In this paper, we address a specific topic within the context of nested transaction implementation, namely, the assignment of identifiers to transactions. We discuss the most important information such identifiers should carry. We do this based on an analysis of the main requirements the components of a general transaction processing system pose on the identifiers. Thereafter, we present some schemes for the assignment of transaction identifiers and discuss their pros and cons with regard to the requirements presented. Finally, we compare one of our schemes to a conventional one by considering the most common operations that are performed with the identifiers. Lastly, we show the performance measurements we have obtained.

Knowledge Base Management Systems (KBMSs) are a growing research area finding applicability in different domains. As a consequence, the demand for ever-larger knowledge bases (KBs) is growing more and more. Inside this context, knowledge sharing turns out to be a crucial point to be supported by KBMSs. In this paper, we propose a way of controlling knowledge sharing. We show how we obtain serializability of transactions providing many different locking granules, which are based on the semantics of the abstraction relationships. The main benefit of our technique is the high degree of potential concurrency, to be obtained through a logical partitioning of the KB graph and the provision of lock types used for each referenced partition. By this way, we capture more of the semantics contained in a KB graph, through an interpretation of its edges grounded in the abstraction relationships, and make feasible a full exploitation of all inherent parallelism in a knowledge representation approach.