Earlier, we saw that each slot is specified for two different attributes: slot realisation and optionality. Accordingly, given examples (134) and (135) above, the relevant slot can be specified for optionality by means of the Boolean feature Optionality, as exemplified in table 4.5.
| frame | ([slot | (Index: 1, [slot_real(Index: 1, CatLabel: np, Subject: subj)]), |
| slot | (Index: 2, Optionality: opt, [slot_real(Index: 1, CatLabel: np, Subject: comp)])]) |
In what follows, for the sake of readability, slot(Index: i) and slot_real(Index: i) will be shortened as slot_i and slot_real_i respectively.
It is not always the case that argument optionality can be stated in the simple terms of the example above. More difficult cases can occur as witnessed by the following examples:
(138) | She paid |
|
(139) | She paid the bill |
|
(140) | She paid the bill to her mother |
|
(141) | * | She paid to her mother |
|
(142) | She wrote |
|
(143) | She wrote the letter |
|
(144) | She wrote the letter to her mother |
|
(145) | She wrote to her mother |
The difference in syntactic behaviour between write and pay cannot be captured conveniently through specification of the attribute Optionality. With write, omission of any slot filler is admissible, and can thus be encoded within the same frame as shown in table 4.6.
On the contrary, with pay, omission of the direct object (e.g. bill in the examples at hand) additionally requires omission of the indirect object. The only way to deal with this case in the present framework is to encode two distinct but possibly related frames, only one of which contains an optional slot, as shown in tables 4.7 and 4.8, where frame_1 (short for frame(Index: 1)) represents the constructions in (138) and (139), and frame_2 (short for frame(Index: 2)) the construction in (140).
| frame | (Index: 1, | |
| [slot_1 | ([slot_real_1(CatLabel: np, Subject: subj)]), | |
| slot_2 | (Optionality: opt, [slot_real_1(CatLabel: np, Subject: comp)])]) |
As the reader will notice, this is not the only possible way of accounting for the constructions above: e.g. one could represent (139) and (140) as a single frame with an optional PP and an obligatory direct object, with (138) being assigned a distinct but possibly related frame.
To sum up, argument optionality is usually expressed by resorting to the attribute Optionality, whose possible values are { opt | no_opt }.
However, in particularly difficult cases such as pay, different but possibly related frames need to be specified. This encoding can be seen as a particular case of frame alternation to whose treatment we turn in the following section. In principle, the representation of optionality in terms of frame alternation can also be extended to the treatment of simpler cases such as write and eat. The lexicographer is left free to choose between the two options.