What is the difference between jcr:primaryType and jcr:mixinTypes?

Question

I am just curious to know what is the difference between jcr:primaryType and jcr:mixinTypes, and why exactly does jcr:mixinTypes is used ? what does it signifies ? If you check

Answer 1

A Node can have only one jcr:primaryType but it can have several jcr:mixinTypes, so it is correct to see the mixins as "traits" or additional aspects of a node.

While http://wiki.apache.org/jackrabbit/DavidsModel "Data First, Structure Later. Maybe" rule recommends using primary node types sparingly due to the strong constraints that they usually imply, mixins are much less constraining and very useful to identify nodes as having specific uses or properties.

The mix:lockable mixin that you mention, for example, is used to express that a node can be locked. As per http://www.day.com/specs/jcr/2.0/17_Locking.html, only nodes with mixin node type mix:lockable may hold locks. Any type of node can potentially be locked, so using a node type for that wouldn't work.