A computer program (10) for analysing a specification, determining what kind of data processing operations are carried out, and deducing or inferring from the kind of internal operations, what data types are appropriate. The data types inferred can be compared with specified data types, to check for errors, or optimise the overall process. This is effectively an extension of type inference from individual programs into the higher level technical field of process analysis. It can also be applied to monitoring and optimising processes during operation of the processes.