Allegories are enriched categories generalizing a category of sets and binary relations. In this paper, we extend a new, recently-introduced conceptual data model based on allegories by adding support for modal operators and developing a modal interpretation of the model in any allegory satisfying certain additional (but natural) axioms. The possibility of… (More)
– We demonstrate how one can use the formal concept analysis (FCA) to obtain the role hierarchy for the role based access control from the existing access control matrix. We also discuss assesed by means of FCA the quality of security system and finding users with excess permissions.
One of the deficiencies of SQL is that it allows little practical support for factoring, parametrization and modularization of complex SQL statements. Using dynamic SQL or macroprocessors for this purpose is error prone and inconvenient. This paper shows how the rewriting systems such as Maude can be used to build better SQL preprocessors which understand… (More)
The article describes the designing process, implementation and development of the middle-class computer project, accomplished by the students of University of Łódź. The project, which is called SUL, is a WWW-based portal with several set up purposes. Services for students (news, e-mails or private web pages including secure and reliable communication… (More)