The Enterprise Architect has a much different role and responsibilities, yet the skill set is built on those of the systems engineer and system architect. Fundamentally, the first responsibility of the Enterprise Architect is enable and support the decision-making process enables and supports effective and cost efficient investments in tools and processes that optimally advance the mission of the organization to reach its vision; I call this the Mission Alignment process. The second is to support the Governance and Policy Management processes to ensure that the organization's policies and standards enable and support the organization's mission alignment for achieving its mission, rather than inhibiting it from the achievement.
In this regard, for the Enterprise Architect, the Mission Alignment process produces the organization's requirements for performing activities to achieve its goal (the organization's performance requirements that are the analog of the system performance requirements for a project). At the same time, for the Enterprise Architect, the policies and standards are the analog of the design constraint type requirements. Consequently, the Enterprise Architect will use many of the same process patterns as the Systems Engineer--just applied to decision-making as opposed to transforming some portion of the architecture.
The post is an extension of a presentation I made at the 2009 SEI SATURN conference.