Preliminary Recommendations

Expression of linear ordering constraints

Linear ordering constraints are attached to the frame at its top level. A linear ordering constraint can link two slots, two slot realisations, one slot and one slot realisation or one slot or slot realisation to the verb (self). It is expressed through two attributes, always present, whose value is the index of the slot within the frame:

* before_slot

- This is the slot that is first in linear ordering in real sentences instantiating the behaviour of a lexical entry associated with the frame concerned.

* after_slot

-- This is the slot that is the last (of the two) in linear ordering.

Slot numbering in a frame starts with 1. Conventionally, referring to slot `0' means we are referring to the verb (self) itself. Thus, constraints linking two slots or a slot and self are expressed in a uniform way. Two more attributes can be present or not:

* before_realisation

-- and respectively

* after_realisation

-- These make it possible to select a particular realisation for the selected slots (before_slot and after_slot, respectively). In this case, only the selected realisations are concerned by the linear ordering constraints. The realisations are selected by pointing to one element in the list of realisations. When no realisations are selected for a slot (before_slot or after_slot or both), this means that all the realisations of this slot are concerned with the linear ordering constraint. When slot 0 (self) is selected, selection on realisation is not relevant, and thus not allowed.

As the above concern linear ordering, which is mainly a grammar problem, and as many (and maybe all, for some languages) regularities are captured by grammar, this descriptive element is not a fundamental one within the recommendations we provide. However, it provides good expressive power for fine-grained descriptions and for some languages, for which these constraints might result in being completely necessary.