Page 1 of 11 Craig Schock, 2003 XML – eXtensible Markup Language What is XML? What is the big fuss about XML? Will XML save the world? Limitations of XML.
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Page 1 of 11 Craig Schock, 2003 XML – eXtensible Markup Language What is XML? What is the big fuss about XML? Will XML save the world? Limitations of XML What are web services and how do they relate to XML?
Page 2 of 11 Craig Schock, 2003 What is XML? XML is a tag based language Html is also a tag-based language XML is similar to HTML, but there are many differences Tags are case-sensitive is different to All tags must be balanced (i.e. open an close tag) In html, not all tags need to be closed - List item tag - Horizontal line - Paragraph
Page 3 of 11 Craig Schock, 2003 What is XML? In Html, all of the tags are defined In XML, the user can define his/her own tags In Html, the tags are all focused on displaying data In XML, tags describe the data Gone With the Wind Clark Gable Vivien Leigh 1939 238
Page 4 of 11 Craig Schock, 2003 What is XML? The tags form a hierarchical “tree” structure
Page 5 of 11 Craig Schock, 2003 What is the Big Fuss About? One of the big problems with applications is that they often save their data in a proprietary format. If they saved their data in an “open” form, people could easily take their data and use it in other applications It is in the interests of application developers to keep people using their software and not migrating to other software packages. This has placed quite a strain on application users. They are often “locked in” to a particular solution with no option for migrating to another solution.
Page 6 of 11 Craig Schock, 2003 Data Portability XML is an “open” format. Data is stored using XML tags Data can be shared between applications as long as the applications involved can save their data in XML form Users are then free to use their data with whatever application they choose.
Page 7 of 11 Craig Schock, 2003 Will XML save the world? Unfortunately, XML has been VERY over-hyped For some reason, people who are involved with technology are continually looking for the “silver bullet” There is no such thing as a silver bullet! No single tool will solve all problems There’s no question, portability of data is a good thing, but not all problems today are centered around data portability.
Page 8 of 11 Craig Schock, 2003 Limitations of XML It is a way of representing data. It is not a programming language Although, some people are trying to turn it into a programming language It can only represent hierarchical, tree like structures XML cannot be (directly) used to represent lattice structures XML data takes up a lot of space All data is represented as ASCII
Page 9 of 11 Craig Schock, 2003 Web Services When a user makes a request to a web-server it sends back an HTML web page in response to the message HTML only describes how to display the data It does not describe what the data is A human can understand what he/she is seeing on the screen, but a computer program cannot easily pick out pieces of data There’s a lot of information on the net, but its usage is limited because it is tied to HTML
Page 10 of 11 Craig Schock, 2003 Web Services and XML The idea behind web services and XML is that when a request is made to a web-server, it can respond by sending back XML If the user wants to see the data, their browser converts the XML to HTML for display purposes. If the request comes from a computer program, the program can pick out relevant data based on the XML tags The XML data can be used in ways other than just display.
Page 11 of 11 Craig Schock, 2003 Problems with Web Services Web services are an interesting idea, but there are some problems Many web sites make their money by selling advertising. Advertising is difficult to filter out because the browser cannot tell the difference between advertising and the real content With XML and web services, the content would be easy to separate from the advertising Users would typically choose to avoid the advertising and the revenue would go away.