The Systems Analyst comes in three distinct flavors (much like vanilla, chocolate, and strawberry). Those just starting out seem to be more document, process, and requirements-solicitation oriented. They walk into a business and hear that we need to build system ABC, and then they ask who knows the most about how ABC should work, and they go about gathering requirements. The more astute Analysts may have tools they employ to promote a cleaner solicitation, certain tricks of the creative trades. Their basic premise, the "flow" of what they manage, is from the "tribal knowledge" of Subject Matter Experts, through documents, and then passed along to Developers. Of course the Systems Analyst has a fair amount of practice in the realm of software development, so she knows how to translate departmental objectives into the procedural data flow and structured specifications required to support the creation of computer software.
Another sort of Analyst exists though, often termed a Business Systems Analyst. To start with, a BSA has more of a business management background, and frames things more in the realm of strategic planning. To a BSA the entire corporation is a means to an end, often a complex blend of monetary and social objectives. Hence the nature of what "flow" a BSA manages is ever so slightly different. He too ends up providing direction to software Developers, but his perspective is less the straight line delivery of departmental information rules to programmers and more the slow changing of the culture of his workplace to facilitate efficiency and service. Some of this includes requirements solicitation, but much more of it encompasses providing a basis for more open channels of communication amongst the staff. He is striving for synchronicity.
Nowadays I suppose you have a third sort of Analyst, although they don't go by that title. In an Agile environment we have the Scrummaster. He has more of an internal entrepreneurs sort of perspective, living within the constant flow of business changes and potentialities at the intersection of resources and technological possibilities. His objectives are both continuous improvement and disruption.
Due to the substrate of personalities required to pull off these three roles, these tend to be distinct people with disparate approaches. It's not unusual however, even a medium size company, to have a Neopolitan mix of representatives from each.