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Construction of Index: (Page 197)

Construction of Index: (Page 197). Objective: Given a document, find the number of occurrences of each word in the document. Example: Computer Science students know computers and computer languages. Keywords: computer, computers, science, students, know, and, languages.

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Construction of Index: (Page 197)

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  1. Construction of Index: (Page 197) • Objective: Given a document, find the number of occurrences of each word in the document. • Example: Computer Science students know computers and computer languages. • Keywords: computer, computers, science, students, know, and, languages.

  2. Linear time algorithm: • Let T be the text, |T| the length of T. We can find the occurrences of each word in T in O(|T|) time.

  3. Constructing an automaton: c o m p u t e r s s c i e n c e s t u d e n t k n o w a n d s l a n g u a g e

  4. Remarks: • There is a final state for each word. • There is a counter on each final state storing the number of occurrences that the final state is reached. • While reading, the algorithm creates new states for the new word. • For words having met before, we just go through the corresponding states. • When the final state is read, add 1 to the counter.

  5. Assignment one (due in week 6 on Friday, 7:30 pm) • Write a program to convert a text into a vector such that each element of the vector is the number of occurrences of the corresponding keyword.

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