1. A computer implemented method comprising: defining a collection of attachments that can be viewed and searched by a corresponding group of at least one user, a user being a searcher who has provided registration information, the corresponding group defined for the collection, each attachment in the collection being between a topic of a defined set of topics and one or more information items of a plurality of information items, such that the collection is defined by the topics and information items of the attachments, and by the corresponding group, the defining of the collection including: accepting from a collection creator a name for the collection, the collection creator being a user, accepting from the collection creator, or from a designate thereof, one or more searchers to be potential members of the corresponding group; and inviting the one or more searchers to become members of the corresponding group, wherein each topic is defined by a user for attachment to one or more information items of the plurality of information items, the defining the topics including: accepting from at least one user at least one topic; and adding the topic to the set of topics, wherein the topics do not necessarily have a hierarchical structure, and wherein the topics that are attached to at least one information item are for searching by a particular searcher for one or more information items of the plurality of information items according to search request information provided by the particular searcher, search request information including at least one topic of the set of topics, the searching including identifying at least one information item that has attachments to the at least one topic of the search request information.