Security, caching and self-management in distributed information systems

In this thesis, we investigate three different aspects of distributed information systems: security, caching, and self-management. We describe our concept of a security system for distributed and open systems using our query processing system ObjectGlobe as an example. One part of this concept is our OperatorCheck server, which validates the semantics of an operator and analyzes its quality before the operator is actually used in queries. This is done semi-automatically using an oracle-based approach to compare a formal specification of an operator against its implementation. Further security measures are integrated into the query processing engine: secure communication channels are established, authentication and authorization are performed, and overload situations are avoided by admission control. Operators are guarded using Java's security model to prevent unauthorized resource access and leakage of data. The resource consumption of operators is monitored and limited to avoid resource monopolization. We present a semantic caching scheme suitable for caching responses from Web services on the SOAP protocol level. Web services are typically described using WSDL documents. For semantic caching we developed an XML-based declarative language to annotate WSDL documents with information about the caching-relevant semantics of requests and responses. Using this information, our semantic cache answers requests based on the responses of similar previously executed requests. Performance experiments---based on the scenarios of TPC-W and TPC-W Version 2---conducted using our prototype implementation demonstrate the effectiveness of the proposed semantic caching scheme. We present a novel autonomic computing concept which is hiding the ever increasing complexity of managing IT infrastructures. For this purpose, we virtualize, pool, and monitor hardware to provide a dynamic computing infrastructure. A fuzzy-logic-based controller supervises all services running on this virtual platform. Higher-level services such as business applications profit from running on this platform. For example, failed services are restarted automatically. A service overload is detected and remedied by either starting additional service instances or by moving the service to a more powerful server. The capabilities and constraints of the services and the hardware environment are specified in a declarative XML language.