Concurrency control for  overlapping  and cooperative workflows

Juha Puustjarvi, Henry Tirri
Department of Computer Science
P. O. Box 26 (Teollisuuskatu 23)
FIN-00014 UNIVERSITY OF HELSINKI
Finland 
e-mail: {puustjar, tirri}@cs.helsinki.fi

Jari Veijalainen 
VTT Information Technology
Multimedia Systems
P.O. Box 1203
FIN-02044 VTT Finland 
e-mail: Jari.Veijalainen@vtt.fi 

				Abstract

In this paper, we will focus on developing concurrency control mechanisms  
supporting  cooperative workflows, which  are characterized by the following
cooperation activities: workflows are allowed  to  see other workflows'
non-committed  persistent data, workflows  may delegate tasks to other
workflows, and workflows  may notify each other of their behaviour.
We also emphasize  workflow task reusability by addressing overlapping workflows
sharing one or several tasks as subworkflows. In our approach 
the required properties of a task are  specified in the call procedure
as types of  task execution modes.  In ddition we will also introduce a general
mechanism called constraint locking which addresses controlling the 
synchronization, atomicity and cooperation in cooperative workflows. 
As opposed to  traditional transaction locking where the order
of the transaction executions is dynamically determined by acquisition
of locks for the shared data,  in constraint locking this ordering is
controlled by constraints both on the shared data state and operations
performed by the participating workflows. Thus constraint locking is a 
generalization of the traditional transaction locking where the unconditional
ordering based on lock conflicts is relaxed to depend on (dynamically defined)
predicates. By constraint locking, we  address the problems of workflow
synchronization, workflow atomicity and workflow cooperation
(i.e., relaxed isolation). We will demonstrate our approach by describing
the concepts in the framework of an example in the banking domain.