A fitness club has a computerised membership system. The system stores information for each club member: name, home address, email address, mobile phone number, date of birth and exercise preferences. Many classes are full, and the club creates a waiting list for each class. The club adds details of members who want to join a class that is full to the waiting list for that class. When the system identifies that a space is available in one of the classes, a new module will send a text message to each member who is on the waiting list.