CHAPTER 4 - SysML—The Systems Modeling Language

Abstract

Systems Modeling Language, or SysML, defines several elements to describe and model requirements, such as response times, size, or functions of a system, which means that it closes a gap in UML. While functional requirements can be modeled with use cases, there is no element in UML to explicitly describe non-functional requirements. An allocation is a general mechanism from the field of systems engineering to interconnect elements from different model areas. There are different types of allocations. SysML proposes three general types and lets the developer introduce additional project-specific variants. The predefined types are behavior allocation, structure allocation, and object flow allocation. Blocks describe the structure of a system. They possess information about the block itself (attribute), or they reference other blocks they are bound with (association). SysML allows one to define parametric relationships between properties of blocks. The relations between properties of different blocks can be described and defined in a parametric diagram. UML use cases are independent of their realization by a system. The activity model specifies flows as well as input and output data, which are required or created during a flow. Flows can run in parallel, or they can be synchronized, or split based on conditions. The UML state model is used in SysML completely and in unchanged form. The state machines and the corresponding diagram are independent of the respective discipline of the system we model, and they do not contain any software-specific elements. Every system, regardless of whether it is a software or hardware system or a social or biological system, has states and state transitions that can be described in a state model.