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可编程控制器的数据库系统外文翻译
Database Systems for Programmable Logic Controllers
ABSTRACT
In this paper, we identify the database issues associated with programmable logic controllers (PLC), special-purpose computers used in scientific and industrial applications, e.g. in factories in manufacturing environments. We propose as a PLC database system a single-user,real-time, scalable main-memory-only relational database system with a two-level architecture having historical data modeling and manipulation capabilities, and query processing techniques incorporating time- and/or error-constrained query evaluation. We revise the ladder logic language, the most common PLC language, to incorporate data manipulation language instructions. We add a separate time component into the PLC processor scan time to handle database updates, backup, integrity enforcement and data archival issues.
1. Introduction
A programmable logic controller (PLC) is a special-purpose computer used within real-time scientific computing systems, and industrial control systems, say, the automated control of a factorys machinery - the running example used in this paper. This paper is a position paper that proposes a PLC database system and discusses its features. In doing so, we touch bases with a number of basic database topics, and, thus, frequently refer to other work for details.
PLCs are mostly used in manufacturing environments - hence, the choice of our running example. However, PLCs are also used in scientific applications for signal data gathering and preliminary data processing. Thus, we think that for some scientific applications, a PLC database may also serve as a local/transient part of a larger scientific database.
With the rapid advances in computer hardware and falling memory prices, in recent years, the capabilities of the new PLCs in the marketplace have been increasing dramatically. This paper is a position paper that argues that a PLC software can now contain a database system to greatly increase its functiona
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