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）近期被提出作为知识表示领域的一个通用框架。在该框架中，过程性任务仍可通过基于逻辑的声明式方式进行建模。本文聚焦于有限访问模式下的查询处理任务——这是数据库文献中一个研究深入的问题。我们证明LIF非常适合对此任务建模。为实现这一目标，我们在一阶逻辑设置中引入LIF的变体"前向"LIF（FLIF）。FLIF采用新颖的图导航方法，其语法类似XPath语言，但最终被证明等价于Nash和Ludäscher定义的一阶逻辑"可执行"片段。FLIF表达式中的变量可进一步分类为输入变量和输出变量。当输入与输出变量互不相交时（称为输入输出不相交FLIF表达式），这些表达式可转化为遵循访问限制的代数查询计划，且转化过程具有高度透明性。最后，我们证明任意FLIF表达式均可转化为输入输出不相交形式。