A system's architecture is a representation of a system in which there is a mapping of (1) onto hardware and software components, a mapping of the (2) onto the hardware architecture, and a concem for the human interaction with these components. That is, system architecture is concerned with a total system, including hardware, software, and humans. Software architectural structures can be divided into three major categories, depending on the broad nature of the elements they show.1) (3) embody decisions as a set of code or data units that have to be constructed or procured. 2) (4) embody decisions as to how the system is to be structured as set of elements that have runtime behavior and interactions. 3) (5) embody decisions as to how the system will relate to nonsoftware structures in its environment (such as CPUs, file systems, networks, development teams, etc. ).
空白（4）处应选择（）
A.Decompostion structures
B.Layer structures
C.Implementation structures
D.Component-and-connector structures
