Focal structures and information types in Prolog

Several studies have suggested that the mental structures of programmers of procedural languages have a close relationship with a model of structural knowledge related to functional information known as programming Plans. It also has been claimed that experienced programmers organize this representation in a hierarchical structure where some elements of Plans are focal or central to them. However, it is not clear that this is the case for other types of programming languages, especially for those which are significantly different from the procedural paradigm.The study reported in this paper investigates whether these claims are true for Prolog, a language which has important differences to procedural languages. Prolog does not have obvious syntactic cues to mark blocks of code (begin/end, repeat/until, etc). Also, its powerful primitives (unification and backtracking) and the extensive use of recursion might influence how programmers comprehend Prolog code in a significant way.The findings of the study suggest that Plans and functional information are important for Prolog programmers, but that there is also at least another model of structural knowledge valid for this language. This model of structural knowledge, Prolog schemas, is related to data structure information and it seems that a hierarchical organisation that highlights the relevance of some of its elements as focal is valid for Prolog. These results support the view that comprehension involves the detection of varying aspects of the code and that each of the structures related to these aspects might have their own organization and hierarchical relations.