"Go on. Imagine you can chose anything you want, go anywhere and do anything. The world is your oyster. Imagine that we can polish your glass and a genie will appear to answer your every wish".

He smiled his nervous smile. He was digging too, wanting to know more, wanting to discover her limits and the things that made her tick.

"Well there is one thing I have always wondered about and you might be able to help advise me about it", said Sarah. "

It's this thing called computerised artificial intelligence. I've never understood it. How can computers which are made of silicon chips, circuit boards actually think? If they can think, can they feel? What do they think about? I've read a bit about it but never seen a 'neural net' program in action. Could it mean that in future the problems in our lives - you know those big questions that are so difficult to solve - will be answered just by switching on a big powerful computer and posing any question we wish"?

She looked up at him saw that she had his full attention so continued

"Then there is the ultimate question - could I ever understand how to program the computer and create that intelligence? Almost like creating a new life. That appeals to me. That's what I would really like to know, if one day I had the chance".

She stopped talking, trying to look as if she had revealed a long concealed secret. If it was the sort of thing Sam liked to play with on his computer in the office upstairs perhaps this could open the door.

It was like pressing a button. Sam seemed to expand. His shoulders came back. A beam of sheer pleasure spread over his face. He was in his favourite role and as he spoke, Sarah caught a glimmer of why his relationships had not lasted. He was a born preacher. A seeker for the adulation that came from dispensing the largess of knowledge.

Modern female expectations of equality would leave him pretty challenged, Sarah thought.

"The first thing you need to know is that all computers are controlled by programs. These are just lists of instructions that tell the computer what to do. The instruction could be to move a file from the hard disk store area into the chip memory, or alternatively, to display a message on the screen or do a multitude of other things. BASIC, COBOL, FORTRAN and many others are all examples of this sort of language".

"This approach works for repetitive or iterative problems like recording order numbers or calculating an invoice because the same sequence of actions must be carried out, without fail, over and over again. But as soon as the outcome becomes uncertain or the rules are not clear for solving the problem then this sort of programming language ceases to be very useful".

He beamed at her again, warming to his task. "It was to solve this problem that a fellow at the University of Marseilles in 1971 invented a programming language called PROLOG. PROLOG does not describe how to solve a problem but instead it describes the logical structure of the problem. The outcome is identified by proving an assertion rather than by following a procedure".

Sarah nodded but he needed little encouragement.

"Artificial intelligence programs in the early days aimed at general problem solving methods or simulations of human intelligence. But we now think that intelligent behaviour is as much to do with the knowledge a system possesses as its' reasoning power".

"So", interjected Sarah, "a computer couldn't think like a human because, apart from anything else, its' knowledge base would not contain the wide variety of inputs a human being gathers in his or her life".

"That's exactly right", beamed Sam, "It's not so much a problem of getting the stuff out of the computer as of acquiring or 'capturing' the data in the first place so that the programs can actually be allowed to work on it".

"So what are the PROLOG programs used for"? said Sarah.

"Oh that's easy. Planning robot behaviour, language understanding, pattern recognition, knowledge representation. That sort of thing".

"One day you will be able to describe your ailments to a computer and have your therapy diagnosed automatically. One day you will be able to load a legal program on your computer and get advice on any branch of the law, including international, as it applies to your particular circumstances".

"These are what are called expert systems. The demand for them will be huge as they come on line within the next twenty years".

Sarah moved over to the sofa with her drink. It was on a lower level than Sam's position on his stool at the breakfast bar. It allowed her to gaze up at him she hoped with the right level of admiration as she posed a question.