Introduction to XML and RSS Data Management Issues Types of data Structured Semi-structured Structured Data data is organized in entities ( tables) entities have attributes Current Database World – Structure Relational Database Management System (DBMS): everything is a table – Query languages: SQL – Software: MS Access, Oracle…. Example of a table (patients) Example of a group of tables MS Access Table Links World of Web Data – Easy document exchange – Unstructured (or poorly structured) data Everything is a document – No standard for query languages 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 RDBMS HTML B 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 Characteristics of SemiStructured Data structure is irregular: missing or additional attributes parts of data lack structure, e.g., images some may yield little structure, e.g., plain text Semi-structured Data Definition Data that is inherently self-describing and does not conform to an explicit and fixed schema is known as Semistructured Data Data Structure is contained within data itself Example of Semi-Structured Data name: Peter Wood email: [email protected], [email protected] [email protected] name: • first name: Mark • last name: Levene email: [email protected] [email protected] name: Alex Smith affiliation: StFX 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 An Example Movie Database IMDB-Irregularity In Structure • • • Different layout for movies and TV series Movie entries show Director, Writers and Stars TV entries show just Stars Captain Phillips (Movie) Lost (TV Series) Traditional Data Management Universe of Discourse Model of the UoD Query Database Post-Internet Data Management Universe of Discourse Retrieval? Query Data XML – An Embodiment of Semi-structured Data XML can be used to represent semistructured data What is XML? XML stands for EXtensible Markup Language XML is a markup language much like HTML (tags) XML was designed to describe data XML tags are not predefined. You must define your own tags 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. 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. <note> <to>John</to> <from>Mary</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note> 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. 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>, <i>, <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. 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. 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), comicML ( for describing comic characters) and musicXML (for musical notes) is written in XML. XML and Microsoft Office Starting with Office 2007, Microsoft changed the format of all Office documents. They are all saved in XML format. So a Word file is a ZIP folder holding a number of files including the text in XML format. Advantages: – Small file size – Compatibility with other software – Older Word files have the extension DOC, new ones use DOCX 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. All XML elements must have a closing tag Elements or tags are basic blocks of any XML document 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: 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> 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> 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> 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. 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 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. Comments in XML The syntax for writing comments in XML is similar to that of HTML. <!-- This is a comment --> 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 also in XML) attributes provide additional information about elements: <img src="computer.gif"> <a href="demo.asp"> XML Attributes Attribute values must always be enclosed in quotes <person sex="female"> XML Attributes Cont. <?xml version="1.0" encoding="UTF-8"?> <note date=12/11/2002> <to>John</to> <from>Mary</from> </note> ---------------------------------------------------------------------<?xml version="1.0" encoding="UTF-8"?> <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 is the XML declaration 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. 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. XML and Web Browsers Internet Explorer 5.0+, Google Chrome & Firefox support XML Viewing XML Files If you open an XML document in IE ( or other browsers), 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. Other Examples Viewing some XML documents will help you get the XML feeling. An XML CD catalog An XML plant catalog A Simple Food Menu This is some CD collection, stored as XML data This is a plant catalog from a plant shop, stored as XML data. This is a breakfast food menu from a restaurant, stored as XML data. 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. The XML Rules (Summary) 1. 2. 3. 4. 5. Single, unique root element Matching open/close tags Consistent capitalisation Correctly nested 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> Authoring XML Documents A basic XML document is an XML element that can, but might not, include nested XML elements. Example: <books> <book ISBN=“123456789”> <title> Second Chance </title> <author> Matthew Dunn </author> </book> </books> Use of XML and HTML together This is pure data in XML file This is a pure Format file to display the same data View the result with Google Chrome or IE 6+ 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) price name phone Store sid stock StoreBook Book title authors bid Converting Relational Database to XML (Cont’d) XML: <store> <sid> 123 </sid> <name> Chapter </name> <phone> 429-8976</phone> <book> <title> The Da Vinci Code</title> <authors> Dan Brown</authors> <bid> 987</bid> </book> <book>…</book> … </store> Examples example of database Example of database converted to XML XML representation of a sample Movie Database <?xml version="1.0" encoding="ISO-8859-1“ standalone=“yes”?> <IMDb> <Movies> <Movie> <Title> The Notebook</Title> <Actor> Ryan Gosling</Actor> <Actor> Rachel McAdams</Actor> <Director> Nick Cassavetes</Director> </Movie> <Movie> <Title> 300 </Title> <Actor> Gerard Butler</Actor> <Actor> Lena Headey </Actor> <Director> Zack Snyder</Director> </Movie> </Movies> <TVShow> FRIENDS </TVShow> <TVShow> Seinfeld </TVShow> </IMDb> Brief Introduction to RSS RSS ( Really Simple Syndication) 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". 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. 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. 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 Posdcast XML Joke Question: When should I use XML? Answer: When you need a buzzword in your resume.