This paper describes a new syntax that can be used to write OWL 2 ontologies. The syntax, which is known as TEX-OWL, was developed to address the need for an easy-to-read and easy-to-write plain text syntax. TEX-OWL is inspired by LATEX syntax, and covers all construct of OWL 2. We designed TEXOWL to be less verbose than the other OWL syntaxes, and easy-to-use especially for quickly developing small-size ontologies with just a text editor. The important features of the syntax are discussed in this paper, and a reference implementation of a Java-based parser and writer is described.
still XML. Another syntax that follows OWL 2’s structural specification is the FunctionalStyle Syntax. It is a human-readable and plain text syntax that removes the burden of XML, however like the previous two, the Functional-Style Syntax is also verbose. In fact, it has an excessive number of keywords, and typically requires the use of a large number of brackets, as its name might suggest. The Manchester Syntax is a user-friendly syntax that can be used to write OWL 2 ontologies. It is the least verbose OWL 2 syntax and when it is used to write ontology documents, it gathers together information about names in a frame-like manner as opposed to the others OWL 2 syntaxes. This nature at a first look may seem a great advantage for the Manchester Syntax, but on the other hand it makes this syntax unable of handling General (GCI) Concept Inclusions (i.e., the Manchester Syntax does not cover the expressivity of the whole OWL 2 language).
The OWL Latex-Style Syntax was created to deal with the above issues and provide users with a lightweight syntax that makes it easier to write ontologies. It has been designed primarily for writing ontology documents in simple textual editor. The syntax is discussed in detail through the rest of this paper. 2
The full specification of the TEX-OWL syntax is available at [
It was also decided that although the syntax should be aligned as much as possible with the OWL specification, for example by using keywords derived from the Functional-Style Syntax specification, the main objective would be to strive for conciseness and a reduction in the amount of time it took users to write axioms. To this end, some new keywords were created and others changed in name or name length. Moreover, it was also decided that the syntax should match as much as possible the LATEX format peculiarities of using keyword and command that start with a backslash (‘n’) symbol, with required parameters inside curly braces and optional parameters inside square brackets.
Although the TEX-OWL Syntax borrows ideas from the OWL Functional-Style
Syntax, it is much less verbose. The ontology in Listing 1.1, the TEX-OWL version of the
example in [2, p. 129], illustrates some of the main constructs of the syntax, while we
refer the reader interested in the syntax of all OWL 2 constructs to the complete
specification in [
Listing 1.1. An African Wildlife Ontology in TEX-OWL n ns <http://www.mydomain.org/african#> n b e g i n f o n t o l o g y g [ <http://www.mydomain.org/african> ] % A n i m a l s form a c l a s s [ C l a s s d e c l a r a t i o n ] a n i m a l n c % P l a n t s form a c l a s s d i s j o i n t from a n i m a l s [ D i s j o i n t c l a s s e s ] a n i m a l n c d i s j o i n t p l a n t % T r e e s a r e a t y p e o f p l a n t [ S u b c l a s s Axiom ] t r e e n c i s a p l a n t % B r a n c h e s a r e p a r t s o f t r e e s [ S u b c l a s s Axiom , O b j e c t P r o p e r t y
U n i v e r s a l Q u a n t i f i c a t i o n ] b r a n c h n c i s a n o f o r a l l f i s p a r t o f gf t r e e g % L e a v e s a r e p a r t s o f b r a n c h e s [ S u b c l a s s Axiom , O b j e c t
P r o p e r t y U n i v e r s a l Q u a n t i f i c a t i o n ] l e a f n c i s a n o f o r a l l f i s p a r t o f gf b r a n c h g % H e r b i v o r e s a r e e x a c t l y t h o s e a n i m a l s t h a t e a t o n l y p l a n t s or p a r t s o f p l a n t s [ C l a s s E q u i v a l e n c e , C l a s s E x p r e s s i o n , O b j e c t P r o p e r t y U n i v e r s a l Q u a n t i f i c a t i o n ] h e r b i v o r e n ceq ( a n i m a l n cand n o f o r a l l f e a t s g f ( p l a n t n cor n o f o r a l l f i s p a r t o f gf p l a n t g ) g ) % C a r n i v o r e s a r e e x a c t l y t h o s e a n i m a l s t h a t e a t a n i m a l s [ C l a s s E q u i v a l e n c e , C l a s s E x p r e s s i o n , O b j e c t P r o p e r t y
E x i s t e n t i a l Q u a n t i f i c a t i o n ] c a r n i v o r e n ceq ( a n i m a l n cand n o e x i s t s f e a t s gf a n i m a l g ) % G i r a f f e s a r e h e r b i v o r e s , and t h e y e a t o n l y l e a v e s [ S u b c l a s s Axiom , C l a s s E x p r e s s i o n , O b j e c t P r o p e r t y U n i v e r s a l
Q u a n t i f i c a t i o n ] g i r a f f e n c i s a ( h e r b i v o r e n cand n o f o r a l l f e a t s gf l e a f g ) % L i o n s a r e a n i m a l s t h a t e a t o n l y h e r b i v o r e s [ S u b c l a s s Axiom , C l a s s E x p r e s s i o n , O b j e c t P r o p e r t y U n i v e r s a l Q u a n t i f i c a t i o n ] l i o n n c i s a ( a n i m a l n cand n o f o r a l l f e a t s gf h e r b i v o r e g ) % T a s t y p l a n t s a r e p l a n t s t h a t a r e e a t e n b o t h by h e r b i v o r e s and c a r n i v o r e s [ S u b c l a s s Axiom , S e q u e n c e I n t e r s e c t i o n o f C l a s s E x p r e s s i o n s , O b j e c t P r o p e r t y U n i v e r s a l
Q u a n t i f i c a t i o n ] 2 Simple IRIs are equivalent to abbreviated IRIs where the default prefix is used and there is no need need of typing the colon (‘:’) symbol. t a s t y p l a n t n c i s a n c a n d o f f p l a n t , n o e x i s t s f e a t e n b y gf h e r b i v o r e g , n o e x i s t s f e a t e n b y gf c a r n i v o r e gg % e a t s and e a t e n b y a r e i n v e r s e o f e a c h o t h e r [ I n v e r s e O b j e c t
P r o p e r t y ] e a t e n b y n o i n v e a t s % E v e r y t h i n g t h a t e a t s i s an a n i m a l [ O b j e c t P r o p e r t y Domain ] e a t s n odomain a n i m a l n end f o n t o l o g y g 3
A TEX-OWL parser and writer
A Java based reference implementation of a TEX-OWL parser and writer were created.3
They use the OWLAPI framework [
In this Section, we present the evaluation performed with the help of ontology experts in order to analyze if the presented syntax is suitable, easy-to-use, and comprehensive enough for ontology authoring.
In order to evaluate TEX-OWL, two questionnaires were designed and sent to knowledge engineers with experience in authoring ontologies with the various OWL syntaxes.
In the first questionnaire,4 all OWL 2 syntaxes and TEX-OWL’s intuitiveness, conciseness, and understandability were compared using ten different examples of use. In details, each example of use consists in a set of axioms expressed by using the 6 syntaxes that we compared, namely, TEX-OWL, Manchester, Turtle, Functional, RDF/XML, and OWL/XML.
Table 1 presents the results extracted from the survey submitted to the ontology experts. Ten knowledge engineers participated to this questionnaire. Each value of the table represents, for each syntax, how many experts, averaged over the whole set of example, judged the syntax intuitive and concise with respect to the proposed examples.
We may observe that, in general, there is a clear distinction between the first three syntaxes (TEX-OWL, Manchester, and Functional) with respect to the other three (Turtle, OWL/XML, and RDF/XML). Such a distinction is clearly visible from the judges about their intuitiveness and their conciseness.
By comparing, directly, the TEX-OWL syntax with the Manchester and the Functional ones, we may notice that the intuitiveness of the TEX-OWL syntax is comparable with the Manchester one, but the TEX-OWL syntax obtained a significant better score 3 The implementation is available from http://github.com/matax87/TexOwl/. 4 Accessible here: http://goo.gl/Cjpqtg for conciseness with respect to the Manchester syntax. Moreover, we recall that the Manchester syntax does not cover the whole OWL 2 language: it does not properly support the expression of General Concept Inclusions (GCIs) (such as “having a parent who is a person, implies being a person”), which instead are expressible in TEX-OWL (resp., “\oexists{hasParent}{Person} \cisa Person”).
The only syntax that has been partially judged concise is the Functional one; however, the difference between the scores obtained with respect to the TEX-OWL syntax is different enough to state that, from the conciseness point of view, the TEX-OWL syntax is the most suitable solution for the ontology authoring task.
The second questionnaire5 was focused on evaluating the usability of the new syntax for authoring a small ontology. The task to be completed consists in developing, by starting from a textual description, the ontology shown in Listing 1.1. Experts were asked to judge how much the developing of a sample ontology was easy and intuitive, and to rate the simpleness of developing the sample ontology with the LaTeX-like syntax with respect to syntaxes previously used by the experts. Ratings were expressed according to the typical five-level Likert scale. More in details, experts were asked to answer to three questions about the TEX-OWL syntax: if it was difficult to develop the ontology (on a scale from 1 to 5, where 5 mean “Very easy”); if the TEX-OWL syntax was easy to remember (on a scale from 1 to 5, where 5 means “Hard to remember”); and, by comparing with their previous authoring experiences with other syntaxes, if the use of the TEX-OWL syntax was better (on a scale from 1 to 5, where 5 means “Definitely better”).
Six knowledge engineers took part to this evaluation. On average, the TEX-OWL syntax obtained a score of 3:5 on the first question, 3:17 on the second questions, and 3:67 on the third one. Therefore, we may state that the experts rated the task of developing an ontology in TEX-OWL more easy than difficult, that the syntax is slightly more easy than difficult to remember, and that the use of TEX-OWL syntax was quite better than previous authoring experiences with other syntaxes. 5
TEX-OWL is a new OWL 2 syntax that was designed in response to a demand from users for a more concise syntax that can be easily used to quickly write small-size on5 Accessible here: http://goo.gl/lbFu4R tologies by hand. A characterizing feature of the syntax is that it is inspired by the LATEX syntax: in particular the syntax uses the same format for parameters and keywords as used in LATEX. The syntax is suited for use in simple textual editor tools. A reference implementation of a Java based parser and writer has been produced, which may be integrated into any tool. The implementation also includes converters, which can transform TEX-OWL to other OWL 2 syntaxes and vice versa.
The evaluation results shown that TEX-OWL is the most concise syntax and has an intuitiveness comparable with the Manchester Syntax, which is the most intuitive among OWL 2 syntaxes. Moreover, users have found it easy to use TEX-OWL for authoring a small example ontology and that, in general, this syntax is better to use for writing ontologies by hands than other OWL 2 syntaxes.