This section shows the structure of
the FNA keys is a hierarchy, at least conceptually; the structure of the database used to store those keys is
explained later in Data Structure
and Node Types & Relationships
Targets with a Single Parent -
A couplet is a parent-child relationship with two children:
If all targets in a key have a single parent, then there is a unique path between the root of the key (a family, genus, species or subspecies) to each target usually one level down from the root. That is, from each target one can unambiguously traverse back up to the root of the hierarchy.
Targets with Multiple Parents -
Unfortunately, as seen in the Attribute Sets
section, some targets in FNA keys can have more than one attribute set, which results in multiple parents for those targets.
That is, depending on which path is chosen, a different attribute set results. When the target is terminal, as is the case for B. repanda, visualizing the multiple paths to the root is relatively easy.
Effect of Single and Multiple Parents on Next-Level Keys -
How keys are connected to the key at the next level is different for targets with single and multiple parents; that is, with targets with single and multiple attribute sets. What follows is an example of each case.
Silene is a target in the Caryophyllaceae key with a single attribute set:
The Silene key has the following connections to the Caryophyllaceae key:
The row numbers in this diagram are relative. In the next section Key Types and Subkeys
renumbering of rows in subkeys is discussed. Row numbers in subkey diagrams in this section are shown before renumbering.
What is important is that the parent for the initial couplet in the Seline key is in the Caryophyllaceae key, so the logic to set up this parent-child relationship is different than if they were in the same key. Row 37 is the Silene target, but it also has a next couplet that is the first couplet in the Silene subkey. For the single parent case there is no zero row representing the root for the Silene key; that is, the row zero shown in the key diagram in Couplets, Targets and Rows
is not needed in this case.
S. scoleri is a target in the Silene key with two attribute sets:
By creating a special node that acts as a target for rows 118 and 143 in the Silene key and as a couplet for rows 1 and 2 in the S. scolari key, all other elements in the Silene and S. scolari keys can be treated as normal parent-child relationships.:
The Node Structure and Types
post discusses how key hierarchies, including these special multiple-attribute-set targets, are represented as data structures.
[Add a short section referring to the Target Subset Index in Node Structure and Types that creates a naming hierarchy, which may deviate from the attributes hierarchy that is defined by the keys.]