XML e Xtensible Markup Language What is XML

XML – e. Xtensible 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?

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 • <Movie> is different to <movie> • All tags must be balanced (i. e. open an close tag) • In html, not all tags need to be closed • <LI> - List item tag • <HR> - Horizontal line • <P> - Paragraph

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 <Movie> <Title>Gone With the Wind</Title> <Actor>Clark Gable</Actor> <Actor>Vivien Leigh</Actor> <Release. Date>1939</Release. Date> <Length>238</Length> </Movie>

What is XML? • The tags form a hierarchical “tree” structure

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.

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.

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.

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

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

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.

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.