The underlying model

The syntactic level of TIGER/SALSA XML corresponds to the syntactic representation of TIGER XML [5]. The syntactic structure is a tree with both node and edge labels. Trees can contain crossing edges to encode discontinuous constituents.

On the role-semantic level, we model each frame instance as a frame tree of depth one with a root labelled with the frame name. A frame tree has at least one edge that points to the frame-evoking element, which is unlabelled in the graphical representation. All other edges point to frame elements and are labelled accordingly.

In order to make the annotation more flexible, we keep all frame trees separate. This means that leaves of frame trees are nodes of the syntactic structure. In principle, however, frame tree leaves could also figure as roots of other frame trees, resulting in a nested semantic structure.

In addition, a model for exhaustive semantic annotation must also be able to encode the following complications:

• A frame element may consist of more than one constituent. Consequently, our model (see [2]) allows for frame trees in which multiple edges bear the same label.

• A frame element or target may consist of only part of a word in the case of (German) compound nouns. For example, the German compound Mietrechtsdiskussion (tenant law discussion) contains both the target (diskussion) that introduces a Conversation frame and its Topic role (Mietrecht). Therefore, our model is able to make reference to sub-word units.

• A frame element may be situated in a different sentence than the target, as often happens with conversation frames. Hence, frame trees can refer to entities in adjacent sentences.

• At times, the meaning of a sentence is ambiguous or vague, and annotators cannot commit to a single tag. For these situations, the model allows to tag multiple annotation referring to the same entity as underspecified, both on the level of frames and the level of frame elements. Consistent with [4], it is left to the user how to interpret this representation (e.g. as disjunction or conjunction).