Load balancing plays a crucial role in realising the benefits of microservices, especially to achieve elastic scalability and performance optimisation. However, it is different from load balancing for virtual machines, because workloads on microservices are harder to predict and the number of services in the systems is large. In this paper, we formalise load balance as an emergent property of the microservices ecosystem, and employ scenario calculus to formally analyse the impact of scheduling on service capability and scalability. We discovered that elastic round robin scheduling is highly scalable but the service capability is limited by the slowest microservice instance. In contrast, shortest waiting queue scheduling is less scalable, but the service capability is higher.

The work reported in this paper is based on our previous work on the formalisation of design patterns and their compositions and instantiations. We define the notion of validity of pattern compositions and analyse whether pattern operators preserve validity. The article is an extended abstract of the paper entitled "On the Composibility of Design Patterns" published in IEEE Transactions on Software Engineering, Vol. 41, No. 11, pp. 1138-1152 (Nov. 2015).

Software-as-a-Service (SaaS) is a model of cloud computing in which software functions are delivered to the users as services. The past few years have witnessed its global flourishing. In the foreseeable future, SaaS applications will integrate with the Internet of Things, Mobile Computing, Big Data, Wireless Sensor Networks, and many other computing and communication technologies to deliver customizable intelligent services to a vast population. This will give rise to an era of what we call Big SaaS systems of unprecedented complexity and scale. They will have huge numbers of tenants/users interrelated in complex ways. The code will be complex too and require Big Data but provide great value to the customer. With these benefits come great societal risks, however, and there are other drawbacks and challenges. For example, it is difficult to ensure the quality of data and metadata obtained from crowd sourcing and to maintain the integrity of conceptual model. Big SaaS applications will also need to evolve continuously. This paper will discuss how to address these challenges at all stages of the software lifecycle.

In real applications, design patterns are almost always to be found composed with each other. It is crucial that these compositions be validated. This paper examines the notion of validity, and develops a formal method for proving or disproving it, in a context where composition is performed with formally defined operators on formally specified patterns. In particular, for validity, we require that pattern compositions preserve the features, semantics and soundness of the composed patterns. The application of the theory is demonstrated by a formal analysis of overlap-based pattern compositions and a case study of a real pattern-oriented software design.

Effective management of diabetes is crucial for patient wellbeing and the prevention of low blood sugar levels (Hypoglycemia) and high blood sugar levels (Hyperglycemia) both of which can be potentially dangerous. Traditionally log books are maintained by patients to record information such as insulin usage and their meals. The ever increasing popularity of smart phones has resulted in various applications being developed to allow patients to log data and help manage their condition. However these applications are often developed simply for the logging of data and only occasionally provide basic calculations to suggest insulin doses following a meal. The goal of this research is to use case-based reasoning techniques to suggest an insulin dosage for the patient as opposed to using a one calculation fits all approach. This is to be achieved by building a knowledge base of the patient's history that is then used to obtain a solution which best fits the current circumstances. The proposed case-based reasoning system is described alongside the development of the system to date and discussion into further research and development. The final implementation will be tested and validated using a diabetic patient simulator to create a knowledge base and observe system behavior and accuracy.

The accurate description of service semantics plays a crucial role in service discovery, composition and interaction. Most work in this area has been focussed on ontological descriptions, which are searchable and machine-understandable, but do not define service functionality in a verifiable and testable way. Formal specification techniques, having evolved over the past 30 years, can define semantics verifiably and testablly, but they have not yet been applied to service computing because formal specifications are not searchable. There is a huge gap between these two methods of semantics description. In this paper, we bridge the gap. Our technique is to specify services formally in an algebraic specification language and then to extract ontological description as profiles in the language OWL-S, with the associated searchability benefits. We present a prototype tool for performing this transformation and report a case study to demonstrate the feasibility of our approach. The algebraic specification language we use is SOFIA (Service Oriented Formalism in Algebras).

A cloud often provides a RESTful interface with which to access its services. These are usually specified through an open but informal document in the IT industry. There is no agreed standard for the specification of RESTful web services. In this paper, we propose the application of an algebraic method to the formal specification of such services and report a case study with the GoGrid's RESTful API, an industrial real system that provides Infrastructure-as-a-Service. The case study demonstrates that the algebraic approach can provide formal unambiguous specifications that are easy to read and write. It also demonstrates that formalisation can identify and eliminate ambiguity and inconsistency in informal documents.

In a pattern-oriented software design process, design decisions are made by selecting and instantiating appropriate patterns, and composing them together. In our previous work, we enabled these decisions to be formalized by defining a set of operators on patterns with which instantiations and compositions can be represented. In this article, we investigate the algebraic properties of these operators. We provide and prove a complete set of algebraic laws so that equivalence between pattern expressions can be proven. Furthermore, we define an always-terminating normalization of pattern expression to a canonical form which is unique modulo equivalence in first-order logic. By a case study, the pattern-oriented design of an extensible request-handling framework, we demonstrate two practical applications of the algebraic framework. First, we can prove the correctness of a finished design with respect to the design decisions made and the formal specification of the patterns. Second, we can even derive the design from these components.

The formal specification of design patterns is widely recognised as being vital to their effective and correct use in software development. It can clarify the concepts underlying patterns, eliminate ambiguity and thereby lay a solid foundation for tool support. This paper further advances an approach that uses first order predicate logic to specify design patterns by capturing the dynamic behaviour represented in sequence diagrams. A case study of all 23 patterns in the Gang of Four catalogue demonstrates that it can not only capture dynamic features but also simplify the specification of structural properties.

Design patterns are traditionally outlined in an informal manner. If they could be formalised, we could derive tools that automatically recognise design patterns and refactor designs and code. Our approach is to deploy predicate logic to specify conditions on the class diagrams that describe design patterns. The structure of class diagrams is itself described with a novel meta-notation that can be used for defining any graphical modelling language. As a result, the constraints, while based on UML, are highly readable and have much expressive power. This enables us not only to recognise design patterns in legacy code, but also to reason about them at the design stage, such as showing one pattern to be a special case of another. The paper discusses our specification of the original 23 design patterns and presents a representative sample of some of them.

Abstract. Nested (or non-uniform, or non-regular) datatypes have recursive definitions in which the type parameter changes. Their folds are restricted in power due to type constraints. Bird and Paterson introduced generalised folds for extra power, but at the cost of a loss of efficiency: folds may take more than linear time to evaluate. Hinze introduced efficient generalised folds to counter this inefficiency, but did so in a pragmatic way: he did not provide categorical or equivalent underpinnings, so did not get the associated universal properties for manipulating folds. We combine the efficiency of Hinze’s construction with the powerful reasoning tools of Bird and Paterson’s.