1. A method implemented by a node for providing a service in a communication network, the method comprising the steps of: receiving a request; evaluating the request, wherein the request comprises an expression, the expression being a function of a plurality of elements, each element relating to data originating from one or more context sources available in the communication network, each of the one or more context sources having an associated context source weight for a query by the service; determining one context source from the one or more context sources for which an evaluation of the expression has a lowest expression evaluation weight, based on the associated context source weights for querying by the service, interrogating first the one context source determined to have the lowest expression evaluation weight; and wherein the expression comprises one or more intermediate expressions, the method further comprising iteratively determining a weight of evaluating the one or more intermediate expressions, until all elements relate only to data originating from the one or more context sources, wherein a lowest weight intermediate expression towards each of the context sources is determined for the expression until the expression elements comprise only context sources, at which point the context source to be interrogated first has been determined.
1. A method implemented by a node for providing a service in a communication network, the method comprising the steps of: receiving a request; evaluating the request, wherein the request comprises an expression, the expression being a function of a plurality of elements, each element relating to data originating from one or more context sources available in the communication network, each of the one or more context sources having an associated context source weight for a query by the service; determining one context source from the one or more context sources for which an evaluation of the expression has a lowest expression evaluation weight, based on the associated context source weights for querying by the service, interrogating first the one context source determined to have the lowest expression evaluation weight; and wherein the expression comprises one or more intermediate expressions, the method further comprising iteratively determining a weight of evaluating the one or more intermediate expressions, until all elements relate only to data originating from the one or more context sources, wherein a lowest weight intermediate expression towards each of the context sources is determined for the expression until the expression elements comprise only context sources, at which point the context source to be interrogated first has been determined. 7. The method according to claim 1 , in which the data from the context sources is a numeric value, and the expression comprises a function of the values of the context sources.