Layers (a)-(h) represent a loose hierarchy of informational details, and in some cases a `higher' type of information cannot be added unless a `lower' (i.e. more basic) type has already been provided: e.g. (a) is a pre-requisite for (b).
Table 9 below summarises which of the features distinguished in (a)-(h) have been implemented in a number of annotation schemes. (It is a `quick overview'; a more detailed overview is given in the documents SASG2 and SASG3.)
|Dependency relations (c)||-||x*||x*||-||-||x||x||-||-|
|Syntactic functions (d)||-||x||x||(x)||x||x**||x||x||x*|
|Logical information (f)||-||x||x||-||-||x*||x||-||-|
|Spoken language (h)||-||x*||-||-||x*||-||x||x||x*|
|* intended for future release|
|** at word level|
|- not implemented|
However, there is no strict precedence between the levels, and many combinations of information types, other than those represented in the table, are in principle possible. It is conceivable, for example, that someone might wish to indicate functional information about syntactic segments in a corpus while ignoring other kinds of information.