GEM (Graph Editor & Modeler)

Jun 2005 – Jul 2005 · age 23

What it was

A graph editor in Java and SWT, built as a graphical front end for probabilistic models at a university research lab, that knew nothing about probabilistic models. It knew about graph types, declared in XML: which kinds of node exist, which edges may join which kinds, how many, and whether the whole must stay acyclic, connected, a tree or moral. The editor enforced those rules live, refusing a bad edge the moment it was drawn. A tensor widget laid out each node's probability table with axes taken from its parents, and when a parent was added it remapped the existing numbers by name instead of wiping them. A compiler turned any graph type into typed C++ readers. Two C++ programs proved the pipeline: a hidden Markov model evaluator, and an automaton that generated Conway's look-and-say sequence. Three weeks, an installer, then summer moved on.

Wins, for the age

At twenty-three, Jeff made graph types data and enforced them at edit time, a year before Eclipse GMF (2006) brought model-driven diagram editors to the mainstream.
One editor served Bayesian networks, dynamic Bayesian networks, influence diagrams, Mealy machines and a board-game map, just by swapping a file.
Conditional probability tables that reshape themselves from the edges and keep their numbers, the thing Hugin and Netica (1995) already did, found again from first principles in three weeks.
Compiled the schema into typed C++ readers with alignment checks, the old CORBA IDL (1991) instinct, and proved it with two unrelated consumers before calling it done. A young mammal, already testing its own abstractions.

What it taught

A good schema deletes most of the UI code. The whole controls package was instantiated from property definitions.
Graph algorithms with a purpose: cycle, morality, connectivity and tree checks, each small, each serving the type system.
Generate the boring readers, and check alignment, because silent format drift is the bug that hides.
Never swallow the exception that says a file no longer matches its schema. The empty catch blocks here said nothing.

Genealogy

Ancestors: none on record. The first time a schema became an editor. Descendants: Jovian Suite: a visual editor compiling a typed model into generated code.

Epitaph

Here lies GEM. Tell it what a graph was allowed to be and it would draw one, refuse the wrong edges and hand you C++ to read it. It spent its one summer between a Bayesian network and Conway's sequence.