Heuristic Solutions for Loading in Flexible Manufacturing Systems

Production planning in flexible manufacturing system deals with the efficient organization of the production resources in order to meet a given production schedule. It is a complex problem and typically leads to several hierarchical subproblems that need to be solved sequentially or simultaneously. Loading is one of the planning subproblems that has to addressed. It involves assigning the necessary operations and tools among the various machines in some optimal fashion to achieve the production of all selected part types. In this paper, we first formulate the loading problem as a 0-1 mixed integer program and then propose heuristic procedures based on Lagrangian relaxation and tabu search to solve the problem. Computational results are presented for all the algorithms and finally, conclusions drawn based on the results are discussed

Lazy updates in key assignment schemes for hierarchical access control

Hierarchical access control policies are used to restrict access to objects by users based on their respective security labels. There are many key assignment schemes in the literature for implementing such policies using cryptographic mechanisms. Updating keys in such schemes has always been problematic, not least because many objects may be encrypted with the same key. We propose a number of techniques by which this process can be improved, making use of the idea of lazy key updates, which have been studied in the context of cryptographic file systems. We demonstrate in passing that schemes for lazy key updates can be regarded as simple instances of key assignment schemes. Finally, we illustrate the utility of our techniques by applying them to hierarchical file systems and to temporal access control policies