This paper is a survey of genetic algorithms for the traveling salesman problem. Genetic algorithms are randomized search techniques that simulate some of the processes observed in natural evolution. In this paper, a simple genetic algorithm is introduced, and various extensions are presented to solve the traveling salesman problem. Computational results… (More)
A simple, graph-oriented database model, supporting object-identity, is presented. For this model, a transformation language based on elementary graph operations is defined. This transformation language is suitable for both querying and updates. It is shown that the transformation language supports both set-operations (except for the powerset operator) and… (More)
A general model for spatial databases is considered , which extends the relational model by a l l o wing as tuple components not only atomic values but also geometrical gures. The model, which i s i n-spired by the work of Kanellakis, Kuper and Revesz on constraint query languages, includes a calculus and an algebra which are equivalent. Given this… (More)
In this paper, we discuss augmentations of the nested relational algebra with programming constructs, such as while-loops and for-loops. We show that the algebras obtained in this way are equivalent to a slight extension of the powerset algebra, thus emphasizing both the strength and the naturalness of the powerset algebra as a tool to manipulate nested… (More)
—We give a language-independent characterization of the expressive power of the relational algebra on finite sets of source-target relation instance pairs. The associated decision problem is shown to be co-graph-isomorphism hard and in coNP. The main result is also applied in providing a new characterization of the generic relational queries.
In reflective programming languages it is possible for a program to generate code that is integrated into the program's own execution. We introduce a reflective version of the relational algebra. Reflection is achieved by storing and manipulating relational algebra programs as relations in the database. We then study the expressibility and complexity of the… (More)