Updating valid `type` elements

[mkavulich]

Currently there are no explicit rules for what variable type elements are valid. In the XML schema file, the following are listed:

• integer
• real
• logical
• character
• double precision
• complex

With the current schema, 5 standard name entries fail to validate, all because they use some custom derived type:

standard_names.xml:643: Schemas validity error : Element 'type': [facet 'pattern'] The value 'physics_state' is not accepted by the pattern '[cC][oO][mM][pP][lL][eE][xX]'.
standard_names.xml:649: Schemas validity error : Element 'type': [facet 'pattern'] The value 'physics_tend' is not accepted by the pattern '[cC][oO][mM][pP][lL][eE][xX]'.
standard_names.xml:1512: Schemas validity error : Element 'type': [facet 'pattern'] The value 'ccpp_constituent_prop_ptr_t' is not accepted by the pattern '[cC][oO][mM][pP][lL][eE][xX]'.
standard_names.xml:4227: Schemas validity error : Element 'type': [facet 'pattern'] The value 'sfcflw_type' is not accepted by the pattern '[cC][oO][mM][pP][lL][eE][xX]'.
standard_names.xml:4240: Schemas validity error : Element 'type': [facet 'pattern'] The value 'sfcfsw_type' is not accepted by the pattern '[cC][oO][mM][pP][lL][eE][xX]'.

In order to have the schema properly validate, I propose the following modifications to the schema file:

diff --git a/standard_names_v1_0.xsd b/standard_names_v1_0.xsd
index 462fa96..a8fc18e 100644
--- a/standard_names_v1_0.xsd
+++ b/standard_names_v1_0.xsd
@@ -13,12 +13,12 @@
 
   <xs:simpleType name="type_type">
     <xs:restriction base="xs:string">
-      <xs:pattern value="[iI][nN][tT][eE][gG][eE][rR]"/>
-      <xs:pattern value="[rR][eE][aA][lL]"/>
-      <xs:pattern value="[lL][oO][gG][iI][cC][aA][lL]"/>
-      <xs:pattern value="[cC][hH][aA][rR][aA][cC][tT][eE][rR]"/>
-      <xs:pattern value="[dD][oO][uU][bB][lL][eE][ ]*[pP][rR][eE][cC][iI][sS][iI][oO][nN]"/>
-      <xs:pattern value="[cC][oO][mM][pP][lL][eE][xX]"/>
+      <xs:pattern value="integer"/>
+      <xs:pattern value="real"/>
+      <xs:pattern value="logical"/>
+      <xs:pattern value="character"/>
+      <xs:pattern value="complex"/>
+      <xs:pattern value="ddt"/>
     </xs:restriction>
   </xs:simpleType>

This change converts all the rules checks to lowercase (no reason to allow mixed-case, in my opinion), removes the double precision entry (which is redundant to real; similar to our discussion on the removal of the kind attribute, this should be application-specific and not specified by the standard names) and adds a new ddt entry to cover the derived data types that we already include.

I will also update the Rules document to explicitly state these allowed types.