Trouble is, real world data are fuzzy. A complex theory behind, in part based on technological limitations of the time... For semantic data to be usable, some constraints are needed.
The Closed World Assumption: O'Reilly - Safari Books Online (video, subscription required)
By: C.J. Date
"The Closed World Assumption (CWA) is an extremely important concept in the database world, despite the fact that it isn’t usually spelled out explicitly. Basically what it says is this:
Everything stated by the database, either explicitly or implicitly, is true; everything else is false.
This presentation explains the CWA in detail and shows why it’s preferred over its rival,The Open World Assumption (OWA). In particular, it examines the claims, sometimes heard, to the effect that the database community operates under the CWA while the semantic web community operates under the OWA. It also explains how “missing information” can be handled without any need for nulls or three-valued logic."
from the presentation, about relational model, based on Ted Codd
"TYPES are sets of things we can talk about;
RELATIONS are (true) statements about those things!"
- Types and relations are both necessary
- Thy are not the same thing
- They are sufficient (as well as necessary)
So database is a "named container for relational variables", a "logical system",
with axioms (tupples), rules of inference and theorems (queries)".
"Integrity is most important feature of databases"
"Integrity is most important feature of databases"
The Chris Date Seminar: The Closed World of Databases meets the Open World of the Semantic Web: Event Material
The Third Manifesto
"by Hugh Darwen and C.J. Date, our proposed foundation for future database systems"
(and language "D")
The Closed World of Databases Meets the Open World of the Semantic Web - ESIWiki
"...The important issue of missing information is something that can be interpreted differently between the CW and OW therefore how to deal with it and in fact the question of what is missing information will be explored..."
Open-world assumption - Wikipedia, the free encyclopedia
"In a formal system of logic used for knowledge representation, the open-world assumption is the assumption that the truth value of a statement may be true irrespective of whether or not it is known to be true. It is the opposite of the closed-world assumption, which holds that any statement that is true is also known to be true.
The Open World Assumption: Elephant in the Room | AI3:::Adaptive Information
'...open world assumption with facile summaries such as it means that a lack of information does not imply the missing information to be false..."
"...The important issue of missing information is something that can be interpreted differently between the CW and OW therefore how to deal with it and in fact the question of what is missing information will be explored..."
Open-world assumption - Wikipedia, the free encyclopedia
"In a formal system of logic used for knowledge representation, the open-world assumption is the assumption that the truth value of a statement may be true irrespective of whether or not it is known to be true. It is the opposite of the closed-world assumption, which holds that any statement that is true is also known to be true.
The open-world assumption (OWA) codifies the informal notion that in general no single agent or observer has complete knowledge, and therefore cannot make the closed-world assumption. The OWA limits the kinds of inference and deductions an agent can make to those that follow from statements that are known to the agent to be true. In contrast, the closed world assumption allows an agent to infer, from its lack of knowledge of a statement being true, anything that follows from that statement being false."
'...open world assumption with facile summaries such as it means that a lack of information does not imply the missing information to be false..."
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