Rudolf Schlatte

Modeling Spatial and Temporal Variability with the HATS Abstract Behavioral Modeling Language

The Abstract Behavioral Specification (ABS) language facilitates to precisely model the behavior of highly configurable, distributed systems. Its basis is Core ABS which is a strongly typed, abstract, object-based, concurrent, fully executable modeling language. Spatial variability of ABS models is represented by feature models, delta modules containing modifications of ABS models, product line configurations linking delta modules with product features and product selections specifying actual product instances. Temporal variability is captured by dynamic delta modules that can be applied to perform runtime updates. The feasibility of ABS is demonstrated by modeling an industrial-scale web merchandising system.

Optique: Towards OBDA Systems for Industry

The recently started EU FP7-funded project Optique will develop an end-to-end OBDA system providing scalable end-user access to industrial Big Data stores. This paper presents an initial architectural specification for the Optique system along with the individual system components.

User-defined schedulers for real-time concurrent objects

Scheduling concerns the allocation of processors to processes, and is traditionally associated with low-level tasks in operating systems and embedded devices. However, modern software applications with soft real-time requirements need to control application-level performance. High-level scheduling control at the application level may complement general purpose OS level scheduling to fine-tune performance of a specific application, by allowing the application to adapt to changes in client traffic on the one hand and to low-level scheduling on the other hand. This paper presents an approach to express and analyze application-specific scheduling decisions during the software design stage. For this purpose, we integrate support for application-level scheduling control in a high-level object-oriented modeling language, Real-Time ABS, in which executable specifications of method calls are given deadlines and real-time computational constraints. In Real-Time ABS, flexible application-specific schedulers may be specified by the user, i.e., developer, at the abstraction level of the high-level modeling language itself and associated with concurrent objects at creation time. Tool support for Real-Time ABS is based on an abstract interpreter that supports simulations and measurements of systems at the design stage.

The ABS tool suite: modelling, executing and analysing distributed adaptable object-oriented systems

Modern software systems must support a high degree of variability to accommodate a wide range of requirements and operating conditions. This paper introduces the Abstract Behavioural Specification (ABS) language and tool suite, a comprehensive platform for developing and analysing highly adaptable distributed concurrent software systems. The ABS language has a hybrid functional and object- oriented core, and comes with extensions that support the development of systems that are adaptable to diversified requirements, yet capable to maintain a high level of trustworthiness. Using ABS, system variability is consistently traceable from the level of requirements engineering down to object behaviour. This facilitates temporal evolution, as changes to the required set of features of a system are automatically reflected by functional adaptation of the system’s behaviour. The analysis capabilities of ABS stretch from debugging, observing and simulating to resource analysis of ABS models and help ensure that a system will remain dependable throughout its evolutionary lifetime. We report on the experience of using the ABS language and the ABS tool suite in an industrial case study.

Formal modeling and analysis of resource management for cloud architectures: an industrial case study using Real-Time ABS

We demonstrate by a case study of an industrial distributed system how performance, resource consumption, and deployment on the cloud can be formally modeled and analyzed using the abstract behavioral specification language Real-Time ABS. These non-functional aspects of the system are integrated with an existing formal model of the functional system behavior, achieving a separation of concerns between the functional and non-functional aspects in the integrated model. The resource costs associated with execution in the system depend on the size of local data structures, which evolve over time; we derive corresponding worst-case cost estimations by static analysis techniques and integrate them into our resource-sensitive model. The model is further parameterized with respect to deployment scenarios which capture different application-level management policies for virtualized resources. The model is validated against the existing system’s performance characteristics and used to simulate, analyze, and compare deployment scenarios on the cloud.

Simulating concurrent behaviors with worst-case cost bounds

Modern software systems are increasingly being developed for deployment on a range of architectures. For this purpose, it is interesting to capture aspects of low-level deployment concerns in high-level modeling languages. In this paper, an executable object-oriented modeling language is extended with resource-restricted deployment components. To analyze model behavior a formal methodology is proposed to assess resource consumption, which balances the scalability of the method and the reliability of the obtained results. The approach applies to a general notion of resource, including traditional cost measures (e.g., time, memory) as well as concurrency-related measures (e.g., requests to a server, spawned tasks). The main idea of our approach is to combine reliable (but expensive) worst-case cost analysis of statically predictable parts of the model with fast (but inherently incomplete) simulations of the concurrent aspects in order to avoid the state-space explosion. The approach is illustrated by the analysis of memory consumption.

Dynamic resource reallocation between deployment components

Todays software systems are becoming increasingly configurable and designed for deployment on a plethora of architectures, ranging from sequential machines via multicore and distributed architectures to the cloud. Examples of such systems are found in, e.g., software product lines, service-oriented computing, information systems, embedded systems, operating systems, and telephony. To model and analyze systems without a fixed architecture, the models need to naturally capture and range over relevant deployment scenarios. For this purpose, it is interesting to lift aspects of low-level deployment concerns to the abstraction level of the modeling language. In this paper, the object-oriented modeling language Creol is extended with a notion of dynamic deployment components with parametric processing resources, such that processor resources may be explicitly reallocated. The approach is compositional in the sense that functional models and reallocation strategies are both expressed in Creol, and functional models can be run alone or in combination with different reallocation strategies. The formal semantics of deployment components is given in rewriting logic, extending the semantics of Creol, and executes on Maude, which allows simulations and test suites to be applied to models which vary in their available resources as well as in their resource reallocation strategies.

Modeling resource-aware virtualized applications for the cloud in real-time ABS

An applications quality of service (QoS) depends on resource availability; e.g., response time is worse on a slow machine. On the cloud, a virtualized application leases resources which are made available on demand. When its work load increases, the application must decide whether to reduce QoS or increase cost. Virtualized applications need to manage their acquisition of resources. In this paper resource provisioning is integrated in high-level models of virtualized applications. We develop a Real-Time ABS model of a cloud provider which leases virtual machines to an application on demand. A case study of the Montage system then demonstrates how to use such a model to compare resource management strategies for virtualized software during software design. Real-Time ABS is a timed abstract behavioral specification language targeting distributed object-oriented systems, in which dynamic deployment scenarios can be expressed in executable models.

Validating timed models of deployment components with parametric concurrency

Many software systems today are designed without assuming a fixed underlying architecture, and may be adapted for sequential, multicore, or distributed deployment. Examples of such systems are found in, e.g., software product lines, service-oriented computing, information systems, embedded systems, operating systems, and telephony. Models of such systems need to capture and range over relevant deployment scenarios, so it is interesting to lift aspects of low-level deployment concerns to the abstraction level of the modeling language. This paper proposes an abstract model of deployment components for concurrent objects, extending the Creol modeling language. The deployment components are parametric in the amount of concurrency they provide; i.e., they vary in processing resources. We give a formal semantics of deployment components and characterize equivalence between deployment components which differ in concurrent resources in terms of test suites. Our semantics is executable on Maude, which allows simulations and test suites to be applied to a deployment component with different concurrent resources.

Integrating deployment architectures and resource consumption in timed object-oriented models

Abstract Software today is often developed for many deployment scenarios; the software may be adapted to sequential, concurrent, distributed, and even virtualized architectures. Since software performance can vary significantly depending on the target architecture, design decisions need to address which features to include and what performance to expect for different architectures. To make use of formal methods for these design decisions, system models need to range over deployment scenarios. For this purpose, it is desirable to lift aspects of low-level deployment to the abstraction level of the modeling language. This paper proposes an integration of deployment architectures in the Real-Time ABS language, with restrictions on processing resources. Real-Time ABS is a timed, abstract and behavioral specification language with a formal semantics and a Java-like syntax, that targets concurrent, distributed and object-oriented systems. A separation of concerns between execution cost at the object level and execution capacity at the deployment level makes it easy to compare the timing and performance of different deployment scenarios already during modeling. The language and associated simulation tool is demonstrated on examples and its semantics is formalized.