Types of GML

As with many of the OGC standards we have studied, GML is still evolving. Once upon a time there was GML version 1 (no one currently uses that). Then there was version 2 (or GML2). GML2 is technically obsolete. However, as we saw in lesson 3, it is still used by WFS 1.0 servers as the default output format. Finally, there is GML version 3 (GML3) which is the default output for WFS 1.1. There are still not a lot of servers out there that support WFS 1.1 yet so not many people have really played with GML3. Another reason why many haven't played with GML3 is because the specification is the size of a small encyclopedia (550 pages)! For this lesson we will concentrate on a simper dialect of GML known as the Simple Features Protocol which was developed to get around exactly this problem.
The advantage of the Simple Feature Protocol is that it contains the benefits and fixes that have been found to be needed in GML2, but provides us with some protection from the extreme ability to encode absolutely everything that GML3 gives us. You might think that being able to encode everything is a good thing (and as an end user it is).