3 3 votes Which of the following classes of languages can validate an $\text{IPv4}$ address in dotted decimal format? It is to be ensured that the decimal values lie between $0$ and $255$. RE and higher CFG and higher CSG and higher Recursively enumerable language Theory of Computation isro-2020 theory-of-computation normal identify-class-language + – Satbir 4.9k views answer comment Share Follow Print See all 4 Comments 4 4 Comments reply Mk Utkarsh commented Jan 13, 2020 reply Follow flag can we challenge this question as it is not clear what is RE? i thought it is Recursively Enumerable and marked D to be at safer side as it includes all languages, Also can someone prove how D is wrong? even if A is right D can't be wrong 0 0 replyShare JashanArora commented Feb 22, 2020 reply Follow flag Mk Utkarsh Option D isn't wrong. And this is a poorly framed question. But we have to play along with questions as such if we want PSUs. If D says Recursively Enumerable, then A by default can't be the same thing, and the abbreviation should mean Regular. (We have to assume it) Also, question says "classes of languages" but then proceeds with "RE" (not a class of language; assuming Regular Expressions), CFG and CSG are also not classes of languages, but grammars. Only Option D is a class of languages technically, and it encompasses all the other classes. So it is trivially true, and GATE would never ask such questions. But this is an ISRO question. We have to assume stuff, and since they give options in hierarchy, we'll also have to assume they're asking for the least powerful class of languages that can do the job. For which Regular Languages would be the answer (because IPv4 addresses are finite). Keep in mind the intelligence of the question creators while solving their questions. 1 1 replyShare Mk Utkarsh commented Feb 22, 2020 reply Follow flag JashanArora yes i didn't challenge, i was pissed off a little at that time. 1 1 replyShare jacknroll commented Dec 6, 2025 reply Follow flag i know ambigious but re and higher here and higher directly re implies regular expression 0 0 replyShare Please log in or register to add a comment.
4 4 votes Answer: a) RE and higher. To validate IPV4 in dotted decimal format the values should be between 0-255. We can draw a DFA for it since the values are finite. For other options if we select them then it means we cannot do it using RE which is false. Thus best option is a). Tuhin Dutta answered Jan 13, 2020 Tuhin Dutta comment Share Follow See all 3 Comments 3 3 Comments reply mrinmoyh commented Jan 22, 2020 reply Follow flag What is RE ?? Regular Expression ?? any value not in [0,255] will go to trap state. Then for a state towards Trap state, there will be infinite transition. How to draw DFA for this 0 0 replyShare srestha commented Jan 23, 2020 reply Follow flag @Tuhin Dutta Why it would be only RE?? It is regular which means it is satisfied by CFG,CSG and RE . right?? So, why not B)? 0 0 replyShare Tuhin Dutta commented Jan 24, 2020 reply Follow flag When Reg Expr is satisfying then it is the best answer that's why and option A) says RE and higher. They are not telling only RE. 1 1 replyShare Please log in or register to add a comment.
0 0 votes the dotted decimal values are from 0 to 255 whicn\h means finite . so we can draw DFA which conforms to Regular Language .Also higher languages CFG,CSG,REC will validate IPV4 address on dotted decimal. DIBAKAR MAJEE answered May 7, 2020 DIBAKAR MAJEE comment Share Follow 0 reply Please log in or register to add a comment.
