Characteristics of modern system implementation languages
Judith Bishop, R. Faria · 1995
Systems are written in systems implementation languages.What characterizes such languages in the mid-1990's?This paper identifies the typical environment that a system is being targeted for these days -as opposed to twenty years agoand emphasizes how this radically affects the language in which development proceeds.It then considers two directions that systems development is taking.The first relies heavily on design tools and methodologies, which are the means for describing the underlying structure of the system.The second interposes an additional layer of description between the design steps and the programming language, and maintains the structure here.The rest of the paper focuses on these intermediate languages, identifying their characteristics and advantages and looking at two examples, Darwin and UniCon.In conclusion, we highlight the (sometimes surprising) results that have emerged so far, and predict the way in which modern systems implementation languages could move.Figure 1 summarizes these simple days.The salient point is that the structure of the system was primarily embodied in the actual SIL code.If one was lucky, and the language was Pascal or an Algol variant, and written according to the structured programming practices which were newly in vogue, then it was still possible for a single person to find their way around a system, maintain and modify it.But for many programmers, a system meant sheaves of assembler, commented or not, documented or not, and working or not.Improving this situation was one of the main activities of computer scientists from the mid-1960s.The bid to make SlLs more effective then followed several routes.Structured programming was the first movement, and it revolutionized coding practice in the 1970s.New SILs had to make sure they had the right programming constructs to support it.Thereafter, stepwise refinement and type checking were promoted, both via the strong voice of the Algol 68 supporters and through the success of Pascal [ Wirth 19771.