10. An apparatus comprising a first broker, wherein the first broker is configured: to provide for storage of a set of subscriptions in a routing table, to provide for sending of a set of messages from the first broker to a second broker according to at least one subscription, to receive a subsequent message to the first broker, to determine a search term based on a data element of the subsequent message, to compare the search term with a set of data elements stored in an operational memory of a repository, to control sending of the subsequent message to the second broker according to a result of said comparison, wherein the set of data elements stored in the operational memory of the repository comprises data elements of the messages previously sent to the second broker, and said set of subscriptions contains at least one existing subscription, which specifies a topic, which is not contained in the set of data elements stored in the operational memory of the repository, and to add a new data point to the operational memory of the repository when the subsequent message has been subscribed by at least one subscriber, and no matching data elements are found in the operational memory of the repository.
10. An apparatus comprising a first broker, wherein the first broker is configured: to provide for storage of a set of subscriptions in a routing table, to provide for sending of a set of messages from the first broker to a second broker according to at least one subscription, to receive a subsequent message to the first broker, to determine a search term based on a data element of the subsequent message, to compare the search term with a set of data elements stored in an operational memory of a repository, to control sending of the subsequent message to the second broker according to a result of said comparison, wherein the set of data elements stored in the operational memory of the repository comprises data elements of the messages previously sent to the second broker, and said set of subscriptions contains at least one existing subscription, which specifies a topic, which is not contained in the set of data elements stored in the operational memory of the repository, and to add a new data point to the operational memory of the repository when the subsequent message has been subscribed by at least one subscriber, and no matching data elements are found in the operational memory of the repository. 14. The apparatus according to claim 10 wherein the search term is at least one of a data element of the subsequent message, an ancestor node of the data element of the subsequent message in a semantic hierarchy tree and a descendant node of the data element of the subsequent message in a semantic hierarchy tree.