OWL ACE Construction Rules

OWL ACE construction rules define sentence structures which are used when verbalizing OWL ontologies in ACE. Every OWL ACE construction is an acceptable ACE construction.

Note that in this document we don't describe those ACE sentence structures that could be used to verbalize OWL's data-valued properties and those property axioms which cannot be reduced to general class inclusion axioms (transitivity, disjoint and super properties, etc).

Note also that ACE allows some sentence structures which while syntactically different from those that are discussed here are in fact semantically equivalent (e.g. some if-then constructions are equivalent to some every-constructions). Such sentences can be used when writing OWL ontologies in ACE but they are currently never used when verbalizing OWL ontologies in ACE.


OWL ACE function words are predefined and cannot be changed by users. Predefined function words are determiners, quantifiers, coordinators, negation words, copula be, and natural numbers.

OWL ACE content words are nouns and transitive verbs. Content words can be simple (code), or compound with hyphen (check-code).


Noun Phrases

Singular countable noun phrases:

a thing, a card, every card, no card

Plural countable noun phrases, using generalized quantifiers (with positive integers):

3 cards, at least 2 cards, at most 1 card, 4 things

Proper names:

John, Mr-Miller

Reflexive pronouns:

itself, themselves

Indefinite pronouns:

something, everything, nothing

Note that `a thing' is equivalent to `something' and it is recommended to use it only in the plural constructions, e.g.

at least 3 things

Modifying Noun Phrases

A relative clause can optionally follow a noun:

a customer that owns a car
Every customer that owns a car
at most 3 customers that own a car
something that owns a car

Propernames and reflexive pronouns cannot be modified by relative clauses.

* John that owns a car
* itself that owns a car

Relative Clause Coordination

Relative clauses can be coordinated by and, or, and ,and (i.e. comma-and).

Coordination by and and or is governed by the standard binding order of logic, i.e. and binds stronger than or. The coordinator ,and can be used to override the standard binding order.

Every man that owns a car or that owns a bike, and that owns a house knows John.

Coordination in relative clauses can cause ambiguity. Consider the following sentence where the relative clause `that is liked by Mary' can either modify the noun phrase `a car' or the noun phrase `every man'.

Every man that drives a car that is owned by John and that is liked by Mary works-for a company.

As specified in the ACE Interpretation Rules, the relative clause is attached to the closest noun phrase, in this case `a car'. It is recommended to avoid such complex sentences when writing ACE texts which lie in the fragment of OWL ACE.

Verb Phrases

OWL ACE verbs are third person singular/plural, indicative, simple present tense, active or passive. Passives must have a prepositional phrase is/are ... by .... Verbs can be only transitive, i.e. they take a noun phrase as an object.

(John) fills-in a form
(John) fills-in at least 3 forms
(Everything) is liked by Mary
(Every animal) defends itself
(Every animal) attacks at least 2 animals that defend themselves 

Verb phrase objects cannot be universally quantified, i.e. `every man', `no man', `everything', `nothing' are not allowed as objects (but only as subjects).

* John knows every customer.

Copula verbs have an obligatory complement which is a noun phrase.

(John) is a customer
(Bill) is William.

In addition to universally quantified noun phrases, copula complements cannot be plural nouns (`3 cars') and reflexive pronouns.

* John is itself.
* a man is at least 3 men

Verb phrase negation

Transitive verbs can be negated.

John does not enter a code. 
John is not liked by Mary.

Also, the copula verb `be' can be negated.

John is not a fireman.


Sentences start with a universally quantified noun phrase or a propername.

No man inserts a card
Every man is a human
John inserts a card

No other kind of beginning is allowed for a sentence.

* A man is a human
* 3 men insert a card
* Itself inserts a card

Every sentence must contain a verb phrase and end with a full-stop.


An OWL ACE text is a sequence of sentences.

Mary enters a card. Everything owns a car.

Formal grammar

The formal grammar is given as Prolog's Definite Clause Grammar (DCG) which bidirectionally maps between the ACE fragment discussed here and OWL 2 functional syntax.

Note that this is a draft version, e.g. the lexicon is very small and some property axioms are not implemented.