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Boolean Constructs

Real norms are rarely flat. A right may apply if condition A and (condition B or condition C), and a fact may be defined as a combination of sub-facts. The Norm Editor models this with boolean constructs — small trees of AND / OR / NOT over frames.

Boolean constructs appear in two places:

  • the precondition of an Act, and
  • the subdivision of a Fact (a fact defined in terms of other facts).

Anatomy of a boolean construct

A boolean construct is a recursive tree. Each node is one of two kinds:

  • Atomic — the node points to a single frame. It is a leaf.
  • Composite — the node has no frame of its own but joins its children with an operator (and or or).

Any node can additionally be negated, expressing NOT.

graph TB
    ROOT["AND"]
    OR["OR"]
    A["Fact: resident"]
    B["Fact: citizen"]
    C["NOT · Fact: bankrupt"]

    ROOT --> OR
    ROOT --> C
    OR --> A
    OR --> B

    style ROOT fill:#dddddd
    style OR fill:#dddddd
    style A fill:#b3d9ff
    style B fill:#b3d9ff
    style C fill:#b3d9ff

The tree above reads: (resident OR citizen) AND NOT bankrupt.

Building a construct

The construct model offers a set of operations that mirror how an interpreter thinks about a condition. The tree view in the frame editor exposes all of them except Add parent:

Operation Effect
Add a frame to an empty node Makes the node atomic, pointing at that frame
Subdivide a node Pushes the node's current content down into a new child and turns the node into a composite, defaulting to and
Add child Adds another operand under a composite node
Add parent Wraps the current node in a new composite parent, so it can be combined with siblings (model only)
Negate Sets the NOT flag on a node; in the tree view, by picking NOT as the node's function
Switch operator Changes a composite node between and and or, via Pick a function
Remove frame / delete Removes a frame from the tree, tidying up empty parents and dropping a now-redundant operator

Frames are added to a construct much as roles are filled: click an empty node to select it (the status bar reads Choosing a condition), then highlight text in the source and pick a frame type in the panel that appears, or click an existing fact in the Frames list to reuse it. The editor tracks which node is currently being edited so the next selected frame lands in the right place.

Editing a construct visually

Preconditions and subdivisions are edited through a tree view that shows the nested structure. A node that joins others has a Pick a function list (AND and OR join the children; NOT marks the node as negated), an Add child button, and a button to subdivide; a leaf node shows its frame with a button to remove it, a button to subdivide, and a button to remove the node. As the tree changes, the same structure can be inspected in the network view of the Frames pane, where composite nodes appear as small anonymous join-points connecting their operands. In the View interpretation tab, the Details pane draws an act's precondition as a tree.

How it is stored

When an interpretation is serialised, a boolean construct becomes a FLINT ComplexFact:

  • the operator becomes flint:hasFunction (flint:and / flint:or),
  • the children become an ordered flint:hasOperands list,
  • atomic nodes are replaced by a reference to their frame, and
  • negation is represented in the function applied to the node.

Empty nodes (no frame and no children) are pruned during export, so only meaningful structure is stored. See the FLINT Ontology reference for the exact RDF shape, including a worked (A or B) and (C and D) example.