- Lehrstuhl für Praktische Informatik (4)
The CHORCH Approach: How to Model B2Bi Choreographies for Orchestration Execution
- The establishment and implementation of cross-organizational business processes is an implication of today's market pressure for efficiency gains.
In this context, Business-To-Business integration (B2Bi) focuses on the information integration aspects of business processes.
A core task of B2Bi is providing adequate models that capture the message exchanges between integration partners.
Following the terminology used in the SOA domain, such models will be called choreographies in the context of this work.
Despite the enormous economic importance of B2Bi, existing choreography languages fall short of fulfilling all relevant
requirements of B2Bi scenarios.
Dedicated B2Bi choreography standards allow for inconsistent outcomes of basic interactions and
do not provide unambiguous semantics for advanced interaction models.
In contrast to this, more formal or technical choreography languages may provide unambiguous modeling semantics,
but do not offer B2Bi domain concepts or an adequate level of abstraction.
Defining valid and complete B2Bi choreography models becomes a challenging task in the face of these shortcomings.
At the same time, invalid or underspecified choreography definitions are particularly costly considering the organizational
setting of B2Bi scenarios.
Models are not only needed to bridge the typical gap between business and IT,
but also as negotiation means among the business users of the integration partners on the one hand
and among the IT experts of the integration partners on the other.
Misunderstandings between any two negotiation partners potentially affect the agreements between all other negotiation partners.
The CHORCH approach offers tailored support for B2Bi by combining the strengths of both dedicated B2Bi standards and formal rigor.
As choreography specification format, the ebXML Business Process Specification Schema (ebBP) standard is used.
ebBP provides dedicated B2Bi domain concepts such as so-called BusinessTransactions (BTs) that abstractly specify the exchange of a request business document
and an optional response business document.
In addition, ebBP provides a format for specifying the sequence of BT executions for capturing complex interaction scenarios.
CHORCH improves the offering of ebBP in several ways.
Firstly, the execution model of BTs which allows for inconsistent outcomes among the integration partners
is redefined such that only consistent outcomes are possible.
Secondly, two binary choreography styles are defined as B2Bi implementation contract format in order to streamline implementation projects.
Both choreography styles are formalized and provided with a formal execution semantics for ensuring unambiguity.
In addition, validity criteria are defined that ensure implementability using BPEL-based orchestrations.
Thirdly, the analysis of the synchronization dependencies of complex B2Bi scenarios is supported
by means of a multi-party choreography style combined with an analysis framework.
This choreography style also is formalized and standard state machine semantics are reused in order to ensure unambiguity.
Moreover, validity criteria are defined that allow for analyzing corresponding models for typical multi-party choreography issues.
Altogether, CHORCH provides choreography styles that are B2Bi adequate, simple, unambiguous, and implementable.
The choreography styles are B2Bi adequate in providing B2Bi domain concepts, in abstracting from low-level implementation details
and in covering the majority of real-world B2Bi scenarios.
Simplicity is fostered by using state machines as underlying specification paradigm.
This allows for thinking in the states of a B2Bi scenario and for simple control flow structures.
Unambiguity is provided by formal execution semantics whereas implementability (for the binary choreography styles) is ensured by providing
mapping rules to BPEL-based implementations.
The validation of CHORCH's choreography styles is performed in a twofold way.
Firstly, the implementation of the binary choreography styles based on Web Services and BPEL technology is demonstrated
which proves implementability using relatively low-cost technologies.
Moreover, the analysis algorithms for the multi-party choreography styles are validated using a Java-based prototype.
Secondly, an abstract visualization of the choreography styles based on BPMN is provided that abstracts from
the technicalities of the ebBP standard.
This proves the amenability of CHORCH to development methods that start out with visual models.
CHORCH defines how to use BPMN choreographies for the purpose of B2Bi choreography modeling
and translates the formal rules for choreography validity into simple composition rules that
demonstrate valid ways of connecting the respective modeling constructs.
In summary, CHORCH allows integration partners to start out with a high-level visual model of their interactions in BPMN
that identifies the types and sequences of the BusinessTransactions to be used.
For multi-party choreographies, a framework for analyzing synchronization dependencies then is available.
For binary choreographies, an ebBP refinement can be derived that fills in the technical parameters that are needed for deriving the implementation.
Finally, Web Services and BPEL based implementations can be generated.
Thus, CHORCH allows for stepwise closing the semantic gap between the information perspective of business process models
and the corresponding implementations.
It is noteworthy that CHORCH uses international standards throughout all relevant layers, i.e., BPMN, ebBP, Web Services and BPEL,
which helps in bridging the heterogeneous IT landscapes of B2Bi partners.
In addition, the adoption of core CHORCH deliverables as international standards of the RosettaNet community
give testament to the practical relevance and promise dissemination throughout the B2Bi community.
Analyzing the Interoperability of WS-Security and WS-ReliableMessaging Implementations
- Since their invention as lightweight integration technology about a decade ago, Web Services have matured significantly. Today, major middleware solution vendors as well as industry communities like RosettaNet are propagating Web services even for exchanging business-critical data and implementing inter-organizational business processes. Core enablers for using Web services in this domain are stateful interactions using the Web Services Business Process Execution Language (WS-BPEL) as well as advanced communication features like security and reliability using the WS-Security and WS-ReliableMessaging standard specifications. However, advanced communication features come at the price of complexity which challenges interoperability across different Web services stack implementations. Interoperability, in turn, is a predominant requirement for an integration technology such as Web services, in particular if inter-organizational business processes are supposed to be implemented on top of that technology. This paper approaches the problem of testing the interoperability of the so-called WS-* standards, advanced Web services communication features that are typically defined as SOAP extensions and configured using WS-Policy. Being essential to business process integration, WS-Security and WS-ReliableMessaging are selected as representatives of this group and the two major Java-based Web services stack implementations Metro and Axis2 are tested for interoperability. We operationalize the notion of interoperability for testing WS-* standards, suppose an approach for deriving test cases from WS-* specifications as well as a method for performing the test cases, and we provide a comprehensive interoperability review of the two selected Web services stack implementations.
A Requirements Analysis of Business-To-Business Integration
- Ever fiercer competition has forced enterprises not only to optimize their own operations but also to cooperate with their suppliers and customers along their supply chains. Thus, competition today usually takes place between supply chains and not between individual enterprises. Business-To-Business integration (B2Bi) is a major task of supply chain management (SCM), and although it already has been researched for years, B2Bi is still an area of active research with a plethora of research questions and according approaches. Hence, management of B2Bi projects necessitates the identification of relevant requirements which is a far from trivial task. This paper identifies a core set of B2Bi challenges and deduces a comprehensive set of B2Bi requirements that are particularly useful for tackling the challenges identified. The derivation of B2Bi requirements follows an inductive approach that is based on the analysis of integration standards, reference architectures and related literature. In order to operationalize the B2Bi requirements for further analysis and concrete B2Bi projects, the requirements are classified according to the abstraction layers of a B2Bi schema. Thus, this report not only offers a requirements check list for B2Bi projects but also helps in deciding when to address which requirements during the course of a B2Bi project.
Modelling and Validating Business Collaborations: A Case Study on RosettaNet
- The way business processes are organised heavily influences the flexibility and the expenses of enterprises. The capability to address changing market needs in a timely manner and to provide appropriate pricing is indispensable in a world of internationalisation and growing competition. Optimising processes that cross enterprise boundaries potentially is a key success factor in achieving this goal but it requires the information systems of the participating enterprises to be consistently integrated. This gives rise to some challenging tasks. The personnel involved in building up business collaborations comes from different enterprises with different business vocabulary and background which requires extensive communication support. The lack of central technical infrastructure, typically prohibited by business politics, often calls for a distributed and computer-aided collaboration structure, so that the resulting complexity must be handled somehow. Nevertheless robustness is an important factor in building business collaborations as these may exchange goods of considerable value. This technical report proposes the use of a two step modelling approach that separates business logic, modelled in the so-called centralised perspective (CP), from its distributed implementation, modelled in the so-called distributed perspective (DP). The separation of these perspectives enables business people to concentrate on business issues and to solve communication problems in the CP whereas technical staff can concentrate on distribution issues. The use of stringent modelling rules is advised in order to provide the basis for formal analysis techniques as one means to achieve robustness. Considering the choreography of RosettaNet Partner Interface Processes (PIPs) as the subject of my analysis, UML activity diagrams for modelling the CP and WSBPEL for modelling the DP are described as enabling techniques for implementing the proposed two step modelling approach. Further, model checking is applied to validate the CP and DP models in order to detect errors in early design phases. As the adequacy of model checking tools highly depends on the detailed modelling techniques as well as the properties to be checked, a major part of our discussion covers relevant properties and requirements for a model checker.