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This paper presents a logic programming language of novel conception, called Reflective Prolog, which allows declarative metaknowledge representation and metareasoning. The language is defined by augmenting pure Prolog (Horn clauses) with capabilities of self-reference and logical reflection. Self-reference is designed as a quotation device (a carefully defined naming relation) which allows the construction of metalevel terms that refer to object-level terms and atoms. Logical reflection is designed as an unquotation mechanism (a distinguished truth predicate) which relates names to what is named, thus extending the meaning of domain predicates. The reflection mechanism is embodied in an extended resolution procedure which automatically switches the context between levels. This implicit reflection relieves the programmer from having to explicitly deal with control aspects of the inference process. The declarative semantics of a Reflective Prolog definite program P is provided in terms of the least reflective Herbrand model of P, characterized by means of a suitable mapping defined over the Herbrand interpretations of P. The extended resolution is proved sound and complete with respect to the least reflective Herbrand model. By illustrating Reflective Prolog solutions to an organic set of problems, and by discussing the main differences with respect to other approaches to logic metaprogramming, we show that the proposed language deploys, within its field of action, greater expressive and inferential power than those available till now. The interpreter of the language has been fully implemented. Because of its enhanced power, logic semantics and working interpreter, Reflective Prolog is offered as a contribution toward making the declarative approach of logic programming applicable to the development of increasingly sophisticated knowledge-based systems.

Information and Communication Technologies have great potential, in the context of natural resources utilization, to improve efficiency by making homes, offices, industries and transportation systems more 'intelligent': more information use can be traded off with less energy use. The paper presents a system to monitor and interactively control water and gas utilization, allowing consumers to be better informed about their consumption behaviour and challenging them to improve efficiency in utilization along with saving costs. In the system, smart meters are used in order to collect data on gas and water consumption; the data collected through this kind of meters are made available, almost in real time, in a graphical representation both to the customer and the supplier. The availability of a higher quantity of information about consumption can be used by consumers to improve utilization efficiency; moreover, it can also be seen as a challenge to modify personal consumption behaviours. As a consequence, in both cases, there can be an increase in saving natural resources and costs. In the paper, the developed system is described and its potential benefits are discussed with reference to similar experiences and a conceptual background.

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