Abstract: A database structure (400) stores data representing a plurality of resource identifiers (200) such as URLs in a computing system. The URLs (200) are each associated with a respective category code (310). Each of resource identifiers (200) is hashed to provide a hash value (300) which is divided into at least first and second hash portions (301, 302). The first hash portions (301) index a main hash array (410) to select a main data block (421) in a main data section (420) holding a set of the second hash portions (302) and the respective category codes (310). For security and compactness, optionally the hash value (300) is further divided to provide a third hash portion (303) which is discarded and is not used to access the database (400).

Abstract: An apparatus method and system are described for categorising Uniform Resource Locators (URLs) when accessing the Internet 20 from a client 12. A request message 500 is generated to request categorisation of a specified URL, and a category is provided in a reply message 600. The specified URL and the category are added to a category cache. In a second or subsequent instance of a URL request referring to the specified URL, the category is determined from the category cache. This reduces communication traffic in a network such as the Internet 20.

Abstract: A system method and apparatus are provided for use in monitoring or controlling internet access at a client device 12. A request message 500 is generated to request categorisation of a specified URL, and a reply message 600 is returned denoting a category of the specified URL amongst a predetermined set of categories. The request message 500 comprises a UDP package including a sequence number, a time stamp, and a data section carrying the specified URL. The reply message 600 comprises a UDP packet and includes the sequence number and the time stamp from the request message 500, and a data section identifying the category. The request message 500 and the reply message 600 are economical and provide efficient communication across a local area network or the Internet 20.

Abstract: An apparatus, method and system for use in categorising Uniform Resource Locators (URLs) when controlling or monitoring access to the Internet 20 from a client 12. A request message 500 is generated to request categorisation of a specified URL. The request message 500 comprises a licensing field carrying a licence key. A remote server 40 receives the licence key and, if valid, generates a reply message 600 denoting a category of the specified URL. The licence key enables workload at the server 40 to be managed efficiently.