Hubble Rules (HRules)

This method is named after the Hubble project, in which they have been proposed. Those rules can be used both as a stylesheet in the Taaabs timeline component, and as a transformation, thanks to this method. A benefit is that such a transformation can be built interactively in the timeline, with a direct visual feedback of its effect, then “materialized” as a user-defined method and applied to other traces.

sources:

1
parameters:
model:the model of the computed trace
origin:the origin of the computed trace
rules:the description of the rules
extensible:

no

If parameter origin is not provided, the origin of the source trace will be used instead.

The parameter model specified the model of the computed trace. It must be specified (as traces computed from rules generally hava a different model from their source trace).

The parameter rules is a JSON string complying with the model below.

Structure of the rules parameter

The rule parameter contains a JSON array. Each item of this array is called a rule.

Each rule is a JSON object with the following attributes:

  • id is an obsel type IRI (from the target model), no two rules must have the same id.
  • rules is an array of subrules.
  • visible is an optional boolean, defaulting to true.

Each subrule is a JSON object with the following attributes:

  • type is an optional obsel type IRI (from the source trace’s model).
  • attribute is an optional JSON array of attribute constraints.

Each attribute constraint is a JSON object with the following attributes:

  • uri is an attribute type IRI (from the source trace’s model).
  • operator is one of the following strings:
    • ==, !=, <, >, <=, >= have their usual meaning;
    • contains checks that a string attribute contains the given value as a substring.
  • value is either a JSON string or a JSON-LD value object.

Semantics of Hubble rules

  • An obsel (from the source trace) matches an attribute constraint if it has the corresponding attribute, and its value satisfies the corresponding operator and value.

    If the value of the attribute constraint is a string, and if the attribute has a single datatype as its range in the source model, then the value will be cast to that datatype before the comparison is computed. Otherwise, it will be converted to a literal as specified by JSON-LD.

  • An obsel matches a subrule with a type if it matches all the attribute constraints of the subrule.

  • An obsel matches a subrule with a type if

    • it has the corresponding obsel type, and
    • it matches all the attribute constraints of the subrule.

  • An obsel matches a rule if it matches at least one of its subrule.

This method produces a new obsel for each source obsel matching a rule (unless this rule has visible set to false); the obsel type of the new obsel is the id of the matching rule; the attributes of the source obsel are copied in the new obsel.

Precedence of subrules

Whenever an obsel matches several subrules (belonging to different rules), the following precedence applies:

  • a subrule which specifies an obsel type has precedence over a subrule which does not, regardless of their number of attribute constraints or position in the rule structure;
  • a subrules with more attribute constraints has precedence over a subrule with less attributes constraints, regardless of their position in the rule structure;
  • a subrule higher in the rule structure has precedence over a subrule lower in the rule structure.

These criteria induce a total order on subrules, making the process totally deterministic.