Event Driven Architecture Modelling and Simulation Tony Clark, Balbir S. Barn School of Engineering and Information Sciences Middlesex University, London, UK {t.n.clark,b.barn}@mdx.ac.uk Abstract—Enterprise Architecture (EA) Modelling aims to Given that EDA and CEP are claimed to be more flexible analyze an organization in terms of its components, IT systems than SOA, how should we design and verify an EA using and business processes. Current modelling approaches are based these concepts? Some specialized languages for CEP exist, on Service Oriented Architecture (SOA) whereby components publish interfaces of operations that are used via message passing. however they are specifically designed to efficiently process It has been argued that SOA leads to tight coupling between com- relatively simple event streams, and do not integrate into a ponents and does not handle complex component interactions, component architecture required by EA. The most widely used with resulting maintenance difficulties. Event Driven Architecture language for modelling systems is UML, however UML does (EDA) is an alternative strategy, based on listening for events, not provide any specific support for this type of EA. that is designed to address SOA shortcomings. However, there are no EA modelling technologies based on EDA. This paper The contribution of this paper is to identify the key charac- reviews EA, SOA and EDA, identifies EDA characteristic features teristic features of EDA and to use them as the basis for both and proposes modelling and simulation technologies that are an EDA modelling notation and a simulation language where introduced through a simple case study. no such technology currently exists. The modelling notation is defined as a UML class diagram stereotype and an extension of I. INTRODUCTION OCL that supports event processing. The simulation notation is Enterprise Architecture (EA) describes a collection of ap- defined as an action language for the modelling notation. The proaches that support the design and analysis of an IT infras- simulation language has been implemented as an interpreter tructure and how it relates to the goals, directives, processes in Java. and organization of a business. There are various approaches to The paper is structured as follows. Section II reviews com- organizing an architecture, but most involve the identification plex event processing and EA modelling languages. Section III of logical or physical business units, or components, that man- performs a domain analysis on EDA and describes an EDA age their own data and resources, implement a collection of modelling language. Section IV describes a case study as an business processes, and communicate with other components EDA model. Section V describes an EDA simulation language using a variety of message passing styles. and provides an example by implementing the case study. Different styles of message passing lead to different types The simulation language has been implemented in Java and of architecture. A Service Oriented Architecture (SOA) in- is described in section VI. volves the publication of logically coherent groups of business functionality as interfaces, that can be used by components II. EVENT DRIVEN EA using synchronous or asynchronous messaging. An alternative A. Service Oriented Architecture style, argued as reducing coupling between components and thereby increasing the scope for component reuse, is Event Service Oriented Architecture (SOA) organizes a system Driven Architecture (EDA) whereby components are event in terms of components that communicate via operations or generators and consumers. EDA is arguably more realistic in a services. Components publish services that they implement sophisticated, dynamic, modern business environment, and can as business processes. Interaction amongst components is be viewed as a specialization of SOA where communication achieved through orchestration at a local level or choreography between components is performed with respect to a single at a global level. generic event interface. Its proponents argue that SOA provides loose coupling, An important difference between SOA and EDA is that the location transparency and protocol independence [1] when latter generally provides scope for Complex Event Processing compared to more traditional implementation techniques. The (CEP) where the business processes within a component are organization of systems into coherent interfaces has been triggered by multiple, possibly temporally related, events. In argued [2] as having disadvantages in terms of: extensions; SOA there is no notion of relating the invocation of a single accommodating new business functions; associating single business process to a condition holding between the data business processes with complex multi-component interac- passed to a collection of calls on one of the component’s tions. These can be addressed in terms of CEP as described interfaces. in the next section. B. Complex Event Processing backtracking to find solutions to goals. Complex Event Processing (CEP) [3] can be used to process C. Enterprise Architecture events that are generated from implementation-level systems Enterprise Architecture (EA) aims to capture the essentials by aggregation and transformation in order to discover the of a business, its IT and its evolution, and to support analysis business level, actionable information behind all these data. It of this information: ‘[it is] a coherent whole of principles, has evolved into the paradigm of choice for the development methods, and models that are used in the design and realization of monitoring and reactive applications [4]. of an enterprise’s organizational structure, business processes, CEP can be viewed as a specialization of SOA where information systems and infrastructure.’ [10]. components are decoupled from multiple interfaces and where A key objective of EA is being able to provide a holistic each component implements a single generic event interface. understanding of all aspects of a business, connecting the Components both raise and handle events in terms of this business drivers and the surrounding business environment, interface and therefore it is more flexible in terms of extension through the business processes, organizational units, roles and maintenance. In addition, CEP implements events in terms and responsibilities, to the underlying IT systems that the of business rules compared to SOA that implements operations business relies on. In addition to presenting a coherent ex- using business processes. Typically, a business rule can depend planation of the what, why and how of a business, EA aims on multiple, possibly temporally related, events, whereas a to support specific types of business analysis including [11], business process is invoked on receipt of a single operation [12], [13], [14], [15]: alignment between business functions request. Therefore, SOA can implement CEP by enforcing and IT systems; business change describing the current state a single operation interface across an architecture and by of a business (as-is) and a desired state of a business (to- providing special machinery to aggregate multiple operation be); maintenance the de-installation and disposal, upgrading, calls. procurement and integration of systems including the pri- There are various proposals for how complex events can be oritization of maintenance needs; quality by managing and used efficiently to process streams of data such as those gener- determining the quality attributes for aspects of the business ated in applications including hotel booking systems, banking such as security, performance to ensure a certain level of on-line credit systems, business activity monitoring (BAM), quality to meet the needs of the business; acquisition and real-time stock analysis, and real-time security analysis. Most mergers describing the alignment of businesses and the effect proposals aim to address efficiency issues related to the scale on both when they merge; compliance in terms of a regulatory and frequency of the information that is generated [5]. The framework, e.g. Sarbanes-Oxley; strategic planning including current state of the art is described in [6] where the key corporate strategy planning, business process optimization, features of an event driven architecture (EDA) are outlined as business continuity planning, IT management. including an architecture diagram showing the processes of the EA has its origins in Zachman’s original EA framework system and their interconnections, a behaviour specification [16] while other leading examples include the Open Group including the rules used to process events and to control data, Architecture Framework (TOGAF) [17] and the framework and the specification of inter-process communications. promulgated by the Department of Defense (DoDAF) [18]. As described in [7] events can be extracted from services, In addition to frameworks that describe the nature of models databases, RFID and activities. The events are processed by required for EA, modelling languages specifically designed for rules that detect relationships between event properties and EA have also emerged. One leading architecture modelling the times at which the events occur. Each rule matches against language is ArchiMate [19]. multiple events that occur from a variety of sources and, when As described in [20] and [21], complex events can be the all required events have been matched, the rule performs a basis for a style of EA design. Event Driven Architecture business action.