I've been told that in Shadowrun 2e, there was a tree of skills that connected to every other skill (with varying degrees of distance), and in order to default you would take a die penalty to move from one skill to its sibling on the tree.
Because all of the skills are connected to each other, it would be possible to use Swimming to do anything if you had a large enough dice pool, such as firing a gun.
This Review on rpg.net says that the web does exist and gives an example of its mechanic:
A skill web provides a series of defaults with each point of distance adding +2 to the target number. So, if a character has no skill levels in Firearms they can default from Quickness at +4, or Gunnery at +2. Some of the defaults can get quite elaborate, especially from Intelligence which can default to Physical Sciences at +6 then to Biotechnology at an additional +8. Or you can simply follow the path directly from Intelligence at +10.
I'm really curious about this mechanic, but the internet sources seem a bit lacking, and hunting down the book seems difficult (the copies appear to be either mint which costs over $100, and not-even-close-to-mint for cheaper).
Is it really possible to default to Swimming from any other skill? If so, how would your reconcile the game mechanic with reality? (I'm a really good swimmer so I'm going shoot you okay with this AK-47).