Model B takes Model A to a much more in depth, and actually uses Jungian functions as they were intended to be used. Model was first developed by Alessandro Bukalov in the early 90s. And yes I am extremely bored, otherwise I wouldn't be writing about Socionics.
There is are a few fundamental problems in the way that functions are assigned in MBTI and Socionics. The first is that with every action that a person's body produces, there is an mental deterministic reason for the action. Every willful action performed is preceded by some mental thought process based around the area of action. Another is that in Model A, there is a failure to realize that the expertise of a function is in every single individual; not just select individuals. What this means is, a person in Model A that would be considered "aggressive" or "action-oriented" would usually have the function Se assigned to them as being dominant. But what of the people that are more "dormant" or "restrained". Most would assume that "Si" would be the function assigned to these traits, but there is a problem with this; as these are positive/extraverted traits that are overtly identifiable. These two issues are the main reasons that Bukalov formed a 16 component model to assign both introverted and extraverted parts of a functional continuum. The 3rd thing, and perhaps the most important thing, is that the model shows the flaws in the J/P issue; and gives them overt functional basis. Usually the behaviors that are idiotically attributed to J/P are usually identified by the quadra's valued perceiving function.
What this means:
It is sort of misleading to identify functions by their ego traits, as information metabolism causes a function to work on several different layers of a person's identity.
-Ti/+Te v.s. +Ti/-Te
-Ti/+Te: Alphas and Deltas use this functional continuum. It is a judging function, meaning that the role of this set of functions isn't so much the area of information that they are using, but more how they deal with the information. The functions main basis is reductionism(not in a philosophical context). The function involves breaking information down. Above all else, the function is a purifier, always looking at the whys and hows; trying to find some sort of explanation to the phenomenon that they are presented with. Because of this, they have a hard time "accepting" information provided as a standard. This is especially true in the case of Alphas(I'll get to this later). In certain contexts, can create awkwardness and social angst due to an inability to accept social decorum as a standard.
+Ti/-Te: Betas and Gammas use this functional continuum. It is a judging function so it doesn't have anything to do with the area of expertise. The functions involves common sense intelligence. This function attempts to find the "proper" way to do something; using the social decorum and repetitious logic as a backbone for solving problems. They usually believe there is a right way to proceed; and this right way is usually based upon a pattern of accepting certain standards.
+Fi/-Fe v.s. -Fi/+Fe
This is the dualized function of -Ti/+Te; which means there is a direct relationship between how they work. This function maintains the logical uncertainty of -Ti/+Te, but brings it into the field of subjective emotions towards certain objects or areas. Usually this results in a lack of subjective emotional "rules" in which to base their subjective emotions upon. This usually results in "universalism". These people have a hard time creating a emotional database of things that they like or dislike completely. This usually results in people that value this function attempting to treat everyone equal without submitting to one philosophy or another(because of the human aspect of things, this will not always be 100% accurate; more of a demeanor). This sometimes can create problems for people with this function because they are unwilling to bend to the will of one person while leaving another stranded.
A dualized function based on +Ti/-Te, which means there is a direct relationship with how they work. The same standard that existed in the logical side of this function are brought into the subjective emotional world. This usually results in a flaw finding demeanor, in which they are looking for a perfected version of the object of desire. Problem with this function is it can(note the word can) cause relationship issues due to the person's inability to accept flaws. For some this may result in the person trying to correct their spouse, in others possibly a complete disconnection/break up. Romantics who constantly dream for the perfect person to come along.
Note on these function: Everyone probably experiences them all from time to time, which is why I do not believe in exact categories and static types.
+Ni/-Ne v.s -Ni/+Ne
This function is shared by Gammas and Deltas. It is a perceiving function so it involves the area in which the person projects themselves in. This function is more or less dependent on looking at themselves as "part of the typical mold". They tend to think of the world as a wonderful place in which they can fit in and enjoy the wonderful little eccentricities that the world has to offer. They are people person's, who are usually loyal and do not like to step on the toes of people. There is a certain level of confidence projected in this, as they feel like the world is a wonderful place in which they are a part of. Enemy of the alternate route(unless the alternate route is something that catches on in the social world). This doesn't mean they aren't creative, just don't like to project change into something they believe is beautiful and wonderful already.
A function that is shared by Alphas and Betas. It is a perceiving function so it involves the area in which the person projects themselves in. Typically enjoys "breaking the mold". Looks at the world as uninteresting and too normal/static. Individualistic, usually believing that they have the potential to be better than the average and mediocre. This does not necessarily mean that they don't have groups of friends and do not like to fit in sometimes(more of a demeanor). Not exactly stable, possibly going in repetitious patterns between aggressive and withdrawn(possibly due to confidence issues). Looks at the world as a tool to reach the higher self, the more creative self. Can be overly selfish given the right circumstances.
Dualized function based on +Ni/-Ne, which means it has a direct relationship. Brings the philosophical energy of the intuitive dualized function into the material world. Static, stabilizing energy. Usually having a lot of willpower because of their loyal belief into their mission following the energy of the social decorum. Wins battles by sticking to the plan. Easily socializes, genuinely feels at one with everyone else.
Dualized function based on -Ni/+Ne. Brings philosophical energy of the intuitive function into the material world. Aggression, creative energy. Usually has a strong desire to be different, and goes head first into it. Can be rather bi-polaresqe with their energy patterns, the massive amounts of energy they put into their creative work can often not be sustained. Often at times finds hidden energy to bring themselves to another level. Can be rather eccentric with their believes and how they express them. In certain scenarios can be selfish, always wanting to get over the average results.
Note: Everyone uses all of these functions to some degree.