System in System Theory can be everything. (Facets of Systems Science, George Klir, 1991) System is on TOP of TREE, Superclass of other categories.
In overall, System Development included 2 major phases:
1- System Analysis: including Planning, requirements, analysis and etc. These items related to specific methodology in system theory.
2- System Design: including design, implementation, test, deploy, maintenance and etc.
As I said, System can be everything. For example:
Mechanical systems, Psychological systems, Social systems, Aircraft Systems and so on. Each category may have detailed and specific analysis and design steps based on mentioned 2 major phases.
In computer world, Software Systems is one of System categories.
Each software Analysis and Design method is based on mentioned 2 major phases too.
Additionally, In Software Systems, we have some paradigms to analysis and design like:
Structural/Process Centered
Data Centered
Object Oriented
Service Oriented
and etc.
Each of them has it's own Analysis and Design Steps. These steps are based on 2 major phases as well. But in details, they have some differences.
To sum up, Systems Analysis and Design is a big picture to all other type of systems. Learning System Analysis and Design helps to understand all other systems analysis and design and specially helps to compare and evaluate them.