10. A computer software product for information gap filling, including a non-transitory computer-readable storage medium in which computer program instructions are stored, which instructions, when executed by a computer, cause the computer to perform the steps of: collecting respective amounts of details concerning members of a set of persons in a social network, wherein additional details are desired regarding the members of the set of persons; identifying online participants in a gap-filling game; defining for the online participants respective sets of candidates, the sets of candidates being subsets of the set of persons, wherein defining comprises computing a candidate score for each member of the set of persons, the candidate score being computed as an increasing function of a relationship strength between the member of the set of persons and the online participants, respectively and a decreasing function of the collected amount of details of the member of the set of persons; presenting the sets of candidates to other online participants, respectively; receiving information items regarding members of the presented sets of candidates from the other online participants, respectively, the information items comprising relationships between the candidates and other entities in the social network; and evaluating the online participants by identifying respective validated information items that are contributed by the online participants, the validated information items being identified with a predefined number of corresponding information items that are contributed by the other online participants; and computing a participant score, wherein the participant score increases according to a number of the validated information items, and for each of the validated information items, the participant score decreases according to a total number of occurrences of the corresponding information items.
10. A computer software product for information gap filling, including a non-transitory computer-readable storage medium in which computer program instructions are stored, which instructions, when executed by a computer, cause the computer to perform the steps of: collecting respective amounts of details concerning members of a set of persons in a social network, wherein additional details are desired regarding the members of the set of persons; identifying online participants in a gap-filling game; defining for the online participants respective sets of candidates, the sets of candidates being subsets of the set of persons, wherein defining comprises computing a candidate score for each member of the set of persons, the candidate score being computed as an increasing function of a relationship strength between the member of the set of persons and the online participants, respectively and a decreasing function of the collected amount of details of the member of the set of persons; presenting the sets of candidates to other online participants, respectively; receiving information items regarding members of the presented sets of candidates from the other online participants, respectively, the information items comprising relationships between the candidates and other entities in the social network; and evaluating the online participants by identifying respective validated information items that are contributed by the online participants, the validated information items being identified with a predefined number of corresponding information items that are contributed by the other online participants; and computing a participant score, wherein the participant score increases according to a number of the validated information items, and for each of the validated information items, the participant score decreases according to a total number of occurrences of the corresponding information items. 11. The computer software product according to claim 10 , wherein the candidate score of one of the members of the set of persons is computed as a function F=(1−F data )+F rel , wherein F rel is a first function that retrieves the relationship strength between the one member of the set of persons and one of the online participants; and Fdata is a second function that retrieves the collected amount of data concerning the one member of the set of persons.