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• Need some clarification on the ANSI/SPARC 3-tier database architecture.

  - by Moonshield

  Hi there, I'm currently revising for a databases exam and looking over some past papers, but there's one question that I'm slightly unsure about and was wondering if someone could offer some assistance. "Describe EACH of the THREE levels of the ANSI SPARC 3 level architecture. Your answer should include the purpose of EACH of the schemas, the level of abstraction they provide and the software tools that would be used to access and support them." As I understand it (although please correct me if I'm wrong): the internal schema specifies the physical storage of the data; the conceptual schema specifies the structure of the database and the domains; and the external schemas are how the database is viewed by "users" (applications, etc.). As for the abstraction, I understand that the conceptual layer means that the physical data storage can be altered without the end user being affected, likewise the The bit that I'm not sure about is what tools are used to access and support each layer. Would the internal schema be handled by the DBMS, the conceptual schema handled by some sort of DDL interpreter and the external schema handled by a DML interpreter (or have I misunderstood what each level does)? Any assistance would be greatly appreciated. Thanks, Moonshield

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• Need some clarification on Bankers Algorithm

  - by Moonshield

  Hi, just a quick query about safe/unsafe states in Dijkstra's Banker's algorithm... If one of the processes in the snapshot of the system (for example the one below) already has all of its needs fulfilled and there are not sufficient resources available to fulfil the needs of any of the other processes, is the system in a safe state? I know normally we assume that once a process receives its required resources it will terminate soon after and return all resources, but is this assumption factored in when we calculate the state of the system? Allocated Maximum Available | A | B | A | B A | B ---+---+--- ---+---+--- ---+--- P1 | 1 | 2 P1 | 1 | 2 1 | 3 P2 | 5 | 3 P2 | 7 | 8

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• Regular Expression to recognise truncated forms of search string?

  - by Moonshield

  I'm trying to formulate a regular expression which will recognise the search term truncated by any number of characters from the right. For example, if the search term is "pickle", the regex should recognise "pi", "pick" but not "pickaxe". Initially I came up with the following: p(i(c(k(l(e)?)?)?)?)? That works perfectly, but seems a crude way of doing it. Is there a better way of doing this? I had a look around for something similar to what I want, but I'm not entirely sure what to search for.

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