The SysML Block is the basic element of SysML to move the UML Class – which is a software thing – to a higher level so that it can more naturally describe systems and other real-world items. A SysML Block defines a collection of features to describe a system.

A SysML ValueType defines values that may be used within a model. SysML blocks are based on UML classes, as extended by UML composite structures. SysML value types are based on UML data types.

A SysML block definition diagram is based on the UML class diagram, with restrictions and extensions as defined by SysML.