Modern distributed applications are long-lived, are expected to provide flexible and adaptive data services, and must meet the functionality and scalability challenges posed by dynamically changing user communities in heterogeneous execution environments. The practical implications of these requirements are that reconfiguration and upgrades are increasingly necessary, but opportunities to perform such tasks offline are greatly reduced. Developers are responding to this situation by dynamically extending or adjusting application functionality and by tuning application performance, a typical method being the incorporation of client- or context-specific code into applications' execution loops. Our work addresses a basic roadblock in deploying such solutions: the protection of key application components and sensitive data in distributed applications. Our approach, termed Dynamic Differential Data Protection (D3P), provides fine-grain methods for providing component-based protection in distributed applications. Context-sensitive, application-specific security methods are deployed at runtime to enforce restrictions in data access and manipulation. D3P is suitable for low- or zero-downtime environments, since deployments are performed while applications run. D3P is appropriate for high performance environments and for highly scalable applications like publish/subscribe, because it creates native codes via dynamic binary code generation. Finally, due to its integration into middleware, D3P can run across a wide variety of operating system and machine platforms. This dissertation introduces D3P, using sample applications from the high performance and pervasive computing domains to illustrate the problems addressed by our D3P solution. It also describes how D3P can be integrated into modern middleware. We present experimental evaluations which demonstrate the fine-grain nature of D3P, that is, its ability to capture individual end users' or components' needs for data protection, and also describe the performance implications of using D3P in data-intensive applications.

The AEC industry has long been in need of effective modes of information exchange and knowledge sharing, but their practice in the industry is still far from satisfactory. In order to maintain their competence in a highly competitive environment and a globalized market, many organizations in the AEC industry have aimed at a move towards the development of learning organizations. Knowledge management has been seen as an effective way to have every member of an organization engaged in learning at all levels. At the very centre of knowledge management and learning is knowledge sharing through effective communication. Unfortunately, however, there is a big gap in the AEC industry between existing practice and the ideal in this area. In order to effectively coordinate information and knowledge flow in the AEC industry, this present research has developed a framework for an information system – a Construction Information and Knowledge Protocol/Portal (CIKP) which integrates within it a publish/subscribe system, Semantic Web technology, and Social Web concepts. Publish/subscribe is an appropriate many-to-many, people-to-people communication paradigm for handling a highly fragmented industry such as construction. In order to enrich the expressiveness of publications and subscriptions, Semantic Web technology has been incorporated into this system through the development of ontologies as a formal and interoperable form of knowledge representation. This research first involved the development of a domain-level ontology (AR-Onto) to encapsulate knowledge about actors, roles, and their attributes in the AEC industry. AR-Onto was then extended and tailored to create an application-level ontology (CIKP-Onto) which has been used to support the semantics in the CIKP framework. Social Web concepts have been introduced to enrich the description of publications and subscriptions. Our aim has been to break down linear communication through social involvement and encourage a culture of sharing, and in the end, the CIKP framework has been developed to specify desired services in communicating information and knowledge, applicable technical approaches, and more importantly, the functions required to satisfy the needs of a variety of service scenarios.

The AEC industry has long been in need of effective modes of information exchange and knowledge sharing, but their practice in the industry is still far from satisfactory. In order to maintain their competence in a highly competitive environment and a globalized market, many organizations in the AEC industry have aimed at a move towards the development of learning organizations. Knowledge management has been seen as an effective way to have every member of an organization engaged in learning at all levels. At the very centre of knowledge management and learning is knowledge sharing through effective communication. Unfortunately, however, there is a big gap in the AEC industry between existing practice and the ideal in this area. In order to effectively coordinate information and knowledge flow in the AEC industry, this present research has developed a framework for an information system – a Construction Information and Knowledge Protocol/Portal (CIKP) which integrates within it a publish/subscribe system, Semantic Web technology, and Social Web concepts. Publish/subscribe is an appropriate many-to-many, people-to-people communication paradigm for handling a highly fragmented industry such as construction. In order to enrich the expressiveness of publications and subscriptions, Semantic Web technology has been incorporated into this system through the development of ontologies as a formal and interoperable form of knowledge representation. This research first involved the development of a domain-level ontology (AR-Onto) to encapsulate knowledge about actors, roles, and their attributes in the AEC industry. AR-Onto was then extended and tailored to create an application-level ontology (CIKP-Onto) which has been used to support the semantics in the CIKP framework. Social Web concepts have been introduced to enrich the description of publications and subscriptions. Our aim has been to break down linear communication through social involvement and encourage a culture of sharing, and in the end, the CIKP framework has been developed to specify desired services in communicating information and knowledge, applicable technical approaches, and more importantly, the functions required to satisfy the needs of a variety of service scenarios.

Τα τελευταία χρόνια οι εφαρμογές συνεχούς μετάδοσης ροών πληροφορίας στο διαδίκτυο έχουν γίνει ιδιαίτερα δημοφιλείς. Με τον συνεχώς αυξανόμενο ρυθμό εισόδου νέων αντικειμένων πληροφορίας, γίνεται ολοένα και πιο επιτακτική η ανάγκη για την ανάπτυξη πληροφορικών συστημάτων που να μπορούν να προσφέρουν στους χρήστες τους μόνο εκείνες τις πληροφορίες που τους ενδιαφέρουν, φιλτράροντας τεράστιους όγκους από άσχετες για τον κάθε χρήστη, πληροφορίες. Ένα μοντέλο διάδοσης πληροφορίας ικανό να ενσωματώσει τέτοιου είδους ιδιότητες, είναι το μοντέλο δημοσιεύσεων/συνδρομών βασισμένο στο περιεχόμενο ( content-based publish/subscribe) Βασική συνεισφορά μας στο χώρο είναι η εφαρμογή του μοντέλου δημοσιεύσεων/συνδρομών βασισμένου στο περιεχόμενο (content-based publish/subscribe) πάνω στα δίκτυα ομοτίμων ώστε να μπορέσουμε να προσφέρουμε στους χρήστες υψηλή εκφραστικότητα κατά την δήλωση των ενδιαφερόντων τους, λειτουργώντας σε ένα πλήρως κατανεμημένο και κλιμακώσιμο περιβάλλον. Ο κορμός των προτεινόμενων λύσεων σε αυτή τη διατριβή είναι: (α) η ανάπτυξη αλγορίθμων για την αποθήκευση των κλειδιών των δημοσιεύσεων σε κατάλληλους κόμβους του δικτύου με βάση τις συνθήκες στο περιεχόμενο που έχουν δηλωθεί και (β) αλγορίθμων δρομολόγησης δημοσιεύσεων στο διαδίκτυο έτσι ώστε να ((συναντούν)) αυτούς τους κόμβους οι οποίοι περιέχουν συνδρομές που ικανοποιούνται από την πληροφορία της δημοσίευσης. Οι προτεινόμενοι αλγόριθμοι υλοποιήθηκαν και εξετάσθηκαν ενδελεχώς με προσομοίωση μελετώντας την απόδοσή τους με βάση μετρικές όπως: η δίκαιη κατανομή του φόρτου στους κόμβους του δικτύου από τη διακίνηση μηνυμάτων κατά την επεξεργασία των συνδρομών/δημοσιεύσεων, ο συνολικός αριθμός μηνυμάτων που διακινούνται, ο συνολικός όγκος επιπλέον πληροφορίας που απαιτούν οι αλγόριθμοι να εισέλθει στο δίκτυο (network bandwidth), και ο χρόνος που απαιτείται για την ανεύρεση των συνδρομών που συζευγνύουν με κάθε δημοσίευση. / In the past few years the continuous data streams applications have become particularly popular. With the continuously increasing rate of entry of new information, it becomes imperative the need for developing appropriate infrastructures that will offer only the information that users are interested for, filtering out large volumes of irrelevant for each user, information. The content-based publish/subscribe model, is capable of handling large volumes of data traffic in a distributed, fully decentralized manner. Our basic contribution in this research area is the coupling of the content-based publish/subscribe model with the structured (DHT-based) peer-to-peer networks, offering high expressiveness to users on stating their interests. The proposed infrastructure operated in a distributed and scalable environment. The proposed solutions in this thesis are related to the development and testing: (a) of a number of algorithms for subscription processing in the network and (b) of a number of algorithms for processing the publication events. The proposed algorithms were developed and thoroughly tested with a detailed simulation-based experimentation. The performance metrics are: the fair distribution of load in the nodes of network from the distribution of messages while processing subscriptions and publication events, the total number of messages that are generated, the total volume of additional information that is required from the algorithms to operate, and the time that is required for matching publication events to subscriptions.