Docs: Data model -> Data models, note that NOT_NULL() is equal to SQL's COALESCE()

Documentation/Books/AQL/Functions/Miscellaneous.mdpp

@@ -6,11 +6,12 @@
 
 `NOT_NULL(alternative, ...) → value`
 
-Return the first alternative that is not *null*, and *null* if all alternatives
-are *null* themselves.
+Return the first element that is not *null*, and *null* if all alternatives
+are *null* themselves. It is also known as `COALESCE()` in SQL.
 
 - **alternative** (any, *repeatable*): input of arbitrary type
-- returns **value** (any):
+- returns **value** (any): first non-null parameter, or *null* if all arguments
+  are *null*
 
 !SUBSECTION FIRST_LIST()
 

Documentation/Books/Manual/DataModeling/README.mdpp

@@ -1,4 +1,4 @@
-!CHAPTER Data model & modeling
+!CHAPTER Data models & modeling
 
 This chapter introduces ArangoDB's core concepts and covers
 

Documentation/Books/Manual/SUMMARY.md

@@ -21,7 +21,7 @@
   * [Data models](Scalability/DataModels.md)
   * [Limitations](Scalability/Limitations.md)
 #
-* [Data model & modeling](DataModeling/README.md)
+* [Data models & modeling](DataModeling/README.md)
 # * [Collections](FirstSteps/CollectionsAndDocuments.md) #TODO
   * [Concepts](DataModeling/Concepts.md)
   * [Databases](DataModeling/Databases/README.md)