Introduction to XML

XML is an acronym for eXtensible-Markup-Language. If you're at all familiar with HTML, you may be familiar with the concept of a markup language.

In casual conversation, we gather information very informally and it usually takes us a while to figure out what's important within a sentence. For example, If I were to ask you to tell me your schedule for the next 6 months, it might take a while. You might first start by saying "I have a meeting with Professor Boynton at 7:30pm on Monday, April 5, but I'm going to dinner before that at the Ram with friends at 6:00." And then continue with, "then on April 6th, I'm going home for a few hours before meeting with Professor Devinatz at Noon..." Eventually we would have to come up with a system if we wanted to make sure we didin't confuse days, times, and other information. Maybe we'd always say the date first, then the time, then the place, then other information. But how would we necessarily know when one thing started and one thing stopped? And if we were to record our conversation, would somebody else be able to understand so we wouldn't have to repeat the entire conversation in a different way?

I can tell you're already ahead of me. For the exact reason alluded to above, we have XML. Its acronym would have you believe XML is like something out of an LED-filled basement at MIT, but it is actually very simple. XML uses descriptive "tags" to say what kind of data is being given, what it pertains to, and where it starts and stops.

XML is used for description of data, whereas HTML is used for the display of data. HTML utilizes pre-defined tags (called Elements) whereas you can define your own tags in XML. We care about this in terms of Podcasting because Podcasting uses RSS which uses a certain agreed-upon set of XML tags.

We use XML to give information to iTunes and other Pod Catchers and Podcast Directories.

In order to use XML, we must understand its form. XML uses tags like HTML, but unlike HTML, all XML tags must have a closing tag. XML tags are also case-sensitive, meaning "<Tag>" is not the same as "<tag>." XML tags must be properly nested and must contain a single root tag. All attributes must be quoted. Below is a simple XML example for music albums...

It is important to note that the tags (the text between the < and >) are completely arbitrary. It is only in application of XML that we have strict definitions for what tags can be used and what kind of data they should contain.

We like to space things out as this example shows, but that is a matter of personal preference that just makes things easier to read and spot errors. XML has no standards about breaking lines or indentation. Your xml file could be entirely on one line.

One very important concept of XML is that of nesting. When you open a tag inside of another tag, you must also close it within that tag. For example, the following is valid: <album><title>Echoes</title></album> while the following is not: <album><title>Echoes</album></title>.

Now that the basic XML markup is known, we can add the RSS. Onward!