Irmo: That is pretty much what I was getting at.
And NW_Kohaku, I think that could work. Though what in what I detailed last time I posted, if one was to implement that, you could have glass blowers coming into being even if the civ doesn't have any or any access to sand provided you have sand in the fort you just founded, as without modeling knowledge, everyone knows how to do everything and could do it.
But let's say we also add "knowledge" into the mess... which could facilitate the "invention" sort of thing and make for a more interesting world history. I think I have some ideas for "invention" sort of... and which I will try to represent with an example of a hypothetical situation in DF were it to have magical game mechanics to do this...
Let's say knowledge mechanics like I sort of mention
here exist in the game. Say there is a distinction between "knowing of" and "knowing how". Also, say there is a game mechanic in place that allows for professionals to spend some of their free time to "play and experiment".
Say you are playing a fort that started off with dwarves that know of and know how to make pottery. Such an industry involves kilns or firing pits, which at least one of your dwarves knows how to build. Say Urist McCurious Kiln Operator accidentally or intentionally sticks some native copper ore into the kiln while working one day. Say the kiln has a chance (or maybe it just can, period) of burning hot enough to melt copper. Urist notices that there is some stuff that is melting out of the rock. Urist happens to like working with stone, and decides to play with the resulting heated rock and shiny orange stuff that melted out of it. Urist, being creative and intelligent soon realizes that hammering the orange stuff yields a substance that is malleable, can hold an edge, and looks pretty if polished. In this way, knowledge of refining ores and copper working is born and can be disseminated by Urist to the rest of the populace. Pretty much anyone in the fort would automatically gain knowledge of the existence of copper, and copper tools and stuff (depending on how this is modeled), but knowledge of how to work with copper would have to be taught by Urist.
Moving on, perhaps the local mason, Thikod, knowing of copper and that it requires a place to heat it, decides (perhaps the player orders him to... I dunno) to make furnace more appropriate for the ore extraction, that burns hot enough to melt copper more consistently. Say Thikod has a chance of building a furnace hotter than it needs to be to melt copper... Thikod then gains knowledge (invents) this model of furnace, and can disseminate this knowledge to others. Anyone with this knowledge could possibly build this furnace of this design and characteristics. Perhaps this furnace, since it could burn hotter than needed, would be able to smelt iron ores when someone decides to experiment with that...
Well, this kind of stuff would be very hard to model, but it is food for thought... I dunno. Maybe it would be too much to do.
And this sort of contains a tech-tree of sorts, though not a restrictive one. In this example, discovery of copper working (generation of "knowledge of" and "knowledge how" of copper working) requires a firing chamber of sorts (kiln or fire pit) operated by someone with a wild hair up his butt that decides to put a native copper rock in there and see what happens. And invention of a furnace able to melt copper requires a builder with motivation to make/design* one who knows of copper working and maybe even knows how to work copper. I dunno. This all seems a bit too convoluted... and would require a hard-coded, well-researched tree of what knowledge could lead to what knowledge... but again, it's food for thought!
*hmmm! that would be another use for the "designing phase" for furnaces and other buildings like trade depots that require designing by a dwarf... maybe everything should have a design phase that not only determines quality of a product, but introduces the opportunity for a dwarf to experiment or improve or generate a design.
Also... this kind of a tech tree might not be too restrictive depending on how things are done...
Like, say Urist never tried anything with copper ore. Maybe Thikod made a hot-burning furnace for another reason (like for glazing or glass-making), and someone tried iron ore in it and found out iron working, bypassing copper or bronze.
Oh, and if this were to be in the game somehow, I'd make it so that pretty much everyone starts with some basic level of technological development... like dwarves would be guaranteed to have people who know how to make picks, and work copper, and stuff in the first place.