Real-world performance modelling of enterprise Service Oriented Architectures: Delivering business value with complexity and constraints

Performance and Scalability Modelling of real-world enterprise systems is challenging due to both the complexity and size of the system being modelled, and constraints imposed by real projects such as the need to provide business value, deadlines, and the accessibility, relevance, quality and quantity of available documentation and performance data. Our hypothesis is that enterprise Service Oriented Architectures (SOAs) are more amenable to performance modelling as services are more granular, visible, and measurable. Since 2007 we have developed, trialled and refined a method with model-driven tool support for directly modelling the performance and scalability of increasingly complex Service Oriented Architectures. This paper reports an illustrative experience modelling a large-scale production SOA Enterprise Service Bus (ESB) upgrade, focussing on lessons learnt related to the complexity and constraints of modelling in the real-world. The key observations are that model construction is a type of theory formation and therefore: (1) Models (functioning as theories) can be simple but powerful enough to model large complex SOAs within the boundaries of real project constraints; (2) Model formation can be incremental, starting with a simple model (as simple theories are easier to refute) and refining as required; (3) Building multiple competing models can be a useful approach if information is inadequate or ambiguous, as the rival models can be tested with the aim of discarding incorrect ones; (4) If insufficient information is available to build a single "über" model to answer all the performance questions, it is often possible to build multiple specialised models for different purposes.