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<p />
<h2><a name="SDD_Part_0_Introduction_and_Prim"></a> SDD Part 0: Introduction and Primer to the SDD Standard </h2>
<p />
<h3><a name="2_4_Dichotomous_keys"></a><a name="2_4_Dichotomous_keys_"></a> 2.4 Dichotomous keys. </h3>
<h4><a name="2_4_1_Traditional_dichotomous_ke"></a> 2.4.1 Traditional dichotomous keys. </h4>
<p />
Dichotomous keys (Box 2.3.1) are specialised identification tools comprising fragments of descriptive data arranged in couplets forming a branching tree. Each fragment (lead) comprises a small (occasionally verbose) natural-language description. Each node in the tree typically has two branches (dichotomy) but may have three (trichotomy) or more branches. Several differing formats of dichotomous keys are traditionally used.
<p />
<h4><a name="Box_2_4_1_Typical_dichotomous_ke"></a> Box 2.4.1 - Typical dichotomous keys </h4>
<p />
<p />
<div align="center">
<table bgcolor="#ddddff" border="0" cellpadding="5" style="border-collapse: collapse" bordercolor="#111111" width="80%" id="table7" >
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px; border-top-style: solid; border-top-width: 1px">
<b>Key to Ascomycete genera</b></td>
<td align="right" style="border-right-style: solid; border-right-width: 1px; border-top-style: solid; border-top-width: 1px"> </td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px; border-top-style: solid; border-top-width: 1px">
<br>
Ascus unitunicate</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px; border-top-style: solid; border-top-width: 1px"> </td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Clypeus present around ostiolar neck</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px"> </td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Clypeus poorly developed</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px">
<i>Glomerella</i></td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Clypeus well developed</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px">
<i>Hyllachora</i></td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Clypeus lacking</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px"> </td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Ascus widest in middle</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px">
<i>Physalospora</i></td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Ascus clavate or cylindrical</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px">
<i>Glomerella</i></td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Ascus bitunicate</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px"> </td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px">
Ascostroma uniloculate</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px">
<i>Guignardia</i></td>
</tr>
<tr>
<td width="409" style="border-left-style: solid; border-left-width: 1px; border-bottom-style: solid; border-bottom-width: 1px">
Ascostroma muliloculate</td>
<td align="right" style="border-right-style: solid; border-right-width: 1px; border-bottom-style: solid; border-bottom-width: 1px">
<i>Botryosphaeria</i></td>
</tr>
</table>
</div>
<br>
<div align="center">
<table bgcolor="#ddddff" border="1" cellpadding="5" style="border-collapse: collapse" bordercolor="#111111" width="80%" id="table8">
<tr>
<td style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: solid; border-top-width: 1px; border-bottom-style: none; border-bottom-width: medium" colspan="3">
<b>Key to Australian skinks in the genus <i>Ctenotus</i></b></td>
</tr>
<tr>
<td width="50" style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: solid; border-top-width: 1px; border-bottom-style: none; border-bottom-width: medium">1</td>
<td style="border-left-style: none; border-left-width: medium; border-right-style: none; border-right-width: medium; border-top-style: solid; border-top-width: 1px; border-bottom-style: none; border-bottom-width: medium">Dark upper lateral zone with one or more distinct series of
pale spots or blotches along the body</td>
<td width="114" valign="bottom" align="right" style="border-left-style: none; border-left-width: medium; border-right-style: solid; border-right-width: 1px; border-top-style: solid; border-top-width: 1px; border-bottom-style: none; border-bottom-width: medium">2</td>
</tr>
<tr>
<td width="50" style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">1a</td>
<td style="border-style: none; border-width: medium">Dark upper lateral zone obscurely mottled or uniform with at
most a few pale spots anteriorly</td>
<td width="114" valign="bottom" align="right" style="border-left-style: none; border-left-width: medium; border-right-style: solid; border-right-width: 1px; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">3</td>
</tr>
<tr>
<td width="50" style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">2</td>
<td style="border-style: none; border-width: medium">Fewer than 25 lamellae under the fourth toe; supralabials 7-8 (usually 7); prefrontals separated</td>
<td width="114" valign="bottom" align="right" style="border-left-style: none; border-left-width: medium; border-right-style: solid; border-right-width: 1px; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">
<i>C. arcanus</i></td>
</tr>
<tr>
<td width="50" style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">2a</td>
<td style="border-style: none; border-width: medium">More than 25 lamellae under the fourth toe; supralabials 8-9
(usually 8); prefrontals usually in contact</td>
<td width="114" valign="bottom" align="right" style="border-left-style: none; border-left-width: medium; border-right-style: solid; border-right-width: 1px; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">
<i>C. alleni</i></td>
</tr>
<tr>
<td width="50" style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">3</td>
<td style="border-style: none; border-width: medium">Pale mid-lateral stripe passes over the hindlimb to continue
along the tail </td>
<td width="114" valign="bottom" align="right" style="border-left-style: none; border-left-width: medium; border-right-style: solid; border-right-width: 1px; border-top-style: none; border-top-width: medium; border-bottom-style: none; border-bottom-width: medium">
<i>C. inornatus</i></td>
</tr>
<tr>
<td width="50" style="border-left-style: solid; border-left-width: 1px; border-right-style: none; border-right-width: medium; border-top-style: none; border-top-width: medium; border-bottom-style: solid; border-bottom-width: 1px">3a</td>
<td style="border-left-style: none; border-left-width: medium; border-right-style: none; border-right-width: medium; border-top-style: none; border-top-width: medium; border-bottom-style: solid; border-bottom-width: 1px">Pale mid-lateral stripe extends to groin, then continues
along the front edge of the hindlimb</td>
<td width="114" valign="bottom" align="right" style="border-left-style: none; border-left-width: medium; border-right-style: solid; border-right-width: 1px; border-top-style: none; border-top-width: medium; border-bottom-style: solid; border-bottom-width: 1px">
<i>C. coggeri</i></td>
</tr>
</table>
<p />
<p />
<div align="center">
<table bgcolor="#ddddff" cellspacing="2" cellpadding="2" style="border-collapse: collapse" bordercolor="#111111" width="80%">
<tr>
<td colspan="4" align="left" style="border-left-style: solid; border-left-width: 1px; border-top-style: solid; border-top-width: 1px; border-right-style: solid; border-right-width: 1px; border-bottom-style: solid; border-bottom-width: 1px"><b>Key to <i>Aira</i> naturalized in Australia</b></td>
</tr>
<tr>
<td style="border-left-style: solid; border-left-width: 1px" width="5%" height="35" rowspan="3" valign="top">1.</td>
<td width="50%" height="15" valign="top">Inflorescence open and spreading</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top">2</td>
</tr>
<tr>
<td width="50%" height="15" valign="top">Inflorescence dense and spike-like</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top"><b>*</b><b>A.
praecox</b></td>
</tr>
<tr>
<td width="50%" height="10" valign="top"></td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="10" valign="top"></td>
</tr>
<tr>
<td style="border-left-style: solid; border-left-width: 1px" width="5%" height="35" rowspan="3" valign="top">2.</td>
<td width="50%" height="15" valign="top">Pedicels 3-8 times spikelet length</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top">3</td>
</tr>
<tr>
<td width="50%" height="15" valign="top">Pedicels up to 3 times spikelet length</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top">4</td>
</tr>
<tr>
<td width="50%" height="10" valign="top"></td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="10" valign="top"></td>
</tr>
<tr>
<td style="border-left-style: solid; border-left-width: 1px" width="5%" height="35" rowspan="3" valign="top">3.</td>
<td width="50%" height="15" valign="top">Spikelets c. 3.5 mm long</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top"><b>*A. provincialis</b></td>
</tr>
<tr>
<td width="50%" height="15" valign="top">Spikelets c. 2 mm long</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top"><b>*A. elegantissima</b></td>
</tr>
<tr>
<td width="50%" height="10" valign="top"></td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="10" valign="top"></td>
</tr>
<tr>
<td style="border-bottom-style: solid; border-bottom-width: 1px; border-left-style: solid; border-left-width: 1px" width="5%" height="35" rowspan="3" valign="top">4.</td>
<td width="50%" height="15" valign="top">Spikelets 2-2.5 mm long</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top"><b>*A. cupaniana</b></td>
</tr>
<tr>
<td width="50%" height="15" valign="top">Spikelets 2.5-3.2 mm long</td>
<td style="border-right-style: solid; border-right-width: 1px" width="45%" height="15" valign="top"><b>*A. caryophyllea</b></td>
</tr>
<tr>
<td style="border-bottom-style: solid; border-bottom-width: 1px" width="50%" height="10" valign="top"></td>
<td style="border-right-style: solid; border-right-width: 1px; border-bottom-style: solid; border-bottom-width: 1px" width="45%" height="10" valign="top"></td>
</tr>
</table>
</div>
</div>
<p />
<p />
<p />
<h3><a name="2_4_2_SDD_representation_of_dich"></a> 2.4.2 SDD representation of dichotomous keys </h3>
<p />
While dichotomous keys can be presented in various formats, the essential elements of all dichotomous keys are identical. Each consists of a tree of questions, each with two (or occasionally more) possible choices, each choice leading to another question or a taxon.
<p />
A dichotomous key rendered in SDD requires three essential items: the names of the taxa being described, a set of questions (leads) used to separate the taxa, and the nodes defining the structure of the leads.
<p />
A simple SDD instance document for dichotomous key data has the basic structure shown below and in Example 2.4.2.
<p />
There are at least two different ways of generating a dichotomous key in a well structured SDD instance document, using statements or questions, these will be dealt with separately.
<p />
<img alt="identificationkey.gif" src="http://wiki.tdwg.org/twiki/static/_publish/identificationkey.gif" />
<p />
<h4><a name="Example_2_4_2_Dichotomous_keys_w"></a> Example 2.4.2 - Dichotomous keys within SDD </h4>
<p />
<table bgcolor="#ddddff" border="0" width="100%" cellpadding="5" cellspacing="5" style="border-collapse: collapse" bordercolor="#111111">
<p />
<tr>
<td>
<p />
<pre>
<Datasets>
<TechnicalMetadata>
... information about the generator (Technical metadata)
</TechnicalMetadata>
<Dataset>
<TaxonNames>
... naming the entities described (Taxon names)
</TaxonNames>
<IdentificationKeys>
<IdentificationKey>
... the dichotomous key structure (see below)
</IdentificationKey>
</IdentificationKeys>
</Dataset>
</Datasets>
</pre>
<p />
</td>
</tr>
<p />
</table>
<p />
<h3><a name="2_4_3_Dichotomous_keys_using_sta"></a> 2.4.3 Dichotomous keys using statements </h3>
<p />
A dichotomous key structured with statements consists mostly of the elements <lead> and <result>. <Lead> points to another couplet while <Result> points to a taxon name.
<p />
<h4><a name="Example_2_4_3_Structure_of_dicho"></a> Example 2.4.3 - Structure of dichotomous keys within SDD (statements) </h4>
<p />
<table bgcolor="#ddddff" border="0" width="100%" cellpadding="5" cellspacing="5" style="border-collapse: collapse" bordercolor="#111111">
<p />
<tr>
<td>
<p />
<pre>
<IdentificationKey id="key1">
<Representation>
<Label>Key to Australian Aira Using statements </Label>
</Representation>
<Leads>
<Lead id="lead1">
<Statement>
<Label>Inflorescence open and spreading </Label>
</Statement>
</Lead>
<Result>
<Statement>
<Label>Inflorescence dense and spike-like </Label>
</Statement>
<TaxonName ref="t1"/>
</Result>
<Lead id="lead2">
<Parent ref="lead1"/>
<Statement>
<Label>Pedicels 3-8 times spikelet length </Label>
</Statement>
</Lead>
<Lead id="lead3">
<Parent ref="lead1"/>
<Statement>
<Label>Pedicels up to 3 times spikelet length </Label>
</Statement>
</Lead>
<Result>
<Parent ref="lead2"/>
<Statement>
<Label>Spikelets c. 3.5 mm long </Label>
</Statement>
<TaxonName ref="t2"/>
</Result>
<Result>
<Parent ref="lead2"/>
<Statement>
<Label>Spikelets c. 2 mm long </Label>
</Statement>
<TaxonName ref="t3"/>
</Result>
<Result>
<Parent ref="lead3"/>
<Statement>
<Label>Spikelets 2-2.5 mm long </Label>
</Statement>
<TaxonName ref="t4"/>
</Result>
<Result>
<Parent ref="lead3".>
<Statement>
<Label>Spikelets 2.5-3.2 mm long </Label>
</Statement>
<TaxonName ref="t5"/>
</Result>
</Leads>
</IdentificationKey>
</pre>
<p />
</td>
</tr>
<p />
</table>
<p />
<p />
<h3><a name="2_4_4_Dichotomous_keys_using_que"></a> 2.4.4 Dichotomous keys using questions </h3>
<p />
When a dichotomous key in an SDD instance document is structured with questions the statements act as answers to questions rather than independent statements.
<p />
<h4><a name="Example_2_4_4_1_Structure_of_dic"></a> Example 2.4.4.1 - Structure of dichotomous keys within SDD (questions) </h4>
<p />
<table bgcolor="#ddddff" border="0" width="100%" cellpadding="5" cellspacing="5" style="border-collapse: collapse" bordercolor="#111111">
<p />
<tr>
<td>
<p />
<p />
<pre>
<IdentificationKey id="key1">
<Representation>
<Label>Key to Ascomycete genera</Label>
</Representation>
<Question>
<Label>Is the ascus unitunicate</Label>
</Question>
<Leads>
<Lead id="lead1">
<Statement>
<Label>yes, unitunicate</Label>
</Statement>
<Question>
<Label>Is a clypeus present</Label>
</Question>
</Lead>
<Lead id="lead2">
<Statement>
<Label>no, bitubinate</Label>
</Statement>
<Question>
<Label>Is ascostroma uniloculate</Label>
</Question>
</Lead>
<Lead id="lead3">
<Parent ref="lead1"/>
<Statement>
<Label>yes, clypeus present around ostiolar neck</Label>
</Statement>
<Question>
<Label>Is clypeus well developed</Label>
</Question>
</Lead>
<Lead id="lead4">
<Parent ref="lead1"/>
<Statement>
<Label>no, clypeus lacking</Label>
</Statement>
<Question>
<Label>Is ascus widest in middle</Label>
</Question>
</Lead>
<Result>
<Parent ref="lead3"/>
<Statement>
<Label>clypeus poorly developed</Label>
</Statement>
<TaxonName ref="taxon1"/>
</Result>
<Result>
<Parent ref="lead3"/>
<Statement>
<Label>clypeus well developed</Label>
</Statement>
<TaxonName ref="taxon2"/>
</Result>
<Result>
<Parent ref="lead4"/>
<Statement>
<Label>ascus widest in middle</Label>
</Statement>
<TaxonName ref="taxon3"/>
</Result>
<Result>
<Parent ref="lead4".>
<Statement>
<Label>ascus clavate or cylindrical</Label>
</Statement>
<TaxonName ref="taxon1"/>
</Result>
<Result>
<Parent ref="lead2"/>
<Statement>
<Label>ascostoma uniloculate</Label>
</Statement>
<TaxonName ref="taxon4"/>
</Result>
<Result>
<Parent ref="lead2"/>
<Statement>
<Label>ascostoma multiloculate</Label>
</Statement>
<TaxonName ref="taxon5"/>
</Result>
</Leads>
</IdentificationKey>
</pre>
<p />
</td>
</tr>
<p />
</table>
<p />
For more information on defining taxon names using the <TaxonNames> element, see the topic <a href="taxonnames.html">Defining taxon names</a>.
<p />
Note that taxa can also be arranged into hierarchies. See the topic <a href="taxonhierarchies.html">Defining taxon hierarchies</a> for more information.
<p />
<Scope> describes the taxon or set of taxa to which the description applies.
<p />
The <Result> element may include a <Subkey> element, which points to another complete dichotomous key. This allows a main/subkey arrangement, for example a key to the genera of a family with results leading to a subkey identifying the species within each genus.
<p />
<h4><a name="Example_2_4_4_2_Subkeys_within_S"></a> Example 2.4.4.2 - Subkeys within SDD dichotomous keys. </h4>
<p />
<table bgcolor="#ddddff" border="0" width="100%" cellpadding="5" cellspacing="5" style="border-collapse: collapse" bordercolor="#111111">
<p />
<tr>
<td>
<p />
<p />
<pre>
<IdentificationKeys>
<IdentificationKey id="key 1">
<Representation>
<Label>Key to genera</Label>
</Representation>
<Leads>
<Lead id="lead1">
<Statement>
<Label>Inflorescence open and spreading</Label>
</Statement>
</Lead>
<Result>
<Statement>
<Label>Inflorescence dense and spike-like</Label>
</Statement>
<Subkey ref="key 2"/> (key to species of first genus))
</Result>
. . . etc.
</IdentificationKey>
</IdentificationKeys>
</pre>
<p />
</td>
</tr>
<p />
</table>
<p />
<p />
-- DonovanSharp - 01 Jun 2006
<p />
<p />
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