Hanpin Wang

A stochastic model for workflow QoS evaluation

Quality (QoS) prediction is one of the most important research topics of workflow. In this paper, we propose a stochastic model to evaluate QoS (make-span, reliability and cost) of workflow systems based on QWF-net, which extends traditional WF-net by associating tasks with firing-rate, failure-rate and cost-coefficient. Through a case study, we show that our framework is capable of modeling real-world workflow-based application. Also, Monte-carlo simulation in the case study indicates our analytical methods are consistent with simulation. We also present a sensitivity analysis technique to identify QoS bottleneck.The paper concludes with a comparison between our approach and related work.

Property-Transition-Net-Based Workflow Process Modeling and Verification

The development of workflow management system requires satisfactory models and concepts. As mentioned in [W.M.P. van der Aalst and Arthur H.M.ter Hofstede, YAWL: Yet Another Workflow Language, QUT Technical report, FIT-TR-2002-06, Queensland University of Technology, Brisbane, 2002], classical Petri nets are not suitable to describe some advanced workflow patterns, thus this paper presents a Petri-net-based model characterized by places with new properties which are suitable to represent some advance workflow patterns. Many workflow models confuse the behaviors of workflow engine and external environment(tasks), and fail to describe the real semantics of workflow engine. In our model, through separating transitions from routings, the place will describe the behaviors of engine and the transition will describe the behavior of task. Because workflow engine is a reactive system, the token-game semantic behavior of a Petri net-based workflow model will differ from its behavior at run time. However, the semantics of property-transition-net-based model with ST firing rules is suitable enough to capture the behavior of workflow process. In this paper the formal definitions and semantics of this model are discussed in detail. This paper concludes with an introduction of a verification technique for structure-soundness detection based on some new reduction rules.

Formalizing Web Service Choreography Interface

All existing Web service composition standards remain at the descriptive level, without providing any formal semantics and method for verifying some important properties. Web service choreography interface (WSCI) describes the flow of messages exchanged by a Web service which participates in choreographed interactions with other services. This paper presents an extended Petri net to formalize WSCI, and proposes several nets to represent the activity, process and interface respectively. Our formal model remarkably focuses on the message exchange and the context of WSCI. Furthermore, we give the formal semantics for the context in a subtle manner, i.e., subprocess and exception handling. According to the characteristic of WSCI, this paper proposes some properties just like well-founded, and introduces technique for checking these properties to ensure the correct implementation and deployment of WSCI.

A modeling language to describe massive data storage management in cyber-physical systems

Massive data storage systems (MDSS, for short) are elementary parts of data gathering and analysis in cyber-physical systems. MDSSs have more features than traditional storage systems. An important one is that data files are split and stored into blocks in MDSSs. And each block is considered as a storage unit. Hence, MDSSs usually have two kinds of storage units: ordinary memory locations and block storage locations. Then it comes the question that how we formally model and describe MDSSs. In this paper we propose a modeling language to describe the management programs in MDSSs. New expressions and commands are introduced which mainly focus on block operations. Their denotational semantics are defined using the concepts of heap and store. According fixed-point theorem is proved. Using this method, management programs of MDSSs can be expressed more clearly and intuitively, and it allows us to analyze MDSSs more easily. A modeling language for Massive Data Storage management in Cyber-Physical Systems is proposed.Based on Separation Logic Modeling Language, new expressions, commands, stores and heaps are introduced.Denotational Semantics are presented and discussed, as well as a sample program.

Modeling and verifying BPEL using synchronized net

Web Service composition, which is an application of the Service-Oriented Architecture, refers to combining existing Web Services to a new one. BPEL (Business Process Execution Language) is a language describing the composition of Web Services. The process of composition is error-prone. In order to guarantee the correctness of service composition, the idea of modeling and verifying BPEL in different levels, the logic level and the semantic level, is put forward. This can not only assure modeling the processes properly, but also lower the complexity of models and verifications. In the logic level, some elements of BPEL, according to the mapping rules, are mapped to WSL_net, which is a special Synchronized Net. Properties such as sound and efficient guarantee the correctness of the basic control flows in BPEL process and avoid unnecessary resource consuming. The construction and verification of the model of the semantic level, in which more elements of BPEL will be introduced, will be given in later papers.

A practical method to analyze workflow logic models

The analysis of workflow is crucial to the correctness of workflow applications. This paper introduces a simple and practical method for analyzing workflow logic models. Firstly, some definitions of the models and some properties, such as throughness, no‐redundant‐transition and boundedness, are presented. Then, we propose an approach based on synchronized reachability graphs (SRGs) to verify these properties. The SRG uses the characteristics of synchronizers in workflow logic models and mitigates the state explosion by constructing synchronized occurrence sequences rather than interleaving occurrence sequences. This paper also proposes some refined and feasible reduction rules which can preserve vital properties of workflow logic models. Using these two techniques, the SRG‐based verification method can achieve higher efficiency. Furthermore, this research also develops a verification tool based on the method, presents the analysis results of some practical cases and compares our method with others. Copyright

Queuing analysis and performance evaluation of workflow through WFQN

Performance prediction is one of the most important research topics of workflow. To investigate the performance of workflow systems in queuing condition, this paper extends traditional WF-net into WFQN (WF queuing network), by modeling tasks as FIFS (first-in-first-service) queues and the source place as the input of tokens following poisson arrival process. Analytical methods are introduced to evaluate the queue-length, wait-time and completion-duration. The case study (especially the case of airline ticket booking application) shows that WFQN can model real-world workflow-based applications effectively. Through Montecarlo simulations in the case study, we show analytical models are verified by simulative results. We also present a sensitivity analysis technique to identify performance bottle-necks of WFQN. This paper concludes with a comparison with relate work.

Semantic Analysis of UML2.0 Sequence Diagram Based on Model Transformation

The Sequence Diagram(SD) of UML2.0 enriches those of previous versions by two new operators, assert and negate, for specifying required and forbidden behaviors. The semantics of SD, however, being based on pairs of valid and invalid sets of traces, is inadequate, and prevents the new operators from being used effectively. The semantic confusions between assert and negate operators in UML SD are significant, since they pose great difficulty to the confirmation of the security of the system they designed. A new Petri-net model named LPNforSD is designed in this paper. Transformation rules from SD to LPNforSD are given out. We take fragment that described by assert or negate operator as independent part and transform it into LPNforSDs. An algorithm is also designed to check whether the SD is safe by comparing its traces with the traces getting from negate and assert fragments. By this way, we cannot only eliminate the semantic confusions between assert and negate operators, but also reduce the numbers of contingent traces. Thus, we can ensure the system more reliable

The Analysis of Sequence Diagram with Time Properties in Qualitative and Quantitative Aspects by Model Transformation

The Sequence Diagram (SD) with time properties is frequently used in the preliminary developing phase of embedded real time system, however, it is not easy to verify due to its informal semantics. An extended time Petri net (TPN) with \emph{weak} semantics–TLOPNforSD–is defined and proved to be decidable as far as reach ability, boundedness and cover ability are concerned. A method for progressively refining the SD is also offered in the transformation phase. The SD with time properties are made to be more reliable in two aspects: (1) an enabled transitions generating algorithm based on \emph{weak} semantics is designed. Based on this algorithm, the verification of SD with time properties in qualitative aspect can be realized by dint of ROMEO, (2) using the state-class diagram obtained in qualitative analysis phase, a scheduling strategy satisfying all the time constraints specified in the SD is worked out. The strategy is used to get compelling time intervals which are more accurate than the static intervals predefined on the SD for every event.

A Formal Descriptive Language and an Automated Detection Method for Complex Events in RFID

RFID technology provides fast data collection with precise identification of objects with unique IDs. Through processing and analyzing RFID data, some complex events can be discovered to support event monitoring and pre-warning. This technology has been applied in a wide area of applications, such as supply chain management, retail, anti-counterfeiting, security, military and health care. In this paper, we propose a formal descriptive language for RFID complex events, named QDDCatt, which extends QDDC (Quantified Discrete-time Duration Calculus) with attributes and their constraints. This language has strong ability to describe quantitative complex events in RFID containing aggregations and nesting operations. We define its syntax and RFID event semantics. Since extended from a logic, it also has logical semantics. An RFID data stream can be modeled by a state sequence, and a complex event occurs during a time interval if and only if a subinterval of the state sequence satisfies the corresponding QDDCatt formula. We also show an automated detection method of QDDCatt, which is developed from the automata-based decision procedure of QDDC.