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Η εργασία αυτή περιλαμβάνει στην συνέχεια τέσσερα κεφάλαια τα οποία έχουν ως εξής. Στο κεφάλαιο 2 περιγράφονται τα σύγχρονα εργαλεία ανάλυσης κειμένου αλλά και οι βάσεις δεδομένων (Corpus) που είναι διαθέσιμα. Περιγράφεται επίσης η βάση δεδομένων που χρησιμοποιούμε για να εξάγουμε πειραματικά αποτελέσματα. Στο κεφάλαιο 3, γίνεται εισαγωγή στα n-grams και αναπτύσσονται τα βασικότερα μέτρα ομοιότητας τα οποία είναι απαραίτητα για τον διαχωρισμό του ύφους γραφής από ηλεκτρονικό κείμενο. Στο κεφάλαιο 4 παρουσιάζονται τα πειραματικά αποτελέσματα που έχουν ληφθεί με τα n-grams. Σε αυτά περιλαμβάνονται και τα δίκτυα νευρωνίων. Τέλος στο κεφάλαιο 5 δίνονται τα συμπεράσματα και προτάσεις για περαιτέρω έρευνα στον τομέα αυτόν. / This work includes then four chapters which are as follows. Chapter 2 describes the modern text analysis tools and databases (Corpus) that are available. Also describes the database used to derive test results. In Chapter 3, are inserted into n-grams and developed the basic similarity measures which are necessary to separate the writing style of electronic text. Chapter 4 presents the experimental results obtained with n-grams. These include neural networks. Finally in Chapter 5 are given conclusions and suggestions for further research in this area

Bibliography: pages 192-195 / The avoidability, or unavoidability of patterns in words over finite alphabets has been studied extensively. The word α over a finite set A is said to be unavoidable for an infinite set B+ of nonempty words over a finite set B if, for all but finitely many elements w of B+, there exists a semigroup morphism φ ∶ A+ → B+ such that φ(α) is a factor of w. In this treatise, we start by presenting a historical background of results that are related to unavoidability. We present and discuss the most important theorems surrounding unavoidability in detail. We present various complexity-related properties of unavoidable words. For words that are unavoidable, we provide a constructive upper bound to the lengths of words that avoid them. In particular, for a pattern α of length n over an alphabet of size r, we give a concrete function N(n, r) such that no word of length N(n, r) over the alphabet of size r avoids α. A natural subsequent question is how many unavoidable words there are. We show that the fraction of words that are unavoidable drops exponentially fast in the length of the word. This allows us to calculate an upper bound on the number of unavoidable patterns for any given finite alphabet. Subsequently, we investigate computational aspects of unavoidable words. In particular, we exhibit concrete algorithms for determining whether a word is unavoidable. We also prove results on the computational complexity of the problem of determining whether a given word is unavoidable. Specifically, the NP-completeness of the aforementioned problem is established. / Decision Sciences / D. Phil. (Operations Research)