BPMN - how to draw a basic BPMN that conforms to well structured choreography?

One 、 What is? BPMN

BPMN（Business Process Modeling Notation）, It refers to business process modeling and annotation , Including how these elements are combined into a business flow chart .

Two 、BPMN Basics

This paper introduces BPMN Include only right Stream object Introduction to . Stream object ： Is the main graphical element that defines the business process , There are three kinds of ： event 、 Activities 、 gateway .
event （Events）： contain The event begins （start event）、 Intermediate Events （activity）、 The end of the incident （end event）. The beginning of the event is represented by a thin circle , The activities of intermediate events are represented by rounded rectangles , The end of the event is indicated by a thick circle .

Activities （Activities）： A series of activities form an intermediate event .

gateway （Gateways）： Used to represent the branching and merging of processes , Use a diamond to show . Only three common gateways are introduced here , Each gateway is also divided into bifurcations （split） And merge （join） gateway ：

• Exclusive gateway （XOR Gateway）： Only one path will be selected
• Parallel gateway （AND Gateway）： All paths will be selected at the same time
• Inclusive gateway （OR Gateway）： Select any one or more paths
  

3、 ... and 、 Example diagram in accordance with well structured arrangement

The green circle here indicates the beginning of the event , The orange circle indicates the end of the event .

Four 、 The significance of well structured arrangement

It is used to convert an arrangement with different structures but the same semantics into an arrangement with unified structure , To eliminate the diversity of structural structures .
The advantage of this is ： When defining the formal semantics of choreography , Just consider the well structured layout to the workflow network （WF-net） Mapping . Besides , Well structured arrangement is mainly to facilitate BPMN Choreograph to workflow network （WF-net） Mapping , It will not lose the generality of the arrangement . in short , For convenience BPMN To WF-net Mapping .

5、 ... and 、 The characteristics of well structured arrangement

Well structured arrangement has the following characteristics ：

(1) The event began with a , And there is only one output stream , Without input stream ;
(2) At the end of the event, there is a , And there is only one input stream , Without output stream ;
(3) An activity has only one input stream and one output stream ;
(4) A fork gateway can only have one input stream , Multiple output streams ;
(5) The merge gateway can only have one output stream , Multiple input streams ;
(6) The gateway must be connected to the activity .

notes ： Input stream and output stream are sequential streams ： Use a solid line with a solid arrow to indicate , Used to specify the order in which activities are executed .