Programming in logic without logic programming

In previous work, we proposed a logic-based framework in which computation is the execution of actions in an attempt to make reactive rules of the form if antecedent then consequent true in a canonical model of a logic program determined by an initial state, sequence of events, and the resulting sequence of subsequent states. In this model-theoretic semantics, reactive rules are the driving force, and logic programs play only a supporting role. In the canonical model, states, actions and other events are represented with timestamps. But in the operational semantics, for the sake of efficiency, timestamps are omitted and only the current state is maintained. State transitions are performed reactively by executing actions to make the consequents of rules true whenever the antecedents become true. This operational semantics is sound, but incomplete. It cannot make reactive rules true by preventing their antecedents from becoming true, or by proactively making their consequents true before their antecedents become true. In this paper, we characterize the notion of reactive model, and prove that the operational semantics can generate all and only such models. In order to focus on the main issues, we omit the logic programming component of the framework.Comment: Under consideration in Theory and Practice of Logic Programming (TPLP

What is a good plan?

The word plan is in English both a verb and a noun, reminding us that to plan is a process resulting in a product, a plan. While the Last Planner System (LPS) is primarily focused on how to plan and control production, other planning concepts are more focused on the plan contents (the plan). A more explicit approach to the characteristics of a good plan could improve LPS as a planning concept. The paper proposes such a list, based on a discussion of the plan contents highlighted by the following planning concepts: Critical Path, the Location-Based Management System, Takt Planning, Critical Chain, Agile, Task Planning and the Last Planner System

Context of Production Control in Construction

It is commonly accepted that production control systems should correspond to the context within which they are operating, i.e. the production situation. However, rarely is this context indicated or made explicit; for example, the boundary conditions or the range of validity of a particular production control method. Thus, it is the aim of this paper to analyze how the production context could more sys- tematically be taken into account when determining which production control system to use. Whilst it is acknowledged that contextual issues can be approached in a variety of ways, this is dependent on the perspective being considered (e.g. from a management hierarchy perspective, or a process stage perspective). This investigation looks at context from a process stage perspective and firstly considers the major production control approaches (such as CPM, Line-of-Balance, Last Planner System and Critical Chain) to determine their range of validity. Secondly, we endeavour to identify a typology of production control situations (ideal types), together with a suggestion for production control in each case. Finally, we attempt to deconstruct production control into its constituent elements and evaluate the alternative suggestions at this elemental level in relation to their contextual assumptions. In the paper, all three approaches are discussed and illustrated, based on prior literature and field observations

Suggestions to Improve Lean Construction Planning

The Last Planner System® has been one of the most popular lean construction tools that offers a solution to tackle the problems of production management on construction sites. Since its inception almost 20 years ago, construction companies across the world have implemented Last Planner with reported success. However, even as Last Planner was originally designed to address some shortcomings of the CPM method, a particular shortcoming – namely task continuity was not addressed directly. Also, excepting PPC and Reasons for Non Completion charts, there are no explicit visual tools offered by the Last Planner system. On the other hand, Line of Balance based approaches intrinsically support the consideration of task continuity, and offer a basic visual management approach in schedule representation. With some exceptions, Line of Balance is seen as a special technique applicable only in linear or repetitive work based schedules. The authors suggest that i) there is a need for a robust theory of planning and scheduling and ii) there is a need for a more suitable approach that addresses critical aspects of planning and scheduling function for example by integrating Line of Balance and Last Planner to provide a more robust support for construction scheduling

The Immune System: the ultimate fractionated cyber-physical system

In this little vision paper we analyze the human immune system from a computer science point of view with the aim of understanding the architecture and features that allow robust, effective behavior to emerge from local sensing and actions. We then recall the notion of fractionated cyber-physical systems, and compare and contrast this to the immune system. We conclude with some challenges.Comment: In Proceedings Festschrift for Dave Schmidt, arXiv:1309.455