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patrickgross.org

What is XML?

XML is a universal data language.

Its primary purpose is to facilitate the sharing of data across different information systems.

XML means eXtensible Markup Language. It became a W3C Recommendation on February 10, 1998.

Points to consider

Before continuing, it is important to understand the above and not to make any confusions about what XML is. XML is absolutely not a new version of HTML:

XML is designed to store information.

HTML is designed to display information, it tells how information should be displayed.

HTML is to do something with the information: it is to display the information. XML is not to do something with the information, it does not display the information. It only describes the information.

HTML consists of known "tags", you would use these tags to tell what must be done with the data. For example, you would the HTML tag <table> to tell that you want to display a table. XML has no tags. You define your own tags. Because only you know what these tags mean, XML does nothing with these tags, it could not know what to do with it.

For example, HTML "knows what to do" when you use the tag <table>. It knows that it means that you want to display a table, and HTML thus does just that.In XML, you can create a tag named <table>. But XML does not know what it is. It does not know whether it means that you are storing information about a piece of furniture, or whether you want to store tabular data.

This does not make XML useless. You can "do something" with data described by XML. But you not "do something" with XML data using XML, you "do something" with XML data using for example HTML to display it.

Of course XML data can be displayed. There are many ways to do something with XML data. But it is not the mission of XML to display data or to do something with the data.

HTML is about displaying information, while XML is about describing information.

Why use XML to store data?

When you use a database management system to store data, you would for example enter a customer's name and address in a data input form, and the database management system can save this input into a database.

Depending on the database management system you would use, the way the data is stored differs.

This means that when you store data with the "X" database management system, a "Y" database management system is generally unable to understand anything about the data stored by the "X" system.

For example, I stored data using "X". The data I stored was like:

When I try to view this data with system "Y" I see:

Because systems "X" and "Y" use different languages to store the data and its description, the data stored using "X" would need to be transformed before system "Y" can handle it as expected.

Years ago, this was not a big issue, because people did not exchange a lot of data. Those who had to tended to solve the issue by agreeing to use the same systems.

But we are now in the Internet era. People now exchange a lot of data over the Internet now.

But the whole world would have a hard time agreeing that everyone must use system "X" rather than system "Y".

XML promoters say that the solution is that systems use the same language to describe and store data: XML.

They say that to store information such as:

You would store something like:

XML is easy to edit.

Look at the above example of information stored using the XML language. As you can see, it is very readable. It is actually much more readable than when such information is stored by system "X", remember:

XML is actually clear text, editable text, and not some binary-coded unreadable, uneditable information when you do not have the required specific software and system. with system "X", only "X" can understand the structure of the information, differientiate the structure of the information and the information content, and display it properly as a report or in a database entry form for editing. XML, on the contray, can be created and edited using any familiar text editor.



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Dimanche, 16 dÚcembre 2018