A domain expert is expected to have considerable knowledge of the business domain and therefore helpfull when exploring the requirements for a system. He doesn't need to know how these requirements will be implemented.
In fact to much concentration on how something will get implemented can make a domain expert less effective - for example when he starts to think in technical terms (database) instead of business terms (information storage) and therefore imposes unnecessary restrictions.
OTOH it doesn't hurt when he shares some common language with the developers (e.g. UML) and has a rough feeling of what can be expected from a computer system...
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus