Excellent researching Ionel...
Let me expand on some points...
The first link isn't a "real" maru system. It is a form of "faux maru" and and simply reflect that standard "t&g" found in most "jointed floors" like "
Parquet." Many of these are actually toe-nailed to the substrate, though I have never recommended this practice in traditional work for parquet floors.
The second linked video is an excellent snap shot of floor boards being fitted into the joist and connecting girt beam work of what appears to be a properly fashioned 청마루 in a modern rebuilding style of 한옥 (Hanok).
The floor can be placed on continuous sub floor (like earthen floor) or over some type of supporting system (joist, etc).
Actually, to be a real maru system, it must be fitted into beam work of some form. The other would be something else...like parquet. Also, just floating this on a simple earth or gravel floor without understanding other possible challenges could lead to a very warped and buckled floor. It can be done, but I don't want readers to believe it is as simplistic as just putting a wood floor over an earth floor, which it can be...but not without understanding the different systems, how they work, and how they must be dealt with if they "misbehave" for some reason.
In the image attached, boards type 1 and possibly 2 need to be supported by the existing structural members or can actually be the supporting members themselves. Board type 4 is larger (why is below) than type 3 boards an lacks one tongue/groove. Board type 2 is notched (red ellipse) for receiving board 4 after previously placing there one by one all type 3 boards and forcing them horizontally (to the left) until all space is filled. Board 4 is placed into position and hammered vertically until best fit.
Lets see if I can assist in defining this, having built them...
The only thing that can be an actual board (if it is going to be an actual maru and not simply a "floating" parquet style floor) is #3 and #4, with #4 being your "key" or locking board (these are sometimes jointed with special sliding tenon or toe-nail peg in some very rustic forms of 한옥.) Board #3 can be free tenoned, tongued, or bevel jointed depending on system.
"BEAMS" #1 and #2 are actually the supporting system you speak of. The members that run between posts (there are several regional style of 한옥 (Hanok) with different subtle variances) are a form of "Connecting Girt," what in some European/America timber framing is sometimes call a "Summer Beam," or the "Bent Girt" (but the Asian modalities don't really often follow a "bent system" per se but a grid.)
By and large, this seems like an elegant system...
This is most true, and a very natural way to employ wood with limited ($$) power tools or only hand tools (but labor intensive as stated.) I would point out that there is much more to this process than what is seen in the linked video and photos. I insist that students be able to "read wood" (understand intimately the grain patterns and what they reflect about the piece of wood, how to deal with them, where the top of the tree vs
root, where the bark was and the pith is...etc) before attempting such as
project as this for themselves, and never doing it for others ($$) unless they have mastered at least the foundation skills of traditional green woodworking.
This is a wondrous craft, but could yield deep and expensive frustration if not understood in its entirety and how the different systems work in concert with one another...For example, you can't tell from these photos how the boards are oriented in the floor. I can tell you from here that some of these "replica Hanok" are being built by Korean "general contractors" and not trained traditional builders as they have lost the traditional (and more enduring) beam and board orientations. These are the nuances that make a traditional system work and modern "reinterpretation" fail or not work properly...