Talk:Four-valued logic

Do not merge, please

The many-valued logic article is very bad, there is a mix of Fuzzy logic and digital logic. This article should be about digital circuits. It could be defined as a subset of 9-valued "VHDL" logic (0,1,Z,L,H,X,U,-,W). — Preceding unsigned comment added by 193.165.212.242 (talk) 10:26, 17 October 2011 (UTC)

Model not Test

I've used "model" rather than "test" in my wordsmithing. Testing if a value is "unknown" is an interesting concept. However, this is a start! We are badly short of articles on the technical foundations for EDA software. Cje 17:06, 15 April 2006 (UTC)

Article Title

I'm not familiar with engineering, I'm a philosopher-logician, so take my question with a grain of salt. Is there a more specific name for the particular logic that this article refers to? The reason I ask is because "four-valued" usually means (in logic parlance) that the logic has a model theory with four semantic values. But there are lots of logics which are four-values in this sense: for instance, the weakest relevance logic FDE is a four-valued logic in the sense I just mentioned. So for clarity I was wondering if this particular logic has a more specific name.

Paraconsistent (talk) 23:04, 1 August 2008 (UTC)

true, false, unknown, and unknowable

What about 'true, false, unknown, and unknowable'?
http://www.orafaq.com/usenet/comp.databases.theory/2004/04/23/0957.htm
http://www.dbdebunk.com/page/page/1543772.htm
just-emery (talk) 21:57, 6 July 2009 (UTC)

Relation Database Model: true, false, (missing but) applicable, (missing and) inapplicable

Edgar F. Codd The Relational Model for Database Management Version 2 (1990) Table 8.2
When data is missing (e.g. an empty cell), the absence should be valued as either Applicable or Inapplicable to an expression depending on semantics.

P	not P
T	F
A	A
I	I
F	T

OR	T	A	I	F
T	T	T	T	T
A	T	A	A	A
I	T	A	I	F
F	T	A	F	F

AND	T	A	I	F
T	T	A	I	F
A	A	A	I	F
I	I	I	I	F
F	F	F	F	F

Move from 3-valued logic, Source

I see that this article has been moved from three-valued logic, much to the detriment of the latter article, and without anything on the talk page by the person who did it. This comment is from that article and placed here as well because it is about both articles and contains a useful source.

Three-valued logic using 1,0, and one of either "don't care" (X,-) or "high-Z" is basic first or second semester digital electronics. The {1,0,Z} encoding is commonly used on data busses and configurable I/O pins. It is essentially a multiplexing scheme. The {1,0,X} (aka {1,0,-} in VHDL) scheme is a metalogical extention - real devices don't have such a value value, but the representation is useful for design. (The actual device will have H,L, occasionally high-Z, or even no wire at all at places marked in the design as "don't care".) Using both {Z,-} is less usual in education, but does frequently happen when dealing with real devices which frequently have tristate outputs on their configurable I/O pins in designs where one also doesn't care about the state of some of the other pins. IEEE standard 1176 defines these states as well as some others less frequently used (9 states total- 1,0,unknown, weak-signal versions of these 3, high-Z, don't' care, uninitialized), and these are used in the VHDL standard (IEEE 1076). For instance see: http://www.ece.gatech.edu/academic/courses/spring2007/ece4170/DesignDocumentation/IEEE_1076.3.pdf pages 8-9 for an older version of the standard (the current version costs money, but the basics haven't changed).Enon (talk) 20:29, 23 February 2011 (UTC)

Which four?

The article says "Digital electronics theory supports four distinct logic values." Then it goes on to list way more than four. I understand that there is a nine-valued logic, but if there is a standard four-valued logic, it's not at all clear what that might be from this article. W0lfie (talk) 18:32, 11 October 2012 (UTC)

The object

The article tells us a lot about the manner in which the new object was conceived, but very little about the object itself. Was it noticed that the "four-valued logic" is nothing but the Boolean algebra P({N,B}), with T={N,B} and F the empty set? (& is the intersection, v the union). עוזי ו. (talk) 09:26, 27 May 2022 (UTC)

Correct. It is a Boolean algebra (structure) and described in that article as the power set on two atoms. The general reader may not know about that algebraic structure; this article sets out introductory comments, not presuming a learned audience.Rgdboer (talk) 03:55, 28 May 2022 (UTC)