Object model

The core of Dragonfly is a language object model revolving around three types: grammars, rules, and elements. This section describes that object model.

Grammars

A grammar is a collection of rules. It manages the rules, loading and unloading them, activating and deactivating them, and taking care of all communications with the speech recognition engine. When they recognition occurs, the associated grammar received the recognition event and dispatches it to the appropriate rule.

Normally a grammar is associated with a particular context or functionality. Normally the rules within a grammar are somehow related to each other. However, neither of these is strictly necessary, they are just common use patterns.

The Grammar class and derived classes are described in section Grammar classes reference.

Rules

A rule represents a voice command or part of one. Its elements define exactly what its contents are, i.e. what can be said to activate this rule. It has several attributes which determine, for example, whether it is a top-level “standalone” command which can be spoken directly, or whether it can only be referenced from a different top level rule.

Each rule has one root element which defines the language content of the rule. Top-level rules have callback methods which are called when the rule is recognized.

Elements

Elements are the basic building blocks of the language model. The define exactly what can be said, inform the content of rules. The most common elements are:

  • Literal(...) – one or more literal words.
  • Sequence(...) – a series of other elements.
  • Alternative(...) – a choice of other elements, only one of which can be said within a single recognition.
  • Optional(...) – an element container which makes its single child element optional.
  • RuleRef(...) – a reference to another rule.
  • ListRef(...) – a reference to a list, which is a dynamic language element which can be updated and modified without reloading the grammar.
  • Dictation(...) – a free-form dictation element which allows the speaker to say one or more natural language words.

The above mentioned element types are at the heart of Dragonfly’s object model. But of course using them all the time to specify every grammar would be quite tedious. There is therefore also a special element which constructs these basic element types from a string specification:

  • Compound(...) – a special element which parses a string spec to create a hierarchy of basic elements. The format of this spec is described Compound elements reference.