The logic of information flows (LIF) has recently been proposed as a general framework in the field of knowledge representation. In this framework, tasks of procedural nature can still be modeled in a declarative, logic-based fashion. In this paper, we focus on the task of query processing under limited access patterns, a well-studied problem in the database literature. We show that LIF is well-suited for modeling this task. Toward this goal, we introduce a variant of LIF called "forward" LIF (FLIF), in a first-order setting. FLIF takes a novel graph-navigational approach; it is an XPath-like language that nevertheless turns out to be equivalent to the "executable" fragment of first-order logic defined by Nash and Lud\"ascher. One can also classify the variables in FLIF expressions as inputs and outputs. Expressions where inputs and outputs are disjoint, referred to as io-disjoint FLIF expressions, allow a particularly transparent translation into algebraic query plans that respect the access limitations. Finally, we show that general FLIF expressions can always be put into io-disjoint form.

翻译：信息流逻辑（LIF）最近被提出作为知识表示领域的一个通用框架。在该框架中，程序性任务仍能以基于逻辑的声明式方式进行建模。本文聚焦于受限访问模式下的查询处理任务，这是数据库文献中一个经过充分研究的问题。我们证明LIF非常适合对此任务进行建模。为此，我们在一阶设置中引入LIF的变体，称为“前向”LIF（FLIF）。FLIF采用了一种新颖的图导航方法；它是一种类似XPath的语言，却等价于Nash和Ludäscher定义的一阶逻辑“可执行”片段。FLIF表达式中的变量可被分类为输入和输出。输入与输出不相交的表达式（称为io不相交FLIF表达式）可实现特别透明的转换，转化为遵守访问限制的代数查询计划。最后，我们证明一般FLIF表达式始终可以转化为io不相交形式。