In this paper we discuss a number of structural problems that we face when we design a machine-oriented controlled natural language for Afrikaans taking the underlying principles of Attempto Controlled English (ACE) and Processable English (PENG) as a starting point. Machine-oriented controlled natural languages are well-de ned subsets of natural languages that can be translated unambiguously into a formal language (and sometimes vice versa) and be used for automated reasoning. Over the last decade, a number of machine-oriented controlled natural languages have been designed and used for speci cation purposes, knowledge acquisition and knowledge representation, and as interface languages to the Semantic Web { among them Attempto Controlled English (ACE) [6], Boeing's Computer-Processable Language (CPL) [2], Common Logic Controlled English (CLCE) [9], and Processable English (PENG) [7]. All these controlled natural languages are based on English, but little work has be done in this domain for other languages. In this paper, we look at Afrikaans and work towards a machine-oriented controlled natural language for Afrikaans, based on PENG. Afrikaans is an Indo-European language derived from 17th century Dutch and mainly spoken in South Africa and Namibia. It is estimated that Afrikaans is the home language of 6.45 million people and the second or third language for 6.75 million people.3 In the following, we will discuss how a subset of ACE and PENG is related to Afrikaans and identify a number of structural problems that we face when we intend to translate Afrikaans automatically into a rst-order notation. In addition to English and Afrikaans, South Africa has nine other o cial languages that belong to the Bantu language family, and di er signi cantly from English and Afrikaans. Investigating the development of controlled natural languages for the South African Bantu languages constitutes a future challenge.
ACE and PENG are machine-oriented controlled natural languages that can be used as speci cation and knowledge representation languages. They are tractable 3 http://www.southafrica.info/about/people/language.htm subsets of English that can be unambiguously translated by a machine into rstorder logic. A subset of the grammar of these two languages covers declarative sentences and questions. Their vocabularies consist of prede ned function words, some prede ned phrases, and content words. In a nutshell, an ACE or PENG text consists of a sequence of declarative sentences that are linked by approved forms of intra- and intersentential anaphoric expressions. 2.1
Simple sentences in ACE and PENG have the following general structure:
subject + verb + [ complements ] + { adjuncts }
Every sentence has a subject and a verb. Complements are required for transitive
verbs and ditransitive verbs but adjuncts are always optional. For example, the
following sentence consists of a subject that has the form of a noun phrase
a customer, a transitive verb inserts that takes the noun phrase a card as a
complement, and an adjunct in form of a prepositional phrase into the slot:
1. A customer inserts a card into the slot.4
Not only the verb can be described in more detail as illustrated by the
prepositional modi er in (
2. John's customer who is new inserts a valid card of Mary into a slot A. the noun customer is further described with the help of a possessive noun and a relative clause, the noun card via an adjective and an of-prepositional phrase, and nally the noun slot via a name as apposition. 2.2
Complex sentences (or composite sentences in \ACE-speak") are built
recursively from simpler sentences through coordination (3 and 4), subordination (
9. It is not the case that a customer inserts a card.
Note that this is only a small subset of complex sentences that are approved by these two controlled natural languages (for details see [6]). 4 The examples have been taken from the speci cation of an ATM [5]. 2.3 ACE and PENG support yes/no-questions (10) and wh-questions (11): 10. Does the customer insert the card into the slot? 11. Where does the customer insert the card? Yes/no-questions can be used to investigate whether or not a speci c situation is true, and wh-questions interrogate di erent aspects of a situation. 3
Afrikaans and English have co-existed in South Africa for many years and the main di erences between the two languages are well documented (see, for example, [1]). We focus on the following ve main aspects of Afrikaans in which the language di ers from English and consequently from ACE and PENG. 3.1
Particle verbs (phrasal verbs) (Afrikaans: partikelwerkwoorde) are common in Afrikaans, as also in English. The verb `indruk' (insert) is one example. In Afrikaans, the verb part of the particle verb behaves like an ordinary central verb in terms of placement in the sentence. The complement/particle has varying positions according to the construction [3, p.104]. For example, in main and simple sentences without an auxiliary verb such as in (13): 12. A customer inserts a card.
13. 'n Klant druk 'n kaart in. the short complement/particle stands at the end of the sentences but in subordinate clauses and after auxiliary verbs it is pre xed to the verb. 3.2
The preterite of the majority of Afrikaans verbs is formed by the auxiliary verb `het' + the past participle of the verb. Moreover, in the presence of complements and/or adjuncts the auxiliary verb `het' is separated from the past participle, with the past participle occurring at the end of the sentence. For example, for the verb `indruk' (insert), we have (15): 14. A customer inserted a card.
15. 'n Klant het 'n kaart ingedruk. 3.3
Similar to English simple sentences in Afrikaans also follow the general structure: subject + verb + complements + adjuncts (S+V+C+A) However, in subordinate clauses the structure is usually S+C+A+V. So composite sentences that consist of a main sentence and a subordinate clause such as in (17) have the following structure [1, pp.46-47] where ( ) indicates optionality: S + V(+C + A) + S(+C + A) + V | m{azin } | subor{dzinate } 16. John's customer who is new inserts a valid card of Mary into a slot A. 17. John se klant wat nuut is druk 'n geldige kaart van Mary in 'n gleuf A in. In composite sentences that consist of a conditional subordinate clause followed by the main sentence such as in (19): 18. If a card is valid then a customer inserts it.
19. As 'n kaart geldig is dan druk 'n klant dit in. the main sentence has a V+S+O structure [3, p.222]. 3.4
One of the most complex issues in Afrikaans is its double negation [1, pp.54-58]. Although double negation is the `rule' there are constructions in which not all negations are doubled. As a guideline, negation in the main sentence is usually doubled, even when they are composed, for example in (21): 20. It is not the case that a customer inserts a card. 21. Dit is nie die geval dat 'n klant 'n kaart indruk nie. 22. It is not the case that a customer does not insert a card.
23. Dit is nie die geval dat 'n klant nie 'n kaart indruk nie.
However, in subordinate clauses that form part of a main sentence that already has negation such as in (23), negation is usually not doubled. 3.5
Both yes/no-questions and wh-questions in Afrikaans are obtained from declarative sentences by means of inversion [4, p.186], for example: 24. Does a customer insert a card? 25. Druk 'n klant 'n kaart in? 26. What does a customer insert? 27. Wat druk 'n klant in? 28. Where does a customer insert a card? 29. Waar druk 'n klant 'n kaart in? In particular, if a declarative sentence has the structure S+V+(C+A) then an associated yes/no-question will have the structure V+S+(C+A) while an associated wh-question has either a WH+V+S(+A) or a WH+V(+S)+A structure.
The experiment was done with PENG Light [8], for which a systematically compiled suite of approximately two hundred test sentences had been developed. As a rst step we translated selected test sentences into Afrikaans to ascertain to what extent PENG Light is suitable for these sentences. The PENG Light lexicon was extended to include the Afrikaans words. We focussed on particle verbs, the past tense and double negation, which all constitute forms of long-distance dependencies. In all cases the Afrikaans constructions could be accommodated by modi cations to the PENG grammar. It remains to consider to subordinate clauses, yes/no questions and wh-questions, and to run PENG Light on the full, translated suite of test sentences. 5
We compared a common subset of ACE and PENG with Afrikaans and identi ed
ve structural aspects in which Afrikaans di ers from these two machine-oriented
controlled natural languages: (