midterm-2007-ans

midterm-2007-ans - Fall, 2007 CIS 550 Database and...

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Fall, 2007 CIS 550 Database and Information Systems Midterm The exam is 80 minutes long. There are 100 points total. Problem 1 [60 points]: Suppose we are building a Web crawler to index pages. We need to keep track of the following attributes: R (docID,docURL,docTitle,docDate,linkedDocID,linkText,wordID,wordText) where each document has an (integer) ID, URL, title, and date; documents link to other documents with a particular text label on their link; and documents contain words (each of which has a word ID) and text (which is potentially different for each word ID). You are given the following FDs: docID docURL,docTitle,docDate docID,linkedDocID linkText wordID wordText wordID,wordText wordID docID,docDate docTitle 1. (7pts) Specify the (or a) minimal cover for the functional dependencies. Answer: docID docURL docID docTitle docID docDate docID,linkedDocID linkText wordID wordText 2. (7pts) Is the FD docID,wordID docDate,wordText in the closure of the functional dependencies? Answer: Yes. 3. (7pts) Provide a relational schema in 3NF for the domain, using the R ( A,B,C ) no- tation, indicating keys with underlines under the attributes. Is the decomposition lossless? Dependency preserving? 1
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Answer: docs ( docID ,docURL,docDate ) titles ( docID ,docDate ,docTitle ) words ( wordID ,wordText ) links ( docID ,linkedDocID ,linkText ) occurs ( wordID,docID,linkedDocID ). occurs ( wordID,docID ) also works although it will not be the result of the normal 3NF Synthesis algorithm. The result is lossless and dependency preserving.
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midterm-2007-ans - Fall, 2007 CIS 550 Database and...

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