The general concept of the Things Library is that every library item has a series of key-value attributes that describe the item. Every item can have attachments which are other items that have key/value attributes. Attributes are global to the item type to which they belong and help explain what the value is and how to parse it such as a pick list item or a date or time or decimal number.
One of the goals is to make the general data structure as simple as possible at the item level. In order to have a proper item data structure, it must have a name, type.
There are two core schema documents. The item schema is designed to be as flexible as possible with the least number of requirements as the only requrements is a name and a type. The library schema is designed to be a robust schema to hold many items that are all tied together in various ways such as item attributes are tied to type attributes.
The latest schema documents are always found in the /latest folder but within the document will refer to the actual version it represents: