sex>female</sex> <firstname>Anna</firstname> <lastname>Smith</lastname> </person> 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 <table> 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 <?xml version=“1.0”?> <company id=“4859”> • <name>3Months.com</name> • <type>Web Development</type> • <address> <street>Wakefield st</street> <city>Wellington</city> <country>New Zealand</country> • </address> </company>

  47. Authoring XML Documents • A basic XML document is an XML element that can, but might not, include nested XML elements. • Example – A bookstore: <books> <book isbn=“123”> <title> Second Chance </title> <author> Matthew Dunn </author> </book> </books>

  48. price stock StoreBook Store Book authors name bid phone sid title 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 (Cont’d) • XML version of the Bookstore database : <store> <sid> 123 </sid> <name> … </name> <phone> … </phone> <book> <title>… </title> <authors> … </authors> <price> … </price> </book> <book>…</book> … </store>

  50. Examples • example of database • Example of database converted to XML

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