The reasons you need to change the standard GN4.XSD schema are:
•You need more or different article elements than the standard schema provides. See About schema elements and Add article elements to the schema.
•You want the article elements to appear in a different order in the article tree. See the initial paragraph in the Add article elements to list in schema topic.
•You need more or different attributes of one or more objects. See Add attributes to the schema.
•You need additional objects.
Note: if you intend to import content from a GN3 articles based system? In that case, the GN4 schema must be as close as possible to the GN3 schema, or you will need to do a lot of work on adjustment of data before being able to start import to GN4.
Use the Table of Contents to find information. See also Using table of contents in help.