Relations
Machine Readability
No Order
- Relational Languages do not imply sequential operation
- No “declaration before use”
Not Syntax Driven
The syntax of relations is very simple
relation (subject, object). Relations can be emitted (output) in any order.This is Important Because…
Emitting machine-readable code is harder when output must be put in some order.
E.G. C requires declaration-before-use, e.g.
void func (a) {
x = 5;
}
int x;
is illegal and must be rewritten as
int x;
void func (a) {
x = 5;
}
In this case, the emitter must make sure that int x; occurs prior to the function definition.
In more complicated examples, this requires the use of various buffers to memorize code sequences, with a final pass that orders the outputting of buffers
Relations, though, can be emitted in any order - the engine takes care of figuring out the order (for searching).