Support for secondary edges #6
Description
The latest rstpp format supports secondary, treebreaking edges, represented as follows in rstWeb. Minimal example (not necessarily linguistically correct!)
<rst>
<header>
<relations>
<rel name="cause" type="rst"/>
<rel name="evaluation" type="rst"/>
</relations>
<sigtypes>
<sig type="DM" subtypes="DM"/>
<sig type="Reference" subtypes="Comparative reference;Demonstrative reference;Personal reference;Propositional reference"/>
</sigtypes>
</header>
<body>
<segment id="1" parent="4" relname="span">Lin wants to go</segment>
<segment id="2" parent="3" relname="cause">because Beth knows Kim -</segment>
<segment id="3" parent="6" relname="span">this won’t happen</segment>
<group id="4" type="span" />
<group id="6" type="span" parent="1" relname="evaluation"/>
<secedges>
<secedge id="2-1" source="2" target="1" relname="cause"/>
</secedges>
<signals>
<signal source="6" type="Reference" subtype="Demonstrative reference" tokens="10"/>
<signal source="2-1" type="DM" subtype="DM" tokens="5"/>
</signals>
</body>
</rst>
Note that secondary edges support signals just like regular edges, and their 'source' field uses a 'src-trg' syntax (1-2), which is also used in the <secedge> element. Since these structures are treebreaking and can form cycles I propose using pointing relations to represent them on top of the existing dominance edge tree, and using a second pointing relation type if cycles occur. This should be very rare if even attested, but the importer should ideally be able to handle it by checking for cycles before generating Salt.