Nexus guide clarifications needed

1. In Scrum guide, refinement is not a mandatory event, its an optional one. Whereas, in Nexus, Refinement is a mandatory event

Why do you think refinement is very very important in Nexus and hence its mandatory ? Multiple teams, more complexity and huge dependency between those multiple teams, wouldnt it help if teams know upfront on dependency and plan better ?

2. In Scrum guide, Sprint goal is not a artifact. Whereas, in Nexus, Nexus goal is an artifact.

What is more important, individual Scrum team increment or an integrated increment when multiple teams working on single product backlog ? What is the goal of Nexus ?

Krishnakumar,

Think of Nexus as an extension of Scrum. Nexus clearly builds upon the foundation of Scrum and expands it in the areas that you mentioned. Nexus is NOT simply a larger version of Scrum, but a more complex set of guidelines for a an environment that requires multiple Scrums teams to collaborate.

Thanks Ankit and Eugene for your answers. 

Ankit, convinced with your thoughts on first question. However, 2nd question is not fully addressed.

Can you or other Nexus folks, elaborate further as my question is more on consistency?

An artifact is something which is produced and consumed. To the extent that the Nexus Goal is produced during Nexus Sprint Planning and consumed by teams in their own planning sessions, it might be seen as an artifact.

I think question 1. is not answered clearly. Does anyone mind giving a better answer?

Thanks Ian Mitchell for the clarity.

Jennifer, as multiple teams are involved in Nexus, there is lot more complexity, dependencies and integration touch points involved, they have made refinement as a mandatory event.

To my knowledge, Refinement has been a required practice in Scrum since 2011.  In the Scrum Guide, it is a required "activity" but does not achieve the higher level formality of an event.

The NG has gone further making it a required event, due to the difficult of cross team dependencies.

Note that the NG says it inherits "intent" and "purpose" attributes from the Scrum Guide, but does NOT say it inherits any other attributes(such as "required vs. optional", "formality level", "involved roles", "duties", etc).  So, for instance, NG refinement has the same intent and purpose of refinement in the SG, but it is more formal in the NG.  As another example, the Nexus SM has the same intent and purpose of a team SM, but has different duties.