RE: Overheads when using structures?

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Yes of course.

> > Is it more efficient to flatten the structure to:
> > person(surname,firstname,dd,mm,yyyy)
> >
> > Is indexing affected by the structure?
>
> SWI-Prolog indexing is `base-line': first argument, using atomic constants
> or name+arity of a term.  So, each clause is indexed on name+2 in the first
> example, and surname in the second.  I think that makes the choice easy :-)

Indeed, the former is no help at all.

> Sometimes the first is a lot nicer to handle in the application, which
> is trivially solved using
>
> person(name(Surname, Firstname), date_of_birth(DD, MM, YYYY)) :-
> person(Surname, Firstname, DD, MM, YYYY).
>
> Now you have nice indexing and no space overhead (except for the
> one clause above).

That's very neat.  This definitely looks the way to go.

> > Also, do the overheads depend on the prolog implementation used?
>
> Space-wise, not very much. Some systems can index inside terms, either
> specified by the user or dynamically, inferred from usage patterns.
>
> With some fantasy you can do more enhanced indexing using term_hash/2 or
> term_hash/4 (latest development source; stable version only has
> hash_term/2).

That's good to know.  If this part of my code turns out to be on the critical path I'll certianly give term hashing a try.

Thanks for the help, Jan, and have a good weekend.
Cheers,
PJ
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