Flex is a hybrid expert system toolkit developed by LPA which incorporates frame-based reasoning with inheritance, rule-based programming and data-driven procedures.
Flex supports both forwards and backward chaining, and they can be interleaved.
Flex provides its own English-like Knowledge Specification Language, KSL, which helps ensure that knowledge-bases are readable by domain experts. Flex KSL can now be generated automatically for certain classes of problems from VisiRule.
Flex is implemented in, and has access to, Prolog. As opposed to most expert system shells, which tend to be constrained, Flex is an open toolkit.
Flex has proved very popular in education and was licensed to the Open University as part of T396: 'Artificial intelligence for technology'.
Much of the material for this course is described by Prof Adrian Hopgood in his book: Intelligent Systems for Engineers and Scientists, Third Edition, and on his web-site.
There is also a Flex tutorial on the LPA web-site.
Flex has been used to power AllerGenius, an expert system specifically developed by leading allergologists to help interpret the results of modern in vitro allergy tests such as the ImmunoCAP ISAC. These tests can typically measure specific antibodies to more than 100 allergen components from more than 50 pre-selected allergen sources and require a lot of expert interpretation.