Περίληψη
Γενικά οι χρήστες πολύ μεγάλων βάσεων πληροφοριών ποτέ δεν χρησιμοποιούν ολόκληρη την πληροφορία που είναι αποθηκευμένη στη βάση, αλλά συνήθως χρησιμοποιούν ένα μικρό μέρος αυτής ανάλογα με τα ενδιαφέροντα τους. Επομένως είναι βασικό οι βάσεις δεδομένων να δίνουν τη δυνατότητα στους χρήστες ή τους σχεδιαστές της βάσης να απομονώνουν και να διαχειρίζονται κομμάτια της βάσης σύμφωνα με τις ανάγκες του καθενός. Για παράδειγμα να ονοματοθετούν δίνοντας οικεία προς αυτούς ονόματα, να ομαδοποιούν αντικείμενα σύμφωνα με τη δική τους αντίληψη των πραγμάτων, κτλ. Δηλαδή, είναι σημαντικό οι βάσεις δεδομένων να παρέχουν ένα μηχανισμό αφαίρεσης που να ανταποκρίνεται στη διαισθητική έννοια του περιβάλλοντος εργασίας (ΠΕ) (context). Σκοπός αυτής της διατριβής είναι να εισάγει την έννοια του ΠΕ στη μοντελοποίηση της πληροφορίας παρέχοντας ένα μηχανισμό αφαίρεσης, και να θεμελιώνει μια τυπική (μαθηματική) έννοια του ΠΕ παρέχοντας παράλληλα δυνατότητα διαχείρησης και ερώτησης των ΠΕ.
Περίληψη σε άλλη γλώσσα
Users of very large information bases are generally concerned with a small portion of the information stored. Different users need to view the same information differently according to their needs. Designers, on the other hand, need to structure information in accordance to the user group which is addressed. It is therefore important for information bases to provide their users and designers with tools that allow them to isolate desired portions of information and manage thwm in their own ways, e.g. by naming information objects using familiar names, grouping objects together according to their own perception, and so on. In other words it is important for information systems to provide an abstraction mechanism that reflects the intuitive notion of context. The aim of this thesis is to introduce a notion of context in information modeling providing a structuring mechanism for large information bases and to establish a formal notion of context along with a general framework for maintaini ...
Users of very large information bases are generally concerned with a small portion of the information stored. Different users need to view the same information differently according to their needs. Designers, on the other hand, need to structure information in accordance to the user group which is addressed. It is therefore important for information bases to provide their users and designers with tools that allow them to isolate desired portions of information and manage thwm in their own ways, e.g. by naming information objects using familiar names, grouping objects together according to their own perception, and so on. In other words it is important for information systems to provide an abstraction mechanism that reflects the intuitive notion of context. The aim of this thesis is to introduce a notion of context in information modeling providing a structuring mechanism for large information bases and to establish a formal notion of context along with a general framework for maintaining and querying contexts. Specifficaly, we define a set of operaions for manipulating contexts. These operations support context creation, update, copy, union, intersection, and difference. In particular, our operations of context union, intersection, and difference are different from these of set theory as they keep track of the context involved. However, they also satisfy the important properties of commutativity, associativity, and distributivity. Then, we show how a particular semantic data model (the Telos data model) can be incorporated into the proposed contextualised framework. Thus, we enhace our notion of context by structuring its contents through the traditional abstraction mechanisms, i.e., classification, generalization, and attribution, and we atudy the interactions between centextualization and those mechanisms as well as the constraints that govern such interactions. Finally, we present a query language for contextualized information bases. The query language can be used for navigating through contexts, as well a
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