A formal model for the interoperability of service clouds

Large-scale service-oriented computing is based on the idea that services from various servers are combined into one distributed application. Referring to a collection of services on one server as a ??service cloud??, the problem investigated in this paper is to define formal high-level specifications of such distributed applications and to enable the location of suitable services for them. Based on the language-independent model of Abstract State Services (AS²s), which serves as a universal integrated model for data and software as services, we extend AS²s by high-level action schemes called ??plots?? as a means to specify permitted sequences of service operations. On these grounds, we develop a model for service mediators, that is, specifications of composed services in which service slots have to be filled by actual services, and investigate matching conditions for slots of mediators and services. For a services to match a slot in a mediator, a (generalised) projection of the mediator must comply with the plot of the service. Furthermore, the service must be semantically adequate, which requires the use of a service ontology.     

A theory of data-intensive software services

We introduce Abstract State Services (AS²s) as an abstraction of data-intensive services that can be made available for use by other systems, e.g. via the web. An AS² combines a hidden database layer with an operation-equipped view layer, and can be anything from a simple function to a full-fledged Web Information System or a Data Warehouse. We adopt the fundamental approach of Abstract State Machines to model AS²s and show that AS²s capture the fundamentals of approaches such as media types, meme media, SOA and web services excluding presentation issues. Then we show how tailored services can be extracted from available AS²s, combined with other AS² components and personalised to user preferences.     

Towards a theory of consistency enforcement

State oriented specifications with invariants occur in almost all formal specification languages. Hence the problem is to prove the consistency of the specified operations with respect to the invariants. Whilst the problem seems to be easily solvable in predicative specifications, it usually requires sophisticated verification efforts, when specifications in the style of Dijkstra's guarded commands as e.g. in the specification language B are used. As an alternative consistency enforcement will be discussed in this paper. The basic idea is to replace inconsistent operations by new consistent ones preserving at the same time the intention of the old one. More precisely, this can be formalized by consistent spezializations, where specialization is a specific partial order on operations defined via predicate transformers. It will be shown that greatest consistent specializations (GCSs) always exist and are compatible with conjunctions of invariants. Then under certain mild restrictions the general construction of such GCSs is possible. Precisely, given the GCSs of simple basic assignments the GCS of a complex operation results from replacing involved assignments by their GCSs and the investigation of a guard. In general, GCS construction can be embedded in refinement calculi and therefore strengthens the systematic development of correct programs. Received: 28 April 1994 / 5 November 1998     

Customising Web Information Systems According to User Preferences

Web Information Systems have to serve a variety of users with very diverse preferences regarding content, functionality and presentation. We first investigate the customisation of functionality at a high-level of abstraction, where possible action sequences are represented by an algebraic expression called plot, and user preferences give rise to equations. We show that the problem can be solved by applying conditional term rewriting on the basis of Kleene algebras with tests. By exploiting the idea of weakest preconditions such expressions can be represented by formal power series with coefficients in a Boolean algebra. This gives rise to a sufficient condition for termination based on well-founded orders on such power series. As confluence cannot be guaranteed, we propose critical pair completion to be used in order to enforce the desirable Church-Rosser property. In a second step we parametrise the actions and replace the Boolean conditions by first-order formulae. We show that still term rewriting can be applied, but termination and Church Rosser property become problems that will require manual interaction, in particular, as preference rules will make use of the parameters. On the other hand the presence of first-order conditions can be used to extend the customisation to the content.     

Asymptotic properties of keys and functional dependencies in random databases

Practical database applications give the impression that sets of constraints are rather small and that large sets are unusual and are caused by bad design decisions. Theoretical investigations, however, show that minimal constraint sets are potentially very large. Their size can be estimated to be exponential in terms of the number of attributes. The gap between observation in practice and theory results in the rejection of theoretical results. However, practice is related to average cases and is not related to worst cases.

The theory used until now considered the worst-case complexity. This paper aims to develop a theory for the average-case complexity. Several probabilistic models and asymptotics of corresponding probabilities are investigated for random databases formed by independent random tuples with a common discrete distribution. Poisson approximations are studied for the distributions of some characteristics for such databases where the number of tuples is sufficiently large. We intend to prove that the exponential complexity of key sets and sets of functional dependencies is rather unusual and almost all minimal keys in a relation have a length which depends mainly on the size of the relation.     

How to Obtain a Mega-Intestine with Normal Morphology: In Silico Modelling of Postnatal Intestinal Growth in a Cd97-Transgenic Mouse

Intestinal cylindrical growth peaks in mice a few weeks after birth, simultaneously with crypt fission activity. It nearly stops after weaning and cannot be reactivated later. Transgenic mice expressing Cd97/Adgre5 in the intestinal epithelium develop a mega-intestine with normal microscopic morphology in adult mice. Here, we demonstrate premature intestinal differentiation in Cd97/Adgre5 transgenic mice at both the cellular and molecular levels until postnatal day 14. Subsequently, the growth of the intestinal epithelium becomes activated and its maturation suppressed. These changes are paralleled by postnatal regulation of growth factors and by an increased expression of secretory cell markers, suggesting growth activation of non-epithelial tissue layers as the origin of enforced tissue growth. To understand postnatal intestinal growth mechanistically, we study epithelial fate decisions during this period with the use of a 3D individual cell-based computer model. In the model, the expansion of the intestinal stem cell (SC) population, a prerequisite for crypt fission, is largely independent of the tissue growth rate and is therefore not spontaneously adaptive. Accordingly, the model suggests that, besides the growth activation of non-epithelial tissue layers, the formation of a mega-intestine requires a released growth control in the epithelium, enabling accelerated SC expansion. The similar intestinal morphology in Cd97/Adgre5 transgenic and wild type mice indicates a synchronization of tissue growth and SC expansion, likely by a crypt density-controlled contact inhibition of growth of intestinal SC proliferation. The formation of a mega-intestine with normal microscopic morphology turns out to originate in changes of autonomous and conditional specification of the intestinal cell fate induced by the activation of Cd97/Adgre5.     

Increased incorporation of fatty acids into phospholipids of lungs and livers of rabbits under the influence of bromhexine and ambroxol

The incorporation of lauric acid, palmitic acid and oleic acid into phospholipids of lung and liver has been studied in tissue slices of control rabbits and of rabbits treated with bromhexine or ambroxol in doses of 10 mg/kg. A marked increase (up to 200% of the controls) of palmitic acid incorporation into phosphatidylcholine (lecithin) and phosphatidylethanolamine of the lung was found whereas the incorporation rate of palmitic acid into lecithin and phosphatidylethanolamine of the liver displayed no significant change. The incorporation of lauric acid and oleic acid into lung phospholipids was not accelerated. The observed effects were more marked in short time experiments (analysis 2 h after drug injection) than after treatements for 7 days. It is concluded that the phospholipid synthesis is stimulated by the drugs especially in the lungs. This seems to be of particular interest with respect to the surfactant system of the lung and might have some therapeutic relevance.