Software Process Engine of BeyondTrack

这只是一个草稿，作为这一个月研究、‘创新’上的一点总结。文章写得比较乱，大家有兴趣的话可以邮件我。

BeyondTrack 的 Software Process Engine 以及 SPDL 看来要暂时告一段落了 :-)

  Software Process Engine of BeyondTrack

 Software Process Engine of BeyondTrack

 1 Motivation

Software process modeling and execution is very specialized unlike general workflows. The relations and associations of tasks of an ordinary workflow are not very closed and coupled. In general, we may consider a task of an ordinary workflow is a work sheet rather than a task. By ISO/IEC 12207(SOFTWARE LIFE CYCLE PROCESSES), a task is a set of elementary or atomic actions. A task consumes inputs (data, information, control) and produces outputs (data, information, control). 
We consider that a software process engine is a subset of workflow engine is true. But, software process is too specialized to use a workflow engine. Software process has its own specifications and practices. So, in process engine of BeyondTrack, we defined a language to depict software process, which named Software Process Definition Language.

Petri Net is a formalized mathematical modeling languages for the description of discrete distributed systems. The Software process is a such system need to be defined and executed by rule and line.

 2 Main Ideas

 2.1 Coloured Petri Net

All process instances defined by the same process definition are marked as the template parameter of a token, and put these process instances into one petri net graph, which generated by the process definition. So, just using one petri net(contains the petri net graph and markings) instance we can depict all process instances defined by the same process definition by markings. Here, we use the coloured petri net to model the process engine as one idea.

Every token associates a process instance, we can treat it as the token was coloured. There is some benefits as followings:

• save storage

          The same type of process instances described by tokens respectively will share one petri net graph, so only one graph need to persist

• more easily to mine associations of process instances

          The process instance was described by coloured token, so easily to find these tokens' associations in one graph

 2.2 Nested Petri Net

TODO: sub-process

 2.3 Concurrency

TODO: concurrency description using petri net.

 3 Design Intentions

 3.1 Meta Model

As far as we know, XML technology is the base of web service, a beautiful solution for distributed heterogeneous application. The role of XML of web service is description of service and transformation of service implementation. At this view, let's have a look at how XML do it.

We decided to use Java classes as the source meta model, and XML Schema as the target meta model.

 3.1.1 SPDL XML Schema

To an XML document of the SPDL, all elements associate with each other by their names. So, the name of every element must unique in one SPDL XML document. The followings are all elements defined by SPDL.

 3.1.1.1 process-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the process definition
description	element	[0..1]	the description of the process definition
actor-definition	element	[1..*]	the actor definitions of the process definition
start-activity-definition	element	1	the start activity definition of the process definition
activity-definition	element	[0..*]	all ordinary activity definitions of the process definition
end-activity-definition	element	[1..*]	all end activity definitions of the process definition

 3.1.1.2 actor-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the actor definition
description	element	[0..1]	the description of the actor definition

 3.1.1.3 start-activity-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the start activity definition
description	element	[0..1]	the description of the start activity definition
task-definition	element	[0..*]	the task definitions of the start activity definition
output-transition-definition	element	[1..*]	the output transition definitions of the start activity definition

 3.1.1.4 activity-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the activity definition
description	element	[0..1]	the description of the activity definition
task-definition	element	[0..*]	the task definitions of the activity definition
input-transition-definition	element	[1..*]	the input transition definitions of the activity definition
output-transition-definition	element	[1..*]	the output transition definitions of the activity definition

 3.1.1.5 end-activity-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the end activity definition
description	element	[0..1]	the description of the end activity definition
task-definition	element	[0..*]	the task definitions of the end activity definition
input-transition-definition	element	[1..*]	the input transition definitions of the end activity definition

 3.1.1.6 input-transition-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the input transition definition
description	element	[0..1]	the description of the input transition definition

 3.1.1.7 output-transition-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the output transition definition
description	element	[0..1]	the description of the output transition definition

 3.1.1.8 task-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the task definition
description	element	[0..1]	the description of the task definition
actor-definition	element	1	the actor definition of the task definition
property-definition	element	[1..*]	the property definition of the task definition

  3.1.1.9 property-definition

Name	Type	Multiplicity	Description
name	attribute	1	the name of the property definition
description	element	[0..1]	the description of the property definition
value-type	element	1	the value type defined by the property definition. At present, the value of this element only "java.lang.String" be allowed

 3.2 TODO....

3.3 Petri net Core

There are two kinds of vertexes in petri net(P/T system), Place and Transition. Place vertex depicts the process control computing, transition vertex depicts the business activity. Them collaborate each other over events.

 3.3.1 Process Events

Process events depict process-level events, such as creation of a process, completion of a activity. These events raise from business logic and will be handled by place vertex event handler. So far, all process events raise synchronously with raiser.See the following illustration:

TODO: illustration and event API snippet

 3.3.2 Transition vertex Logic

Transition vertex depicts the business logic of process engine of BeyondTrack. In classic petri net, a transition of a petri net may fire. We can consider there is a fire event raised. The condition of firing please refers to petri net theory for details. When a transition fired, tokens of place connected with this transition changed.
The fire event corresponds to a business operation performed. 
TODO: API snippets

 3.3.3 Place vertex Event Handler

A transition fire, a event raise like just we mentioned. So, there must exist a event handler to deal with that. Place vertex depicts the event handling. There are two responsibilities of place event handler mainly:

• move of token

          Token move means the token related process instance's status has changed.

• generation of the next activity node

          Caused by move of token, a activity or concurrent activities will be created in process instance.

TODO: code snippets

 3.4 Task Management

 3.4.1 Task property Customizing

To depict the various of tasks of user's project is very hard in general. So, let user to customize the properties of a task is necessary.  The property customizing of a task was performed in process modeling.
There are three property types has been considered:

1. Pure text
   A pure text property is implemented by java.lang.String.
2. Date
   A date property is implemented by java.util.Date.
3. List
   TODO: list property

4 Implementation

4.1 Using JAXB for SPDL

In 3.1 Meta Model, we decided to use Java classes as the source meta model. And, the transformation rules and transformation engine have been defined by JAXB(JSR 222). The scenario of proceeding transformation as the following illustration(cut from JavaEE Tutorials):

Author: Liang Ding, <DL88250@gmail.com>

Status: Draft