Knowledge Representation Questions and Answers

Answer: D

Early networks used links whose meaning varied between systems and sometimes within one, so what a diagram entailed was unclear. Giving them a translation into first order logic settled the matter and showed they were a notational variant of a fragment of it. Relations were exactly what they represented, and memory and scale were practical issues. A representation whose inferences cannot be stated precisely cannot be debugged, which is why formal semantics matters even for an informal looking notation.

Answer: A

A frame groups everything known about an object or a category into named slots with values, defaults and attached procedures, which matches how people organise knowledge and makes retrieval efficient. Frames and semantic networks are largely notational variants of each other. Temporal windows, scope boundaries and logical sentences are different notions. Organising knowledge around objects rather than around sentences is a difference of packaging that nevertheless changes what is easy to do with it.

Answer: B

Stating that birds fly once, and that a canary is a bird, saves stating it for every species, and the inference is a matter of following the is a links upward. It is the principal economy such representations offer. Run time transfer, system migration and caching are different notions. Storing a property at the most general level at which it holds is an economy of expression whose price is the difficulty of handling exceptions.

Answer: C

Penguins are birds and do not fly, so the inherited default must be overridden, which means the representation is no longer monotonic and adding a fact can retract a conclusion. Handling that properly requires default or non-monotonic logic. Exceptions are representable, circularity is a separate hazard, and new categories are one workaround among several. A representation that is convenient until exceptions appear, and exceptions always appear, is the recurring difficulty of this area.

Answer: D

Classical logic is monotonic: adding premises never invalidates a conclusion, whereas real reasoning from defaults must retract when an exception is learned. Learning that Tweety is a penguin withdraws the conclusion that Tweety flies. Certainty decay, directionality and operator properties are different notions. Departing from a property so basic that classical logic takes it for granted is what makes this family of logics both necessary and difficult.

Answer: A

Circumscription formalises the assumption that things are as normal as the facts permit, by minimising the set of objects satisfying an abnormality predicate. Birds fly unless abnormal, and only known exceptions are abnormal. Scope limitation, fragment restriction and inference bounding are different techniques. Making the assumption that nothing is unusual unless stated into a formal minimisation is what turns an informal habit of thought into an inference rule.

Answer: B

Default logic adds rules of the form: if this holds and it is consistent to assume that, then conclude that, which lets birds fly by default while permitting exceptions. Multiple defaults may conflict, giving several extensions and requiring a choice. Truth values, axiom libraries and typicality restriction are different notions. A rule whose applicability depends on what cannot be proved, rather than on what can, is what makes such logics computationally awkward and expressively necessary.

Answer: C

A TMS stores why each conclusion was drawn, so when a premise is withdrawn the conclusions depending on it can be retracted efficiently rather than by rebuilding everything from scratch. It is the practical machinery that makes non-monotonic reasoning affordable. Verification, consistency enforcement and timestamps are related but different. Recording the derivation as well as the result is what allows a system to change its mind without starting again.

Answer: D

Description logics restrict expressiveness deliberately so that subsumption, whether one concept necessarily includes another, remains decidable and often tractable. They underpin the web ontology language. Program logics, single object restriction and natural language are different notions. Choosing what to give up in order to keep reasoning decidable, rather than seeking maximum expressiveness, is the design philosophy that distinguishes this family.

Answer: A

Subsumption asks whether one concept description necessarily includes another, which arranges the concepts into a hierarchy computed rather than declared. Instance checking is the related question about individuals, and knowledge base merging and simplification are different operations. That the taxonomy is derived from the definitions rather than asserted by hand is the principal advantage of the approach and it keeps the hierarchy consistent automatically.