## 1 Introduction  
Business Process Model and Notation (BPMN) is an Object Management Group (OMG) standard for specifying business processes. The current version is 2.0.2 [1], and it allows the modelling of business processes both from a graphical perspective and from a machine-readable perspective (using an XML-based representation). It makes BPMN a suitable language for the description of processes in a visual way and their subsequent analysis using data analytic or process mining techniques [2]. Presently, BPMN is a leading industry standard for specifying workflows. It is broadly used, for example, in the domain of health-care protocols [3], software process tailoring [4], Data Quality management [5] or Internet of Things proceedings [6], among many other cases. This paper describes an approach for the simplification of a BPMN process model aimed to optimise the number of elements included in the workflow. During the simplification task, the behaviour described initially must be preserved, i.e., the new simplified workflow model must be coherent with the original one, offering the same flow logic. This simplification procedure aims to achieve two primary goals, namely:  
* Provide a cleaner and easier to understand graphic representation. Therefore, a better understanding with less effort of these workflows will be provided to human readers [7]. * Reduce the complexity of the model for its processing by software agents. An optimised version of a BPMN model will yield more efficient results for process mining software and data analytic techniques. It must be borne in mind that an efficient BPMN simplification can be a complicated task. In real scenarios, the number of possible paths in a workflow can grow very fast as the number of activities increases. Furthermore, due to loops and other structures in the model, the number of different combinations in the activities execution can cause an explosion in the number of states. This paper shows an iterative procedure to achieve the simplification objective. In the proposed approach, the deployment of a Pattern Repository will play a principal role in the simplification procedure. This pool of BPMN-based patterns is gathered by the authors, and it contains the core of the proposal. The main goal of this contribution is to provide a mechanism to simplify, if possible, a given BPMN Process type workflow (that describes a sequence or flow of activities with the objective of carrying out work). This type of workflows are commonly created in a non-automatic manner, i.e., a human operator creates them. First of all, this manual creation process is prone to introduce redundant or repetitive paths that do not provide new information to the behaviour of the model. In this situation, the proposed algorithm will identify the unnecessary elements and will generate a new simplified BPMN diagram offering an equivalent description of the workflow. Secondly, the application of the simplification algorithm is also intended for more complex issues. In particular, presently, it is common the generation of BPMN diagrams involving hundreds of activities from different perspectives and different levels of abstraction [8]. It provides a series of advantages [8] but also results in more complex flowcharts and more analysis time demanding models. To illustrate that issue, the reader can consider Figure 1. It represents a process involving activities from three different roles: Project Manager (PM), Operator (Op), and Administrative (Ad). Let us suppose now that due to particular constraints, only a subset of these activities are relevant for concrete analysis. In a specific context, it could be interesting to focus on a particular role (or a set of them). Let's assume that we are concerned just with management operations, i.e., those performed by the Project Manager and Administrative roles. Therefore, it would be required to eliminate those activities in which the other roles (i.e., the Operator) participate.