It just occurred to me that validation may be more of a backward-chaining concept. You have a goal, i.e. a valid input set for the rules, and want to prove that the current set is actually valid.
Is it right that a pure forward chaining rule engine will have difficulty handling the absence of things? I've been using JRules in the recent past, which has rules that match working memory itself if it contains a certain number of instances of a class - or if there are none. This sort of thing made validation rules easier to write. It also had initial and final actions which provided some mode support for free. However, I got the feeling that the implementation was becoming complicated and less 'pure' whatever that means. Maybe the answer is to write rules that match working memory, then - and perhaps supply a working memory implementation that can count instances for you. ********************************************************************** This e-mail and any attachment is intended for the named addressee(s) only, or person authorised to receive it on their behalf. The content should be treated as confidential and the recipient may not disclose this message or any attachment to anyone else without authorisation. Unauthorised use, copying or disclosure may be unlawful. If this transmission is received in error please notify the sender immediately and delete this message from your e-mail system. Any view expressed by the sender of this message or any attachment may be personal and may not represent the view held by First Choice Holidays PLC and its subsidiaries. All electronic transmissions to and from First Choice are recorded, may be monitored and are scanned for viruses and content. E-mails containing viruses will be deleted without notification. Whilst we maintain virus checks on inbound e-mails we accept no liability for viruses or other material introduced with this message. All companies form part of the First Choice Holidays PLC group of companies. First Choice Holidays PLC Company Registration No: 48967 (England) Registered Office: First Choice House, London Road, Crawley, WestSussex RH10 9GX **********************************************************************
