component.two_terminal

What it is ¶

component.two_terminal(part, a, b) yields one row per part whose pins sit on exactly two distinct nets, naming those two nets in name order, so a sorts before b and each part answers once.

It is decided by connectivity and not by class. A resistor, a capacitor, an inductor, a ferrite, a diode, a fuse and a crystal are all two-terminal, and so is a two-pin connector or a three-pin part with two of its pins tied together. A part with both pins on one net touches only one net and is not included. A zero-ohm link to itself and a shorted part are both like that. Add a component.class atom when you mean one kind of part.

For hardware engineers ¶

A tester can measure a two-terminal part from outside the part. In-circuit test drives a known current or voltage between two nodes and reads back a resistance, a capacitance or a diode drop, so every measurable part is defined by the pair of nets it sits between. Asking about the pair finds test coverage, series elements in a signal path, and parts bridging a rail to ground.

One limitation follows from the measurement itself. Two parts in parallel between the same pair of nets are measured together, and a tester sees their combined value. This relation lists them as two rows and says nothing about that.

For software engineers ¶

It joins component.net_count (to keep parts on exactly two nets) with component.net twice (to bind both of them), and the ?a < ?b comparison turns an unordered pair into one ordered row. A query that needs either orientation can read both, two_terminal(?r, ?x, ?y) and two_terminal(?r, ?y, ?x), as component.probed_one does.

Datalog ¶

Two-terminal parts with a rail on one side:

component.two_terminal(?r, ?a, ?b), net.rail(?a) => ?r, ?a, ?b

Only the resistors:

component.two_terminal(?r, ?a, ?b), component.class(?r, "resistor") => ?r, ?a, ?b

How it is defined ¶

component.two_terminal(r: component, a: net, b: net), a derived relation in the component module, defined in Datalog in stdlib/lib/component.dl. In a clause, a bare name is another member of the same module and a dotted name is a full path.

two_terminal(?r: component, ?a: net, ?b: net) :- component.net_count(?r, 2), component.net(?r, ?a), component.net(?r, ?b), ?a < ?b;

agni query --relations component.two_terminal prints the same definition. Adding a library member explains how the library is built.