Web Feature Services (WFS) is an OGC standard method to access and, in some cases, edit (WFS-T) vector data over the Internet. When you need full attribute tables, local style control, or editing, WFS is the way to go. Like most other web services, the biggest advantage over a local layer is that you don't have to copy or load the whole layer at once.
Tip
If you just need to view the layer, often WMS or a Tile service (described in other recipes within this chapter) are more efficient.
You need the URL of a WFS service to use and a working Internet connection. We will use the public Mapserver demo website (http://demo.mapserver.org/).
Tip
To try WFS-T, which involves editing, you will need to get access to a service (typically, password protected) or make one yourself. Do you need a WFS-T test server? This is a great case where OSGeo-Live comes in handy, as you can run your own WFS-T server in a virtual machine at http://live.osgeo.org.